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ANATOMY AND PHYSIOLOGY
The Cardiovascular System
The heart and circulatory system make up the cardiovascular system. The heart works
as a pump that pushes blood to the organs, tissues, and cells of the body. Blood delivers oxygen
and nutrients to every cell and removes the carbon dioxide and waste products made by those
cells. Blood is carried from the heart to the rest of the body through a complex network of
arteries, arterioles, and capillaries. Blood is returned to the heart through venules and veins.
The one-way circulatory system carries blood to all parts of the body. This process of
blood flow within the body is called circulation. Arteries carry oxygen-rich blood away from the
heart, and veins carry oxygen-poor blood back to the heart. In pulmonary circulation, though,
the roles are switched. It is the pulmonary artery that brings oxygen-poor blood into the lungs
and the pulmonary vein that brings oxygen-rich blood back to the heart. (Rod R. Seeley et. al,
Essentials of Anatomy and Physiology 5th edition, McGraw-Hill Int. NY 10020 2005)
Twenty major arteries make a path through the tissues, where they branch into smaller
vessels called arterioles. Arterioles further branch into capillaries, the true deliverers of oxygen
and nutrients to the cells. Most capillaries are thinner than a hair. In fact, many are so tiny, only
one blood cell can move through them at a time. Once the capillaries deliver oxygen and
nutrients and pick up carbon dioxide and other waste, they move the blood back through wider
vessels called venules. Venules eventually join to form veins, which deliver the blood back to
the heart to pick up oxygen. Vasoconstriction or the spasm of smooth muscles around the
blood vessels causes and decrease in blood flow but an increase in pressure. In vasodilation, the
lumen of the blood vessel increase in diameter thereby allowing increase in blood flow. There is
no tension on the walls of the vessels therefore, there is lower pressure. (Rod R. Seeley et. al,
Essentials of Anatomy and Physiology 5th edition, McGraw-Hill Int. NY 10020 2005)
Various external factors also cause changes in blood pressure and pulse rate. An
elevation or decline may be detrimental to health. Changes may also be caused or aggravated
by other disease conditions existing in other parts of the body. The blood is part of the
circulatory system. Whole blood contains three types of blood cells, including: red blood cells,
white blood cells and platelets.
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Blood also contains important proteins called clotting factors, which are critical to the
clotting process. Although platelets alone can plug small blood vessel leaks and temporarily
stop or slow bleeding, the action of clotting factors is needed to produce a strong, stable clot.
Platelets and clotting factors work together to form solid lumps to seal leaks, wounds,
cuts, and scratches and to prevent bleeding inside and on the surfaces of our bodies. The
process of clotting is like a puzzle with interlocking parts. When the last part is in place, the clot
is formed.
When large blood vessels are cut the body may not be able to repair itself through
clotting alone. In these cases, dressings or stitches are used to help control bleeding.
In addition to the cells and clotting factors, blood contains other important substances,
such as nutrients from the food that has been processed by the digestive system. Blood also
carries hormones released by the endocrine glands and carries them to the body parts that
need them. (Rod R. Seeley et. al, Essentials of Anatomy and Physiology 5th edition, McGraw-Hill
Int. NY 10020 2005)
Blood is essential for good health because the body depends on a steady supply of fuel
and oxygen to reach its billions of cells. Even the heart couldn't survive without blood flowing
through the vessels that bring nourishment to its muscular walls. Blood also carries carbon
dioxide and other waste materials to the lungs, kidneys, and digestive system, from where they
are removed from the body. (Rod R. Seeley et. al, Essentials of Anatomy and Physiology 5th
edition, McGraw-Hill Int. NY 10020 2005)
The Nervous System
The Nervous system is a network of specialized cells that communicate information
about an animals surroundings and its self, it processes this information and causes reactions in
other parts of the body. It is composed of neurons and other specialized cells called glia, that
aid in the function of the neurons.
The nervous system is divided broadly into two categories; the peripheral nervous
system and the central nervous system. Neurons generate and conduct impulses between and
within the two systems. The peripheral nervous system is composed of sensory neurons and
the neurons that connect them to the nerve cord, spinal cord and brain, which make up the
central nervous system. In response to stimuli, sensory neurons generate and propagate signals
to the central nervous system which then process and conduct back signals to the muscles and
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glands. (Rod R. Seeley et. al, Essentials of Anatomy and Physiology 5th edition, McGraw-Hill Int.
NY 10020 2005)
The neurons of the nervous systems of animals are interconnected in complex
arrangements and use electrochemical signals and neurotransmitters to transmit impulses from
one neuron to the next. The interaction of the different neurons form neural circuits that
regulate an organisms perception of the world and what is going on with its body, thus
regulating its behavior. Nervous systems are found in many multicellular animals but differ
greatly in complexity between species.
