The essentials of human systems and Health Management volume 1

ORUIKOR GABRIEL JEREMIAH, DrPH
ii
THE ESSENTIALS OF HUMAN SYSTEMS AND HEALTH MANAGEMENT
VOLUME 1
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THE ESSENTIALS
OF
HUMAN SYSTEMS
AND
HEALTH MANAGEMENT
VOLUME 1
BY
Senior Lecturer Faculty of Biological Sciences, West African
Union University Republic of Benin (WAUU)

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(C) ORUIKOR GABRIEL JEREMIAH, DrPH
Department of biological sciences, West African Union
University Republic of Benin (WAUU)
All rights reserved. No part of this publication may be
reproduced, stored in a retrieval system, or transmitted in any
form or by any means, electronic, manual, mechanical,
photocopying, recording or otherwise without the prior
permission of the copyright owner.
All enquiries about this book should be directed to
ORUIKOR GABRIEL JEREMIAH @ oruikorgabriel@gmail.com,
+2348132030519
First Published 2022
Published by: Danchels Nigeria
Location: Zone A, Iba housing estate, Estate main gate, Iba,
Lagos. Tel: 08038054527, Email: danchelsnig@gmail.com
Printed by: Success Printers
Location: 17, Oba Akran Street, Badagry, Lagos State
Tel: 08056133738, 08023885572, 08028749335, 08100800638
ISBN: 0123-4567

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CONTENTS
CONTENTS................................................................................................vi
DEDICATION..........................................................................................viii
FOREWORD..............................................................................................ix
PREFACE ..................................................................................................xvi
ACKNOWLEDGMENTS .........................................................................ix
CHAPTER ONE
HUMAN PHYSIOLOGICAL PROCESS IN RELATION
WITH HEALTH...........................................................................................1
CHAPTER TWO
THE BASIC FUNCTIONING SYSTEMS OF THE
HUMAN BODY..........................................................................................6
CHAPTER THREE
HUMAN BODY DEFENSE MECHANISM .....................................125
CHAPTER FOUR
HUMAN RESPONSE TO SUBSTANCE ABUSE I
(DRUG ABUSE).....................................................................................133
CHAPTER FIVE
HUMAN RESPONSE TO SUBSTANCE ABUSE II
(ADDICTION)........................................................................................147
CHAPTER SIX

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HUMAN RESPONSE TO SUBSTANCE ABUSE III
(ALCOHOLISM)....................................................................................152
CHAPTER SEVEN
MAINTAINING HEALTHY LIVING I
(KEYS FOR HEALTHY LIVING).........................................................163
CHAPTER EIGHT
MAINTAINING HEALTHY LIVING
(EXERCISE AS MEDICINE).................................................................173
CHAPTER NINE
FOOD MATERIALS IN HUMAN HEALTH I
(THE KEY CLASSES OF FOOD NUTRIENTS) ...............................181
CHAPTER TEN
FOOD MATERIALS IN HUMAN HEALTH II
(SERVING FRUITS FOR THERAPEUTIC PURPOSES).................201
REFERENCES.........................................................................................238

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DEDICATION
I dedicate this to book to:
The first Love of my life, GOD the creator of all, who gave me
this privilege to be a writer and my LOVELY wife, Dr. Mrs
Gabriel Jeremiah, who always stood by me in everything good.

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ACKNOWLEDGMENTS
I wish to thank some of my Colleagues in west African Union
University, International University of Bamenda, My Mentees
in TOCHIDWORFI, Mr. Henry Okobooh Ehis, the founder of
Leadpreneur Academy, Nascreative company, the designer of
this book, Abundance private schools, Rivers/Bayelsa Union,
Jesus witness International Mission, world peace tract
ambassadors, The directors of total Child development world
International, Dr Paul Nwala, my beloved brother, and my
lovely wife, Dr Mrs Gabriel Jeremiah for their support and
encouragement during the writing of this book. I am most
grateful to Prof DJIBRIL M.Najibou, Alphonsus Izuchukwu
Opurum, Pharm. Victor Cheluchukwu Nwankpor, and
OKPANACHI MICHAEL ,my friends for their useful comments
and suggestions which helped to build the manuscript of this
book. I am indebted to all my teachers and lecturers,
especially Sir ThankGod George Ikor, Sir Samuel, Sir Eboju
Andrew, Dr. Mrs Okocha, and Prof. Wirba Amenu Foven who
educated me while I was in School as a student.
I will not fail to recognize my Parents, Mr and Mrs Jeremiah
Oruikor Alfred, My Brothers and Sisters, Especially Mr Nsan
Jeremiah Oruikor, My Uncles, Capt. George C Iboroma, Mr
Oruikor Alfred Alfred and others who had supported me in all
my stages of life.
Very importantly, I am grateful to Pst & Dr Mrs Madukor, the
founder of Abundance Private Schools, Pst (Engr) & Pst Mrs

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Tony Chukwu, the Founder of Jesus Witness International
Mission, Dr Godwin Onwe, the founder of Christ life
Tabernacle, Pst Tonybede Ohaeri, the resident Pastor of
House of Victory Bible Church Benin, Dr George Tanko,
Director of IUB campus, Pst Useful Nsoghai, Mr & Mrs
Tchandjoun, Sis Hortence EWANE, Mr Wisdom Maxwell, Sis
Constance Ikpe, Rev Jehoshaphat Omaka, the founder of
Good shepherd Internal, Pst. Jacob Amaechi, Rev. Dr Azu
Emanuel, the founder of Christ Evangelical team, Mr.Promise
Obulor Ahamefula, and Emmanuel UKACHUKWU
Njoku,Chairmen of Rivers/Bayelsa Union Benin, Mr Robert.
N.K, the International students affairs IUB, and Mrs Glory Eke,
they have been my great encouragers and supporters.
My Profound gratitude goes to Prof. Stephen Nwawolo, the
DVC West African Union University, Dr. Bishop Adeyemi
Olayemi, the President of West African Union University, Alhaji
Onifade A. Abdulkabir, the Registrar of WAUU, Mrs Johnson
Alice, the Deputy Registrar WAUU, Dr. Dave Aghwe, Dean
faculty of Biological sciences, Dr. Timothee Demahou the
Medical director Clinique la Masses Des Figures, Dr Emanuel,
the medical director Debrose medical center and Dr. Engr
Oladayo. A, the director of heritage foundation, for the
opportunity to work in their institutions.
Finally, for all Persons who by one way or the other supported
me, I appreciate you.

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FOREWORD
Teaching in health science's setting presents student
educators with challenges that are different from those
encountered in the classroom. In Nursing education, the
classroom and clinical environment are linked, because
students must apply in health sciences the biological practices
that they have learned in the classroom.
However, the first edition of this publication entitled "THE
ESSENTIALS OF HUMAN BODY SYSTEM AND HEALTH
MANAGEMENT " provides innovative approaches to teaching,
for it clinical environment is highly complex and rapidly
changing to a transformative health care delivery system that
has to produce a variety of new concepts, including settings
and roles in which student nurses must be prepared to follow
as a model and practice.
The purposes of this multidimensional edition are to
examine concepts of Anatomy and Physiology within the
"ESSENTIALS OF HUMAN BODY SYSTEMS AND HEALTH
MANAGEMENT "of clinical teaching that provides a
comprehensive framework for planning, guiding, monitoring
and evaluating learning activities for students in medicine,
Nursing, midwifery, pharmacy, public health, Nutrition and
dietetic, chiropractic, chemotherapy, chemistry and
biochemistry.

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While the focus of the book is the "essentials of human body
systems and management "in Nursing education, the content
is above all applicable to teaching students and individuals in
other fields related to undergraduate and postgraduate
studies because this book describes vital aspects in human
systems and its physiological functions with efficiency,
effectiveness and pragmatic illustrations, it also examines
challenges and complexities of understanding the topics on
course and addresses solutions and recommendations for
effective needs and efficient comprehension of the presented
in nine chapters.
The Author of the ESSENTIALS of human body systems and
management, Dr. ORUIKOR GABRIEL JEREMIAH, well known
for his simplicity in transforming the complexities to fingertips
of each interested individual to acquire and achieve
substantial and potential knowledge in "human body systems
and management",has laid more emphasis on its innovations
by clearly defining all the concepts, segments, and discussing
the intended and unintended results with realistic cognitive,
psychomotor and effective outcomes aim at facilitating and
promoting each student quantitative and qualitative
achievements in the field of health sciences.
We appreciate the sense of creativity and innovation of
Dr.OGJ,a great visionary, and scientist who try to make things
better, easier, cheaper,faster and understandable to effect
change in our educational communities.

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This book is organized in 3 major sections, the first section of
the book addresses human physiological mechanisms and
processes in relation to the basic functioning of the human
systems and its constituent biologically experimented in
human beings, which are made up of many parts emanating
from millions of cells differentiating into organs and systems
all working in synergy, synchronise in a well defined and
functioning mechanism that is contained in two chapters such
as chapter one and two. These chapters present a
philosophical evidence of clinical analysis and basic
functioning systems of the human body and the authors'
recommendations for effective planning, implementation and
evaluation of the human body.
The second section of the book explores the process of
defense mechanisms as seen from chapter 3 to 6, these
chapters specify strategies for preparing human body defense
mechanisms and response to addiction of substances, which
are nuisance to human body. This process assist faculty staff
and students to blend theoretical knowledge to practical and
equally permits them to acquire tremendous knowledge in
their courses. These chapters, include, suggestions, remarks,
proposals for selecting diagnostic and clinical learning where
teaching and assessment are discussed for proper
organisational and orientation of the learners in health
sciences.

