SYSTEMS OF HUMAN BODY AND ITS FUNCTIONS

SYSTEMS OF HUMAN
BODY
PRESENTED BY
D. JASMINE PRIYA, B.Sc., DCA., M.Sc., PGDCLT.
DR. NGP ARTS AND SCIENCE COLLEGE
COIMBATORE

 Human beings are arguably the most complex organisms on this planet. Imagine billions of microscopic parts, each with
its own identity, working together in an organized manner for the benefit of the total being.
 The human body is a single structure but it is made up of billions of smaller structures of four major kinds:
CELLS
 Cells have long been recognized as the simplest units of living matter that can maintain life and reproduce themselves.
 The human body, which is made up of numerous cells, begins as a single, newly fertilized cell.
TISSUES
 Tissues are somewhat more complex units than cells.
 By definition, a tissue is an organization of a great many similar cells with varying amounts and kinds of nonliving,
intercellular substance between them.

ORGANS
 Organs are more complex units than tissues.
 An organ is an organization of several different kinds of tissues so arranged that together they can perform a special
function.
 For example, the stomach is an organization of muscle, connective, epithelial, and nervous tissues. Muscle and
connective tissues form its wall, epithelial and connective tissues form its lining, and nervous tissue extends throughout
both its wall and its lining.
SYSTEMS
 Systems are the most complex of the component units of the human body.
 A system is an organization of varying numbers and kinds of organs so arranged that together they can perform complex
functions for the body.

Twelve major systems compose the human body:
1. Skin and appendages
2. Skeletal system
3. Muscular / muscle system
4. Nervous system
5. Endocrine system
6. Cardiovascular system
7. Lymphatic system
8. Respiratory system
9. Digestive system
10. Urinary / excretory system
11. Reproductive system
12. Blood and immune system

 Skin is the largest organ in the body and covers the body's entire external surface.
 It is made up of three layers, 1. Epidermis
2. Dermis
3. Hypodermis
 All three of which vary significantly in their anatomy and function.
 The skin's structure is made up of an intricate network which serves as the body’s initial barrier against pathogens,
UV light, and chemicals, and mechanical injury.
 It also regulates temperature and the amount of water released into the environment.
Skin Thickness
 The thickness of each layer of the skin varies depending on body region and categorized based on the thickness of
the epidermal and dermal layers.
 Hairless skin found in the palms of the hands and soles of the feet is thickest because the epidermis contains an extra
layer, the stratum lucidum.

EPIDERMIS
The layers of the epidermis include the stratum basale (the deepest portion of the epidermis), stratum spinosum, stratum
granulosum, stratum lucidum, and stratum corneum (the most superficial portion of the epidermis).
Stratum basale
 It is also known as stratum germinativum, is the deepest layer, separated from the dermis by the basement membrane (basal
lamina) and attached to the basement membrane by hemidesmosomes.
 The cells found in this layer are cuboidal to columnar mitotically active stem cells that are constantly producing
keratinocytes.
 This layer also contains melanocytes.
Stratum spinosum
 8-10 cell layers, also known as the prickle cell layer contains irregular, polyhedral cells with cytoplasmic processes,
sometimes called “spines”, that extend outward and contact neighboring cells by desmosomes.
 Dendritic cells can be found in this layer.

Stratum granulosum
 3-5 cell layers
 It contains diamond shaped cells with keratohyalin granules and lamellar granules.
Stratum lucidum
 2-3 cell layers
 present in thicker skin found in the palms and soles, is a thin clear layer consisting of eleidin which is a transformation
product of keratohyalin.
Stratum corneum
 20-30 cell layers
 It is the uppermost layer, made up of keratin and horny scales made up of dead keratinocytes, known as anucleate
squamous cells.
 This is the layer which varies most in thickness, especially in callused skin. Within this layer, the dead keratinocytes
secrete defensins which are part of our first immune defense.

Cells of the Epidermis
1. Keratinocytes 3. Langerhans’ cells
2. Merkel’s cell 4. Melanocytes
DERMIS
 The dermis is connected to the epidermis at the level of the basement membrane and consists of two layers, of connective
tissue, the papillary and reticular layers which merge together without clear demarcation.
 The papillary layer is the upper layer, thinner, composed of loose connective tissue and contacts epidermis.
 The reticular layer is the deeper layer, thicker, less cellular, and consists of dense connective tissue/ bundles of collagen
fibers.
 The dermis houses the sweat glands, hair, hair follicles, muscles, sensory neurons, and blood vessels.
HYPODERMIS
 The hypodermis is deep to the dermis and is also called subcutaneous fascia.
 It is the deepest layer of skin and contains adipose lobules along with some skin appendages like the hair follicles, sensory
neurons, and blood vessels.

FUNCTIONS OF SKIN
 It serves as a barrier to water, invasion by microorganisms, mechanical and chemical trauma, and damage from UV light.
 The epidermal water barrier established by the cell envelop, a layer of insoluble proteins on the inner surface of the plasma
membrane.
 It provides mechanical protection to the tissues.
 It prevents loss of water from the body.
 It maintains the body temperature.
 Skin is an very important sensory organ and it contains receptors for touch and sensations.
 Protection from environment.
 Prevents penetration
 Wound repair
 Absorption and excretion
 Production of Vitamin- D.

