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Human Organ Systems
The nervous system is composed of the brain, spinal cord, nerves, and
sensory organs. It's main function is to coordinate the body's
activities, detect all stimuli and form responses to them. The
brain is the control center of the the nervous system.
The Central Nervous System is made up of the brain and
spinal cord. The spinal cord transports sensory and motor
information from other parts of the body to the brain.
The brain only weighs 3 pounds, but is composed of more than 12
billion neurons and 50 billion supporting glial cells. With the spinal
cord, the brain monitors and regulates many unconscious bodily processes
such as heart rate and breathing, and coordinates most voluntary
movements. Most important, it is the site of consciousness and of all
the intellectual functions that allow humans to think and create.
The brain produces electrical signals, which,
together with chemical reactions, let the parts of the body communicate.
Nerves send these signals throughout the body.
The Nerve Cell
Each neuron consists of a nucleus situated in the cell body, where
outgrowths called processes originate from. The main one of these
processes is the axon, which is responsible for carrying outgoing
messages from the cell. This axon can originate from the central
nervous system (CNS) and extend all the way to the body's
extremities, providing an efficient highway for messages.
Dendrites are smaller secondary processes that grow from the cell body
and axon. On the end of these dendrites lie the axon terminals, which
plug into a cell where the electrical signal from a nerve cell to the
target cell can be made. This 'plug' (the axon terminal) connects into a
receptor on the target cell and can transmit information between cells.
Autonomic Nervous System (ANS)
The Autonomic Nervous System is divided into 3 parts:
sympathetic nervous system
enteric nervous system
It is responsible for regulating
muscles and glands
Spinal Cord Vertebrae
cervical (neck) segments
The skeletal system consists of the bones, tendons, ligaments, and
cartilage. It's main function is to support the body and provide
protection for the internal organs.
The muscular system consists of skeletal muscles. These
muscles attach to the skeleton and provide movement and locomotion.
There are 3 main types of muscle tissue as you will see listed below.
Spindle shaped cells
Hair, Skin, and Nails
The integumentary system consists of the skin and its
derivatives; hair and nails. This system is the body's first line of
defense against foreign invaders and protects against mechanical
injury, infection (disease) and also prevents the inner organs
from drying out by retaining body fluids. Your skin also plays an
important role to eliminate waste products, regulate body temperature
and protects the body from harmful ultraviolet rays from the sun.
Everyone, young and old, should minimize exposure to
the sun and protect themselves from Ultraviolet Radiation. UVA and
UVB rays damage the DNA in skin cells and can lead to deadly forms of
skin cancer (Melanoma Carcinoma). Sun exposure increases the fine lines
on skin, known as wrinkles, and accelerates the timeline of the aging
process. Prevention is easily achieved by limiting the amount of
time you are exposed to UV rays and by using products that help prevent
exposure to UVA and UVB rays. With this said, it is understandable
why it is important to take care of your skin!
Secretions from the sebaceous and sweat glands maintain the pH on the
skin's surface at the pH of about 3 to 5. This acidic surface keeps many
invaders from making a home on your skin. Your body's natural
flora of bacteria have adapted to this acidic surface.
The digestive system begins at the mouth and ends at the anus.
Consists of mouth, pharynx, esophagus, stomach, intestines, liver,
pancreas, and anus. The main function of the digestive system is
to process food through ingestion through the mouth, digestion, in the
stomach, absorption of water and nutrients in the intestines, and
elimination through the anus.
The excretory system is responsible for the disposal of metabolic
wastes and the regulation of osmotic balance of the blood. This
organ system consists of the kidneys, ureters, urinary bladder,
and urethra. The kidneys are bean shaped and lie in the superior
lumbar region of the posterior abdominal wall. The right kidney is
crowded by the liver and is slightly inferior to the left kidney.
The average kidney is about the size of a large bar of soap. The
convex portion of the kidney shown in the photograph is called the
lateral portion. The concave portion is called the renal
hilus. This is where the renal artery, renal vein and renal pelvis
leave the kidney. The smaller image displays the kidneys, adrenal
gland (superior to kidney) which is part of the endocrine system, the
inferior vena cava, aorta, ureter, and urinary bladder. The
kidneys filter waste particles from the blood and send toxins,
excess water, and metabolic wastes out of the body in the form of urine,
while the useful substances from the filtrate are sent back into the
blood. The three nitrogenous compounds that are eliminated from
the body are urea, uric acid and creatinine. Eliminating wastes is
only one job of the kidneys, they also regulate the volume and chemical
makeup of the blood by maintaining equilibrium between acids and bases
and between water and salts.
The respiratory system consists of the lungs, trachea, and other
breathing tubes. It main function is gas exchange; simply put, the
uptake of oxygen and the disposal or removal of carbon dioxide.
When you breath in you inhale the oxygen that the lungs need to
re-supply red blood cells with oxygen, which is then transported to the
rest of the body. When you breath out or exhale, you are getting
rid of the carbon dioxide that the body is trying to eliminate.
The respiratory system works in conjunction with the circulatory system.
