functional organization of the human body

Copyright © 2006 by Elsevier, Inc.
Chapter 1
Functional organization of the
human body and control of the “
internal environment”

Physiology
Physiology is the science that seeks to explain the physical
and chemical mechanisms that are responsible for the
origin, development, and progression of life

Therefore, the vast field of physiology
can be divided into viral physiology,
bacterial physiology, cellular physiology,
plant physiology, human physiology, and
many more subdivisions.

The science of human physiology attempts to
explain the specific characteristics and
mechanisms of the human body that make it a
living being.

Cells are the living unit of the body
• Cells: the basic structural and functional unit
• Tissues: (e.g. muscles, epithelial, nervous )
• Organs: (e.g. kidney, heart, liver, pancreas)
• Organ systems: (e.g. cardiovascular, urinary)

Cells as the Living Units of the Body
• The basic living unit of the body is the cell.
Each tissue and organ is an aggregate of many
different cells held together by intercellular
supporting structures.

• For example, the red blood cells, numbering about 25
trillion in each human being, transport oxygen from
the lungs to the tissues.
• Although the red blood cells are the most abundant
of any single type of cell in the body, about 75 trillion
additional cells of other types perform functions
different from those of the red blood cell.
• The entire body, then, contains about 100 trillion
cells.

• Almost all cells also have the ability to reproduce
additional cells of their own kind.
• Fortunately, when cells of a particular type are
destroyed from one cause or another, the remaining
cells of this type usually generate new cells until the
supply is replenished.

Extracellular Fluid—The “Internal
Environment”
• About 60 percent of the adult human body is fluid,
mainly a water solution of ions and other substances.
• Although most of this fluid is inside the cells and is
called intracellular fluid.

Extracellular Fluid
• The fluid outside the cells and is called extracellular fluid.
• This extracellular fluid is in constant motion throughout the
body.

• In the extracellular fluid are the ions and nutrients needed by the
cells to maintain life.
• Thus, all cells live in essentially the same environment—the
extracellular fluid.
• For this reason, the extracellular fluid is also called the
internal environment of the body, or the milieu intérieur

• Differences Between Extracellular and
Intracellular Fluids.
The extracellular fluid contains large
amounts of sodium, chloride, and
bicarbonate ions plus nutrients for the
cells, such as oxygen, glucose, fatty
acids, and amino acids.

It also contains carbon dioxide that is being
transported from the cells to the lungs to be
excreted, plus other cellular waste products
that are being transported to the kidneys for
excretion.

The intracellular fluid differs significantly
from the extracellular fluid; specifically, it
contains large amounts of potassium,
magnesium, and phosphate ions instead of
the sodium and chloride ions found in the
extracellular fluid.

Homeostasis
• The term homeostasis is used by
physiologists to mean maintenance of
nearly constant conditions in the internal
environment.

Disease is often considered to be a state of
disrupted homeostasis

• Extracellular Fluid Transport and Mixing
System-the blood circulatory system
• ECF is transported through all parts of the
body in two stages:
1. The first stage is movement of blood
through the body in the blood vessels.
2. The second is movement of fluid between
the blood capillaries and the intercellular
spaces between the tissue cells.

• All the blood in the circulation traverses the
entire circulatory circuit an average of once
each minute (at rest).
• as many as six times each minute when
(active).

Origin of Nutrients in the Extracellular
Fluid
Respiratory System.
Each time the blood passes through the body, it
also flows through the lungs. The blood picks
up oxygen in the alveoli, thus acquiring the
oxygen needed by the cells.

Gastrointestinal Tract.
different dissolved nutrients, including
carbohydrates, fatty acids, and amino acids, are
absorbed from the ingested food into the
extracellular fluid of the blood.

• Liver and Other Organs That Perform
Primarily Metabolic Functions
• Liver, kidneys, and endocrine glands (help modify
the absorbed substances or store them until they are
needed).
• Eliminates certain waste products produced in the
body and toxic substances that are ingested.

Musculoskeletal System.
• the body could not move to the appropriate
place at the appropriate time to obtain the
foods required for nutrition.
• The musculoskeletal system also provides
motility for protection against adverse
surroundings

Removal of Metabolic End Products
1. Removal of CO2 by Lungs:
CO2 is released from blood to lung alveoli; CO2 most
abundant of all end products.
2. Kidneys:
• removes from the plasma (urea, uric acid, excess ions and
water
• Re-absorption into blood (glucose, amino acids, water, many
more ions).
• Metabolic end products; through renal tubules into the urine.

3. GI Tract:
Eliminates Feces
4. Liver:
detoxification of drugs and chemicals and eliminated in feces

1. Nervous System:
the nervous system is composed of three major parts
1. Sensory Input Portion
2. The central nervous system (CNS)
3. Motor output portion
Regulation of Body Functions

sensory receptors detect the state of the body and its
surroundings
 For example, receptors in the skin alert us whenever an
object touches the skin.
 The eyes are sensory organs that give us a visual image of the
surrounding areas.
 The ear are also sensory organs

B. CNS or Integrative Portion:
The CNS is composed of brain and spinal cord.
The brain stores information, generate thoughts, create ambition,
and determine reactions.
C. Motor Output Portion:
carry out one’s desire.

2. Hormone Systems:
endocrine glands; secrete hormones
- Thyroid Hormone: Increase rate of most chemical reactions
in cells.
- Insulin: glucose metabolism
- Adrenocortical Hormones: sodium ion, potassium ion, and
protein metabolism
- Parathyroid hormone-controls bone calcium and phosphate

Protection of the body
1. Immune System:
The immune system includes WBC, tissue cells, thymus, lymph
nodes, lymph vessels; protection from pathogens (bacteria,
viruses, parasites, fungi).
A. Distinguish own cells from foreign cells and substances.
B. Destroy invaders (phagocytosis-cell eating); producing
sensitized lymphocytes/specialized proteins (antibodies) that
destroys or neutralize invaders.

2. Integumentary System:
• The skin generally comprises about 12-15% of body weight).
• The skin and its various appendages ( including the hair, nails,
glands) provide a boundary between the body’s internal
environment and the outside world
• temperature regulation
• Provides a sensory interface between the body and the external
environment.
• excretion of wastes

Negative Feedback Control of Arterial
Pressure Promotes Stability
Art. Pressure Sympathetic
Activity
Heart Rate
Vasoconstriction

Baroreceptor Reflex :
Negative Feedback System - Promotes Stability
Blood vessels,
Heart
Baroreceptors
Set-point
Error signal
Vasomotor
Centers
Sympathetic
System
Effectors
Blood
Pressure
Sensor
Controlled
Variable
+

Cardiopulmonary Reflexes:
Feed-Forward Control of Blood Pressure –
Anticipates a Change
Blood vessels,
Heart
Baroreceptors
Error signal
Vasomotor
Centers
Sympathetic
System
Effectors
Blood
Pressure
Sensor
Controlled
Variable
Set-point
Cardiopulmonary
Receptors
Cardiopulmonary
Pressures
+

Feedback and Feed-Forward Control
• Negative feedback: promotes stability
• Feed-forward: anticipates change
• Positive feedback: promotes a change
in one direction, often leading to
instability, disease, and sometimes death.

Positive Feedback of Hemorrhagic Shock
Figure 1-3;
Guyton & Hall

Hemorrhagic Shock:
Positive Feedback
Severe Hemorrhage
Venous Return
Cardiac Output
Blood Pressure
Coronary Blood Flow
Cardiac Contractility
+

Thank you

functional organization of the human body

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