HUMAN SKELETAL SYSTEM
 It is the combination of all the bones and tissues associated with cartilages and joints.
 Almost all the rigid or solid parts of the body are the main components of the skeletal system.
 Joints play an important role in the skeletal system as it helps in permitting the different types of movements at different
locations.
 If the skeleton were without joints, then there would be no sign of the movements in the human body.
 This skeletal system can be divided into the axial and appendicular systems.
 In an adult body, it is mainly composed of 206 individual bones which are organized into two main divisions:
1. Axial skeleton
2. Appendicular skeleton.

AXIAL SKELETON
The axial skeleton runs along the body’s central axis, therefore it is called
the central core of the human body. The axial skeleton is composed of 80
bones and it consists of:
1.Skull Bone – It includes 8 cranial bones, 14 facial bones, 6 auditory
ossicles, and the Hyoid Bone
2.The bone of the Thoracic Cage – It includes 25 bones of the thorax- a
breastbone and 24 ribs.
3.The bone of the Vertebral column- It includes 24 vertebrae bones, the
sacrum bone, and the coccyx bone.
APPENDICULAR SKELETON
The appendicular skeleton is composed of 126 bones and it comprises of the
1.Pelvic girdle
2.Upper Limbs
3.Lower Limbs
4.Shoulder Girdle or the Pectoral

FUNCTIONS OF SKELETAL SYSTEM
The primary functions of the skeletal system include movement, support, protection production of blood cells, storage of
minerals and endocrine regulation.
Support
The primary function of the skeletal system is to provide a solid framework to support and safeguard the human body and
its organs. This helps in maintaining the overall shape of the human body.
Protection
The skeletal system also helps to protect our internal organs and other delicate body organs, including the brain, heart,
lungs and spinal cord by acting as a buffer. Our cranium (skull) protects our brain and eyes, the ribs protect our heart and
lungs and our vertebrae (spine, backbones) protect our spinal cord.
Movement
Bones provide the basic structure for muscles to attach themselves onto so that our bodies are able to move. Tendons are
tough inelastic bands that attach our muscle to that particular bone.

Storage
The bone matrix of the skeletal system is mainly involved in storing or preserving different types of essential minerals
which are required to facilitate growth and repair of the body cells and tissues. The cell-matrix acts as our calcium bank
by storing and releasing calcium ions into the blood cell when required.
Regulation of Endocrine glands
The bone cells present within the skeletal system plays an important role in releasing the synthesized hormones from the
respective endocrine glands for the further requirement by the body for different metabolisms. Apart from these functions,
the skeletal system also contributes to the regulation of blood sugar.

MUSCULAR SYSTEM
 The muscular system is an organ system, involved majorly in the movement of the body.
 There are nearly 700 muscles that are connected to the bones of the skeletal system, which roughly half make up the
human’s body weight.
 Every muscle is a different organ made of blood vessels, skeletal muscle tissue, nerves, and tendons.
 Muscle tissues are found in the heart, blood vessels, and digestive system.
 There are three kinds of muscle tissues,
1. Cardiac
2. Visceral
3. Skeletal.

CARDIAC MUSCLE
 This muscle is present only in the Heart and responsible for
supplying blood all over the body.
 It is also an involuntary muscle since it cannot be controlled.
 When the brain signals adapt the rate of contraction, the cardiac
muscle triggers by itself to contract.
 The natural pace of the heart is composed of cardiac muscle tissue
and triggers other cardiac muscle cells to shrink.
 The cardiac muscle cells are straight which reveals that they seem to
have dark and light stripes when seen under a microscope.
 The protein fibres arrangement within the cells is responsible for
these dark and light stripes.

Visceral Muscle
 These muscles are found in the organs like intestines, blood vessels, and stomach.
 It is the weakest of all muscle tissues and causes contraction of organs to pass substances through the organ.
 It is said to be an involuntary muscle because it cannot be controlled directly by the conscious mind, but controlled by
the unconscious part of the brain.
 It is also known as a smooth muscle since it has a uniform and a smooth appearance when observed under the
microscope.
Skeletal Muscle
 It is the voluntary muscle tissue that can be controlled in conscious condition.
 All physical actions that a human performs (e.g. walking, writing) needs skeletal muscle.
 The skeletal muscle is responsible for moving the body parts that are connected to the bone.
 Skeletal muscles from many ancestor cells combine themselves together to produce a straight, long fibre.
 These skeletal muscles are strong just like cardiac muscles.
 The name is derived from the known fact that these are connected to the skeleton in one region at least.

FUNCTIONS OF MUSCUCLAR SYSTEM
1.Mobility
 Your skeletal muscles are responsible for the movements you make. Skeletal muscles are attached to your bones and partly
controlled by the central nervous system (CNS).
 You use your skeletal muscles whenever you move. Fast-twitch skeletal muscles cause short bursts of speed and strength.
Slow-twitch muscles function better for longer movements.
2.Circulation
 The involuntary cardiac and smooth muscles help your heart beat and blood flow through your body by producing electrical
impulses.
3.Respiration
 Your diaphragm is the main muscle at work during quiet breathing.
 Heavier breathing, like what you experience during exercise, may require accessory muscles to help the diaphragm.
 These can include the abdominal, neck, and back muscles.

