Human systems

The Human Body Systems
(Zoology Lecture)

Circulatory System – The Circle of Blood Page 2

The circulatory or
cardiovascular system is the
blood circulation with heart,
arteries and veins. It is made
up of the vessels and the
muscles that help and control
the flow of the blood around
the body. This process is
called circulation. The main
parts of the system are the
heart, arteries, capillaries and
veins.
As blood begins to
circulate, it leaves the heart
from the left ventricle and
goes into the aorta. The aorta
is the largest artery in the
body. The blood leaving the
aorta is full of oxygen. This
is important for the cells in
the brain and the body to do
their work. The oxygen rich
blood travels throughout the
body in its system of arteries
into the smallest arterioles.
On its way back to bloodstream by passing through the
the heart, the blood travels through a walls of the small intestine into the
system of veins. As it reaches the lungs, capillaries. The blood then carries most
the carbon dioxide (a waste product) is of the nutrients to the liver, where some
removed from the blood and replace of these are extracted and stored for
with fresh oxygen that we have inhaled release back into the blood as and when
through the lungs. the body needs them.
Other nutrients are converted by
FUNCTIONS OF THE SYSTEM the liver into substances which are
The circulatory system plays an required in the production of energy,
important role in many of the body's enzymes, and new building materials for
processes including respiration, the body. Hormones, which affect or
nutrition, and the removal of wastes and control the activities of various organs
poisons. In respiration it delivers oxygen and tissues, are produced by the
to the body's cells and removes carbon endocrine glands – including the thyroid,
dioxide from them. In nutrition, it carries pituitary, adrenal, and sex glands – and
digested food substances to the cells. they too are transported by the blood
Nutrients from food enter the through the body.


TYPES OF THE CIRCULATORY Arteries therefore require strong walls to
SYSTEM withstand the pressure of the blood
Open Circulatory System. The Open flowing through them. They have elastic
Circulatory System is a system in which tissue in their walls that can stretch and
fluid (called hemolymph) in a cavity recoil with the force of the blood. Artery
called the hemocoel bathes the organs walls also contain muscle and this
directly with oxygen and nutrients and determines the amount of blood that can
there is no distinction between blood and flow through them, and the blood
interstitial fluid; this combined fluid is pressure.
called hemolymph or haemolymph. Heart. The heart is actually two separate
Muscular movements by the animal pumps. The left side pumps blood to the
during locomotion can facilitate body (systemic circulation) and the right
hemolymph movement, but diverting side pumps blood to the lungs
flow from one area to another is limited. (pulmonary circulation). Each side has
When the heart relaxes, blood is drawn an atrium and a ventricle. They do not
back toward the heart through open- work on their own, but together as a
ended pores (ostia). team. The body's blood is circulated
Close Circulatory System. The through the heart more than 1,000 times
cardiovascular systems of humans are per day. Between five and six thousand
closed, meaning that the blood never quarts of blood are pumped each day.
leaves the network of blood vessels. In Your heart is about the same size as your
contrast, oxygen and nutrients diffuse
across the blood vessel layers and enters
interstitial fluid, which carries oxygen
and nutrients to the target cells, and
carbon dioxide and wastes in the
opposite direction. The other component
of the circulatory system, the lymphatic
system, is not closed. The heart is
located more towards the left side of the
body because it is accompanying the
lungs.
fist.
MAIN COMPONENTS
The job of the heart is to pump
Blood Vessels. There are three major
blood around your body. Its muscles
types of blood vessels: arteries that carry
contract and squeeze out blood. The left-
blood from the heart; veins that return
hand side pumps blood from the lungs to
blood to the heart; and capillaries –
the rest of your body. The right-hand
extremely tiny vessels connecting the
side pumps stale blood from your body
arteries and the veins. When blood is
back to your lungs for a fresh supply of
pumped out of the heart into the arteries
oxygen.
it is forced out at high pressure by
contractions of the muscular ventricles.

Blood. Blood is thicker than water and
has a little bit salty taste. In an adults
body there is 10.6 pints of blood

circulating around. In their blood there is
billions of living blood cells floating in a WASTE DISPOSAL
liquid called plasma. If you took a small In addition to feeding and
sample of this blood and poured it into a nourishing the body, the circulatory
test tube and then put it in a machine system also helps to dispose of waste
called a centrifuge, you would be able to products and poisons which would prove
see the layers of this blood. This harmful if allowed to accumulate.
machine spins the blood around so fast Carbon dioxide, produced by the body's
that it separates the red blood cells, from cells as they respire, diffuses through the
the white blood cells, from the platelets. walls of the capillaries into the blood.
The red blood cells sink to the bottom The blood containing carbon dioxide is
because they are the heavier, more solid returned via the heart to the lungs and
parts, but the plasma remains at the top passed out of the body on expiration. In
because it is lighter. The plasma is 95% processing food, the liver removes
water and the other 5% is made up of ammonia and other wastes, together with
dissolved substances including salts. various poisons that enter the body
through the digestive system. These are
converted into water-soluble substances,
which are carried by the blood to the
kidneys. The kidneys then filter out
these wastes and expel them from the
body in urine.

TEMPERATURE CONTROL
As well as the heat produced
generally by cells during respiration,
some parts of the body, such as the liver
Human blood has two parts,
and muscles, produce heat in the course
liquid (plasma) and cells. Plasma
of their activities. This heat is
contains dissolved gasses, nutrients,
transported by the blood to warm other
wastes, salts, and proteins. Cells are red
parts of the body. As the temperature of
blood cells which are biconcave disks
the body rises, the flow of blood into
filled with hemoglobin and continuously
vessels in the skin increases as a result of
produced in the red marrow of the skull,
small arteries expanding, and excess heat
ribs, vertebrae, and ends of the long
is conveyed to the surface where it is
bones; and white blood cells or
lost. When the temperature of the body
leukocytes are cells of the immune
drops the flow of blood to the skin is
system defending the body against both
restricted. Thus, the circulatory system
infectious disease and foreign materials.

acts as a natural thermostat allowing the
body to maintain an optimum and stable
temperature.

Digestive System – The Food Processor Page 5

The human digestive system is
a complex series of organs and glands
that processes food. In order to use the
food we eat, our body has to break the
food down into smaller molecules that
it can process; it also has to excrete
waste.
Most of the digestive organs
(like the stomach and intestines) are
tube-like and contain the food as it
makes its way through the body. The
digestive system is essentially a long,
twisting tube that runs from the mouth
to the anus, plus a few other organs
(like the liver and pancreas) that
produce or store digestive chemicals.
system defending the body against both
infectious disease and foreign
materials.

THE DIGESTIVE PROCESS
The start of the process: the mouth.
The digestive process begins in the
mouth. Food is partly broken down by
the process of chewing and by the
chemical action of salivary enzymes
(these enzymes are produced by the This muscle movement gives us the
salivary glands and break down starches ability to eat or drink even when we're
into smaller molecules). upside-down.
On the way to the stomach: the In the stomach. The stomach is a large,
esophagus. After being chewed and sack-like organ that churns the food and
swallowed, the food enters the bathes it in a very strong acid (gastric
esophagus. The esophagus is a long tube acid). Food in the stomach that is partly
that runs from the mouth to the stomach. digested and mixed with stomach acids
It uses rhythmic, wave-like muscle is called chyme.
movements (called peristalsis) to force In the small intestine. After being in the
food from the throat into the stomach. stomach, food enters the duodenum, the

first part of the small intestine. It then the small intestine help in the breakdown
enters the jejunum and then the ileum of food.
(the final part of the small intestine). In In the large intestine. After passing
the small intestine, bile (produced in the through the small intestine, food passes
liver and stored in the gall bladder), into the large intestine. In the large
pancreatic enzymes, and other digestive intestine, some of the water and
enzymes produced by the inner wall of electrolytes (chemicals like sodium) are

