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INTRODUCTION TO ANATOMY & PHYSIOLOGY
The name of our course is Anatomy and Physiology. Anatomy is the science of the
structure of the body. It includes not only its form and structure but also how
those structures relate to each other. Anatomy literally means cutting open and was
first studied by dissection. Physiology is the science of the functions of the body; it
includes how body parts work. While it is possible to study anatomy & physiology
separately, the two are not inseparable. Anatomy provides clues about the function
of body parts & physiology can only be explained in terms of the underlying
anatomy. Science terms this thee principle of complementarity of structure &
function; which means that structure determines function. What a structure can do
depends on its form. Bones support & protect body organs because of their
structure. They contain hard mineral deposits. Blood flows in one direction
because of valves. The lungs serve as the sites of gas exchange because they
contain air sacs which are extremely thin.
Anatomy is a large topic with many subdivisions; each could be a course in itself.
There is microscopic & gross or macroscopic anatomy. Microscopic anatomy
studies structures that can only be seen under magnification. A light microscope
shows cell structure; an electron microscope allows one to see individual
molecules only a few nm across. There are 2 main divisions of microscopic
anatomy. One of those divisions is cytology, the study of the structure of individual
cells. The other division is histology, the study of the structure of tissues or
specialized cells working together to perform a specific function.
Gross anatomy studies larger structures that can be seen with the unaided eye.
Levels of Organization
The human body has many levels of structural organization. The organization of
each level determines the characteristics and functions of higher levels.
The chemical or molecular level of organization is the simplest level. Atoms, the
smallest stable units of matter combine to form molecules such as water, sugar,
proteins which have complex shapes. These special shapes determine molecular
function.
The cellular level of organization is due to molecules interacting to form
organelles, the basic structural & functional components of cells. These include
protein filaments such as actin & myosin which are found in muscle cells.
The tissue level of organization includes group of similar cells working in unison
to perform one or more specific functions. There are 4 basic types: epithelium,
muscle, connective & nervous. The organ level of organization includes 2 or more
tissues, usually 4, working together to perform specific functions. The organ
system level of organization involves organs working together for one common
purpose. For example: blood which is a tissue + blood vessels + the heart form the
cardiovascular system. The human body has 11 organ systems including the
integumentary, bone, muscle, nervous, respiratory, circulatory, respiratory,
digestive, immune, endocrine & reproductive systems.
The highest level of organization is the organismal level which includes all organ
systems working as a unit to produce life & health.
Basic Life Processes
There are several processes that occur in all living organisms. These processes in
fact define what life is. These include metabolism, responsiveness, movement,
growth, differentiation and reproduction. Metabolism is defined as the sum of all
chemical processes that take place in the body. There are two major processes of
metabolism-catabolism and anabolism. Catabolism is when larger macromolecules
are broken down into smaller subunits or monomers. An example is when we eat
protein and digest them into the amino acids that comprise them. Anabolism is
when larger macromolecules are formed from smaller submits. An example is
when our body takes amino acids and builds them into proteins.
The second life process is responsiveness. This refers to the ability to detect and
respond to changes. For example if our body temperature increases there must be a
receptor which notices this change so the body can make the necessary changes to
not overheat. Movement is the third basic life process. This can refer to the
movement of muscle and joints to allow us to walk and throw a ball. It also refers
to the movement inside our body such as when food is moved through our
digestive tract by the process of peristalsis. The next life process is growth. Tissues
must have a way to increase in size. The fifth basic life process is differentiation.
This is the ability of cells to develop from an unspecialized cell into a specialized
cell. This is very evident in the growing embryo and fetus; one cell divides and
divides and eventually stem cells develop into very specialized cells such as heart,
liver, brain and bone cells. The last basic process that defines life is reproduction.
This include making a whole new organism and it also refers to cells being able to
divide and make new cells for growth and replacement.
Homeostasis
As we discussed earlier there are 11 organ systems in the body. These systems are
interdependent; they interconnect and are packaged together into a small space,
the body. One system cannot operate properly without proper operation of all
others. If something affects one then all are affected. All reside in the same shared
environment. If that environment such as body fluid composition, temperature,
blood glucose levels, etc. becomes abnormal then all cells will be injured or
destroyed. To prevent disaster, physiological mechanisms are in place to prevent
upsets in body fluid composition. Mechanisms which maintain a consistent internal
environment together are termed homeostasis. Homeostasis ensures the existence
of a stable, internal environment. For survival homeostasis must be maintained.
Homeostasis is so important that most disease is regarded as a result of a
disturbance or homeostatic imbalance. This is the foundation of physiology.
Homeostasis means unchanging or a condition of equilibrium. This is a bit of a
misnomer because homeostasis is a dynamic state. That means it is always
changing but maintains a balance within specific normal values. Internal conditions
vary but within narrow limits. This specific normal value is termed a set point. By
definition a set point is an average value for a variable. Conditions will cause the
specific value at any given time to fluctuate slightly around that value. Set points
are specific for each individual determined by genetics but as a species the value
varies between 2 extreme values. Set points vary between persons. They are
influenced by gender, age, general health, activity levels and environmental
conditons. For example while asleep, the set point for body temperature lowers.