4.Digestion
 Digestion is controlled by smooth muscles found in your gastrointestinal tract. This comprises the:
• Mouth
• Esophagus
• Stomach
• Small and large intestines
• Rectum
• Anus
5. Stability
 The skeletal muscles in your core help protect your spine and help with stability.
 Your core muscle group includes the abdominal, back, and pelvic muscles.
 This group is also known as the trunk. The stronger your core, the better you can stabilize your body.
 The muscles in your legs also help steady you.

NERVOUS SYSTEM
 The nervous system or the neural system is a complex network of neurons specialized to carry messages.
 The complexity of the nervous system increases as we move towards higher animals.
 In the human body, the neural system integrates the activities of organs based on the stimuli, which the neurons detect
and transmit.
 They transmit messages in the form of electrical impulses and convey messages to and from the sense organs.
 Thus, the nervous coordination involves the participation of the sense organs, nerves, spinal cord, and brain.
 The human nervous system consists of two parts, namely:
1. Central Nervous System (consists of the brain and spinal cord)
2. Peripheral Nervous System (includes all the nerves of the body)

1.Central Nervous System
 Central Nervous System (CNS) is often called the central processing unit of the body. It
consists of the brain and the spinal cord.
Brain
 The brain is one of the important, largest and central organ of the human nervous system.
 It is the control unit of the nervous system, which helps us in discovering new things,
remembering and understanding, making decisions, and a lot more.
 It is enclosed within the skull, which provides frontal, lateral and dorsal protection.
 The human brain is composed of three major parts:
1. Forebrain: The anterior part of the brain, consists of Cerebrum, Hypothalamus
and Thalamus.
2. Midbrain: The smaller and central part of the brainstem, consists of Tectum and
Tegmentum.
3. Hindbrain: The central region of the brain, composed of Cerebellum, Medulla
and Pons.

Spinal Cord
 The spinal cord is a cylindrical bundle of nerve fibers and associated
tissues enclosed within the spine and connect all parts of the body to the
brain.
 It begins in continuation with the medulla and extends downwards.
 It is enclosed in a bony cage called vertebral column and surrounded by
membranes called meninges.
 The spinal cord is concerned with spinal reflex actions and the
conduction of nerve impulses to and from the brain.

2. Peripheral Nervous System
Peripheral Nervous System (PNS) is the lateral part of the nervous system that develops from the central nervous system which
connects different parts of the body with the CNS. We carry out both voluntary and involuntary actions with the help of
peripheral nerves.
PNS includes two types of nerve fibers:
1.Afferent nerve fibers – These are responsible for transmitting messages from tissues and organs to the CNS.
2.Efferent nerve-fibers – These are responsible for conveying messages from CNS to the corresponding peripheral organ.
CLASSIFICATION OF
PERIPHERAL NERVOUS
SYSTEM
Somatic neural
system (SNS)
Autonomic
neural system
(ANS)
Para
sysmpathetic
nervous system
Sympathetic
nervous system

Classification of the peripheral nervous system:
Somatic neural system (SNS): It is the neural system that controls the voluntary actions in the body by
transmitting impulses from CNS to skeletal muscle cells. It consists of the somatic nerves.
Autonomic neural system (ANS): The autonomic neural system is involved in involuntary actions like
regulation of physiological functions (digestion, respiration, salivation, etc.). It is a self-regulating system which
conveys the impulses from the CNS to the smooth muscles and involuntary organs (heart, bladder and pupil).
The autonomic neural system can be further divided into:
1.Sympathetic nervous system
2.Parasympathetic nervous system

NEURON
A Neuron is a structured and functional unit of the nervous system and unlike other
cells, neurons are irregular in shape and able to conduct electrochemical signals.
The different parts of a neuron are discussed below.
 Dendrite stretches out from the cell body of a neuron, and it is the shortest fibre in
the cell body.
 Axon is the longest thread on the cell body of a neuron and has an insulating and
protective sheath of myelin around it.
 Cell body consists of cytoplasm and nucleus.
 Synapse is the microscopic gap between a pair of adjacent neurons over which
nerve impulses pass, when moving from one neuron to the other.

NERVES
Nerves are thread-like structures that emerge from the brain and spinal cord.
It is responsible for carrying messages to all the parts of the body.
There are three types of nerves. Some of these neurons can fire signals at speeds of over 119
m/s or above 428 km/h.
1. Sensory nerves send messages from all the senses to the brain.
2. Motor nerves carry messages from the brain to all the muscles.
3. Mixed nerves carry both sensory and motor nerves.

ENDOCRINE SYSTEM
 Hormones are chemicals that affect a lot of the bodily functions ranging from hunger, reproduction and growth to much
more complicated functions like human emotions and behaviour.
 These hormones are produced in our body through nine primary glands and these glands, along with other organs that
provide auxiliary functions make up the endocrine system.

Endocrine Glands
Unlike exocrine glands(sweat, salivary), endocrine glands secrete their respective substances directly into the bloodstream
rather than through a duct.
These endocrine glands belong to the body’s control system and they produce hormones which help to regulate the
functions of cells and tissues. Some glands are specific to either male (testes) or female (ovaries)
Major Endocrine Glands
1. Pituitary gland
 Enclosed deep within the skull, the pituitary gland is the size of a pea.
 It hangs on a stalk at the base of the brain.
 It consists of an anterior portion that produces hormones and a posterior portion that has many neural links.
 This gland is regarded as the master gland as it controls the functions of all the other glands (such as the adrenal,
thyroid glands) in the endocrine system.
 The pituitary gland stimulates the adrenal gland to secrete cortisol, a steroid hormone controls a range of activities from
controlling the body’s metabolism to stimulating blood pressure.
 The pituitary gland also secretes prolactin, which stimulates the production of milk.