removed from the food. Many microbes acids. Chyme goes on to the small
(bacteria like Bacteroides, Lactobacillus intestine for further digestion.
acidophilus, Escherichia coli, and Descending colon. The part of the large
Klebsiella) in the large intestine help in intestine that run downwards after the
the digestion process. The first part of transverse colon and before the sigmoid
the large intestine is called the cecum colon.
(the appendix is connected to the Duodenum. The first part of the small
cecum). Food then travels upward in the intestine; it is C-shaped and runs from
ascending colon. The food travels across the stomach to the jejunum.
the abdomen in the transverse colon, Epiglottis. The flap at the back of the
goes back down the other side of the tongue that keeps chewed food from
body in the descending colon, and then going down the windpipe to the lungs.
through the sigmoid colon. When you swallow, the epiglottis
The end of the process. Solid waste is automatically closes. When you breathe,
then stored in the rectum until it is the epiglottis opens so that air can go in
excreted via the anus. and out of the windpipe.
Esophagus. The long tube between the
DIGESTIVE SYSTEM GLOSSARY mouth and the stomach. It uses rhythmic
Anus. The opening at the end of the muscle movements (called peristalsis) to
digestive system from which feces force food from the throat into the
(waste) exits the body. stomach.
Appendix. A small sac located on the Gall bladder. A small, sac-like organ
cecum. located by the duodenum. It stores and
Ascending colon. The part of the large releases bile (a digestive chemical which
intestine that run upwards; it is located is produced in the liver) into the small
after the cecum. intestine.
Bile. A digestive chemical that is Ileum. The last part of the small
produced in the liver, stored in the gall intestine before the large intestine
bladder, and secreted into the small begins.
intestine. Jejunum. The long, coiled mid-section
Cecum. The first part of the large of the small intestine; it is between the
intestine; the appendix is connected to duodenum and the ileum.
the cecum. Liver. A large organ located above and
Chyme. Food in the stomach that is in front of the stomach. It filters toxins
partly digested and mixed with stomach from the blood, and makes bile (which

breaks down fats) and some blood intestines. Enzymes from the pancreas
proteins. help in the digestion of carbohydrates,
Mouth. The first part of the digestive fats and proteins in the small intestine.
system, where food enters the body. Peristalsis. Rhythmic muscle
Chewing and salivary enzymes in the movements that force food in the
mouth are the beginning of the digestive esophagus from the throat into the
process (breaking down the food). stomach. Peristalsis is involuntary - you
Pancreas. An enzyme-producing gland cannot control it. It is also what allows
located below the stomach and above the you to eat and drink while upside-down.

Rectum. The lower part of the large Stomach. A sack-like, muscular organ
intestine, where feces are stored before that is attached to the esophagus. Both
they are excreted. chemical and mechanical digestion takes
Salivary glands. Glands located in the place in the stomach. When food enters
mouth that produce saliva. Saliva the stomach, it is churned in a bath of
contains enzymes that break down acids and enzymes.
carbohydrates (starch) into smaller Transverse colon. The part of the large
molecules. intestine that runs horizontally across the
Sigmoid colon. The part of the large abdomen.
intestine between the descending colon
and the rectum.

Endocrine System – The Communicator Page 8

Although we rarely think
about the endocrine system, it
influences almost every cell,
organ, and function of our
bodies. The endocrine system is
instrumental in regulating mood,
growth and development, tissue
function, metabolism, and sexual
function and reproductive
processes.
In general, the endocrine
system is in charge of body
processes that happen slowly,
such as cell growth. Faster
processes like breathing and
A gland is a group of cells that
body movement are controlled by the
produces and secretes, or gives off,
nervous system. But even though the
chemicals. A gland selects and removes
nervous system and endocrine system
materials from the blood, processes
are separate systems, they often work
them, and secretes the finished chemical
together to help the body function
product for use somewhere in the body.
properly.
The major glands that make up the
The foundations of the endocrine
human endocrine system include the:
system are the hormones and glands. As
hypothalamus, pituitary gland, thyroid,
the body's chemical messengers,
parathyroids, adrenal glands, pineal
hormones transfer information and
body, and reproductive glands (which
instructions from one set of cells to
include the ovaries and testes).
another. Many different hormones move
Hypothalamus. The hypothalamus, a
through the bloodstream, but each type
collection of specialized cells that is
of hormone is designed to affect only
located in the lower central part of the
certain cells.
brain, is the main link between the
endocrine and nervous systems. Nerve
MAJOR GLANDS
cells in the hypothalamus control the

pituitary gland by producing chemicals The production and secretion of
that either stimulate or suppress pituitary hormones can be influenced by
hormone secretions from the pituitary. factors such as emotions and changes in
Pituitary. Although it is no bigger than the seasons. To accomplish this, the
a pea, the pituitary (pronounced: puh- hypothalamus provides information
too-uh-ter-ee) gland, located at the base sensed by the brain (such as
of the brain just beneath the environmental temperature, light
hypothalamus, is considered the most exposure patterns, and feelings) to the
important part of the endocrine system. pituitary.
It's often called the "master gland" The tiny pituitary is divided into
because it makes hormones that control two parts: the anterior lobe and the
several other endocrine glands.

posterior lobe. The ANTERIOR LOBE contractions of the uterus in a woman
regulates the activity of the thyroid, having a baby.
adrenals, and reproductive glands. The Thyroid. The thyroid, located in the
anterior lobe produces hormones such front part of the lower neck, is shaped
as: like a bow tie or butterfly and produces
Growth hormone, which stimulates the the thyroid hormones thyroxine and
growth of bone and other body tissues triiodothyronine. These hormones
and plays a role in the body's handling of control the rate at which cells burn fuels
nutrients and minerals; from food to produce energy.
Prolactin, which activates milk The production and release of
production in women who are thyroid hormones is controlled by
breastfeeding; thyrotropin, which is secreted by the
Thyrotropin, which stimulates the pituitary gland. The more thyroid
thyroid gland to produce thyroid hormone there is in a person's
hormones; bloodstream, the faster chemical
Corticotropin, which stimulates the reactions occur in the body.
adrenal gland to produce certain Parathyroids. Attached to the thyroid
hormones. are four tiny glands that function
The pituitary also secretes together called the parathyroids. They
endorphins, chemicals that act on the release parathyroid hormone, which
nervous system and reduce feelings of regulates the level of calcium in the
pain. In addition, the pituitary secretes blood with the help of calcitonin, which
hormones that signal the reproductive is produced in the thyroid.
organs to make sex hormones. The Adrenal Glands. The adrenal glands
pituitary gland also controls ovulation have two parts, each of which produces a
and the menstrual cycle in women. set of hormones and has a different
The POSTERIOR LOBE of the function: The OUTER PART, the
pituitary releases antidiuretic hormone, adrenal cortex, produces hormones
which helps control the balance of water called corticosteroids that influence or
in the body. The posterior lobe also regulate salt and water balance in the
produces oxytocin, which triggers the body, the body's response to stress,

metabolism, the immune system, and
sexual development and function. The

INNER PART, the adrenal medulla, These hormones tell a guy's body when
produces catecholamines, such as it's time to make the changes associated
epinephrine. Also called adrenaline, with puberty, like penis and height
epinephrine increases blood pressure and growth, deepening voice, and growth in
heart rate when the body experiences facial and pubic hair. Working with
stress. hormones from the pituitary gland,
Pineal. The pineal body, also called the testosterone also tells a guy's body when
pineal gland, is located in the middle of it's time to produce sperm in the testes.
the brain. It secretes melatonin, a A girl's gonads, the ovaries, are
hormone that may help regulate when located in her pelvis. They produce eggs
you sleep at night and when you wake in and secrete the female hormones
the morning. estrogen and progesterone. Estrogen is
involved when a girl begins to go
through puberty. During puberty, a girl
will experience breast growth, will begin
to accumulate body fat around the hips
and thighs, and will have a growth spurt.
Estrogen and progesterone are also
involved in the regulation of a girl's
menstrual cycle. These hormones also
play a role in pregnancy.
The pancreas is also part of the
body's hormone-secreting system, even
though it is also associated with the
digestive system because it produces and
Reproductive Glands. The GONADS secretes digestive enzymes. The
are the main source of sex hormones. pancreas produces two important
Most people don't realize it, but both hormones, insulin and glucagon. They
guys and girls have gonads. work together to maintain a steady level
In guys the male gonads, or of glucose, or sugar, in the blood and to
testes, are located in the scrotum. They keep the body supplied with fuel to
secrete hormones called androgens, the produce and maintain stores of energy.
most important of which is testosterone.

Excretory System – The Waste-Eliminator Page 11

The urinary system is
made-up of the kidneys, ureters,
bladder, and urethra. The
nephron, an evolutionary
modification of the nephridium, is
the kidney's functional unit.
Waste is filtered from the blood
and collected as urine in each
kidney. Urine leaves the kidneys
by ureters, and collects in the
bladder. The bladder can distend
to store urine that eventually
leaves through the urethra.
Excretion is the removal
of the metabolic wastes of an
organism. Wastes that are
removed include carbon dioxide,
water, salt, urea and uric acid. All
excreted wastes travel at some
time in the blood.
Nephron. The nephron consists
of a cup-shaped capsule
containing capillaries and the
glomerulus, and a long renal tube.
Blood flows into the kidney Proximal Convoluted Tubule, Reabsorbs
through the renal artery, which branches 75% of the water, salts, glucose, and
into capillaries associated with the amino acids;
glomerulus. Arterial pressure causes Loop of Henle, Countercurrent
water and solutes from the blood to filter exchange, which maintains the
into the capsule. Fluid flows through the concentration gradient;
proximal tubule, which include the loop Distal Convoluted Tubule, Tubular
of Henle, and then into the distal tubule. secretion of H ions, potassium, and
The distal tubule empties into a certain drugs.
collecting duct. Fluids and solutes are Functions of Nephron. (a) Glomerular
returned to the capillaries that surround filtration of water and solutes from the
the nephron tubule. blood; (b) tubular reabsorption of water
There are several components of and conserved molecules back into the
Nephron, these are: blood; and (c) tubular secretion of ions
Glomerulus, mechanically filters blood; and other waste products from
Bowman's Capsule, mechanically filters surrounding capillaries into the distal
blood; tubule.