For these reasons normal values are hard to define. Clinically, the values are used
to determine possible pathology & represent averages or ranges that include 95%
of the population. The resting body temperature range is between 36.7 & 37.2. This
means that 95% of adults will have a body temperature set point between these 2
values, but 5% will have a resting body temperature below 36.7 or above 37.2
which is normal for them.
Homeostatis Regulation
Regulation or adjustment of physiological systems is often needed to preserve
homeostasis. There are several ways the body maintains homeostasis. Two of the
most typical types are via the nervous & endocrine systems. Both of these systems
can control or adjust activities of other systems . For example, during exercise via
the nervous system the heart rate increases which causes blood to circulate faster.
The nervous system also sends less blood to less active areas such as the stomach
which conserves O2 in circulating blood for use by active muscles. The nervous
system is generally used for crisis management or rapid, short term very specific
responses, sometimes called reflexes. The endocrine system is used for more long
term regulation. Glands of the endocrine system release chemical messengers or
hormones which travel via the bood stream to other organs. The effects may not be
immediate but when they appear, they last for days or weeks.
Feedback Systems
Homeostatic regulation is conducted via feedback systems. A feedback system is a
cycle of events used by the body to monitor, evaluate, change, remoniter,
reevalute, etc. conditions within the body. Each monitored variable is called a
controlled condition. Any disruption that changes a controlled condition is a
stimulus.
A feedback system consists of three parts-a receptor, control center and an effector.
The receptor or sensor is sensitive to environmental change or stimuli. It monitors
changes in a controlled condition. The pathways is termed afferent (going inward).
The input can be a nerve impulse of a chemical signal. The control center has
several jobs. It sets the range of values within which a controlled condition should
be maintained. It evaluates input from the receptor and it generates an outward
command when needed. This is an efferent or outward path. The effector receives
output from the control center. It produces a response or effect to change the
controlled condition.
The activity of the effector is called feedback and will either oppose (negative
feedback) or enhance (positive feedback) the instigating stimulus. Because
feedback mechanisms alter the original changes that triggered them they are called
feedback loops.
If the response of the effector or feedback decreases the initiating stimulus, it is
labeled negative. If the response or feedback increases the initiating stimulus it is
called positive. Most homeostatic regulation in the body is of the negative type.
In negative feedback the output of a system shuts off or reduces the intensity of an
initiating stimulus. Example: room temperature regulation. The thermostat is the
control center. It sets the room temperature (set point) and receives information
about room temperature from a receptor or thermometer. When the receptor
detects a temperature higher than the set point, it turns on the air conditioner or
effector. When the receptor detects a temperature within the accepted range of the
set point it turns off the air conditioner. The temperature does not stay at the set
point but fluctuates around that given temperature.
For the human body control of body temperature is termed thermoregulation. The
control center is the hypothalamus a small organ in the brain which sets the body
temperature & receives information from receptors in the skin & from inside itself.
The normal set point is 37oC or 98.6oF. As the body temperature increases, the
control center is activated and directs 2 effectors-muscle tissue in the walls of
blood vessels which supply the skin & sweat glands.
As body temperature increasesmuscle tissue in blood vessels walls
relaxesblood vessels dilate which increases blood flow through vessels near the
surface of the body. The skin acts as a radiator & loses heat to the environment.
This is termed vasodilation. As body temperature decreasesmuscle tissue in
blood vessels constrictsblood flow through vessesl near the surface of the body
constrict. This is termed vasoconstriction.
As body temperature increasessweat glandsincrease their secretion
evaporation of moisture from skin speeds cooling.
Another example of negative feedback is the control of blood sugar. The body
needs a continual supply of glucose which is maintained at 90mg/100ml of blood.
Lets suppose you just have to have 4 jelly doughnutsthis causes massive
amounts of sugar to enter the blood streamglucose levels increasehomeostasis
is upset. Rising glucose levels are detected by pancreatic cellswhich secrete
insulinaccelerates uptake of glucose by cells & encourages storage of excess
glucose as glycogen in liver & muscle cellsblood sugar returns to normal
homeostatic range. If blood sugar levels drop, the pancreas releases glucagon
which raises blood sugar levels.
In postitive feedback, the initial stimulus produces a response that exaggerates or
enhances its effect. The change occurs in the same direction as the stimulus. This
method of control is often incorporated into things that are life threatening or
stressful. Example-severe cutloss of bloodlowers blood pressurereduces
heart efficiencydeath unless blood flow is stopped. Body mediates by forming a
blood clot. During this process platelets cling to the site of injury and release
chemicals which attract more platelets to the areablood cloting begins. As
clotting continuesother chemicals are released which increase blood clotting.