2. Thyroid gland
 The thyroid glands can be found at the front of the neck.
 It sits low in the throat, between the windpipe. Brownish red, it has blood vessels coursing through it.
 It secretes hormones that are collectively called thyroid hormones.
 The most prominent are T3 and T4, which influence the body’s rate of metabolism.
3. Parathyroid glands
 The parathyroid glands consist of four small glands that are located behind the thyroids in the neck.
 They influence the calcium levels in the body by producing a hormone called Parathyroid Hormone.
 Sometimes, when the gland produces excess parathyroid hormones, it can have negative effects such as brittle bones and
kidney stones.
4. Adrenal glands
 The adrenal glands sit atop the kidneys and are no larger than a walnut.
 These glands produce over 150 hormones that regulate different functions in the body. The most well known is
Adrenaline, which triggers the flight or fight response.
 In other words, this is a stress hormone that helps the organism to either face a dangerous situation or to avoid it
altogether.

5. Pancreas
 The pancreas is exocrine as well as an endocrine gland that sits behind the stomach. It is roughly 6 inches long and rather
flat.
 The pancreas has two primary roles to play:
1. Producing digestive enzymes
2. Producing hormones such as insulin and glucagon.
 Insulin is produced by the β cells in the pancreas and it helps in regulating the blood glucose levels in the body from getting
too high.
6. Gonads
 Some glands are specific to males or females.
 For instance, the ovaries are specific to females and are located in the pelvic cavity. While the testes are specific to males.
 Ovaries produce estrogen that is important for reproduction and female sex characteristics.
 Testes produce testosterone that is responsible for male sex characteristics.
 Also, it results in increased muscle mass and body hair.

Circulatory System / Cardiovascular System
 A network of organs that allow the circulation of blood throughout the body is also known as the cardiovascular system or
vascular system.
 The vital function of the circulatory system is to transport blood to all parts of the body, which is extremely important
because it carries nutrients, oxygen, carbon dioxide, hormones and blood cells which are required for the nourishment and
growth the cells of every organ.
 It is a closed network consisting of four major components:
1. The heart
2. Blood
3. Blood vessels
 These four, with the help of certain other organs such as the lungs, are responsible for the circulation of blood in the human
body.
 Major Components of the human circulatory system are mentioned below.
1. Heart
2. Blood

1. The Heart
 The heart is a muscular organ, located roughly at the body’s midline in the thoracic region, and responsible for the pumping
of blood in the body.
 The heart is divided into four chambers: Right atrium, right ventricle, left atrium and left ventricles.
 The atriums collect the blood in the heart and the ventricles pump it to different organs.
2. Blood
 Blood is a fluid connective tissue which plays an essential role in the circulatory system.
 It carries oxygen and nutrients to all parts of the body. It also regulates the temperature and acidic balance of the body.
Types of blood circulation
i. The systemic circulation:
 It carries oxygenated blood from the heart to all parts of the body through a complex system of arteries and capillaries.
 It also carries deoxygenated blood from these organs back to the heart through veins.

ii. The pulmonary circulation:
 After the heart receives the deoxygenated blood from different parts of the body, it pumps those to the lungs for
expelling the carbon dioxide and other impurities and collect oxygen, after which the oxygenated blood is sent back
to the heart for systemic circulation.
3. Blood Vessels
There are three types of blood vessels in the human body:
i. Artilleries– They carry blood away from the heart. The arteries in the systemic loop carry oxygenated blood to
different parts of the body while the ones in the pulmonary loop carry deoxygenated blood to the lungs.
ii. Veins– They carry deoxygenated blood from the body and oxygenated blood from the lungs into the heart.
iii. Capillaries– Arteries break down into a minuscule network of capillaries, which are the smallest blood vessels and
present in the lungs and muscles.

LYMPHATIC SYSTEM
 The lymphatic system is part of the immune system. It also maintains fluid balance and plays a role in absorbing fats
and fat-soluble nutrients.
 The lymphatic system is a network of lymph nodes connected by lymphatic vessels.
 This system transports lymph throughout the body.
 The whole body is encompassed with the lymph vessels similar to the blood vessels and has a complex nature.
 The cells of the body are supported really well by them as it receives oxygen and nutrients from the same.
 The lymph gets recirculated through the vessels themselves as they have no endpoint.
Functions of the lymphatic system
The three main functions of lymphatic system are given below
1. Maintains the balance of fluid between the blood and tissues, also called fluid homeostasis.
2. Forms a vital part of the body’s immune system and helps defend against bacteria and other intruders.
3. Facilitates the absorption of fats and fat-soluble nutrients in the digestive system.