Excretory System – The Waste-Eliminator Page 12

Nephrons filter 125 ml of body fluid per Urinary System. Kidneys filter the
minute; filtering the entire body fluid blood to form urine, which is excess
component 16 times each day. In a 24 water, salt, urea and uric acid.
hour period nephrons produce 180 liters
of filtrate, of which 178.5 liters are THE URINARY SYSTEM
reabsorbed. The remaining 1.5 liters Urine. The first nitrogenous waste to be
forms urine. formed from the breakdown of protein is
Urine Production. (a) Filtration in the ammonia, a highly toxic chemical that is
glomerulus and nephron capsule; (b) quickly converted by the liver to urea
reabsorption in the proximal tubule; and and uric acid. These are less toxic than
(c) tubular secretion in the Loop of ammonia and are transported in the
Henle. blood to the kidneys for excretion in
Kidney Stones. In some cases, excess urine. Urine consists of excess water,
wastes crystallize as kidney stones. They excess salt, urea and uric acid.
grow and can become a painful irritant
that may require surgery or ultrasound PARTS OF THE URINARY
treatments. Some stones are small SYSTEM
enough to be forced into the urethra, Renal Arteries. 2 renal arteries
others are the size of huge, massive constantly transport blood to the
boulders. kidneys.
Infection, environmental toxins Kidneys. 2 kidneys composed of
such as mercury, and genetic disease can millions of nephrons constantly filter
have devastating results by causing about 170 to 200 litres of blood to
disruption of kidney function. Many produce about 1.5 to 2 litres of urine
kidney problems can be treated by daily.
dialysis, where a machine acts as a Renal Veins. 2 renal veins return useful
kidney. Kidney transplants are an nutrients back into the bloodstream.
alternative to dialysis. Ureters. 2 ureters carry urine from the
kidneys to the urinary bladder.
ORGANS OF EXCRETORY Urinary Bladder. The urinary bladder
SYSTEM temporarily stores urine until it is
Lungs. Removal of excess carbon released from the body.
dioxide. Urethra. The urethra is the tube that
Liver. Produces urea and uric acid as a carries urine from the urinary bladder to
by-product of the breakdown of proteins. the outside of the body. The outer end of
Skin. Removal of excess water, salt, the urethra is controlled by a circular
urea and uric acid. muscle called a sphincter.

Immune System – The Defender Page 13

The human
immune system is made
up of a number of
interdependent cell
types which
collectively protect the
person's body from
various parasitic,
fungal, bacterial and
viral infections, as well
as from the growth of
tumor cells.
The human
immune system is made
up of a number of
interdependent cell
types which
collectively protect the
person's body from Bone Marrow. Every cell involved in a
various parasitic, fungal, bacterial and person's immune system is initially
viral infections, as well as from the derived from bone marrow. These cells
growth of tumor cells. A number of form through a process referred to as,
these cell types have specialized 'Hematopoiesis.' During hematopoiesis
functions, are able to kill parasites, bone marrow derived stem cells
engulf bacteria, or kill tumor cells or differentiate into one of two things;
viral-infected cells. Frequently, these either mature cells of the immune
cells are dependent upon the, 'T,' helper system, or precursors of cells which then
subset for activation signals in the form migrate out of the person's bone marrow,
of secretions which are more formally continuing their maturation elsewhere in
referred to as, 'Lymphokines,' the body. Bone marrow produces, 'B,'
'Cytokines,' or specifically as, cells, killer cells, immature thymocytes,
'Interleukins.' An understanding of the T and granulocytes, as well as platelets and
helper subset may assist in red blood cells.
comprehension of the root of immune Thymus. The Thymus' function is to
deficiencies, as well as perception of the produce mature, 'T,' cells. Immature
potential avenues that the human Tymocytes, also referred to as,
immune system can be modulated in the 'Prothymocytes,' emerge from the
case of particular diseases. person's bone marrow and move into
their thymus. Through a process called,
IMMUNE SYSTEM ORGANS

'Thymic Education,' these T cells which response are removed. Mature T cells
are beneficial to the person's immune are released into the person's blood
system are spared while T cells that may stream.
cause a detrimental autoimmune

Spleen. A person's spleen is an subsets is the, 'T Helper Subset,' also
immunological filter, filtering their referred to as the, 'CD4+ T Cell,' which
blood. The spleen is comprised of T is a coordinator of a person's immune
cells, B cells dendritic cells, regulation. The primary function of the
macrophages, red blood cells and natural T helper cell is augmentation of the
killer cells. Macrophages and dendritic person's immune responses through
cells not only capture foreign materials secretion of specialized factors which
called, 'Antigens,' from a person's blood activate additional white blood cells in
which passes through the spleen, they order to fight off an infection.
bring these antigens to the spleen itself CD8+ T Cells. CD8+ T Cells are also
from the person's blood stream. A called T killer/suppressor cells and are
person's body experiences an immune important because they are involved in
response when the macrophage or directly killing viral infected cells,
dendritic cells present the antigen to specific tumor cells, and sometimes
appropriate T or B cells. In a person's parasites. CD8+ T cells are important
spleen, B cells are activated and produce because they also down-regulate
great amounts of antibody. The spleen immune responses. While both types of
also destroys old red blood cells. T cells are found throughout a person's
Lymph Nodes. A person's lymph nodes body, they are many times dependent on
work as an immunological filter for their the lymph nodes and spleen as places
bodily fluid referred to as, 'Lymph.' where activation happens, yet are also
People have lymph nodes throughout found in other tissues in a person's body,
their body. Lymph nodes are made notably the person's lungs, liver, blood
mostly of B cells, T cells, macrophages, and intestinal and reproductive tracts.
and dendritic cells. A person's lymph Natural Killer Cells. Natural killer cells
nodes drain fluid from the majority of are also called, 'NK Cells,' and are
their tissues. Lymph nodes filter out similar to cells from the killer T cell
antigens from lymph prior to returning subset. Natural killer cells work as
lymph to the person's body for effector cells, killing specific tumors like
circulation. In a manner much like the lymphomas, melanomas, and viral
spleen, dendritic cells and macrophages infected cells such as herpes and
that capture antigens present foreign cytomegalovirus infected cells. Natural
materials to both B and T cells, initiating killer cells kill their targets in the
an immune response. person's lymphoid organs; however,
these cells which have been activated
IMMUNE SYSTEM CELLS through secretions from CD4+ T cells
T Cells. T Lymphocytes are commonly will kill viral-infected targets or tumors
placed into two major subsets which are more efficiently.
identifiably different. One of these

B Cells. The primary function of B cells bind to one other particular protein
is to produce antibodies in response to which also specifically recognize and
foreign proteins such as viruses, bacteria bind to one particular protein. The
and tumor cells. Antibodies are proteins production of antibodies and binding to
that specifically first recognize and then


foreign substances or antigens is often Dendritic Cells. Dendritic cells also
critical as a means of signaling originate in a person's bone marrow,
additional cells to engulf and kill, or working as antigen presenting cells
remove a substance from the person's (APC's). Interestingly, dendritic cells are
body. more efficient APC's than macrophages.
Polymorphonuclear (PMN) Dendritic cells are commonly found in
Leukocytes or Granulocytes. There is a the structural compartment of a person's
group of white blood cells which is lymphoid organs, such as their spleen,
collectively referred to by medical lymph nodes and thymus. These cells
personnel as, 'Polymorphonuclear can also be found in the person's blood
Leukocytes (PMN's),' or, 'Granulocytes.' stream, as well as in other tissues in their
Granulocytes are made of three cell body. Science believes that these cells
types which are referred to as, capture antigen, or bring it to the
'Eosinophils,' 'Neutrophils,' and, person's lymphoid organs, where an
'Basophils.' The names for them are immune response is initiated. One of the
based on their staining characteristics reasons that scientists know very little
with specific dyes. The cells are about dendritic cells is because they are
important because they are involved in difficult to isolate; something that is
the removal of parasites and bacteria often a prerequisite for studying the
from a person's body. These cells first functional qualities of exact cell types.
engulf foreign bodies and then degrade Of particular note is a recent finding that
them by using their powerful enzymes. dendritic cells bind high amount of HIV
Macrophages. Macrophages are and could be a reservoir of virus which
important due to their function in the is transmitted to CD4+ T cells during
regulation of immune responses. and activation event.
Macrophages are many times referred to
as, 'scavengers,' or, 'Antigen-Presenting IMMUNE RESPONSE
Cells (APC's),' because they both pick The presence of an APC,
up and ingest foreign materials, and then combined with a T cell or B cell, is
present these antigens to other cells in a required in order for there to be an
person's immune system like B cells and immune response to a foreign antigen.
T cells. The process is one of the steps Should an APC present an antigen on it's
involved in initiating an immune cell surface to a B cell, for example, the
response. Microphages that have been B cell is signaled to proliferate and
stimulated show increased levels of, produce antibodies. The antibodies then
'Phagocytosis,' and are also secretory. specifically bind to that antigen. If the
antibodies bind to antigens on parasites