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The final section of the book focuses on the effective
maintenance of healthy lifestyle in chapter 7, 8 and 9,
identifying learning objectives assessing learning needs,
planning learning activities, guiding students on various
classes of foods, evaluating performance, suggest criteria for
selecting appropriate assignments and chapter 7, discusses a
variety of methods on maintaining healthy lifestyle, while
chapter 8 focuses on self-discipline, self-awareness, self-
directed learning activities, it reviews various approaches to
meeting the individual needs through variety of exercises,
simulations and games which are designed effective, creative
in preparing students for clinical practices and at the same
time add interest and variety to the learning process.
Chapter 9, which is the ultimate in the publication describes
approaches to using simulations, role play, decision making,
communication and interpersonal knowledge of classes of
foods susceptible to effect change in human morphology,
solving critical problems and remarkable development which
are the important factors of this concept of human body
systems.
Conclusively, the "ESSENTIALS of human body systems and
health management "has been shaped over many years by a
number of high rated and qualified lecturers, mentors and Dr.
OGJ. It's impossible to acknowledge the specific contributions
of each, but we hope that by the publication of this ever first
edition of the book, they will know how much they have

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influenced the education curriculum and community in the
world.
We express our sincere gratitude to our academic colleague
DR OGJ. For his courage, and close encouragement in the
course of writing this edition. It was a privilege to Foreword
this magnificent write-up that will contribute enormously to
educate the youths and pave a new perspective for academics.
PROFESSOR WIRBA AMENU FOVEN, FOUNDER AND VICE
CHANCELLOR OF CONTINENTAL UNIVERSITY INSTITUTE OF
SCIENCE AND TECHNOLOGY CAMEROON
FORMER DIRECTOR OF SCHOOL OF MEDICINE AND
PHARMACY IN IUB CAMEROON
SENIOR LECTURER IN THE FACULTY OF MEDICINE AND
PHARMACY- NAPISCTECH CAMEROON
DIRECTOR OF ACADEMIC AFFAIRS KING'S UNIVERSITY
POLAND.

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PREFACE
The book entitled "THE ESSENTIALS OF HUMAN BODY
SYSTEMS AND HEALTH MANAGEMENT" is a book with
multiple uses, But Primarily for students in health sciences and
biological sciences, who are studying the following courses:
Medicine, Nursing, Pharmacy, public health, Physiotherapy,
Medical laboratory science, Biochemistry, Anatomy,
Physiology, and others.
This book is also useful for individuals who want to
understand how their body systems basically works and live
healthy.
The writer covered some vital areas needed for the above
students in other textbooks, such as the concept of health, the
human systems and basic functions, Nutritional values and
concepts. Some aspects of mental health and ill health. The
book also explained clearly how human beings can naturally
improve their health and prevent sickness.
It's worthy to appreciate that many authors have written on
the above subjects or areas. But the scope and depths of these
books vary and some of the authors presented it in a very
complex form, making it difficult for so many readers to
comprehend. Some of these books, the authors bombarded
with much details with no simplification. This becomes more
tedious for readers who do not have much time to cover it.

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This book is written solely for the purpose of making the
covered areas easier to understand within a short duration. To
further make the reader understand and to achieve the
purpose, I have detached the information I considered not
necessary at the early stage of students, and for those who
aren't students in the above mentioned majors but just want
to study to obtain useful information on their body systems
and health.
In this book, I have presented and acknowledged most current
scientific evidenced researches on the subjects by other
authors believed to be true without discussing the
experimented data on which the views are gotten from or
included the names of the researchers. It doesn't mean that I
ignored or slight them. If I included all of the names,
references, papers, data and experimental evidences it will
make this book to be unnecessarily bulky, and the readers will
find it difficult to understand. Nevertheless, I am not
ungrateful to thank and appreciate all the researchers and
authors who their works built up this text book.
Therefore, I acknowledge with thanks the use of figures or
words, either in original form or in adaptable form, from other
books or authors.

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CHAPTER ONE
HUMAN PHYSIOLOGICAL PROCESS IN
RELATION WITH HEALTH
INTRODUCTION
Humans are created as super-beings, and every part of their
body are carefully formed for higher functions. The basic
concept of biology described humans as Animals, but a higher
and specialized ones. Humans are higher Animals because
they have a well-organized brain, large enough to assimilate
information, communicate effectively, solve problems and
others.
Biologically, human beings are made up of many parts which
take their origin from millions of cells which differentiate into
organs and systems all working in harmony while health
exists. Humans are made up of physical, mental and social
dimensions, and Spiritual, each distinct in character, yet
functioning as a unit. Since these dimensions function as a
unit, it then implies that whatever affects any of the other
parts brings about certain changes in the other parts or causes
disequilibrium in the individual’s constitution to a point
whereby his/her functioning is either slightly or grossly
impaired. Being in health has nothing to do with whether an
individual is a midget, a giant or physically disabled. A person
is regarded as being in health if in spite of the examples of
conditions mentioned above, he is able to function effectively,
physiologically, mentally, intellectually and socially within his

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limitations. So disability isn't inability. An individual can be
physically disabled, but he/she can function in other
parameters well, like Mental, Social and Spiritual. In view of
this, such individual is in health.
UNDERSTANDING THE TERM HEALTH
According to WHO, health is the state of complete Physical,
Social and Mental well-being of individual, not merely the
absent of diseases or infirmity.
But let's add another perspective to improve WHO definition
of health. There is another perspective, health also has to do
with spiritual life. Every human has a spiritual life, hence
there's need to have spiritual health mentioned. Humans are
also spiritual beings, just as social beings.
When our spiritual health is affected, it will definitely affect
every other constituents of health. Because it's the spiritual
that controls the physical. There would be no social, physical,
and mental without the spiritual. Therefore, Health is the total
status of Spiritual, Social, Physical and Mental well-being of an
individual, but not necessarily the state of being freed from
illness or diseases.
“Health” is a word that has a common use. It features
prominently in consumer goods advertisement, especially
with those dealing with food, drugs and cosmetics. It also
features in our everyday conversations, good wishes and
greetings. It is expressed either implicitly or explicitly and has
become the concern of every individual, family, community

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and the government. It is a term that was not defined in any
precise way until when the World Health Organisation put
forth its definition which has now been accepted as a standard
definition among health practitioners. There are two parts
considered in WHO definition of health. The first part sees
health as “a state of complete physical, mental and social well-
being” and the second part views health as not necessarily the
“mere absence of disease or infirmity”. This first part of the
definition clearly points out the fact that health has at least
three dimensions or components – mental, physical and social
components. The second part confirms the above view by
clearly pointing out that the absence of disease and infirmity
does not mean that health necessarily exists. In other words,
health cannot be determined by observing or evaluating the
physical or physiological status of a person. Over the years,
the World Health Organization definition remained supreme,
but later some authorities in health education began to
question some aspects of the definition. Take a look at the
definition again. The questionable aspect is that which speaks
of a state of complete physical, mental and social health.
Although health is usually considered positive, there is no
question of its completeness, because it fluctuates on a
continuum. At any moment, health may be located anywhere
on this continuum. If located near the extreme positive end of
the continuum, it would represent the highest level of health.
But if located at the opposite end, it would represent a low
level of health. Therefore a state of completeness is ruled out
because no one ever attains the highest level of optimum

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health. However a location of health status at the low level of
health is the beginning of ill-health and that absolute low level
of health is death. As a result of the limitations in the WHO
definition some other definitions have arisen. These are not
necessarily more satisfactory than the WHO definition, but
they clearly show the area of emphasis of the respective
authors. Such definitions include:
1. Health is a quality, resulting from the total functioning of
the individual in his environment that empowers him to
achieve a personally satisfying and socially useful life (Johns
et al, 1975).An analysis of this definition shows that there are
four components – (i) as the unity of the individual, (ii) as a
quality of life, (iii) as an achievement of personality satisfying
life, and (iv) as an achievement of socially useful life.
2. Health is that state or quality of life which enables an
individual to face up to crisis, carry out his daily
responsibilities efficiently and relate to other persons
effectively. The above definition gives health the pride of
place. By implication, only the person who is in health can
function in any meaningful way and the functional level is
dependent on the level of health such a person is enjoining.
3. Health is that quality which enables one to “live most and
serve best” (Williams, 1933).This is a more philosophical
definition which could be said to be a summary of the
definition it follows. Only a person in health can be in a
position to “live most and serve best”. When you wake up in

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the morning, stretch yourself and throw up your arms and yell,
“I feel wonderful and good this morning”, that is an evidence
of health. Health is the most prized possession of human
beings, although man often takes it for granted until he
begins to lose it. Let us examine the following situation. You
might say “my head aches” but not that “my head is ill” or “my
head does not enjoy health today”. Although there are times
you might say “my fever is better today” or that “my head is
alright now”, but the more natural and rational expression
might be to say, “My headache is cured”. The disposition of a
person due to headache or his freedom from ache is a
condition, just like a variety of other conditions which
positively or negatively affect the status of such an individual’s
total health that is, his physical, mental and social health
combined. These dimensions are inseparable. They are the
factors which make an individual a unique personality and
which set him out from any other individual. Since health
fluctuates on the health continuum, it is therefore a quality of
life which results from one’s total functioning within one’s
physical, biological and social environment. Effective living is
also a result of a person’s functioning in a variety of life’s
situations which include his physical, mental, social and
spiritual experiences. What you do – such as your work, leisure
activities, social engagements, food habits. It's the level of
your health that determines your activities in life. The food you
would eat is determined buy your health status. Health is an
investment.