Human Digestive System
 The digestive system of the human body comprises a group of organs working together to convert food into energy for
the body.
 Anatomically, the digestive system is made up of the gastrointestinal tract, along with accessory organs such as the liver,
pancreas and gallbladder.
 The hollow organs that make up the gastrointestinal tract (GI tract) include the mouth, stomach, esophagus, small
intestine and large intestine that contains the rectum and anus.
 Human Digestive System and Nutrition involve the intake of food by an organism and its utilization for energy. This is a
vital process which helps living beings to obtain their energy from various sources.
 The food which we eat undergoes much processing before the nutrients present in them are utilized to generate energy.
This processing is known as digestion.
 Humans and other animals have specialized organs and systems for this process.
 The digestion process involves the alimentary canal along with various accessory organs and organ systems.
 In humans, the process is quite simple due to our monogastric nature.

 The alimentary canal is the long tube through which the food that we eat is passed.
 It begins at the mouth (buccal or oral cavity), passes through the pharynx, oesophagus or food pipe, stomach, small
intestines, large intestines, rectum and finally ends at the anus.
 The food particles gradually get digested as they travel through various compartments of the alimentary canal.
 Accessory organs are organs which participate in the digestion process but are not actually a part of GIT. They stimulate
the digestion by releasing certain enzymes that help in breaking down the food.
Mouth
Food starts its journey from the mouth or the oral cavity. There are many other organs that contribute to the digestion
process, including teeth, salivary glands, and tongue. Teeth are designed for grinding food particles into small pieces and are
moistened with saliva before the tongue pushes the food into the pharynx.
Pharynx
A fibromuscular y-shaped tube attached to the terminal end of the mouth. It is mainly involved in the passage of
chewed/crushed food from the mouth through the oesophagus. It also has a major part in the respiratory system, as air
travels through the pharynx from the nasal cavity on its way to the lungs.

Oesophagus
This is a muscular tube that connects the pharynx, which is a part of an upper section of the gastrointestinal tract. It supplies
swallowed food along with its length.
Stomach
It serves as a muscular bag which is situated towards the left side of the abdominal cavity, beneath the diaphragm. This vital
organ acts as a storage for the food and provides enough time to digest meals. The stomach also produces digestive
enzymes and hydrochloric acid that maintains the process of digestion.
Small Intestine
The small intestine is a thin, long tube of about 10 feet long and a part of the lower gastrointestinal tract. It is present just
behind the stomach and acquires a maximum area of the abdominal cavity. The complete small intestine is coiled and the
inner surface consists of folds and ridges.
Large Intestine
This is a thick, long tube measuring around 5 feet in length. It is present just beneath the stomach and wraps over the
superior and lateral edges of the small intestine. It absorbs water and consists of bacteria (symbiotic) that support the
breakdown of wastes to fetch small nutrients.

Rectum
Waste products are passed into the end of the large intestine called the rectum and eliminated out of the body as a solid
matter called stool. It is stored in the rectum as semi-solid faeces which later exits from the body through the anal canal
through the process of defecation.
Accessory Organs
Pancreas
It is a large gland present just behind the stomach. It is short with its anterior connected to the duodenum and posterior
pointing towards the left part of the abdominal cavity. The pancreas releases digestive enzymes to complete the process of
chemical digestion.
Liver
The liver is a roughly triangular, reddish-brown accessory organ of the digestive system located to the right of the stomach.
It produces bile, which helps in the digestion of fat in the small intestine. The bile is stored and recycled in the gallbladder.
It is a small, pear-shaped organ which is located just next to the liver

Digestion Process
 The process of digestion begins from the mouth and ends in the small intestine.
 The large intestines’ main function is to absorb the remaining water from the undigested food and
enable bacterial fermentation of materials that can no longer be digested.
 The alimentary canal or the gastrointestinal tract is a series of hollow organs and tubes that begins
from the mouth cavity and continues into the pharynx, through the stomach, small intestines, large
intestines, and finally ending at the anus.
 Food particles gradually get digested as they travel through various compartments of the
gastrointestinal tract.

Digestion
process
Ingestion
Mixing &
movement
Secretion
Digestion
Absorption
Excretion
6
5
4
3
2
1

1. Ingestion
 The very first step involves mastication (chewing).
 The salivary glands, along with the tongue, helps to moisten and lubricate food, before being pushed down into the food pipe.
2. Mixing and Movement
 It involves the process of lubricating and manipulating food and pushing it down the food through the food pipe
(using peristalsis), and into the stomach.
3. Secretion
 The stomach, small intestine, liver, and pancreas secrete enzymes and acids to aid the process of digestion.
 It functions by breaking down food particles into simple components and easily absorbable components.
4. Digestion
 The process of converting complex food particles into simpler substances in the presence of enzymes and acids secreted by
different digestive organs.
5. Absorption
 This process begins in the small intestine where most of the nutrients and minerals are absorbed.
 The excess water in the indigestible matter is absorbed by the large intestines.

6. Excretion
 The process of removing indigestible substances and waste by-products from the body through the process of defecation.
Functions of the Human Digestive System
 Digestion and absorption are the two main functions of the digestive system.
 Digestion is necessary for breaking down food particles into nutrients that are used by the body as an energy source, cell
repair and growth.
 Food and drink need to be converted into smaller molecules of nutrients before it is absorbed by the blood and carried to
the cells throughout the body. The body breaks the nutrients present in the drinks and food into carbohydrates, vitamins,
fats and proteins.