Image: Encyclopaedia Britannica, 2008
The circulatory system consists of the heart, blood vessels and
blood. It's main function is to distribute materials throughout
Blood is a connective tissue, the ground substance is plasma,
and the blood cells are called formed elements. Plasma makes up 55% and
cellular/formed elements make up 45%. The three formed elements are
erythrocytes, leukocytes and platelets, which develop from a single
population of pluripotent stem cells in the red marrow of bones.
This marrow is found in the ribs, vertebrae, breastbone, and pelvis of
the fetus. The pluripotent stem cells are unique because
they have the potential to develop into any type of blood cell or cells
that produce platelets.
Erythrocytes (red blood cells)
Transport oxygen and carbon dioxide.
Leukocytes (white blood cells)
Play a major role in our immune and defense system.
sources combine the monocytes and lymphocytes into one category and just
call them all 'mononuclear leukocytes.'
1. Granulocytes (These are also called
|Granulocytes include the neutrophils,
eosinophils, and basophils (their cytoplasm is often
filled with granules). These are the work horses of
acute inflammation (and other processes). Make sure you
learn the neutrophil. In pathology and immunology,
you'll call this same cell the PMN (polymorphonuclear
Eosinophils are involved in allergic reactions and
|Another cell to mention here
(although it is NOT a granulocyte) is
the Mast Cell. It's very similar to the
basophil: both release histamine (and
other mediators). Some think that the
mast cell is derived from the basophil.
Just remember that the basophil
circulates and the mast cell is found in
peripheral tissues. Other than that,
they are quite similar. |
|Monocytes include the monoctye and the
macrophage. The monocytes, like all leukocytes, use the
bloodstream to reach the connective tissues. There,
they transform into macrophages, phagocytic cells that
possess pseudopods and ingest a wide variety of foreign
cells, molecules, and tiny particles of debris. Once in
the tissue, it matures into the macrophage. It can also
mature even further into other cells. The
monocyte/macrophage is the work horse of chronic
|Lymphoctyes are white blood cells. They
originate in the bone marrow and are derived from the
same stem cell as the rest of the erythrocytes and
leukocytes. These are the T-cells and B-cells that
direct the immune system and produce antibodies,
respectively. They are the central cells in our
cell-mediated and humeral (antibody) defense mechanisms.
The B-cell can mature into the plasma cell. |
*Know that as a rule of thumb, bacterial infections cause
granulocytosis and viral infections cause lymphocytosis. There are
exceptions to this, but this is a very basic (and important) concept.
Important in clotting and scab formation. The mineral calcium, vitamin
K, and a protein called fibrinogen help the platelets form a clot.
If your body is deficient in calcium and vitamin K it will take
much longer for your blood to form a clot. If these nutrients are
missing you could bleed to death. A scab is an external blood clot
that we can easily see, but there are also internal blood clots. A
bruise, or black-and-blue mark, is the result of a blood clot. Both
scabs and bruises are clots that lead to healing. Not all blood
clots are beneficial. If a clot forms in a blood vessel it will
stop the blood flow (which means the oxygen flow) to whatever
organ it's servicing, i.e. heart attack, stroke. Loss of oxygen to the
brain would cause paralysis, brain damage, loss of sensory perceptions
heart -> elastic arteries -> muscular arteries -> arterioles ->
capillaries -> venules -> veins -> heart
Arteries take blood AWAY from the heart to other tissues. They carry
blood high in oxygen (exception: pulmonary arteries) through
thick, springy walls. As a result the blood pressure is higher in
arteries than in veins. Veins take blood back to the heart and
carry blood low in oxygen and high in carbon dioxide (exception:
pulmonary veins). Their walls are thinner, and lumen is much
larger than arteries. The blood pressure, therefore, is lower in
veins. Connecting arteries and veins are tiny vessels called
capillaries where gas exchange occurs.
BLOOD VESSEL STRUCTURE
Tunica Externa (Tunica Adventitia): outermost layer,
areolar connective tissue and largest layer in veins.
Tunica Media: middle layer, circularly arranged smooth muscle
fibers and largest layer in arteries.
Tunica Intima: innermost layer - endothelium (simple squamous
epithelium) and areolar connective tissue
Vascular System -Three Basic Layers: Tunica Intima (with endothelial
lining), Tunica Media (smooth muscle), Tunica Adventitia (outer
Elastic Arteries vessel wall contains large amounts of elastin
(a protein fiber). Muscular Arteries diameter ranges from .3mm -
1cm, they have less elastin than elastic arteries, and more smooth
muscle in the tunica media. Arterioles diameter is
less than .3 mm, and tunica media consists of 5 or fewer layers of
smooth muscle. Capillaries have a diameter only slightly
larger than the diameter of an erythrocyte, consisting only of
a tunica intima. They form capillary bed and are the site for gas
and nutrient exchange. Venules collect blood from capillaries.
Veins are formed when venules merge together, composed of tunica intima,
and most veins have valves to prevent back flow.