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CHAPTER TWO
THE BASIC FUNCTIONING SYSTEMS OF THE
HUMAN BODY
 INTRODUCTION
Basically, Cells are the basic structural, and functional units of
life. It's the metamorphosis of cells that gave rise to tissues,
Organs and finally SYSTEMS.
The Human body works as a result of certain connected
organs. These organs come together with similar functions to
aid the body. The organization of these organs is called
SYSTEM.
The human body is everything that makes up you. The basic
parts of the human body are the head, neck, torso, arms and
legs.
Our bodies consist of a number of biological systems that
carry out specific functions necessary for everyday living and
as well, numerous cells and proteins that defend the body
against microorganisms. Our bodies are trained in such a way
that reflect our internal protection and defence Mechanism.
Scientists are working tirelessly to understand the total
components and working operation of Humans. They have
also concluded some facts about humans as follows:
 The human body contains nearly 100 trillion cells.

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 There are at least 10 times as many bacteria in the human
body as cells.
 The average adult takes over 20,000 breaths a day.
 Each day, the kidneys process about 200 quarts (50
gallons) of blood to filter out about 2 quarts of waste and
water
 Adults excrete about a quarter and a half (1.42 liters) of
urine each day.
 The human brain contains about 100 billion nerve cells
 The human brain can read up to 1,000 words per minute.
 Inside your belly button are thousands of bacteria that
form an ecosystem the size of an entire rainforest.
 When in love, the human brain releases the same cocktail
of neurotransmitters and hormones that are released by
amphetamines. This leads to increased heart rate, loss of
appetite and sleep, and intense feelings of excitement.
 An adult is made up of
7,000,000,000,000,000,000,000,000,000 (7 octillion) atoms.
For perspective, there's a 'measly' 300,000,000,000 (300
billion) stars in our galaxy.
 Our muscles are actually incredibly more powerful than
they appear to be. Human strength is limited to protect
our tendons and muscles from harming themselves. This
limitation can be removed during an adrenaline rush,
during which some people have lifted boulders or even
cars off themselves.

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 A full head of human hair is strong enough to support 12
tonnes.
 In 30 minutes, the human body gives off enough heat to
bring a gallon of water to the boil. We have the same
amount of hairs on our body as a chimpanzee. Most are
useless and so fine that they are invisible..
 If the human brain were a computer, it could perform 38
thousand-trillion operations per second. The world's most
powerful supercomputer, BlueGene, can manage only.
002% of that.
 The focusing muscles in your eyes move around 100,000
times a day. To give your leg muscles the same workout,
you'd need to walk 50 miles.
 For every pound of fat or muscle gained, your body creates
seven miles of new blood vessels. Loneliness is physically
painful. Just as you have a drive to avoid physical pain, you
have a similarly powerful drive to connect with others and
seek companionship - in order to avoid the pain of
loneliness.
 A single human sperm contains the 37.5mb of male DNA
required to create a human child. That means an average
ejaculation sees the transfer of 1,500 terabytes of
information.
 Your body produces 25 million new cells each second.
Every 13 seconds, you produce more cells than there are
people in the United States.

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 If you stretched out the 300,000,000 capillaries in your
lungs end to end, the line would extend from Seattle to
San Diego, or about 1,300 miles.
 Some women see more colors than everyone else. Most
people have three types of color receptors to see color
vision, while some women have four or even five of these
receptors and can see a wider range of colors.
 Crying alleviates stress and allows humans to decrease
feelings of anger and sadness. It physically does help to let
it out.
 The need to breathe so much is due to carbon dioxide
build-up more than the need for oxygen. If there was a
different way to get rid of carbon dioxide from the blood,
we would only need to breathe at a rate of about once per
minute.
 Humans shed 40 pounds of skin in their lifetime,
completely replacing their outer skin every month.
 In one day, your blood travels 12,000 miles around your
body. That's four times the distance across the US from
coast-to-coast.
 Around 90% of the cells that make humans aren't “human"
in origin. We're mostly fungi and bacteria.
 The human brain uses 20% of the entire body's oxygen
and calorie intake, despite only accounting for about 2%
of an adult's body mass. Our brain's connected neurons
look similar to the structure of the universe. In a way, our
brains are modelled after the universe.

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Along with the five traditional senses of sound, sight, touch,
smell and taste, humans have 15 “other senses." These include
balance, temperature, pain and time as well as internal senses
for suffocation, thirst, and fullness.
2.1. VITAL ORGANS FOR THE BODY’S CARDINAL SIGNS
AND SYSTEMS
Humans have five vital organs that are essential for survival.
These are the brain, heart, kidneys, liver and lungs. The vital
organs are very useful in medicine and health. It enable the
health personnel understands the normal and abnormal state
of an individual when visited the hospital. These cardinal
sectional Organs help to signal negative health state of an
individual.
The human brain is the body's control center, receiving and
sending signals to other organs through the nervous system
and through secreted hormones. It is responsible for our
thoughts, feelings, memory storage and general perception of
the world.
The human heart is a responsible for pumping blood
throughout our body.
The job of the kidneys is to remove waste and extra fluid
from the blood. The kidneys take urea out of the blood and
combine it with water and other substances to make urine.

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The liver has many functions, including detoxifying of harmful
chemicals, breakdown of drugs, filtering of blood, secretion of
bile and production of blood-clotting proteins.
The lungs are responsible for removing oxygen from the air
we breathe and transferring it to our blood where it can be
sent to our cells. The lungs also remove carbon dioxide, which
we exhale.
Fig 2.1: Organs of the human body.
Source: 1999 Encyclopaedia, Britannica, Inc

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2.2. HUMAN FUNCTIONING SYSTEMS
Human systems are very vital parts of the body since they
constitute the necessary parts that keep the light of the body
and other body mechanisms. It's the combination of organs
that have similar functions that gave rise to systems.
These systems are:
 NERVOUS SYSTEM
The Nervous system is the part of the body that determines
what happens to others. The activities of other parts are
championed by the nervous system.
The nervous system controls both voluntary action (like
conscious movement) and involuntary actions (like breathing),
and sends signals to different parts of the body.
Parts of the Nervous system
The nervous system is divided into; 1 the central nervous
system and 2 the peripheral nervous system.
1. Central Nervous system: The central Nervous System is
made up of the brain and spinal cord.
The central nervous system;
- Co-ordinate the activities of the nervous system.
- Receives constant input of impulses relating to changes in
animals internal and external environment.
- Processes, integrate information and sends out impulse to
relevant effectors for action.

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- Impulses transmitted along sensory nerves are called
sensory impulses.
THE HUMAN BRAIN
The brain, a soft, wrinkled organ that weighs about 3 pounds,
is located inside the cranial cavity, where the bones of the skull
surround and protect it.
The approximately 100 billion neurons of the brain form the
main control center of the body.
The brain and spinal cord together form the central nervous
system (CNS), where information is processed and responses
originate.
The brain, the seat of higher mental functions such as
consciousness, memory, planning, and voluntary actions, also
controls lower body functions such as the maintenance of
respiration, heart rate, blood pressure, and digestion.
Fig 2.2: The features of the human brain
Source: NNmda Manual

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The structure and nature of the Human brain
1. Human brain weighs about 1.2 to 1.4kg.
2. It consumes 25% of the body oxygen supply to generate
energy;
3. It is covered by a membrane called the Meninges.
4. It is enclosed in a bony case called the skull or cranium.
5. It is made up of 2 types of nervous tissues, (Nerves cells or
grey matter and Nerves fibers or white matter.)
Human brain is divided into 3 parts
a. Fore brain (i.e. Large, forward part). b. Mid brain (i.e. narrow
brain).c. Hind brain (i.e. rare path).
Fore Brain: - it consist mainly cerebrum, thalamus and
hypothalamus.
Midbrain: links the forebrain to the hindbrain. It controls
auditory and visual reflexes.
Hindbrain: composed of 3 parts (A) Cerebellum (B) Pons
varolii (C) Medulla oblongota
Functions of the parts of the brain
i. Cerebrum controls all the bodies’ voluntary action and
consciousness.
ii. Frontal lobe – seat of intelligence, Memory, Imagination,
thought, judgment, emotional reaction and movement of
skeletal muscles.

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iii. Parietal lobe – Receives and interprets the sensations of
pressure, temperature and position.
iv. Temporal lobe is concerned with hearing, memory and
understanding of speech.
Fig 2.3: Functions of the different parts of the human
brain.
Source: NNmda Manual
SPINAL CORD
The spinal cord is a long, thin mass of bundled neurons that
carries information through the vertebral cavity of the spine
beginning at the medulla oblongata of the brain on its
superior end and continuing inferiorly to the lumbar region of
the spine.

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In the lumbar region, the spinal cord separates into a bundle
of individual nerves called the cauda equina (due to its
resemblance to a horse’s tail) that continues inferiorly to the
sacrum and coccyx.
The white matter of the spinal cord functions as the main
conduit of nerve signals to the body from the brain. The grey
matter of the spinal cord integrates reflexes to stimuli.
Functions Of the Spinal Cord
1. Forms a connecting link between the brain and the PNS
2. Provides structural support and builds a body posture
3. Facilitates flexible movements
4. Myelin present in the white matter acts as an electrical
insulation
5. Communicate messages from the brain to different parts
of the body
6. Coordinates reflexes
7. Receives sensory information from receptors and
approaches towards the brain for processing.
2. Peripheral Nervous System: The peripheral nervous
system is divided into; i. Sensory system. ii. Motor system. iii
Somatic nervous system. iv. Autonomic nervous
Sensory system
The sensory system allows organisms to perceive, respond to,
and interact with their environments. Sensory perceptions
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known as the common five senses, but there are actually eight
senses in the sensory system.
Sensory systems include the visual, auditory, gustatory (taste),
olfactory (smell), somatosensory (touch, pain, temperature,
and proprioception), and vestibular (balance, spatial
orientation) systems.
All sensory systems have receptor cells that are specialized to
detect a particular type of stimulus. For example, hair cells in
the inner ear have cilia that move in the presence of sound
waves, while olfactory receptor neurons in the nasal cavity
have receptors that bind to odorant molecules.
The presence of an appropriate stimulus triggers
electrochemical changes in the nervous system. This stimulus
typically changes the membrane potential of a sensory
neuron, triggering an action potential. The information is then
transmitted from the sensory organ to the spinal cord and
then the brain, or directly to the brain (as in the visual system).
The different types of sensory information—also called
modalities—travel in different pathways through the central
nervous system, but most are transmitted to the thalamus—a
structure in the middle of the brain. From here, sensory
information is typically sent to areas of the cerebral cortex
dedicated to the analysis of specific modalities—for instance,
primary visual cortex or primary auditory cortex.