RESPIRATORY SYSTEM
 Human Respiratory System is a network of organs and tissues that helps us breathe.
 The primary function of this system is to introduce oxygen into the body and expel carbon dioxide from the
body.
 Aside from the lungs, there are also muscles and a vast network of blood vessels that facilitate the process of
respiration.
Respiratory System Parts and Functions
1. Nose
 Humans have exterior nostrils, which are divided by a framework of cartilaginous structure called the septum.
 This is the structure that separates the right nostril from the left nostril.
 Tiny hair follicles that cover the interior lining of nostrils act as the body’s first line of defence against
foreign pathogens. Furthermore, they provide additional humidity for inhaled air.

2. Larynx
 Two cartilaginous chords lay the framework for the larynx.
 It is found in front of the neck and is responsible for vocals as well as aiding respiration.
 Hence, it is also informally called the voice box.
 When food is swallowed, a flap called the epiglottis folds over the top of the windpipe and prevents food from entering
into the larynx.
3. Pharynx
 The nasal chambers open up into a wide hollow space called the pharynx.
 It is a common passage for air as well as food.
 It functions by preventing the entry of food particles into the windpipe.
4. Trachea
 The trachea or the windpipe rises below the larynx and moves down to the neck.
 The walls of the trachea comprise C-shaped cartilaginous rings which give hardness to the trachea and maintain it by
completely expanding.
 The trachea extends further down into the breastbone and splits into two bronchi, one for each lung.

5. Bronchi
 The trachea splits into two tubes called the bronchi, which enter each lung individually.
 The bronchi divide into secondary and tertiary bronchioles, and it further branches out into small air-sacs called
the alveoli.
 The alveoli are single-celled sacs of air with thin walls.
 It facilitates the exchange of oxygen and carbon dioxide molecules into or away from the bloodstream.
6. Lungs
 Lungs are the primary organs of respiration in humans and other vertebrates.
 They are located on either side of the heart, in the thoracic cavity of the chest. Anatomically, the lungs are spongy
organs with an estimates total surface area between 50 to 75 sq meters.
 The primary function of the lungs is to facilitate the exchange of gases between the blood and the air.
 Interestingly, the right lung is quite bigger and heavier than the left lung.

RESPIRATION PROCESS
The respiratory tract in humans is made up of the following parts:
1. External nostrils – For the intake of air.
2. Nasal chamber – which is lined with hair and mucus to filter the air from dust and dirt.
3. Pharynx – It is a passage behind the nasal chamber and serves as the common passageway for both air and food.
4. Larynx – Known as the soundbox as it houses the vocal chords, which are paramount in the generation of sound.
5. Epiglottis – It is a flap-like structure that covers the glottis and prevents the entry of food into the windpipe.
6. Trachea – It is a long tube passing through the mid-thoracic cavity.
7. Bronchi – The trachea divides into left and right bronchi.
8. Bronchioles – Each bronchus is further divided into finer channels known as bronchioles.
9. Alveoli – The bronchioles terminate in balloon-like structures known as the alveoli.
10. Lungs – Humans have a pair of lungs, which are sac-like structures and covered by a double-layered membrane known
as pleura.

RESPIRATORY SYSTEM FUNCTIONS
 Ihalation and exhalation
 Exchange of Gases between Lungs and Bloodstream
 Exchange of Gases between Bloodstream and Body Tissues
 The Vibration of the Vocal Cords
 Olfaction or Smelling

EXCRETORY SYSTEM
 We all obtain our nutrients from different sources which are later digested and metabolized in our body.
 After metabolic reactions, the body starts to sort out useful and toxic substances in an individual.
 As we all know, the accumulation of the toxins may be harmful and the body removes all the metabolic wastes by
the process called excretion.
 Different organisms follow different modes of excretion such as kidney, lungs, skin and eyes depending on their
habitat and food habit.
Excretory System Organs
The human excretory system organs include:
 A pair of kidneys
 A pair of ureters
 A urinary bladder
 A urethra

Kidneys
 Kidneys are bean-shaped structures located on either side of
the backbone and are protected by the ribs and muscles of the
back.
 Each human adult kidney has a length of 10-12 cm, a width
of 5-7 cm and weighs around 120-170g.
 The kidneys have an inner concave structure. The blood
vessels, ureter and nerves enter the kidneys through the
hilum, which is a notch at the inner concave surface of the
kidney.
 The renal pelvis, a large funnel-shaped space is present inner
to the hilum, is has many projections known as calyces.

Ureter
 A pair of thin muscular tubes called the ureter comes out of
each kidney extending from the renal pelvis.
 It carries urine from the kidney to the urinary bladder.
Urinary Bladder
 It is a muscular sac-like structure, which stores urine.
 The urinary bladder is emptied by the process of micturition,
i.e. the act of urination.
Urethra
 This tube arises from the urinary bladder and helps to expel
urine out of the body.
 In males, it acts as the common route for sperms and urine.
 Its opening is guarded by sphincter muscles.