or bacteria, it acts as a signal for referred to as, 'Complement,' first bind to
macrophages or PMN's to engulf and kill immobilized antibodies, and then
them. One addition and important destroy the bacteria through creating
function of antibodies is to start holes in the bacteria. Antibodies may
something referred to as a, 'Complement also signal macrophages and natural
Destruction Cascade.' When antibodies killer cells to kill bacterial infected cells
bind to bacteria or cells, serum proteins or viral cells.
Integumentary System – Skin, Hair & Nails Page 16

The integumentary system, eyelashes to the thick skin of the soles—
formed by the skin, hair, nails, and the integumentary system protects the
associated glands, enwraps the body. It body from the outside world and its
is the most visible organ system and one many harmful substances. It utilizes the
of the most complex. Diverse in both Sun's rays while at the same time
form and function—from delicate shielding the body from their damaging

effects. In addition, the system helps to tissues that performs a specialized
regulate body temperature, serves as a function. As an organ, the skin is the
minor excretory organ, and makes the largest and heaviest in the body. In an
inner body aware of its outer average adult, the skin covers about 21.5
environment through sensory receptors. square feet (2 square meters) and
Skin. Although the skin is not often accounts for approximately 7 percent of
thought of as an organ, such as the heart body weight, or about 11 pounds (5
or liver, medically it is. An organ is any kilograms) in a 160-pound (73-kilogram)
part of the body formed of two or more person. It ranges in thickness from 0.04

to 0.08 inches (1 to 2 millimeters), but Integument, in animals and plants, any
can measure up to 0.2 inches (6 natural outer covering, such as skin,
millimeters) thick on the palms of the shell, membrane, or husk.
hands and the soles of the feet. The skin Keratin, tough, fibrous, water-resistant
in these areas is referred to as thick skin protein that forms the outer layers of
(skin elsewhere on the body is called hair, calluses, and nails and coats the
thin skin). surface of the skin.
Lunula, white, crescent-shaped area of
PARTS OF THE the nail bed near the nail root.
INTEGUMENTARY SYSTEM Melanocyte, cell found in the lower
Apocrine sweat glands, sweat glands epidermis that produces the protein
located primarily in the armpit and pigment melanin.
genital areas. Organ, any part of the body formed of
Arrector pili muscle, smooth muscle two or more tissues that performs a
attached to a hair follicle that, when specialized function.
stimulated, pulls on the follicle, causing Sebaceous gland, exocrine gland in the
the hair shaft to stand upright. dermis that produces sebum.
Dermal papillae, finger-like projections Sebum, mixture of oily substances and
extending upward from the dermis fragmented cells secreted by sebaceous
containing blood capillaries, which glands.
provide nutrients for the lower layer of Squamous cells, cells that are flat and
the epidermis; also form the scalelike.
characteristic ridges on the skin surface Subcutaneous, tissues between the
of the hands (fingerprints) and feet. dermis and the muscles.
Dermi , thick, inner layer of the skin.
Eccrine sweat glands, body's most FUNCTIONS OF THE
numerous sweat glands, which produce INTEGUMENTARY SYSTEM
watery sweat to maintain normal body The integumentary system has
temperature. multiple roles in homeostasis. All body
Epidermis, thin, outer layer of the skin. systems work in an interconnected
Epithelial tissue, tissue that covers the manner to maintain the internal
internal and external surfaces of the conditions essential to the function of the
body and also forms glandular organs. body. The skin has an important job of
protecting the body and acts as the

body’s first line of defense against d. Protect the body against abrupt
infection, temperature change, and other changes in temperature
challenges to homeostasis. Functions e. Help excrete waste materials through
include: perspiration
a. Protect the body’s internal living f. Act as a receptor for touch, pressure,
tissues and organs pain, heat, and cold
b. Protect against invasion by infectious g. Protect the body against sunburns
organisms h. Generate vitamin D through exposure
c. Protect the body from dehydration to ultraviolet light
i. Participate in temperature regulation

TWO PRINCIPAL LAYERS OF
THE SKIN
The skin has two principal only layer of the epidermis that receives
layers: the epidermis and the dermis. nutrients (from the underlying dermis).
The epidermis is the thin, outer layer, The cells of this layer, called basal cells,
and the dermis is the thicker, inner layer. are constantly dividing and creating new
Beneath the dermis lies the subcutaneous cells daily, which push the older cells
layer or hypodermis, which is composed toward the surface. Basal cells produce
of adipose or fatty tissue. Although not keratin, an extremely durable and water-
technically part of the skin, it does resistant fibrous protein.
anchor the skin to the underlying Another type of cell found in the lower
muscles. It also contains the major blood epidermis is the melanocyte.
vessels that supply the dermis and Melanocytes produce melanin, a protein
houses many white blood cells, which pigment that ranges in color from yellow
destroy foreign invaders that have to brown to black. The amount of
entered the body through breaks in the melanin produced determines skin color,
skin. which is a hereditary characteristic. The
Epidermis. The epidermis is made of melanocytes of dark-skinned individuals
stratified squamous epithelial tissue. continuously produce large amounts of
Epithelial tissue covers the internal and melanin. Those of light-skinned
external surfaces of the body and also individuals produce less. Freckles are the
forms glandular organs. Squamous cells result of melanin clumping in one spot.
are thin and flat like fish scales. The outermost layer of the
Stratified simply means having two or epidermis consists of about twenty to
more layers. In short, the epidermis is thirty rows of tightly joined flat dead
composed of many layers of thin, cells. All that is left in these cells is their
flattened cells that fit closely together keratin, which makes this outer layer
and are able to withstand a good deal of waterproof. It takes roughly fourteen
abuse or friction. days for cells to move from the inner
The epidermis can be divided layer of the epidermis to the outer layer.
into four or five layers. Most important Once part of the outer layer, the dead
of these are the inner and outer layers. cells remain for another fourteen days or
The inner or deepest cell layer is the so before flaking off slowly and steadily.

Dermis. The dermis, the second layer of Connective tissue forms the
skin, lies between the epidermis and the dermis. Bundles of elastic and collagen
subcutaneous layer. Much thicker than (tough fibrous protein) fibers blend into
the epidermis, the dermis contains the the connective tissue. These fibers
accessory skin structures. Hair, sweat provide the dermis strength and
glands, and sebaceous (oil) glands are all flexibility.
rooted in the dermis. This layer also The upper layer of the dermis has
contains blood vessels and nerve fibers. fingerlike projections that extend into
Nourished by the blood and oxygen the epidermis. Called dermal papillae,
provided by these blood vessels, the they contain blood capillaries that
cells of the dermis are alive. provide nutrients for the basal cells in

the epidermis. On the skin surface of the system. In 1901, he established
hands and feet, especially on the tips of England's first fingerprint bureau, called
the fingers, thumbs, and toes, the dermal the Fingerprint Branch, within the
papillae form looped and whorled ridges. Scotland Yard police force. Henry's
These print patterns, known as system is still used today in Great
fingerprints or toeprints, increase the Britain and the United States.
gripping ability of the hands and feet. Within the dermis are sensory
Genetically determined, the patterns are receptors for the senses of touch,
unique to every individual. pressure, heat, cold, and pain. A specific
Fingerprints (the pattern of ridges type of receptor exists for each
on an individual's fingertips and thumbs sensation. For pain, the receptors are free
formed by dermal papillae) are unique to nerve endings. For the other sensations,
each individual and the patterns never the receptors are encapsulated nerve
change. People have long known about endings, meaning they have a cellular
the distinctiveness of fingerprints, but structure around their endings. The
their use in identifying people did not number and type of sensory receptors
arise until the nineteenth century. present in a particular area of skin
It is generally acknowledged that determines how sensitive that area is to a
English scientist Francis Galton (1822– particular sensation. For example,
1911) was the first person to devise a fingertips have many touch receptors
system of fingerprint identification. In and are quite sensitive. The skin of the
the 1880s, Galton obtained the first upper arm is less sensitive because it has
extensive collection of fingerprints for very few touch receptors.
his studies on heredity. He also
established a bureau for the registration ACCESSORY STRUCTURES
of civilians by means of fingerprints and The accessory structures of the
measurements. integumentary system include hair, nails,
and sweat and sebaceous glands.
Galton's ideas were further Hair. Roughly 5 million hairs cover the
developed by fellow Englishman body of an average individual. About
Edward R. Henry (1850–1931). In the 100,000 of those hairs appear on the
1890s, Henry developed a more scalp. Almost every part of the body is
simplified fingerprint classification covered by hair, except the palms of the