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These areas, in turn, send information to the association
cortex, where sensory information is integrated with other
types of information for higher-level analysis. Ultimately, the
neural processing that occurs throughout these pathways and
networks allows for accurate perception of sensory stimuli—
such as the identity and location of objects in the visual world,
or the understanding of speech.
Motor system
Motor neurons (also referred to as efferent neurons) are the
nerve cells responsible for carrying signals away from the
central nervous system towards muscles to cause movement.
They release neurotransmitters to trigger responses leading
to muscle movement.
These movements can be voluntary, such as reaching out to
pick up an item, or involuntary, such as causing a hand to
move away from a hot surface.
Motor neurons are responsible for integrating signals from
the brain to the muscles, glands, and organs that intend to
carry out the required motor function. Motor neurons allow
us to move, talk, eat, swallow, and breathe, therefore without
these cells, we would not be able to complete many basic life
functions.
Autonomics Nervous system
The autonomic nervous system regulates certain body
processes, such as blood pressure and the rate of breathing.

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No conscious efforts is required by an individual in this. This
system possed the ability to work automatically
(autonomously), without a person’s conscious effort.
The autonomic nervous system is the part of the nervous
system that supplies the internal organs, including the blood
vessels, stomach, intestine, liver, kidneys, bladder, genitals,
lungs, pupils, heart, and sweat, salivary, and digestive glands.
After the autonomic nervous system receives information
about the body and external environment, it responds by
stimulating body processes, usually through the sympathetic
division, or inhibiting them, usually through the
parasympathetic division.
An autonomic nerve pathway involves two nerve cells. One
cell is located in the brain stem or spinal cord. It is connected
by nerve fibers to the other cell, which is located in a cluster
of nerve cells (called an autonomic ganglion). Nerve fibers
from these ganglia connect with internal organs. Most of the
ganglia for the sympathetic division are located just outside
the spinal cord on both sides of it. The ganglia for the
parasympathetic division are located near or in the organs
they connect with.
The autonomic nervous system has two main divisions:
Sympathetic and Parasympathetic autonomic nervous system.

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Sympathetic Autonomic Nervous System: It is the part of
the autonomic nervous system, located near the thoracic and
lumbar regions in the spinal cord. Its primary function is to
stimulate the body’s fight or flight response. It does this by
regulating the heart rate, rate of respiration, pupillary
response and more.
Parasympathetic Autonomic Nervous System: It is located
in between the spinal cord and the medulla. It primarily
stimulates the body’s “rest and digest” and “feed and breed”
responses.
The autonomic nervous system function in these capacities:
-The autonomic nervous system controls internal body
processes such as the following
-Blood pressure -Heart and breathing rates -Body
temperature -Digestion
-Metabolism (thus affecting body weight) -The balance of
water and electrolytes (such as sodium and calcium) -The
production of body fluids (saliva, sweat, and tears) -Urination
Defecation -Sexual response
Nervous Tissue
The majority of the nervous system is tissue made up of two
classes of cells neurons and neuroglia.

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 Neurons-Neurons, also known as nerve cells,
communicate within the body by transmitting
electrochemical signals.
Neurons look quite different from other cells in the body due
to the many long cellular processes that extend from their
central cell body.
The cell body is the roughly round part of a neuron that
contains the nucleus, mitochondria, and most of the cellular
organelles.
Small tree-like structures called dendrites extend from the cell
body to pick up stimuli from the environment, other neurons,
or sensory receptor cells.
Long transmitting processes called axons extend from the cell
body to send signals onward to other neurons or effector cells
in the body.
There are 3 basic classes of neurons afferent neurons, efferent
neurons, and interneurons. Afferent neurons- Also known as
sensory neurons, afferent neurons transmit sensory signals to
the central nervous system from receptors in the body.
Efferent neurons- Also known as motor neurons, efferent
neurons transmit signals from the central nervous system to
effectors in the body such as muscles and glands.
Interneurons- Interneurons form complex networks within
the central nervous system to integrate the information

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received from afferent neurons and to direct the function of
the body through efferent neurons.
Neuroglia- Neuroglia, also known as glial cells, act as the
“helper” cells of the nervous system.
Each neuron in the body is surrounded by anywhere from 6 to
60 neuroglia that protect, feed, and insulate the neuron.
Because neurons are extremely specialized cells that are
essential to body function and almost never reproduce,
neuroglia are vital to maintaining a functional nervous system.
Nerves
Nerves are bundles of axons in the peripheral nervous system
(PNS) that act as information highways to carry signals
between the brain and spinal cord and the rest of the body.
Each axon is wrapped in a connective tissue sheath called the
endoneurium.
Individual axons of the nerve are bundled into groups of
axons called fascicles, wrapped in a sheath of connective
tissue called the perineurium.
Finally, many fascicles are wrapped together in another layer
of connective tissue called the epineurium to form a whole
nerve.

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The wrapping of nerves with connective tissue helps to
protect the axons and to increase the speed of their
communication within the body.
Afferent, Efferent, and Mixed Nerves
Some of the nerves in the body are specialized for carrying
information in only one direction, similar to a one-way street.
Nerves that carry information from sensory receptors to the
central nervous system only are called afferent nerves.
Other neurons, known as efferent nerves, carry signals only
from the central nervous system to effectors such as muscles
and glands.
Finally, some nerves are mixed nerves that contain both
afferent and efferent axons.
Mixed nerves function like 2-way streets where afferent axons
act as lanes heading toward the central nervous system and
efferent axons act as lanes heading away from the central
nervous system.
Cranial Nerves
Extending from the inferior side of the brain are 12 pairs of
cranial nerves.
Each cranial nerve pair is identified by a Roman numeral 1 to
12 based upon its location along the anterior-posterior axis of
the brain.

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Each nerve also has a descriptive name (e.g. olfactory, optic,
etc.) that identifies its function or location.
The cranial nerves provide a direct connection to the brain for
the special sense organs, muscles of the head, neck, and
shoulders, the heart, and the GI tract.
The 12 Cranial nerves and functions include:
I. Olfactory nerve: The olfactory nerve sends sensory
information to your brain about smells that you encounter.
When you inhale molecules with a scent, known as aromatic
molecules, they dissolve in a moist lining at the roof of your
nasal cavity.
This lining is called the olfactory epithelium. It stimulates
receptors that generate nerve impulses that move to your
olfactory bulb. Your olfactory bulb is an oval-shaped structure
that contains specialized groups of nerve cells.
From the olfactory bulb, nerves pass into your olfactory tract,
which is located below the frontal lobe of your brain. Nerve
signals are then sent to areas of your brain concerned with
memory and recognition of smells.
II. Optic nerve: The optic nerve is the sensory nerve that
involves vision.
When light enters your eye, it comes into contact with special
receptors in your retina called rods and cones. Rods are found

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in large numbers and are highly sensitive to light. They’re
more specialized for black and white or night vision.
Cones are present in smaller numbers. They have a lower light
sensitivity than rods and are more involved with color vision.
The information received by your rods and cones is sent from
your retina to your optic nerve. Once inside your skull, both of
your optic nerves meet to form something called the optic
chiasm. At the optic chiasm, nerve fibers from half of each
retina form two separate optic tracts.
Through each optic tract, the nerve impulses eventually reach
your visual cortex, which then processes the information. Your
visual cortex is located in the back part of your brain.
III. Oculomotor nerve: The oculomotor nerve has two different
motor functions: muscle function and pupil response.
Muscle function. Your oculomotor nerve provides motor
function to four of the six muscles around your eyes. These
muscles help your eyes move and focus on objects.
Pupil response. It also helps to control the size of your pupil
as it responds to light.
This nerve originates in the front part of your midbrain, which
is a part of your brainstem. It moves forward from that area
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IV. Trochlear nerve: The trochlear nerve controls your superior
oblique muscle. This is the muscle that’s in charge of
downward, outward, and inward eye movements.
It emerges from the back part of your midbrain. Like your
oculomotor nerve, it moves forward until it reaches your eye
sockets, where it stimulates the superior oblique muscle.
V. Trigeminal nerve: The trigeminal nerve is the largest of your
cranial nerves and has both sensory and motor functions.
The trigeminal nerve has three divisions, which are:
Ophthalmic. The ophthalmic division sends sensory
information from the upper part of your face, including your
forehead, scalp, and upper eyelids.
Maxillary. This division communicates sensory information
from the middle part of your face, including your cheeks,
upper lip, and nasal cavity.
Mandibular. The mandibular division has both a sensory and
a motor function. It sends sensory information from your ears,
lower lip, and chin. It also controls the movement of muscles
within your jaw and ear.
The trigeminal nerve originates from a group of nuclei —
which is a collection of nerve cells — in the midbrain and
medulla regions of your brainstem. Eventually, these nuclei
form a separate sensory root and motor root.