Excretion in Humans
 Excretion is the process where all the metabolic wastes are removed from the body.
 Excretion in humans is carried through different body parts and internal organs in a series of processes.
 Blood contains both useful and harmful substances. Hence, we have kidneys which separate useful substances by
reabsorption and toxic substances by producing urine.
 Kidney has a structural filtration unit called nephron where the blood is filtered. Each kidney contains a million
nephrons.
 Capillaries of kidneys filter the blood and the essential substances like glucose, amino acids, salts, and the required
amount of water get reabsorbed and the blood goes into circulation.
 Excess water and nitrogenous waste in humans are converted to urine.
 Urine thus produced is passed to the urinary bladder via the ureters.
 The urinary bladder is under the control of the Central Nervous System.
 The brain signals the urinary bladder to contract and through the urinary opening called the urethra, we excrete the urine.

REPRODUCTION PROCESS
 Reproduction can be defined as the biological process of producing a new individual or an offspring identical to the
parents. This process ensures the increase in the number of individuals of a species when conditions are favourable.
 It is one of the fundamental characteristics of living things and an essential life process.
TYPES OF REPRODUCTION
There are two types of reproduction – asexual and sexual.
1. Sexual Reproduction –This process of reproduction is very complex that involves the formation and transfer of gametes,
followed by fertilization, the formation of the zygote, and embryogenesis.
2. Asexual Reproduction — This process of reproduction involves only one parent and the new offspring produced is
genetically similar to the parent.

Reproduction in Human BeingS
 All human beings undergo a sexual mode of reproduction. In this process, two parents are involved in producing a
new individual.
 Offspring are produced by the fusion of gametes (sex cells) from each parent.
 Hence, the newly formed individual will be different from parents, both genetically and physically.
 Human reproduction is an example of sexual reproduction.
 In human beings, both males and females have different reproductive systems; hence, they are known to exhibit
sexual dimorphism.
 Males have testes- also called testicles, while the females have a pair of ovaries.
Human Reproductive System
The reproduction in human beings involves the fusion of male and female gametes produced in their reproductive
system. The male reproductive system is different from the female reproductive system, both in structure and in
function.

Male reproductive system
1. Testicles (testes): A pair of oval-shaped organs masked in a pouch called the
scrotum. They are responsible for the production of sperms and the male
hormone testosterone.
2. Scrotum: It is a sac-like organ that hangs below the penis and behind it. It is the
houses of the testicles, or testes, and maintains a temperature that is required for
the production of sperm by it.
3. Vas deferens: The sperms produced in testes are stored in a tube called the
epididymis. Here the sperms get matured and pass to urethra through the
muscular tube called vas deferens.
4. Accessory glands: This includes three glands, namely seminal vesicles, prostate
gland, and Cowper’s gland. The secretions from the three glands mix to form a
fluid called semen. Semen nourishes the sperm, increases the volume and helps
in lubrication.
5. Penis: Penis is a cylindrical tube which serves as both reproductive organ and an
excretory organ. It delivers sperms into the vagina during sexual intercourse.

Female Reproductive System
1. A pair of ovaries: Ovaries produce and store ovum in them. They
also produce a female hormone called estrogen.
2. Fallopian tubes (Oviducts): They are the site of fertilization.
They connect ovaries with the uterus.
3. Uterus: Uterus is the site of development for the embryo.
4. Vagina: It is the part which connects the cervix to the external
female body parts. It is the route for the penis during coitus as
well as a fetus during delivery.

Reproduction Process in Human Beings
 The process of fusion of sperm with egg (ovum) to produce
zygote is called fertilization.
 Fertilization is a crucial stage of reproduction in human
beings.
 The fertilized egg is called the zygote. Zygote starts to divide
into many cells and develops into an embryo.
 Embryo moves into the uterus and gets attached to its walls.
This process is referred to as implantation, and the implanted
embryo eventually develops into a fetus.

What is the Immune system?
 The Immune System consists of different types of cells and molecules, which protect our body against
pathogens.
 Pathogens are defined as everything from parasites to fungi, bacteria, viruses and haptens .
 Haptens are molecules that may cause an immune response when they come in contact with a protein.
 All these cells and molecules are distributed in all the tissues of the body as well as lymphoid organs,
which eliminate or prevent microbial infections to decrease the growth of tumors and start the repairing
process of damaged tissues.
 The main parts of the immune system are:
 Spleen.
 Thymus.
 Antibodies.
 Bone marrow.
 White blood cells.
 Lymphatic system.
 Complement system.

Types of Immune System
Immune System fights against microbes and is divided into different types of reactions. The four types of immunity are:
1. Innate immunity
 We all are born with innate (or natural) immunity, a type of natural protection.
 The immunity, which is present in an organism by birth is called innate Immunity.
 Innate immunity refers to the body’s defence system.
 For example, the skin, the barrier of the human body functions by protecting the entry of germs and other disease-
causing pathogens.
2. Adaptive immunity
 An individual acquires immunity after birth, hence is called adaptive or acquired immunity.
 Adaptive immunity develops throughout our lives.
 We acquire adaptive immunity when we are exposed to infectious diseases and allergies or when we are immunized
against them with vaccines.

3. Passive immunity
 Passive immunity is developed by antibodies that are produced outside the body.
 This immunity lasts for a short time.
 For example, antibodies present in a mother’s breast milk provides a baby with temporary immunity against
the diseases.
4. Active Immunity
 Active immunity is a type of adaptive immunity, which is developed due to the production of antibodies in
one’s own body.
 This type of immunity occurs when we are in contact with the pathogen or its antigen.
 When the active immunity happens for the first time, it is called a primary response.
 Once a body experiences a pathogen for the first time, it keeps a few of the antibodies that attacked the
pathogen just in case it attacks for the second time. This is known as natural active immunity.

