Human physiology (book)
LECTURE 1
Chapter 1 (37-54)
• Physiology is the study of the normal functioning of a living organism and its component parts,
including all its chemical and physical processes.
• The term physiology literally means “knowledge of nature.”
• Aristotle (384–322 bce) used the word in this broad sense to describe the functioning of all living
organisms, not just of the human body.
• Hippocrates (ca. 460–377 bce), considered the father of medicine, used the word physiology to
mean “the healing power of nature,” and thereafter the field became closely associated with
medicine.
1.1 Physiology Is an Integrative Science
• Many complex systems—including those of the human body— possess emergent properties,
which are properties that cannot be predicted to exist based only on knowledge of the system’s
individual components.
- An emergent property is not a property of any single component of the system, and it is
greater than the simple sum of the system’s individual parts.
- Emergent properties result from complex, nonlinear interactions of the different
components.
• Proteomics, the study of proteins in living organisms.
• new areas in biological research are called functional genomics, systems biology, and integrative
biology, but fundamentally these are all fields of physiology.
• The integration of function across many levels of organization is a special focus of physiology.
(To integrate means to bring varied elements together to create a unified whole.)
• atoms of elements link together to form molecules. Collections of molecules in living organisms
form cells, the smallest unit of structure capable of carrying out all life processes.
• A lipid and protein barrier called the cell membrane (also called the plasma membrane)
separates cells from their external environment.
• Simple organisms are composed of only one cell, but complex organisms have many cells with
different structural and functional specializations. 1
, • Collections of cells that carry out related functions are called tissues {texere, to weave}. Tissues
form structural and functional units known as organs {organon, tool}, and groups of organs inte-
grate their functions to create organ systems.
• The 10 physiological organ systems in the human body.
- Several of the systems have alternate names, given in parentheses, that are based on the
organs of the system rather than the function of the system.
1. The integumentary system {integumentum, covering}, composed of the skin, forms a
protective boundary that separates the body’s internal environment from the external
environment (the outside world).
2. The musculoskeletal system provides support and body movement.
Four systems exchange materials between the internal and external environments.
3. The respiratory (pulmonary) system exchanges gases.
4. the digestive (gastrointestinal) system takes up nutrients and water and eliminates wastes;
the urinary (renal) system removes excess water and waste material.
5. reproductive system produces eggs or sperm.
The remaining four systems extend throughout the body.
6. The circulatory (cardiovascular) system distributes materials by pumping blood through
vessels.
7. The nervous and endocrine systems coordinate body functions.
8. immune system, which includes but is not limited to the anatomical structures known as the
lymphatic system. The specialized cells of the immune system are scattered throughout the
body. They protect the internal environment from foreign substances by intercepting
material that enters through the intestines and lungs or through a break in the skin. In
addition, immune tissues are closely associated with the circulatory system.
,1.2 Function and Mechanism
• We define physiology as the normal functioning of the body, but physiologists are careful to
distinguish between function and mechanism.
• The function of a physiological system or event is the “why” of the system or event: Why does a
certain response help an animal survive in a particular situation? In other words, what is the
adaptive significance of this event for this animal?
• Thinking about a physiological event in terms of its adaptive significance is the teleological
approach to science
• Most physiologists study physiological processes, or mechanisms—the “how” of a system. The
mechanistic approach to physiology examines process.
• Applying the concept of integrated functions and mechanisms is the underlying principle in
translational research, an approach sometimes described as “bench to bedside.” Translational
research uses the insights and results gained from basic bio- medical research on mechanisms to
develop treatments and strategies for preventing human diseases
1.3 Themes in Physiology
• “Physiology is not a science or a profession but a point of view.”
• five major themes emerge:
1. structure and function across all levels of organization
2. energy transfer, storage, and use
3. information flow,storage,and use within single organisms and within a species of organism
4. homeostasis and the control systems that maintain it
5. evolution
Theme 1: Structure and Function Are Closely Related
• The integration of structure and function extends across all levels of organization, from the
molecular level to the intact body. This theme subdivides into two major ideas: molecular
interactions and compartmentation.
- Molecular Interactions
o The ability of individual molecules to bind to or react with other molecules is
essential for biological function.
o A molecule’s function depends on its structure and shape, and even a small change
to the structure or shape may have significant effects on the function
o biological molecules called proteins. Functional groups of proteins include enzymes
that speed up chemical reactions, signal molecules and the receptor proteins that
bind signal molecules, and specialized proteins that function as biological pumps,
filters, motors, or transporters.
- Compartmentation Compartmentation is the division of space into separate compartments.
Compartments allow a cell, a tissue, or an organ to specialize and isolate functions.
Theme 2: Living Organisms Need Energy
• Growth, reproduction, movement, homeostasis—these and all other processes that take place
in an organism require the continuous input of energy.
, Theme 3: Information Flow Coordinates Body Functions
• Information flow in living systems ranges from the transfer of information stored in DNA from
generation to generation (genetics) to the flow of information within the body of a single
organism.
• At the organismal level, information flow includes translation of DNA’s genetic code into
proteins responsible for cell structure and function.
• In the human body, information flow between cells coordinates function.
• Cell-to-cell communication uses chemical signals, electrical signals, or a combination of both.
Information may go from one cell to its neighbors (local communication) or from one part of the
body to another (long-distance communication).
Theme 4: Homeostasis Maintains Internal Stability
• Organisms that survive in challenging habitats cope with external variability by keeping their
internal environment relatively stable, an ability known as homeostasis {homeo-, similar +
@stasis, condition}.
1.4 Homeostasis
• Cannon proposed a list of variables that are under homeostatic control. Cannon divided his
variables into what he described as environmental factors that affect cells (osmolarity,
temperature, and pH) and “materials for cell needs” (nutrients, water, sodium, calcium, other
inorganic ions, oxygen, as well as “internal secretions having general and continuous effects”).
Cannon’s “internal secretions” are the hormones and other chemicals that our cells use to
communicate with one another.
• the word homeostasis to describe the regulation of the body’s internal environment. He
explained that he selected the prefix homeo- (meaning like or similar) rather than the prefix
homo- (meaning same) because the internal environment is maintained within a range of values
rather than at an exact fixed value. He also pointed out that the suffix -stasis in this instance
means a condition, not a state that is static and unchanging.
• we should use the word homeodynamics instead, to reflect the small changes constantly taking
place in our internal environment {dynamikos, force or power}. Whether the process is called
homeostasis or homeodynamics, the important concept to remember is that the body monitors
its internal state and takes action to correct disruptions that threaten its normal function.
• If the body fails to maintain homeostasis of the critical variables listed by Walter Cannon, then
normal function is disrupted and a disease state, or pathological condition {pathos, suffering},
may result
• Diseases fall into two general groups according to their origin:
those in which the problem arises from internal failure of some
normal physiological process, and those that originate from
some outside source
• The study of body functions in a disease state is known as
pathophysiology.
• One very common pathological condition in the United States is
diabetes mellitus, a metabolic disorder characterized by
abnormally high blood glucose concentrations. Although we
speak of diabetes as if it were a single disease, it is actually a
whole family of diseases with various causes and manifestations.