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The sensory root of your trigeminal nerve branches into the
ophthalmic, maxillary, and mandibular divisions.
The motor root of your trigeminal nerve passes below the
sensory root and only connects to the mandibular division.
VI. Abducens nerve: The abducens nerve controls another
muscle that’s associated with eye movement called the lateral
rectus muscle. This muscle is involved in outward eye
movement. For example, you would use it to look to the side.
This nerve, also called the abducens nerve, starts in the pons
region of your brainstem. It eventually enters your eye socket,
where it controls the lateral rectus muscle.
VII. Facial nerve: The facial nerve provides both sensory and
motor functions, including:
moving muscles used for facial expressions as well as some
muscles in your jaw
providing a sense of taste for most of your tongue supplying
glands in your head or neck area, such as salivary glands and
tear-producing glands sending sensations from the outer
parts of your ear.
Your facial nerve has a very complex path. It originates in the
pons area of your brainstem, where it has both a motor and
sensory root. Eventually, the two nerves fuse together to form
the facial nerve.

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Both within and outside of your skull, the facial nerve branches
further into smaller nerve fibers that stimulate muscles and
glands or provide sensory information.
VIII. Vestibulocochlear nerve: Your vestibulocochlear nerve
has sensory functions involving hearing and balance. It
consists of two parts, the cochlear portion and vestibular
portion:
Cochlear portion. Specialized cells within your ear detect
vibrations from sound based on the sound’s loudness and
pitch. This generates nerve impulses that are sent to the
cochlear nerve.
Vestibular portion. Another set of special cells in this portion
can track both linear and rotational movements of your head.
This information is transmitted to the vestibular nerve and
used to adjust your balance and equilibrium.
The cochlear and vestibular portions of your vestibulocochlear
nerve originate in separate areas of the brain.
The cochlear portion starts in an area of your brain called the
inferior cerebellar peduncle. The vestibular portion begins in
your pons and medulla. Both portions combine to form the
vestibulocochlear nerve.
IX. Glossopharyngeal nerve: The glossopharyngeal nerve has
both motor and sensory functions, including:

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sending sensory information from your sinuses, the back of
your throat, parts of your inner ear, and the back part of your
tongue providing a sense of taste for the back part of your
tongue stimulating voluntary movement of a muscle in the
back of your throat called the stylopharyngeus.
The glossopharyngeal nerve originates in a part of your
brainstem called the medulla oblongata. It eventually extends
into your neck and throat region.
X. Vagus nerve: The vagus nerve is a very diverse nerve. It has
both sensory and motor functions, including:
conveying sensation information from your ear canal and
parts of your throat
sending sensory information from organs in your chest and
trunk, such as your heart and intestines allowing motor
control of muscles in your throat stimulating the muscles of
organs in your chest and trunk, including those that move
food through your digestive tract providing a sense of taste
near the root of your tongue.
Out of all of the cranial nerves, the vagus nerve has the longest
pathway. It extends from your head all the way into your
abdomen. It originates in the part of your brainstem called the
medulla.
XI. Accessory nerve: Your accessory nerve is a motor nerve that
controls the muscles in your neck. These muscles allow you to
rotate, flex, and extend your neck and shoulders.

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It’s divided into two parts: spinal and cranial. The spinal
portion originates in the upper part of your spinal cord. The
cranial part starts in your medulla oblongata.
These parts meet briefly before the spinal part of the nerve
moves to supply the muscles of your neck. The cranial part
follows the vagus nerve.
XII. Hypoglossal nerve: Your hypoglossal nerve is the 12th
cranial nerve. It’s responsible for the movement of most of the
muscles in your tongue.
It starts in the medulla oblongata and moves down into the
jaw, where it reaches the tongue.
Spinal Nerves
Extending from the left and right sides of the spinal cord are
31 pairs of spinal nerves.
The spinal nerves are mixed nerves that carry both sensory
and motor signals between the spinal cord and specific
regions of the body.
The 31 spinal nerves are split into 5 groups named for the 5
regions of the vertebral column.
Thus, there are 8 pairs of cervical nerves, 12 pairs of thoracic
nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves, and
1 pair of coccygeal nerves.

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Each spinal nerve exits from the spinal cord through the
intervertebral foramen between a pair of vertebrae or
between the C1 vertebra and the occipital bone of the skull.
Cervical Nerves
Cervical means of the neck. There are 8 cervical nerves that
emerge from the cervical spine (C1-C8).
Thoracic Nerves
Thoracic means of the chest. There are 12 thoracic nerves that
emerge from the thoracic spine (T1-T12).
Lumbar Nerves
Lumbar means from the lower back region. There are 5 lumbar
nerves that emerge from the lumbar spine (L1-L5).
Sacral Nerves
Sacral means of the sacrum. The sacrum is a bony plate at the
base of the vertebral column.
There are 5 sacral nerves that emerge from the sacral bone
(S1-S5)
Coccygeal Nerves
Coccygeal means of the tailbone. There is 1 nerve that
emerges from the coccygeal bone.
Meninges
The meninges are the protective coverings of the central
nervous system (CNS). They consist of three layers the dura
mater, arachnoid mater, and pia mater.

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Dura matter
The dura mater, which means “tough matter,” is the thickest,
toughest, and most superficial layer of meninges.
Made of dense irregular connective tissue, it contains many
tough collagen fibers and blood vessels.
Dura mater protects the CNS from external damage, contains
the cerebrospinal fluid that surrounds the CNS, and provides
blood to the nervous tissue of the CNS.
Arachnoid matter
The arachnoid mater, which means “spider-like mother,” is
much thinner and more delicate than the dura mater.
It lines the inside of the dura mater and contains many thin
fibers that connect it to the underlying pia mater.
These fibers cross a fluid-filled space called the subarachnoid
space between the arachnoid mater and the pia mater.
Pia matter
The pia mater, which means “tender mother,” is a thin and
delicate layer of tissue that rests on the outside of the brain
and spinal cord. Containing many blood vessels that feed the
nervous tissue of the CNS, the pia mater penetrates into the
valleys of the sulci and fissures of the brain as it covers the
entire surface of the CNS.

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Cerebrospinal Fluid
The space surrounding the organs of the CNS is filled with a
clear fluid known as cerebrospinal fluid (CSF).
CSF is formed from blood plasma by special structures called
choroid plexuses.
The choroid plexuses contain many capillaries lined with
epithelial tissue that filters blood plasma and allows the
filtered fluid to enter the space around the brain.
Cerebrospinal fluid provides several vital functions to the
central nervous system.
CSF absorbs shocks between the brain and skull and between
the spinal cord and vertebrae. This shock absorption protects
the CNS from blows or sudden changes in velocity, such as
during a car accident.
The brain and spinal cord float within the CSF, reducing their
apparent weight through buoyancy.
The brain is a very large but soft organ that requires a high
volume of blood to function effectively.
The reduced weight in cerebrospinal fluid allows the blood
vessels of the brain to remain open and helps protect the
nervous tissue from becoming crushed under its own weight.
CSF helps to maintain chemical homeostasis within the central
nervous system.

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It contains ions, nutrients, oxygen, and albumins that support
the chemical and osmotic balance of nervous tissue.
CSF also removes waste products that form as byproducts of
cellular metabolism within nervous tissue.
 LYMPHATIC SYSTEM
The lymphatic system includes lymph nodes, lymph ducts and
lymph vessels, and also plays a role in the body's defenses. Its
main job is to make is to make and move lymph, a clear fluid
that contains white blood cells, which help the body fight
infection. The lymphatic system also removes excess lymph
fluid from bodily tissues, and returns it to the blood.
 ENDOCRINE SYSTEM
The endocrine system consists of eight major glands that
secrete hormones into the blood. These hormones, in turn,
travel to different tissues and regulate various bodily
functions, such as metabolism, growth and sexual function.
Endocrine system is controlled by Hypothalamus.
Hypothalamus
The hypothalamus is a part of the brain located superior and
anterior to the brain stem and inferior to the thalamus.
It serves many different functions in the nervous system, and
is also responsible for the direct control of the endocrine
system through the pituitary gland.

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The hypothalamus contains special cells called neurosecretory
cells—neurons that secrete hormones:
 Thyrotropin-releasing hormone (TRH)
 Growth hormone-releasing hormone (GHRH)
 Growth hormone-inhibiting hormone (GHIH)
 Gonadotropin-releasing hormone (GnRH)
 Corticotropin-releasing hormone (CRH)
 Oxytocin
 Antidiuretic hormone (ADH)
All of the releasing and inhibiting hormones affect the
function of the anterior pituitary gland. TRH stimulates the
anterior pituitary gland to release thyroid-stimulating
hormone.
GHRH and GHIH work to regulate the release of growth
hormone—GHRH stimulates growth hormone release, GHIH
inhibits its release.
GnRH stimulates the release of follicle stimulating hormone
and luteinizing hormone while CRH stimulates the release of
adrenocorticotropic hormone.
The last two hormones—oxytocin and antidiuretic hormone—
are produced by the hypothalamus and transported to the
posterior pituitary, where they are stored and later released.

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Fig 2.4: Major Endocrine Glands
Source:http://en.wikipedia.org/wiki/endocrine
PITUITARY GLAND
The pituitary gland, also known as the hypophysis, is a small
pea-sized lump of tissue connected to the inferior portion of
the hypothalamus of the brain.
Many blood vessels surround the pituitary gland to carry the
hormones it releases throughout the body.
Situated in a small depression in the sphenoid bone called the
sella turcica, the pituitary gland is actually made of 2
completely separate structures: the posterior and anterior
pituitary glands.