SPLEEN
 The spleen is an organ in the upper far left part of the
abdomen, to the left of the stomach.
 The spleen varies in size and shape between people, but it’s
commonly fist-shaped, purple, and about 4 inches long.
 Because the spleen is protected by the rib cage, you can’t
easily feel it unless it’s abnormally enlarged.
 The spleen plays multiple supporting roles in the body.
 It acts as a filter for blood as part of the immune system.
 Old red blood cells are recycled in the spleen, and platelets
and white blood cells are stored there.
 The spleen also helps fight certain kinds of bacteria that
cause pneumonia and meningitis.

THYMUS
 The thymus is a primary lymphoid organ located in the
mediastinum.
 It consists of two lobes connected by an isthmus.
Histologically, the thymus is divided into lobules, each
one consisting of a central medulla and a peripheral
cortex.
 The thymus is an essential component of our immune
systems.
 It functions as the initial site of T cell immune maturation
through positive and negative selection processes.
 T cells gain their name as they mature in the thymus
and B cells are so named, as they mature in the bone
marrow.

What Are Antibodies?
 Antibodies, also known as immunoglobulins, are Y-shaped proteins that are
produced by the immune system to help stop intruders from harming the body.
When an intruder enters the body, the immune system springs into action.
 These invaders, which are called antigens, can be viruses, bacteria, or other
chemicals.
 When an antigen is found in the body, the immune system will create antibodies
to mark the antigen for the body to destroy.
Function
 The antibodies act sort of like the immune system's scouts.
 They find antigens, stick to them, and identify for the immune system the exact
type of antigen so that it can be destroyed. Each antibody is made for one and
only one antigen, and it's fitted with special receptors that will only bind to that
antigen.
 For instance, a specific antibody is created to help destroy the chickenpox virus.
Only that particular antibody will attack a chickenpox virus.

BONE MARROW
 Bone marrow is pronounced as bone MAYR-oh and marrow is basically the soft
and spongy tissue that has many blood vessels and cell producing tissues and it is
found in the centre of most bones in the human body.
 The human bone marrow produces approximately 500 billion blood cells per day,
which functions in the joining of the systemic blood circulation via the permeable
vasculature sinusoids or capillaries within the medullary cavity which is the
innermost part of the central cavity of the bone shafts.
 The bone marrow approximately comprises 5 percent of the total body mass in a
healthy adult human.
 Types of Bone Marrow The types of bone marrow are depending on the location of
it on the bone.
 The red bone marrow contains the hematopoietic tissue, which are the stem cells
that form blood cells and are primarily found in the medullary cavity located
towards the outer surface of the bone.
 And the yellow bone marrow is in the medullary cavity in the shaft of long bones
and is often surrounded by a layer of red bone marrow.

Bone Marrow Function
 The T cells and B cells that are important to the immune system are produced and migrated through the bone
marrow.
 The bone marrow produces all of the lymphoid cells that migrate to the thymus to mature into T cells, which are
important for adaptive immune responses.
 The B cells mature in the bone marrow and they are primarily responsible for mediating the production of
antibodies that are antigen-specific immunoglobulin (Ig) and undergo selection for non-self before making their
way to the peripheral lymphoid tissues.
 The bone marrow which constitutes the hemopoietic cells that are derived from the multipotential stem cells gives
rise to all of the lymphoid cells found in the lymphoid tissue, along with all of the cells found in the blood.
 The red bone marrow cells produce platelets, which are crucial for the blood clotting process that stops the loss of
blood in case of cuts and injuries.
 This fat stored in the yellow bone marrow can be used as a source of energy as needed.

BLOOD
 Blood is the only fluid connective tissue, which functions by circulating and transporting oxygen, nutrients and
other essential minerals to various cells and tissues of our body.
 In humans, blood is mainly composed of plasma, blood cells and platelets.
 Overall, blood makes up 7 to 8 percent of total body weight and an average, healthy person possesses around 5
to 6 litres of blood.
 A drop of blood contains millions of red blood cells, thousands of white blood cells and lakhs of blood platelets.
Overall, a healthy adult human body comprises approximately 1.325 gallons of blood cells.
 Types of Blood Cells
1. Erythrocytes (Red blood cells)
2. Leucocytes (White blood cells)
3. Thrombocytes (Blood Platelets)

 WBC-white blood cells are also called leukocytes or leucocytes. They are cells of the immune
system, which is mainly responsible for:
 Protecting and fighting against invading pathogens.
 Stimulates the production of the progesterone hormone
 Play a vital role in the human reproductive system by producing a network of blood vessels
within the ovary.
 On an average, the total count of white blood cells in every microliter of blood ranges between 4
and11 thousands and a healthy person will produce around 80 to 100 billions of white blood cells
every day.
 The lifespan of white blood cells ranges between 13 and 20 days.
 White blood cells are nucleotide blood cells which are white in color, hence they are called white
blood cells.
 These blood cells are characterized into granulocytes and agranulocytes.

SYSTEMS OF HUMAN BODY AND ITS FUNCTIONS

SYSTEMS OF HUMAN BODY AND ITS FUNCTIONS

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