hands, the soles of the feet, the sides of follicle, epithelial cells grow and divide,
the fingers and toes, the lips, and certain forming the hair bulb or enlarged hair
parts of the outer genital organs. base. Keratin, the primary component in
Each hair originates from a tiny these epithelial cells, coats and stiffens
tubelike structure called a hair follicle the hair as it grows upward through the
that extends deep into the dermis layer. follicle. The part of the hair enclosed in
Often, the follicle will project into the the follicle is called the hair root. Once
subcutaneous layer. Capillaries and the hair projects from the scalp or skin, it
nerves attach to the base of the follicle, is called a hair shaft.
providing nutrients and sensory The older epithelial cells forming
information. Inside the base of the the hair root and hair shaft die as they

are pushed upward from the nutrient-rich Nails. Nails in humans correspond to the
follicle base by newly formed cells. Like hooves of horses and cattle and the
the upper layers of the epidermis, the claws of birds and reptiles. Found on the
hair shaft is made of dead material, ends of fingers and toes, nails are
almost entirely protein. The hair shaft is produced by nail follicles just as hair is
divided into two layers: the cuticle or produced by hair follicles. The nail root
outer layer consists of a single layer of is that portion of the nail embedded in
flat, overlapping cells; the cortex or the skin, lying very near the bone of the
inner layer is made mostly of keratin. fingertip. Here, cells produce a stronger
Hair shafts differ in size, shape, form of keratin than is found in hair. As
and color. In the eyebrows, they are new cells are formed, older cells are
short and stiff, but on the scalp they are pushed forward, forming the nail body
longer and more flexible. Elsewhere on or the visible attached portion of the nail.
the body they are nearly invisible. Oval- The free edge is that portion of the nail
shaped hair shafts produce wavy hair. that extends over the tip of the finger or
Flat or ribbonlike hair shafts produce toe. Healthy fingernails grow about 0.04
kinky or curly hair. Perfectly round hair inches (1 millimeter) per week, slightly
shafts produce straight hair. The faster than toenails.
different types of melanin—yellow, rust, The nail body is made of dead
brown, and black—produced by cells, but the nail bed (the tissue
melanocytes at the follicle base combine underneath the nail body) is alive. The
to create the many varieties of hair color, blood vessels running through the nail
from the palest blonde to the richest bed give the otherwise transparent nail
black. With age, the production of body a pink color. Near the nail root,
melanin decreases, and hair color turns however, these blood vessels are
gray. obscured. The resulting white crescent is
Attached to each hair follicle is a called the lunula (from the Latin word
ribbon of smooth muscle called an luna , meaning "moon").
arrector pili muscle. When stimulated, Sweat Glands. More than 2.5
the muscle contracts and pulls on the million sweat glands are distributed over
follicle, causing the hair shaft to stand most surfaces of the human body. They
upright.

are divided into two types: eccrine sweat waste materials such as urea, and
glands and apocrine sweat glands. vitamin C form the remainder (the salts
Eccrine glands, the more give sweat its characteristic salty taste).
numerous of the two types, are found all Sebaceous Gland. Sebaceous glands,
over the body. They are especially also known as oil glands, are found in
numerous on the forehead, upper lip, the dermis all over the body, except for
palms, and soles. The glands are simply the palms and soles. They secrete sebum,
coiled tubes that originate in the dermis. a mixture of lipids (fats), proteins, and
A duct extends from the gland to the fragments of dead fatproducing cells.
skin's surface, where it opens into a pore. The function of sebum is to prevent the
Eccrine glands produce sweat or drying of skin and hair. It also contains
perspiration, a clear secretion that is 99 chemicals that kill bacteria present on
percent water. Some salts, traces of

the skin surface. While most sebaceous Arrector pili muscles, which contract to
glands secrete sebum through ducts into elevate hairs, also squeeze sebaceous
hair follicles, some secrete sebum glands, forcing out sebum.
directly onto the surface of the skin.

Muscular System – Movement using Muscles Page 21

The muscular system is the
body's network of tissues that controls
movement both of the body and within
it. Walking, running, jumping: all these
actions propelling the body through
space are possible only because of the
contraction (shortening) and relaxation
of muscles. These major movements,
however, are not the only ones directed
by muscular activity. Muscles make it
possible to stand, sit, speak, and blink.
Even more, were it not for muscles,
blood would not rush through blood
vessels, air would not fill lungs, and
food would not move through the
digestive system. In short, muscles are
the machines of the body, allowing it to
work.

PARTS OF THE MUSCULAR
SYSTEM
The muscles of the body are
divided into three main types: skeletal,
smooth, and cardiac. As their name
implies, skeletal muscles are attached to
the skeleton and move various parts of
the body. They are composed of tissue from the pattern of the filaments
fibers that are striated or striped. The (threadlike proteins) within each muscle
alternating bands of light and dark result cell. Skeletal muscles are called

voluntary muscles because a person and vein walls, and in various hollow
controls their use, such as in the flexing organs. They are called involuntary
of an arm or the raising of a foot. muscles because a person generally
There are just over 650 skeletal cannot consciously control them. They
muscles in the whole human body. Some are regulated by the autonomic nervous
authorities state there are as many as 850 system (a division of the nervous system
muscles in the body. No exact figure is that affects internal organs such as the
available because scientists disagree heart, lungs, stomach, and liver). Unlike
about which ones are separate muscles skeletal muscles, smooth muscles have
and which ones are part of larger no striations or stripes.
muscles. There is also some variability In a vessel or organ, smooth muscles are
in muscular structure between arranged in sheets or layers. Often, there
individuals. are two layers, one running circularly
Smooth muscles are found in the (around) and the other
stomach and intestinal walls, in artery

longitudinally (up and down). As the Muscle tone, sustained partial
two layers alternately contract and relax, contraction of certain muscle fibers in all
the shape of the vessel or organ changes muscles.
and fluid or food is propelled along. Myofibrils, cylindrical structures lying
Smooth muscles contract slowly and can within skeletal muscle fibers that are
remain contracted for a long period of composed of repeating structural units
time without tiring. called sarcomeres.
Acetylcholine, neurotransmitter chemical Myofilament, protein filament
released at the neuromuscular junction composing the myofibrils; can be either
by motor neurons that translates thick (composed of myosin) or thin
messages from the brain to muscle (composed of actin).
fibers. Neuromuscular junction, region where a
Adenosine triphosphate, high-energy motor neuron comes into close contact
molecule found in every cell in the body. with a muscle fiber.
Aerobic metabolism, Chemical reactions Prime mover (or agonist), muscle whose
that require oxygen in order to create contractions are chiefly responsible for
adenosine triphosphate. producing a particular movement.
Antagonist, muscle that acts in Rigor mortis, rigid state of the body after
opposition to a prime mover. death due to irreversible muscle
Cramp, prolonged muscle spasm. contractions.
Fascicle, Bundle of myofibrils wrapped Sarcomere, unit of contraction in a
together by connective tissue. skeletal muscle fiber containing a
Lactic acid, chemical waste product precise arrangement of thick and thin
created when muscle fibers break down myofilaments.
glucose without the proper amount of Spasm, sudden, involuntary muscle
oxygen contraction.
Strain, slight tear in a muscle; also called
a pulled muscle.