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Posterior Pituitary: The posterior pituitary gland is actually not
glandular tissue at all, but nervous tissue instead.
The posterior pituitary is a small extension of the
hypothalamus through which the axons of some of the
neurosecretory cells of the hypothalamus extend.
These neurosecretory cells create 2 hormones in the
hypothalamus that are stored and released by the posterior
pituitary:
 Oxytocin triggers uterine contractions during childbirth and
the release of milk during breastfeeding.
 Antidiuretic hormone (ADH) prevents water loss in the
body by increasing the re-uptake of water in the kidneys
and reducing blood flow to sweat glands.
 Anterior Pituitary: The anterior pituitary gland is the true
glandular part of the pituitary gland.
 The function of the anterior pituitary gland is controlled by
the releasing and inhibiting hormones of the
hypothalamus. The anterior pituitary produces 6 important
hormones:
 Thyroid stimulating hormone (TSH), as its name suggests,
is a tropic hormone responsible for the stimulation of the
thyroid gland.
 Adrenocorticotropic hormone (ACTH) stimulates the
adrenal cortex, the outer part of the adrenal gland, to
produce its hormones.

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 Follicle stimulating hormone (FSH) stimulates the follicle
cells of the gonads to produce gametes—ova in females
and sperm in males.
 Luteinizing hormone (LH) stimulates the gonads to produce
the sex hormones—estrogens in females and testosterone
in males.
 Human growth hormone (HGH) affects many target cells
throughout the body by stimulating their growth, repair,
and reproduction.
 Prolactin (PRL) has many effects on the body, chief of which
is that it stimulates the mammary glands of the breast to
produce milk.
PINEAL GLAND
The pineal gland is a small pinecone-shaped mass of
glandular tissue found just posterior to the thalamus of the
brain. The pineal gland produces the hormone melatonin that
helps to regulate the human sleep-wake cycle known as the
circadian rhythm. The activity of the pineal gland is inhibited
by stimulation from the photoreceptors of the retina. This
light sensitivity causes melatonin to be produced only in low
light or darkness. Increased melatonin production causes
humans to feel drowsy at night-time when the pineal gland is
active.

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THYROID GLAND
The thyroid gland is a butterfly-shaped gland located at the
base of the neck and wrapped around the lateral sides of the
trachea. The thyroid gland produces 3 major hormones:
 Calcitonin
 Triiodothyronine (T3)
 Thyroxine (T4)
Calcitonin is released when calcium ion levels in the blood rise
above a certain set point.
Calcitonin functions to reduce the concentration of calcium
ions in the blood by aiding the absorption of calcium into the
matrix of bones.
The hormones T3 and T4 work together to regulate the body’s
metabolic rate. Increased levels of T3 and T4 lead to increased
cellular activity and energy usage in the body.
PARATHYROID GLANDS
The parathyroid glands are 4 small masses of glandular tissue
found on the posterior side of the thyroid gland.
The parathyroid glands produce the hormone parathyroid
hormone (PTH), which is involved in calcium ion homeostasis.
PTH is released from the parathyroid glands when calcium ion
levels in the blood drop below a set point.

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PTH stimulates the osteoclasts to break down the calcium
containing bone matrix to release free calcium ions into the
bloodstream.
PTH also triggers the kidneys to return calcium ions filtered
out of the blood back to the bloodstream so that it is
conserved.
ADRENAL GLANDS
The adrenal glands are a pair of roughly triangular glands
found immediately superior to the kidneys.
The adrenal glands are each made of 2 distinct layers, each
with their own unique functions: the outer adrenal cortex and
inner adrenal medulla.
Adrenal cortex: The adrenal cortex produces many cortical
hormones in 3 classes: glucocorticoids, mineralocorticoids,
and androgens.
Glucocorticoids have many diverse functions, including the
breakdown of proteins and lipids to produce glucose.
Glucocorticoids also function to reduce inflammation and
immune response.
Mineralocorticoids, as their name suggests, are a group of
hormones that help to regulate the concentration of mineral
ions in the body.

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Androgens, such as testosterone, are produced at low levels
in the adrenal cortex to regulate the growth and activity of
cells that are receptive to male hormones.
In adult males, the amount of androgens produced by the
testes is many times greater than the amount produced by the
adrenal cortex, leading to the appearance of male secondary
sex characteristics.
Adrenal medulla: The adrenal medulla produces the
hormones epinephrine and norepinephrine under stimulation
by the sympathetic division of the autonomic nervous system.
Both of these hormones help to increase the flow of blood to
the brain and muscles to improve the “fight-or-flight”
response to stress.
These hormones also work to increase heart rate, breathing
rate, and blood pressure while decreasing the flow of blood
to and function of organs that are not involved in responding
to emergencies.
PANCREAS
The pancreas is a large gland located in the abdominal cavity
just inferior and posterior to the stomach.
The pancreas is considered to be a heterocrine gland as it
contains both endocrine and exocrine tissue.

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The endocrine cells of the pancreas make up just about 1% of
the total mass of the pancreas and are found in small groups
throughout the pancreas called islets of Langerhans.
Within these islets are 2 types of cells—alpha and beta cells.
The alpha cells produce the hormone glucagon, which is
responsible for raising blood glucose levels.
Glucagon triggers muscle and liver cells to break down the
polysaccharide glycogen to release glucose into the
bloodstream.
The beta cells produce the hormone insulin, which is
responsible for lowering blood glucose levels after a meal.
Insulin triggers the absorption of glucose from the blood into
cells, where it is added to glycogen molecules for storage.
GONADS
The gonads—ovaries in females and testes in males—are
responsible for producing the sex hormones of the body.
These sex hormones determine the secondary sex
characteristics of adult females and adult males.
Testes: The testes are a pair of ellipsoid organs found in the
scrotum of males that produce the androgen testosterone in
males after the start of puberty.
Testosterone has effects on many parts of the body, including
the muscles, bones, sex organs, and hair follicles.

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This hormone causes growth and increases in strength of the
bones and muscles, including the accelerated growth of long
bones during adolescence.
During puberty, testosterone controls the growth and
development of the sex organs and body hair of males,
including pubic, chest, and facial hair.
In men who have inherited genes for baldness testosterone
triggers the onset of androgenic alopecia, commonly known
as male pattern baldness.
Ovaries: The ovaries are a pair of almond-shaped glands
located in the pelvic body cavity lateral and superior to the
uterus in females.
The ovaries produce the female sex hormones progesterone
and estrogens.
Progesterone is most active in females during ovulation and
pregnancy where it maintains appropriate conditions in the
human body to support a developing fetus.
Estrogens are a group of related hormones that function as
the primary female sex hormones.
The release of estrogen during puberty triggers the
development of female secondary sex characteristics such as
uterine development, breast development, and the growth of
pubic hair.

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Estrogen also triggers the increased growth of bones during
adolescence that lead to adult height and proportions.
THYMUS
The thymus is a soft, triangular-shaped organ found in the
chest posterior to the sternum.
The thymus produces hormones called thymosins that help to
train and develop T-lymphocytes during fetal development
and childhood.
The T-lymphocytes produced in the thymus go on to protect
the body from pathogens throughout a person’s entire life.
The thymus becomes inactive during puberty and is slowly
replaced by adipose tissue throughout a person’s life.
 CIRCULATORY SYSTEM
The job of the circulatory system is to move blood, nutrients,
oxygen, carbon dioxide, and hormones, around the body.
We shall briefly look at circulation of materials in the
following:
Heart: The cardiac muscle tissue of the heart is capable of
producing the hormone atrial natriuretic peptide (ANP) in
response to high blood pressure levels.
ANP works to reduce blood pressure by triggering
vasodilation to provide more space for the blood to travel
through.

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ANP also reduces blood volume and pressure by causing
water and salt to be excreted out of the blood by the kidneys.
Kidneys: The kidneys produce the hormone erythropoietin
(EPO) in response to low levels of oxygen in the blood.
EPO released by the kidneys travels to the red bone marrow
where it stimulates an increased production of red blood cells.
The number of red blood cells increases the oxygen carrying
capacity of the blood, eventually ending the production of
EPO.
Digestive System: The hormones cholecystokinin (CCK),
secretin, and gastrin are all produced by the organs of the
gastrointestinal tract.
CCK, secretin, and gastrin all help to regulate the secretion of
pancreatic juice, bile, and gastric juice in response to the
presence of food in the stomach.
CCK is also instrumental in the sensation of satiety or
“fullness” after eating a meal.
Adipose: Adipose tissue produces the hormone leptin that is
involved in the management of appetite and energy usage by
the body.
Leptin is produced at levels relative to the amount of adipose
tissue in the body, allowing the brain to monitor the body’s
energy storage condition.

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When the body contains a sufficient level of adipose for
energy storage, the level of leptin in the blood tells the brain
that the body is not starving and may work normally. If the
level of adipose or leptin decreases below a certain threshold,
the body enters starvation mode and attempts to conserve
energy through increased hunger and food intake and
decreased energy usage. Adipose tissue also produces very
low levels of estrogens in both men and women. In obese
people the large volume of adipose tissue may lead to
abnormal estrogen levels.
Placenta: In pregnant women, the placenta produces several
hormones that help to maintain pregnancy.
Progesterone is produced to relax the uterus, protect the fetus
from the mother’s immune system, and prevent premature
delivery of the fetus.
Human chorionic gonadotropin (HCG) assists progesterone
by signaling the ovaries to maintain the production of
estrogen and progesterone throughout pregnancy.
Local Hormones: Prostaglandins and leukotrienes are
produced by every tissue in the body (except for blood tissue)
in response to damaging stimuli.
These two hormones mainly affect the cells that are local to
the source of damage, leaving the rest of the body free to
function normally.