The immune and lymphatic system consist of bone marrow, lymph nodes,
thymus, spleen, lymph vessels, and white blood cells. It's main
function is fighting infection and cancer. better known as the body's
line of defense
line of defense
line of defense
The lymphatic and immune systems are so closely related that we will
place them under the same heading.
The main components of the lymphatic system are the lymphatic
vessels. Think of the these vessels as the highway in which the
disease organisms travel. It is through the lymphatic vessels that
escaped fluid from blood vessels is returned to the blood stream.
These vessels run all through the human body collecting a fluid called
lymph. This fluid travels in a one-way direction toward the heart
(due to flap-like mini-valves which prevent backflow) and empties
into the great veins in the base of the neck. The lymphatic
vessels also return leaked proteins from the surrounding blood
capillaries back to the bloodstream. The lymphatic system has no
organ (like the heart) to pump lymph through the body, and therefore
relies on the pulsing of surrounding blood vessels, body movement and
muscle contractions to move or squeeze fluid through the vessels.
The main components of the immune system are
lymphocytes, lymphoid tissue, and lymphoid organs (spleen, lymph nodes,
thymus, tonsils, lymphoid nodules in the small intestine, and the
appendix). Think of the lymphoid tissue and organs as the
parking garage or battle ground where the disease organisms are
detained and ultimately destroyed.
Artificially Acquired Immunity
antibodies in response
to stimulation by an
formed, those antibodies
can be removed from the
host and transferred
into another recipient
where they provide
dead, or fragments of
microbes) are introduced
Preformed antibodies in
an immune serum
are introduced into the
body by injection (e.g.
anti-venom used to treat
body produces antibodies
body does not produce
The endocrine system consists of many glands; the pituitary, thyroid,
adrenal glands, pancreas, and ovaries/testicles (which also secrete
hormone is a chemical substance produced by an animal or plant which
acts as a "chemical messenger." Hormones act to help different parts of
an organism to function in a coordinated way. Typically, hormones are
formed in one part of an organism, and their effect occurs in a
different area. The word hormone is derived from Greek and means, "to
set in motion."
These chemicals regulate:
function & reproduction
of various blood components
of other hormones
It was not until the early 1900's that the existence of these
substances became known. Since then, over 30 human hormones have been
identified, and we have developed the ability to extract them from
tissues and synthesize them in the lab. In humans, most hormones are
produced by certain glands called endocrine glands. Doctors that
specialize in the evaluation and treatment of hormone conditions are
In humans and animals, hormones control a number of bodily functions
including growth, development, and reproduction. In plants, hormones
mainly regulate growth. Decreased production of these chemical
messengers can lead to serious diseases and even death.
||Divided into 2 regions;
secrete hormones that
influence the body's
chemicals, and body
characteristics, as well
as influence the part of
the nervous system that
is involved in the
response and defense
||Activates and controls
the part of the nervous
system that controls
functions, the hormonal
system, and many body
functions, such as
regulating sleep and
Ovaries and testicles
||Secrete hormones that
influence female and
||Secretes a hormone
(insulin) that controls
the use of glucose by
||Secrete a hormone that
maintains the calcium
level in the blood.
||Involved with daily
||Produces a number of
different hormones that
influence various other
||Plays a role in the
body's immune system.
||Produces hormones that
stimulate body heat
production, bone growth,
and the body's
The reproductive system consists of the ovaries, testes, and other
associated organs. It's main function is reproduction.
The cervix is lined with a layer of cells called epithelial cells.
Epithelial cells are a general type of cells found throughout the body,
and they vary in shape and size depending on where they are. In the
cervix, the epithelial cells inside the canal are very different from
the cells that line the part of the cervix that borders the vagina. In
the canal the cells are tall and are referred to as columnar epithelium.
On the outside wall of the cervix, where the cervix meets the vagina the
epithelial cells are flat, or squamous. A very delicate area of the
cervix is called the squamous columnar junction, where the tall columnar
cells end and the flat, squamous cells begin. It is here that
pre-cancerous lesions are usually detected and where cells are sampled
for Pap smear screening.
The male pelvis is narrower, deeper and has thicker, stronger bones
than the female pelvis. The male reproductive glands, testes, lie within
the scrotum, which is outside the body between the legs. The testes
produce sperm and male hormones. From the testes, sperm pass into a
coiled tube called the epididymis where they mature and are stored until
ejaculation through the urethra or until reabsorbed by the body. The
prostate is about the size of a walnut. It lies just below the urinary
bladder and surrounds the upper part of the urethra.
The prostate is an integral part of the reproductive system for men,
providing the fluid necessary to transport sperm during ejaculation.
However, as men age, the prostate can be a source of problems. Three
common diseases of the prostate are: benign prostatic hyperplasia (BPH),
prostatitis and prostate cancer. Each of these conditions affects the
Many foreign invaders such as bacteria, viruses, pathogens in the
air, and abnormal body cells can cause disease. Scientists from research
and development (R&D) teams all over the world are constantly working on
new ways to defeat/control these intrusions.
January 19, 2018