Synergist, muscle that cooperates with many as 100 or more nuclei. The nuclei
another to produce a particular are located on the surface of the fiber,
movement. just under its thin membrane. Another
Tendon, tough, white, cordlike tissue difference between muscle fibers and
that attaches muscle to bone. other body cells is their size. They can
extend the entire length of a muscle. For
STRUCTURE OF MUSCLE CELLS example, a muscle fiber in a thigh
Each muscle is made of hundreds muscle could measure 0.0004 inch
to thousands of individual muscle cells. (0.001 centimeter) in diameter and 12 to
Unlike most other cells in the body, 16 inches (30 to 40 centimeters) in
these cells are unusually shaped: they are length.
elongated like a cylinder or a long rod. When a person dies, blood stops
Because of their shape, muscle cells are circulating through the body. The
normally referred to as muscle fibers. skeletal muscles (along with all other
Whereas most cells have a single parts of the body) are deprived of
nucleus (the part of the cell that controls
its activities), muscle fibers have as

oxygen and nutrients, including ATP. contains bundles of threadlike proteins
Calcium ions leak out of their storage or filaments called myofilaments, which
area in the membranes of muscle fibers, can be either thick or thin. The larger
causing thick myofilaments to attach to thick myofilaments are made mostly of
and pull thin myofilaments. While the bundled molecules of the protein
muscle fibers still have a stored supply myosin. The thin myofilaments are
of ATP, the heads of thick myofilaments composed of the protein actin. In each
are able to detach from the thin myofibril, the thick and thin
myofilaments. When the supply of ATP myofilaments are combined into
runs out, however, the heads cannot thousands of units or segments that
detach and the muscle fibers stay in a repeat over and over. These units are
contracted position. The rigid state of called sarcomeres. Thick myofilaments
muscle contraction that results is called lie in the center of a sarcomere. Thin
rigor mortis. Depending on the person's myofilaments are attached at either end
physical condition at death, the onset of of a sarcomere and extend toward the
rigor mortis may vary from ten minutes center, passing among the thick
to several hours after death. Facial myofilaments. This regular arrangement
muscles are usually affected first, of the varying myofilaments within each
followed by other parts of the body. sarcomere produces the striated or
Rigor mortis lasts until the muscle fibers striped appearance of each myofibril
begin to decompose fifteen to twenty- and, by extension, of muscle fibers.
five hours after death. As are most living cells, muscle
Each muscle fiber is composed fibers are soft and fragile. Even so, they
of hundreds of smaller filaments or can exert tremendous power without
threads called myofibrils (the prefix being ripped apart. The reason is that
myocomes from the Latin word myos , muscles are composed of different types
meaning "muscle"). Each myofibril of tissue (like all other organs in the

body). In addition, those tissues are muscle usually converge or come
bundled together, providing strength and together at the end of the muscle to form
support. Each myofibril is enclosed in a a tough, white, cord-like tissue called a
delicate sheath or covering made of tendon. Tendons attach muscles to bone.
connective tissue (tissue found Because they contain fibers of the tough
everywhere in the body that connects protein collagen, tendons are much
body parts, providing support, storage, stronger than muscle tissue. The
and protection). Numerous sheathed collagen fibers are arranged in a tendon
myofibrils are then bundled together and in a wavy way so that it can stretch and
wrapped with thicker connective tissue provide additional length at the muscle-
to form what is called a fascicle (from bone junction. As muscles are used, the
the Latin word fasciculus , meaning "a tendons are able to withstand the
bundle"). Many fascicles are then constant pulling and tugging.
bundled together by an even tougher Muscles are always attached at both of
coat of connective tissue to form the their ends. The end that is attached to a
muscle. bone that moves when the
Tendons. The layers of connective
tissue that bundle the various parts of a

muscle contracts is called the insertion. bone of the skull. Other muscles are
The other end, attached to a bone that named for their relative size. Terms such
does not move when the muscle as maximus (largest), minimus
contracts, is called the origin. It is (smallest), and longus (long) are often
important to note that not all muscles are used as part of a muscle's name. Still
attached to bones at both ends. The ends other muscles are named for their shape.
of some muscles are attached to other The deltoid muscle is so named because
muscles; some are attached to the skin. it has the shape of the Greek letter delta
, which is triangular-shaped. And some
MAJOR MUSCLES OF THE BODY muscles are named for their actions.
Skeletal muscles that support the Terms such as flexor (to flex or bend in),
skull, backbone, and rib cage are called extensor (to extend or straighten out),
axial skeletal muscles. These include the adductor (to draw toward a line that runs
muscles of the head and neck and those down the middle of the body), and
of the trunk. Roughly 60 percent of all abductor (to draw away from a line that
skeletal muscles in the body are axial runs down the middle of the body) are
muscles. The skeletal muscles of the often added as part of a muscle's name.
limbs (arms and legs) are called distal or Muscles of the Head and Neck. The
appendicular skeletal muscles. These muscles of the face are unique: they are
include the muscles of the shoulders and attached to the skull on one end and to
arms and those of the hip and legs. the skin or other muscles on the other
Muscle names are descriptive. end. Muscles that are attached to the skin
Some muscles are named according to of the face allow people to express
their location in the body. For example, emotions through actions such as
the frontalis muscle overlies the frontal smiling, frowning, pouting, and kissing.

As mentioned, the frontalis side of the head, allows the head to
covers the frontal bone or forehead. The rotate and the neck to flex.
temporalis is a fan-shaped muscle Muscles of the Trunk. On the front
overlying the temporal bone on each side part of the trunk or torso, the pectoralis
of the head above the ear. The major are the large, fan-shaped muscles
orbicularis oculi encircles each eye and that cover the upper part of the chest.
helps close the eyelid. The orbicularis They flex the shoulders and pull the
oris is the circular muscle around the arms into the body. The rectus
lips. It closes and extends the lips. abdominis are the strap-like muscles of
The masseter, located over the the abdomen, extending from the ribs to
rear of the lower jaw on each side of the the pelvis. Better known as the stomach
face, opens and closes the jaw, allowing muscles, they flex the vertebral column
chewing. The buccinator, running or backbone and provide support for the
horizontally across each cheek, flattens abdomen and its many organs. The
the cheek and pulls back the corners of muscles making up the side walls of the
the mouth. The sternocleidomastoid, abdomen are the external oblique. In
located on either side of the neck and addition to helping compress the
extending from the clavicle or abdomen, they rotate the trunk and allow
collarbone to the temporal bone on the it to bend sideways.

On the rear part of the trunk, the thin and long. Of these many muscles,
trapezius are the kite-shaped muscles the flexor carpi bend the wrist and the
that run from the back of the neck and flexor digitorum bend the fingers. The
upper back down to the middle of the muscles that have the opposite effect,
back. They raise, lower, and adduct the extending the wrist and fingers, are the
shoulders. The large, flat muscles that extensor carpi and the extensor
cover the lower back are the latissimus digitorum.
dorsi. They adduct and rotate the arms Muscles of the Hips and Legs. Muscles
and help extend the shoulders. of the lower limbs cause movement at
Muscles of the Shoulders and Arms. the hip, knee, and foot joints. These
The fleshy, triangular-shaped muscles muscles are among the largest and
that form the rounded shape of the strongest muscles in the body. Muscles
shoulders are the deltoid. They help on the thigh (upper portion of the leg)
abduct the arm, or move it away from are especially massive and powerful
the middle of the body. The most since they hold the body upright against
familiar muscle of the upper arm is the the force of gravity.
biceps brachii Located on the front of The gluteus maximus are the
the upper arm, the bicep makes a large muscles that form most of the flesh
prominent bulge as it flexes the elbow. of the buttocks. These powerful muscles
On the rear portion of the upper arms is help extend the hip in activities such as
the triceps brachii. Its action is just the climbing stairs and jumping. The
opposite of the biceps: it extends or adductor muscles are a group of muscles
straightens the forearm. that form a mass on the inside of the
The muscles of the forearm, thighs. As their name indicates, they
which move the bones of the hands, are adduct or press the thighs together.

On the front of the thigh is a legged position with the knees wide
group of four muscles known apart.
collectively as the quadriceps. Together, On the back part of the lower leg
the quadriceps help powerfully extend or is the calf muscle, properly known as the
straighten the knee, such as when an gastrocnemius. This diamond-shaped
individual kicks a soccer ball. On the muscle, formed in two sections, helps
back of the thigh, a group of three extend or lower the foot, such as when
muscles performs the opposite effect. an individual walks on his or her toes.
Known as hamstrings, these muscles flex The strong tendon that attaches the
or bend the knee. The sartorius is long, gastrocnemius to the heel of the foot is
straplike muscle that crosses the front of the well-known Achilles tendon in
the thigh diagonally from the outside of Greek mythology, a hero of the Trojan
the hip to the inside of the knee. War who is killed by an arrow shot into
Although it is not that powerful, it does his heel. The main muscle on the front
lie on upper surface of the thigh and is part of the lower leg, the tibialis anterior,
easily seen. The sartorius helps rotate the opposes the action of the gastrocnemius.
leg so an individual can sit in a cross- It flexes and inverts or elevates the foot.