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Prostaglandins cause swelling, inflammation, increased pain
sensitivity, and increased local body temperature to help
block damaged regions of the body from infection or further
damage.
They act as the body’s natural bandages to keep pathogens
out and swell around damaged joints like a natural cast to
limit movement.
Leukotrienes help the body heal after prostaglandins have
taken effect by reducing inflammation while helping white
blood cells to move into the region to clean up pathogens and
damaged tissues.
Fig 2.5: The Circulatory System
Source: http://en.wikipedia.org/wiki/circulatory system

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 CARDIOVASCULAR SYSTEM
This has to do with blood circulation, and it includes: The
heart, blood and blood vessels.
The Heart
The heart is a muscular pumping organ located medial to the
lungs along the body’s midline in the thoracic region.
The bottom tip of the heart, known as its apex, is turned to
the left, so that about 2/3 of the heart is located on the body’s
left side with the other 1/3 on right.
The top of the heart, known as the heart’s base, connects to
the great blood vessels of the body: the aorta, vena cava,
pulmonary trunk, and pulmonary veins.
Fig. 2.6: Human heart

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Circulatory Loops
There are 2 primary circulatory loops in the human body: the
pulmonary circulation loop and the systemic circulation loop.
Pulmonary circulation transports deoxygenated blood from
the right side of the heart to the lungs, where the blood picks
up oxygen and returns to the left side of the heart.
The pumping chambers of the heart that support the
pulmonary circulation loop are the right atrium and right
ventricle.
Systemic circulation carries highly oxygenated blood from the
left side of the heart to all of the tissues of the body (with the
exception of the heart and lungs).
Systemic circulation removes wastes from body tissues and
returns deoxygenated blood to the right side of the heart. The
left atrium and left ventricle of the heart are the pumping
chambers for the systemic circulation loop.
BLOOD VESSELS
Blood vessels are the body’s highways that allow blood to flow
quickly and efficiently from the heart to every region of the
body and back again.
The size of blood vessels corresponds with the amount of
blood that passes through the vessel. All blood vessels contain
a hollow area called the lumen through which blood is able to
flow.

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Around the lumen is the wall of the vessel, which may be thin
in the case of capillaries or very thick in the case of arteries.
All blood vessels are lined with a thin layer of simple
squamous epithelium known as the endothelium that keeps
blood cells inside of the blood vessels and prevents clots from
forming.
The endothelium lines the entire circulatory system, all the
way to the interior of the heart, where it is called the
endocardium.
There are three major types of blood vessels: arteries,
capillaries and veins. Blood vessels are often named after
either the region of the body through which they carry blood
or for nearby structures.
For example, the brachiocephalic artery carries blood into the
brachial (arm) and cephalic (head) regions. One of its
branches, the subclavian artery, runs under the clavicle; hence
the name subclavian. The subclavian artery runs into the
axillary region where it becomes known as the axillary artery.
Arteries and Arterioles: Arteries are blood vessels that carry
blood away from the heart. Blood carried by arteries is usually
highly oxygenated, having just left the lungs on its way to the
body’s tissues.
The pulmonary trunk and arteries of the pulmonary circulation
loop provide an exception to this rule – these arteries carry

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deoxygenated blood from the heart to the lungs to be
oxygenated.
Arteries face high levels of blood pressure as they carry blood
being pushed from the heart under great force.
To withstand this pressure, the walls of the arteries are thicker,
more elastic, and more muscular than those of other vessels.
The largest arteries of the body contain a high percentage of
elastic tissue that allows them to stretch and accommodate
the pressure of the heart.
Smaller arteries are more muscular in the structure of their
walls. The smooth muscles of the arterial walls of these smaller
arteries contract or expand to regulate the flow of blood
through their lumen.
In this way, the body controls how much blood flows to
different parts of the body under varying circumstances.
The regulation of blood flow also affects blood pressure, as
smaller arteries give blood less area to flow through and
therefore increases the pressure of the blood on arterial walls.
Arterioles are narrower arteries that branch off from the ends
of arteries and carry blood to capillaries.
They face much lower blood pressures than arteries due to
their greater number, decreased blood volume, and distance
from the direct pressure of the heart.

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Thus arteriole walls are much thinner than those of arteries.
Arterioles, like arteries, are able to use smooth muscle to
control their aperture and regulate blood flow and blood
pressure.
Capillaries: Capillaries are the smallest and thinnest of the
blood vessels in the body and also the most common.
They can be found running throughout almost every tissue of
the body and border the edges of the body’s avascular tissues.
Capillaries connect to arterioles on one end and venules on
the other.
Capillaries carry blood very close to the cells of the tissues of
the body in order to exchange gases, nutrients, and waste
products.
The walls of capillaries consist of only a thin layer of
endothelium so that there is the minimum amount of
structure possible between the blood and the tissues.
The endothelium acts as a filter to keep blood cells inside of
the vessels while allowing liquids, dissolved gases, and other
chemicals to diffuse along their concentration gradients into
or out of tissues.
Precapillary sphincters are bands of smooth muscle found at
the arteriole ends of capillaries. These sphincters regulate
blood flow into the capillaries.

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Since there is a limited supply of blood, and not all tissues
have the same energy and oxygen requirements, the
precapillary sphincters reduce blood flow to inactive tissues
and allow free flow into active tissues.
Veins and Venules: Veins are the large return vessels of the
body and act as the blood return counterparts of arteries.
Because the arteries, arterioles, and capillaries absorb most of
the force of the heart’s contractions, veins and venules are
subjected to very low blood pressures.
This lack of pressure allows the walls of veins to be much
thinner, less elastic, and less muscular than the walls of
arteries.
Veins rely on gravity, inertia, and the force of skeletal muscle
contractions to help push blood back to the heart.
To facilitate the movement of blood, some veins contain many
one-way valves that prevent blood from flowing away from
the heart.
As skeletal muscles in the body contract, they squeeze nearby
veins and push blood through valves closer to the heart.
When the muscle relaxes, the valve traps the blood until
another contraction pushes the blood closer to the heart.
Venules are similar to arterioles as they are small vessels that
connect capillaries, but unlike arterioles, venules connect to

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veins instead of arteries. Venules pick up blood from many
capillaries and deposit it into larger veins for transport back
to the heart.
Coronary Circulation
The heart has its own set of blood vessels that provide the
myocardium with the oxygen and nutrients necessary to
pump blood throughout the body.
The left and right coronary arteries branch off from the aorta
and provide blood to the left and right sides of the heart. The
coronary sinus is a vein on the posterior side of the heart that
returns deoxygenated blood from the myocardium to the
vena cava.
Hepatic Portal Circulation
The veins of the stomach and intestines perform a unique
function: instead of carrying blood directly back to the heart,
they carry blood to the liver through the hepatic portal vein.
Blood leaving the digestive organs is rich in nutrients and
other chemicals absorbed from food. The liver removes toxins,
stores sugars, and processes the products of digestion before
they reach the other body tissues. Blood from the liver then
returns to the heart through the inferior vena cava.
THE BLOOD
The average human body contains about 4 to 5 liters of blood.
As a liquid connective tissue,

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it transports many substances through the body and helps to
maintain homeostasis of nutrients, wastes, and gases.
Blood is made up of red blood cells, white blood cells,
platelets, and liquid plasma.
Red Blood Cells: Red blood cells, also known as erythrocytes,
are by far the most common type of blood cell and make up
about 45% of blood volume.
Erythrocytes are produced inside of red bone marrow from
stem cells at the astonishing rate of about 2 million cells every
second.
The shape of erythrocytes is biconcave—disks with a concave
curve on both sides of the disk so that the center of an
erythrocyte is its thinnest part.
The unique shape of erythrocytes gives these cells a high
surface area to volume ratio and allows them to fold to fit into
thin capillaries.
Immature erythrocytes have a nucleus that is ejected from the
cell when it reaches maturity to provide it with its unique
shape and flexibility.
The lack of a nucleus means that red blood cells contain no
DNA and are not able to repair themselves once damaged.
Erythrocytes transport oxygen in the blood through the red
pigment hemoglobin. Hemoglobin contains iron and proteins

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joined to greatly increase the oxygen carrying capacity of
erythrocytes.
The high surface area to volume ratio of erythrocytes allows
oxygen to be easily transferred into the cell in the lungs and
out of the cell in the capillaries of the systemic tissues.
White Blood Cells: White blood cells, also known as
leukocytes, make up a very small percentage of the total
number of cells in the bloodstream, but have important
functions in the body’s immune system.
There are two major classes of white blood cells: granular
leukocytes and agranular leukocytes.
Granular Leukocytes: The three types of granular leukocytes
are neutrophils, eosinophils, and basophils.
Each type of granular leukocyte is classified by the presence
of chemical-filled vesicles in their cytoplasm that give them
their function.
Neutrophils contain digestive enzymes that neutralize
bacteria that invade the body.
Eosinophils contain digestive enzymes specialized for
digesting viruses that have been bound to by antibodies in
the blood.
Basophils release histamine to intensify allergic reactions and
help protect the body from parasites.

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Agranular Leukocytes: The two major classes of agranular
leukocytes are lymphocytes and monocytes.
Lymphocytes include T cells and natural killer cells that fight
off viral infections and B cells that produce antibodies against
infections by pathogens.
Monocytes develop into cells called macrophages that engulf
and ingest pathogens and the dead cells from wounds or
infections.
Platelets: Also known as thrombocytes, platelets are small cell
fragments responsible for the clotting of blood and the
formation of scabs.
Platelets form in the red bone marrow from large
megakaryocyte cells that periodically rupture and release
thousands of pieces of membrane that become the platelets.
Platelets do not contain a nucleus and only survive in the body
for up to a week before macrophages capture and digest
them.
PLASMA
Plasma is the non-cellular or liquid portion of the blood that
makes up about 55% of the blood’s volume.
Plasma is a mixture of water, proteins, and dissolved
substances. Around 90% of plasma is made of water, although
the exact percentage varies depending upon the hydration
levels of the individual.

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The proteins within plasma include antibodies and albumins.
Antibodies are part of the immune system and bind to
antigens on the surface of pathogens that infect the body.
Albumins help maintain the body’s osmotic balance by
providing an isotonic solution for the cells of the body.
Many different substances can be found dissolved in the
plasma, including glucose, oxygen, carbon dioxide,
electrolytes, nutrients, and cellular waste products.
The plasma functions as a transportation medium for these
substances as they move throughout the body.
BLOOD GROUP
We have four distinct blood groups namely:
_ Blood Group A,
_ Blood Group B,
_ Blood Group AB, and
_ Blood Group O.
This depends on the antigens and antibodies that are present
in the blood.
Antigens are foreign agents, which cause lymphocyte (white
blood cell) to produce antibodies e.g. invading micro-
organisms. There are twotypes of antigens: Antigen A and
Antigen B.

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Antibodies protect the body from the harmful effects of
disease- causing micro- organism.
They give immunity against disease.
Clumping of red blood cells is called agglutination, caused by
the reaction of either antigen.
Absence or presence of antigens forms the basis of blood
group.
Group A – A agglutinogen
Group B – B agglutinogen
Group AB – Both A and B agglutinogen
Group O
GROUP O
– No agglutinogen
Receive blood from Group O only.
Donates blood to any recipients
They are call universal donor
GROUP B
Person with blood group B can only receive blood from B and
O.
GROUP A
Group A receive blood from O and A
GROUP AB
Group AB can only donate to AB. Receive small quantity of
blood from the entire group.

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Large quantity of mismatched blood can result to
agglutination.
RHESUS FACTORS
Rhesus factors determine the positivity and negativity of the
blood.
Rhesus positive (Rh+) if the blood has this factor
Rhesus negative (Rh-) if the blood does not have this factor.
 THE DIGESTIVE SYSTEM
The digestive system consists of a series of connected organs
that together, allow the body to break down and absorb food,
and remove waste. It includes the mouth, esophagus,
stomach, small intestine, large intestine, rectum, and anus. The
liver and pancreas also play a role in the digestive system
because they produce digestive juices.
fig 2.7: Human digestive system

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Mouth
Food begins its journey through the digestive system in the
mouth, also known as the oral cavity.
Inside the mouth are many accessory organs that aid in the
digestion of food—the tongue, teeth, and salivary glands.
Teeth chop food into small pieces, which are moistened by
saliva before the tongue and other muscles push the food into
the pharynx. Oral cavity, cross-section
Teeth
The teeth are 32 small, hard organs found along the anterior
and lateral edges of the mouth.
Each tooth is made of a bone-like substance called dentin and
covered in a layer of enamel—the hardest substance in the
body.
Teeth are living organs and contain blood vessels and nerves
under the dentin in a soft region known as the pulp. The teeth
are designed for cutting and grinding food into smaller
pieces.
Tongue.
The tongue is located on the inferior portion of the mouth just
posterior and medial to the teeth.
It is a small organ made up of several pairs of muscles covered
in a thin, bumpy, skin-like layer.

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The outside of the tongue contains many rough papillae for
gripping food as it is moved by the tongue’s muscles.
The taste buds on the surface of the tongue detect taste
molecules in food and connect to nerves in the tongue to
send taste information to the brain.
The tongue also helps to push food toward the posterior part
of the mouth for swallowing.
Salivary Glands.
Surrounding the mouth are 3 sets of salivary glands. The
salivary glands are accessory organs that produce a watery
secretion known as saliva.
Saliva helps to moisten food and begins the digestion of
carbohydrates. The body also uses saliva to lubricate food as
it passes through the mouth, pharynx, and esophagus.
Pharynx
The pharynx, or throat, is a funnel-shaped tube connected to
the posterior end of the mouth. The pharynx is responsible for
the passing of masses of chewed food from the mouth to the
esophagus.
The pharynx also plays an important role in the respiratory
system, as air from the nasal cavity passes through the
pharynx on its way to the larynx and eventually the lungs.

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Because the pharynx serves two different functions, it contains
a flap of tissue known as the epiglottis that acts as a switch to
route food to the esophagus and air to the larynx.
Esophagus
The esophagus is a muscular tube connecting the pharynx to
the stomach that is part of the upper gastrointestinal tract.
It carries swallowed masses of chewed food along its length.
At the inferior end of the esophagus is a muscular ring called
the lower Stomach, gallbladder and pancreasesophageal
sphincter or cardiac sphincter.
The function of this sphincter is to close of the end of the
esophagus and trap food in the stomach.
Stomach
The stomach is a muscular sac that is located on the left side
of the abdominal cavity, just inferior to the diaphragm.
In an average person, the stomach is about the size of their
two fists placed next to each other. This major organ acts as a
storage tank for food so that the body has time to digest large
meals properly.
The stomach also contains hydrochloric acid and digestive
enzymes that continue the digestion of food that began in the
mouth.

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Small Intestine
The small intestine is a long, thin tube about 1 inch in diameter
and about 10 feet long that is part of the lower
gastrointestinal tract.
It is located just inferior to the stomach and takes up most of
the space in the abdominal cavity.
The entire small intestine is coiled like a hose and the inside
surface is full of many ridges and folds. These folds are used
to maximize the digestion of food and absorption of nutrients.
By the time food leaves the small intestine, around 90% of all
nutrients have been extracted from the food that entered it.
Liver and Gallbladder
The liver is a roughly triangular accessory organ of the
digestive system located to the right of the stomach, just
inferior to the diaphragm and superior to the small intestine.
The liver weighs about 3 pounds and is the second largest
organ in the body.
The liver has many different functions in the body, but the
main function of the liver in digestion is the production of bile
and its secretion into the small intestine.
The gallbladder is a small, pear-shaped organ located just
posterior to the liver.

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The gallbladder is used to store and recycle excess bile from
the small intestine so that it can be reused for the digestion
of subsequent meals.
Pancreas
The pancreas is a large gland located just inferior and
posterior to the stomach.
It is about 6 inches long and shaped like short, lumpy snake
with its “head” connected to the duodenum and its “tail”
pointing to the left wall of the abdominal cavity.
The pancreas secretes digestive enzymes into the small
intestine to complete the chemical digestion of foods.
Intestines
Large Intestine
The large intestine is a long, thick tube about 2 ½ inches in
diameter and about 5 feet long.
It is located just inferior to the stomach and wraps around the
superior and lateral border of the small intestine.
The large intestine absorbs water and contains many
symbiotic bacteria that aid in the breaking down of wastes to
extract some small amounts of nutrients.
Feces in the large intestine exit the body through the anal
canal.

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 THE IMMUNE SYSTEM
The immune system is the body's defense against bacteria,
viruses and other pathogens that may be harmful. It includes
lymph nodes, the spleen, bone marrow, lymphocytes
(including B-cells and T-cells), the thymus and leukocytes,
which are white blood cells.
 THE MUSCULAR SYSTEM
The body's muscular system consists of about 650 muscles
that aid in movement, blood flow and other bodily functions.
There are three types of muscle: skeletal muscle which is
connected to bone and helps with voluntary movement,
smooth muscle which is found inside organs and helps to
move substances through organs, and cardiac muscle which
is found in the heart and helps pump blood.
There are three types of muscle tissue: Visceral, cardiac, and
skeletal.
Visceral Muscle….. Visceral muscle is found inside of organs
like the stomach, intestines, and blood vessels. The weakest of
all muscle tissues, visceral muscle makes organs contract to
move substances through the organ. Because visceral muscle
is controlled by the unconscious part of the brain, it is known
as involuntary muscle—it cannot be directly controlled by the
conscious mind. The term “smooth muscle” is often used to
describe visceral muscle because it has a very smooth, uniform
appearance when viewed under a microscope. This smooth

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appearance starkly contrasts with the banded appearance of
cardiac and skeletal muscles.
Cardiac Muscle……. Found only in the heart, cardiac muscle
is responsible for pumping blood throughout the body.
Cardiac muscle tissue cannot be controlled consciously, so it
is an involuntary muscle. While hormones and signals from
the brain adjust the rate of contraction, cardiac muscle
stimulates itself to contract. The natural pacemaker of the
heart is made of cardiac muscle tissue that stimulates other
cardiac muscle cells to contract. Because of its self-
stimulation, cardiac muscle is considered to be autorhythmic
or intrinsically controlled.
The cells of cardiac muscle tissue are striated—that is, they
appear to have light and dark stripes when viewed under a
light microscope. The arrangement of protein fibers inside of
the cells causes these light and dark bands. Striations indicate
that a muscle cell is very strong, unlike visceral muscles.
The cells of cardiac muscle are branched X or Y shaped cells
tightly connected together by special junctions called
intercalated disks. Intercalated disks are made up of fingerlike
projections from two neighboring cells that interlock and
provide a strong bond between the cells. The branched
structure and intercalated disks allow the muscle cells to resist
high blood pressures and the strain of pumping blood
throughout a lifetime. These features also help to spread

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