Nervous System – Brain and Nerves Page 26

The nervous system is the master body. It interprets incoming sensory
controller of the body. Each thought, information, then sends out instructions
each emotion, each action—all result on how the body should react. The CNS
from the activity of this system. Through consists of two major parts: the brain
its many parts, the nervous system and the spinal cord.
monitors conditions both within and The peripheral nervous system
outside the body. It then processes that (PNS) is the part of the nervous system
information and decides how the body outside of the CNS. It consists mainly of
should respond, if at all. Finally, if a nerves that extend from the brain and
response is needed, the system sends out spinal cord to areas in the rest of the
electrical signals that spur the body into body. Cranial nerves carry impulses to
immediate action. Although one of the and from the brain while spinal nerves
smallest of the body's systems in terms carry impulses to and from the spinal
of weight, the nervous system is the cord. The PNS can be divided into two
most complex and versatile. systems: the somatic nervous system and
the autonomic nervous system. The
PARTS OF THE NERVOUS somatic nervous system controls the
SYSTEM voluntary movements of the skeletal
The nervous system is a muscles. The autonomic nervous system
collection of cells, tissues, and organs. It control activities in the body that are
can be split into two separate divisions: involuntary or automatic. These include
the central nervous system and the the actions of the heart, glands, and
peripheral nervous system. digestive organs and associated parts.
The central nervous system The autonomic nervous system
(CNS) acts as the command center of the can be divided further into two

subdivisions: the parasympathetic and Axon, taillike projection extending out a
sympathetic nervous systems. These two neuron that carries impulses away from
subdivisions work against each other. the cell body.
The parasympathetic nervous system Basal ganglia, paired masses of gray
regulates involuntary activities that keep matter within the white matter of the
the body running smoothly under cerebrum that help coordinate
normal, everyday conditions. The subconscious skeletal muscular
sympathetic nervous system controls movement.
involuntary activities that help the body Brain, central controlling and
respond to stressful situations. coordinating organ of the nervous
Arachnoid, weblike middle layer of the system.
three meninges covering the brain and Cauda equine, spinal nerves that hang
spinal cord. below the end of the spinal cord.
Autonomic nervous system, part of the Central nervous system, part of the
peripheral nervous system that controls nervous system consisting of the brain
involuntary actions, such as the and spinal cord.
heartbeat, gland secretions, and Cerebral cortex, outermost layer of the
digestion. cerebrum made entirely of gray matter.
Cerebrum, largest part of the brain,
involved with conscious perception,

voluntary actions, memory, thought, and Gyri, outward folds on the surface of the
personality. cerebral cortex.
Corpus callosum, large band of neurons Hippocampus, structure in the limbic
connecting the two cerebral system necessary for the formation of
hemispheres. long-term memory.
Dendrites, branchlike extensions of Hypothalamus, region of the brain
neurons that carry impulses toward the containing many control centers for
cell body. body functions and emotions; also
Diencephalon, rear part of the forebrain regulates the pituitary gland's secretions.
that connects the midbrain to the Limbic system, group of structures in the
cerebrum and that contains the thalamus cerebrum and diencephalon that are
and hypothalamus. involved with emotional states and
Dura mate, outermost and toughest of memory.
the three meninges covering the brain Medulla oblongata, part of the brain
and spinal cord. located at the top end of the spinal cord
Ganglion, any collection of nerve cell that controls breathing and other
bodies forming a nerve center in the involuntary functions.
peripheral nervous system. Meninges, membranes that cover the
Gray matter, grayish nerve tissue of the brain and spinal cord.
central nervous system containing Midbrain, part of the brain between the
neuron cell bodies, neuroglia, and hypothalamus and the pons that
unmyelinated axons. regulates visual, auditory, and rightening
reflexes.

Myelin, soft, white, fatty material that system that controls involuntary
forms a sheath around the axons of most activities that keep the body running
neurons. smoothly under normal, everyday
Nerve, bundle of axons in the peripheral conditions.
nervous system. Peripheral nervous system, part of the
Neuroglia, also known as glial cells, nervous system consisting of the cranial
cells that support and protect neurons in and spinal nerves.
the central nervous system. Pia mater, delicate innermost layer of
Neuron, nerve cell. the three meninges covering the brain
Neurotransmitter, chemical released by and spinal cord.
the axon of a neuron that travels across a Pons, part of the brain connecting the
synapse and binds to receptors on the medulla oblongata with the midbrain.
dendrites of other neurons or body cells. Reflex, involuntary and rapid response to
Node of Ranvier, small area between a stimulus.
Schwann cells on an axon that is Schwann cell, cell that forms the myelin
unmyelinated or uncovered. sheath around axons of neurons in the
Oligodendrocyte, cell that produces the peripheral nervous system.
myelin sheath around the axons of Somatic nervous system, part of the
neurons in the central nervous system. peripheral nervous system that controls
Parasympathetic nervous system, the voluntary movements of the skeletal
division of the autonomic nervous muscles

Spinal cord, long cord of nerve tissue Neurons. The cells making up the brain,
running through the spine or backbone spinal cord, and nerves are called
that transmits impulses to and from the neurons. They are special cells capable
brain and controls some reflex actions. of receiving a stimulus (nerve or
Sulci, shallow grooves on the surface of electrical impulse), transmitting that
the cerebral cortex. stimulus throughout their length, and
Sympathetic nervous system, division of then delivering that stimulus to other
the autonomic nervous system that cells next to them. The human body
controls involuntary activities that help contains about 200 billion neurons.
the body respond to stressful situations. Almost half of them are located in the
Synapse, small space or gap where a brain.
nerve impulse passes between the axon A neuron consists of three main
of one neuron and a dendrite of the next parts: the cell body, dendrites, and an
neuron. axon (dendrites and axons are both
Thalamus, part of the brain behind the referred to as nerve fibers). The cell
hypothalamus that acts as the brain's body has most of the same structures
main relay station, sending information found in typical body cells, such as a
to the cerebral cortex and other parts of nucleus (the part of the cell that controls
the brain. its activities). It is ball shaped, about
White matter, whitish nerve tissue of the 0.001 inch (0.002 centimeter) in
central nervous system containing diameter.
bundles of myelinated axons.

Dendrite comes from the Greek Some (such as those in the central
word dendron , meaning "tree." nervous system) are very short, no
Dendrites are hairlike threads branching longer than 0.01 inch (0.02 centimeter).
off of the cell body like branches of a Others (such as those in the peripheral
tree. Extensions of the cell body, they nervous system) can be 3 feet (1 meter)
contain the same cytoplasm or cellular long.
fluid found in the cell body. Dendrites Most long axons are surrounded
are the points through which signals by a white, fatty material called myelin.
from adjacent neurons enter a particular The tubelike covering formed is known
neuron (the signal is then transmitted to as a myelin sheath. It serves the same
the cell body). Since each neuron kind of function as the wrapping on a
contains many dendrites, a neuron can telephone line or an electrical cable. It
receive signals from many other protects the axon and prevents electrical
surrounding neurons. impulses traveling through it from
An axon is a taillike projection becoming lost.
extending out of one end of the cell Special cells form the myelin
body. It ends in a cluster of branches sheath by wrapping themselves around
called terminal branches or axon the axons of neurons. In the CNS, the
terminals. Axons have the opposite cells forming the myelin sheath are
function of dendrites: they carry nerve called oligodendrocytes. In the PNS,
impulses away from the cell body. special cells known as Schwann cells
Axons vary in length and diameter. form the myelin sheath. The gap or

Types of Neurons. Neurons in the body
indentation on an axon where one may be divided into three groups:
Schwann cell ends and another begins is sensory neurons, motor neurons, and
known as a node of Ranvier. The nodes interneurons. As their name implies,
are unmyelinated (lack a myelin sheath), sensory neurons carry impulses or
and the nerve or electrical impulse jumps sensations from receptors to the brain or
from node to node as it passes along an spinal cord (central nervous system).
axon (in unmyelinated axons, the Receptors, which are located in the skin,
impulse travels continuously along the skeletal muscles, joints, and internal
axon). Scientists believe Schwann cells organs, detect changes both inside and
produce a chemical that helps regenerate outside the body. Motor neurons work in
or restore damaged neurons in the the opposite direction. They carry
peripheral nervous system. For example, impulses from the brain or spinal cord to
if surgeons are able to reattach a person's muscles and glands, causing muscles to
severed hand, that person may regain contract and glands to secrete. Both
some sensation and movement in that sensory and motor neurons make up the
hand as neurons grow and make peripheral nervous system. Interneurons
connections. Conversely, work entirely within the central nervous
oligodendrocytes lack this ability. This is system. They conduct impulses from
why an injury to the brain or spinal cord sensory to motor neurons.
often results in some permanent loss of
function.

Supporting Cells. Neuroglia, or glial Nerves are categorized like
cells, are cells that surround neurons in neurons according to the direction in
the central nervous system. They do not which they conduct impulses. Sensory
conduct impulses, but help to support nerves, made of the axons of sensory
and protect neurons, combining with neurons, carry impulses to the brain and
them to form what is known as nerve spinal cord. Motor nerves, made of the
tissue. They also supply neurons with axons of motor neurons, carry impulses
nutrients and remove their wastes. to the muscles and glands. Mixed nerves
Neuroglia are abundant, accounting for contain axons of both sensory and motor
some ten times the number of neurons. neurons. The most abundant nerves,
An example of neuroglia in the CNS are mixed nerves can conduct impulses both
oligodendrocytes. to and from the central nervous system.
Nerves. A nerve is a bundle of axons in The Brain. The human brain is a soft,
the PNS. Each axon or nerve fiber is shiny, grayish white, mushroom-shaped
wrapped in delicate connective tissue. structure encased within the skull. At
Groups of axons are then bound in birth, a typical human brain weighs
coarser connective tissue to form between 12 and 14 ounces (350 and 400
bundles. Finally, many bundles are grams). By the time an average person
bound together (along with blood vessels reaches adulthood, the brain weighs
to nourish the axons and Schwann cells) about 3 pounds (1.36 kilograms).
by even tougher connective tissue to Because of greater average body size,
form a nerve. the brains of male are generally about 10
percent larger than those of females.

Although brain size varies considerably cerebrospinal fluid, a liquid that
among humans, there is no correlation or circulates between the arachnoid.
link between brain size and intelligence. The Brain Stem. The brain stem is the
The human brain is composed of stalk of the brain and is a continuation of
up to one trillion nerve cells. One the spinal cord. It consists of the medulla
hundred billion of these are neurons, and oblongata, pons, and midbrain. The
the remainder are the supporting medulla oblongata is actually a portion
neuroglia. The brain consists of gray and of the spinal cord that extends into the
white matter. Gray matter is nerve tissue brain. All messages that are transmitted
in the CNS composed of neuron cell between the brain and spinal cord pass
bodies, neuroglia, and unmyelinated through the medulla. Nerves on the right
axons; white matter is nerve tissue in the side of the medulla cross to the left side
CNS composed chiefly of bundles of of the brain, and those on the left cross
myelinated axons. to the right. The result of this
The brain is protected by the arrangement is that each side of the brain
skull and by three membranes called the controls the opposite side of the body.
meninges. The outermost membrane is Three vital centers in the medulla
known as the dura mater, the middle as control heartbeat, rate of breathing, and
the arachnoid, and the innermost as the diameter of the blood vessels. Centers
pia mater. Also protecting the brain is that help coordinate swallowing,

vomiting, hiccuping, coughing, information from the eyes. The only
sneezing, and other basic functions of exception is the vagus nerve (vagus
life are also located in the medulla. A comes from the Latin word meaning
region within the medulla helps to "wandering"). It is the lone cranial nerve
maintain the conscious state. The pons that serves other areas of the body. The
(from the Latin word meaning "bridge") vagus nerve branches extensively to the
conducts messages between the spinal larynx, heart, lungs, stomach, and
cord and the rest of the brain, and intestines. Among other functions, it
between the different parts of the brain. helps promote digestive activity and
The midbrain conveys impulses from the regulate heart activity.
hypothalamus to the pons and spinal The Diecephalon. The diencephalon
cord. It also contains visual and audio lies above the brain stem, and includes
reflex centers involving the movement the thalamus and hypothalamus. The
of the eyeballs and head. thalamus is an important relay station for
Twelve pair of cranial nerves sensory information coming to the
originate in the underside of the brain, cerebral cortex from other parts of the
mostly from the brain stem. They leave brain. The thalamus also interprets
the skull through openings and extend as sensations of pain, pressure,
peripheral nerves to their destinations. temperature, and touch, and is concerned
Cranial nerves bring information to the with some of our emotions and memory.
brain from regions in the face, head, and It receives information from the outside
neck. For example, the olfactory nerve environment in the form of sound, smell,
transmits messages about smell from the and taste.
nose and the optic nerve transmits visual

The Cerebrum. The cerebrum makes up The Cerebellum. The cerebellum is
about 80 percent of the brain's weight. It located below the cerebrum and behind
lies above the diencephalon. The the brain stem, and is shaped like a
cerebrum's outer layer, the cerebral butterfly. The "wings" are the cerebellar
cortex, is made entirely of gray matter hemispheres, and each consists of lobes
(white matter makes up the inner portion that have distinct grooves or fissures.
of the cerebrum). The tissue of the The cerebellum controls the actions of
cerebral cortex is about 0.08 to 0.16 inch the muscular system needed for
(2 to 4 millimeters) thick. The cerebral movement, balance, and posture. All
cortex is folded extensively. The folds motor activity in the body depends on
are called convolutions or gyri, and the the cerebellum.
shallow grooves between the folds are The Limbic System. The limbic system
sulci. Deeper grooves, which are less is a horseshoe-shaped area of the brain
numerous, are called fissures. The folds located along the border between the
greatly increase the surface area of the cerebrum and diencephalon. Key
cerebral cortex—it would have a surface structures of the limbic system include
area of about 5 square feet (1.5 square the almond-shaped amygdala and the sea
meters) if spread out—and thus the total horse-shaped hippocampus. The limbic
number of nerve cell bodies it contains. system is concerned with emotional

states (such as rage, fear, and sexual to and from the brain and controls some
arousal) and memory. The hippocampus, reflex actions. On average, the spinal
in particular, plays a vital role in cord measures about 18 inches (45
learning and long-term memory. centimeters) in length and about 0.5 inch
The Spinal Cord. The spinal cord, a (14 centimeters) in width. It weighs
glistening white rope, is a continuation about 1.25 ounces (35 grams).
of the brain stem. It transmits impulses

Respiratory System – Breathing Page 32

Breathing,
controlled by the
respiratory system, is a
continuous process of
which a person is
normally unaware. If
breathing stops,
however, a person
becomes acutely aware
of the fact. An individual
can go days without food
and water and hours
without sleep, but only
five or six minutes
without air. Anything
beyond that would be
fatal. The trillions of cells in the body

need a constant and generous amount of cell parts and chemicals, and the
oxygen to carry out their vital functions. movement of compounds through cells
As they use that oxygen, they give off and the body as a whole.
carbon dioxide as a waste product. It is
the role of the respiration system, PARTS OF THE RESPIRATORY
working in conjunction with the SYSTEM
cardiovascular system, to supply the Breathing describes the process
oxygen and dispose of the carbon of inhaling and exhaling air. The
dioxide. exchange of gases (oxygen and carbon
Main Function. The main function of dioxide) between living cells and the
the respiratory system is to provide environment is a process known as
oxygen for the body's cells and remove respiration. The respiratory system,
the carbon dioxide they produce. which controls breathing and respiration,
Oxygen is the most important energy consists of the respiratory tract and the
source for the cells. They need it for lungs.
cellular respiration: the process by which The respiratory tract cleans,
the simple sugar glucose is oxidized warms, and moistens air on its way to
(combined with oxygen) to form the the lungs. The tract can be divided into
energy-rich compound adenosine an upper and a lower part. The upper
triphosphate (ATP). Glucose is produced part consists of the nose, nasal cavity,
in cells by the breakdown of more pharynx (throat), larynx, and upper part
complex carbohydrates, including starch, of the trachea (windpipe). The lower part
cellulose, and complex sugars such as consists of the lower part of the trachea,
sucrose (cane or beet sugar) and fructose bronchi, and lungs (which contain
(fruit sugar). ATP is the compound used bronchioles and alveoli).
by all cells to carry out their ordinary The nose and nasal cavity. The nose
functions: growth, the production of new
Respiratory System – Breathing Page 33

is the only external part of the cavity, separating it from the mouth or
respiratory system. It is made of bone oral cavity below. Three flat, spongy
and cartilage (tough connective tissue) folds or plates project toward the nasal
and is covered with skin. The two septum from the sides of the nasal
openings to the outside, called nostrils, cavity. These plates, called nasal
allow air to enter or leave the body conchae, help to slow down the passage
during breathing. The nostrils are lined of air, causing it to swirl in the nasal
with coarse hairs that prevent large cavity.
particles such as dust, insects, and sand Alveoli, air sacs of the lungs.
from entering. Breathing, process of inhaling and
The nostrils open into a large exhaling air.
cavity, the nasal cavity. This cavity is Bronchi, largest branch of the bronchial
divided into right and left cavities by a tree between the trachea and
thin plate of bone and cartilage called bronchioles.
the nasal septum. The hard portion of the
palate forms the floor of the entire nasal

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