The central nervous system (CNS) is the largest part of the nervous system, and includes
the brain and spinal cord. The spinal cavity holds and protects the spinal cord, while the head
contains and protects the brain. The CNS is covered by the meninges, a three layered protective
coat. The brain is also protected by the skull, and the spinal cord is also protected by the
vertebrae. (Rod R. Seeley et. al, Essentials of Anatomy and Physiology 5th edition, McGraw-Hill
Int. NY 10020 2005)
Brain is a part of the Central Nervous System, it plays a central role in the control of
most bodily functions, including awareness, movements, sensations, thoughts, speech, and
memory. Some reflex movements can occur via spinal cord pathways without the participation
of brain structures. (Rod R. Seeley et. al, Essentials of Anatomy and Physiology 5th edition,
McGraw-Hill Int. NY 10020 2005)
The cerebrum is the largest part of the brain and controls voluntary actions, speech,
senses, thought, and memory. The surface of the cerebral cortex has grooves or infoldings
(called sulci), the largest of which are termed fissures. Some fissures separate lobes. The
convolutions of the cortex give it a wormy appearance. Each convolution is delimited by two
sulci and is also called a gyrus (gyri in plural). The cerebrum is divided into two halves, known as
the right and left hemispheres. A mass of fibers called the corpus callosum links the
hemispheres. The right hemisphere controls voluntary limb movements on the left side of the
body, and the left hemisphere controls voluntary limb movements on the right side of the body.
Almost every person has one dominant hemisphere. Each hemisphere is divided into four lobes,
or areas, which are interconnected.
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The frontal lobes are located in the front of
the brain and are responsible for voluntary
movement and, via their connections with
other lobes, participate in the execution of
sequential tasks; speech output;
organizational skills; and certain aspects of
behavior, mood, and memory.
The parietal lobes are located behind the
frontal lobes and in front of the occipital lobes. They process sensory information such as
temperature, pain, taste, and touch. In addition, the processing includes information about
numbers, attentiveness to the position of ones body parts, the space around ones body, and
one's relationship to this space.
The temporal lobes are located on each side of the brain. They process memory
and auditory (hearing) information and speech and language functions.
The occipital lobes are located at the back of the brain. They receive and process visualinformation (Rod R. Seeley et. al, Essentials of Anatomy and Physiology 5th edition, McGraw-
Hill Int. NY 10020 2005)
Cranial nerve I: Olfactory nerve
The olfactory nerve is composed of axons from the olfactoryreceptors in the nasal sensory epithelium. It carries olfactory
information (sense of smell) to the olfactory bulb of the brain. This
is a pure sensory nerve fiber.
Cranial nerve II: Optic nerve
The optic nerve is composed of axons of the ganglion cells in theeye. It carries visual information to the brain. This is a pure sensory
nerve fiber. This nerve travels posteromedially from the eye,
exiting the orbit at the optic canal in the lesser wing of the
sphenoid bone. The optic nerves join each other in the middle
cranial fossa to form the optic chiasm.
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Cranial nerve III: Oculomotor nerve
The oculomotor nerve is composed of motor axons coming from
the oculomotor nucleus and the edinger-westphal nucleus in the
rostral midbrain located at the superior colliculus level. This is a
pure motor nerve. It provides somatic motor innervation to four of the extrinsic eye muscles: the superior rectus, inferior rectus,
medial rectus, and the inferior oblique muscles. It also innervates
the muscles of the upper eyelid and the intrinsic eye muscles (the
pupillary eye muscle.) Together, CN III, CN IV and CN VI control the six muscles of the eye.
Cranial nerve IV: Trochlear nerve
The trochlear nerve provides somatic motor innervation to the superior oblique eye muscle.
This cranial nerve originates at the trochlear nucleus located in the tegmentum of the midbrain
at the inferior colliculus level and exits the posterior side of the brainstem. It is also a pure
motor nerve fiber.
Cranial nerve V: Trigeminal nerve
The trigeminal is the largest cranial nerve . It provides sensory
information from the face, forehead, nasal cavity, tongue, gums
and teeth (touch, and temperature) and provides somatic motorinnervation to the muscles of mastication or chewing.
This cranial nerve has 3 branches: the ophthalmic, maxillary and
mandibular branches.
It is composed of both sensory and motor axons. The sensory fibers are located in the
trigeminal ganglion and the motor fibers project from nuclei in the pons.
Cranial nerve VI: Abducens nerve
The abducens nerve carries somatic motor innervation to one of
the extrinsic eye muscles, the lateral rectus muscle. It is another pure
motor nerve fiber and originates from the abducens nucleus located in
the caudal pons at the facial colliculus level.
Cranial nerve VII: Facial nerve
The facial nerve carries somatic motor innervation to the many
muscles for facial expression. It carries sensory information form
the face (deep pressure sensation) and taste information from the
anterior two thirds of the tongue. It arises at the pons in thebrainstem and it emerges through openings in the temporal bone
and stylomastoid foramen and has many branches. It is composed
of both sensory and motor axons.
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Cranial nerve VIII: Vestibulocochlear nerve
The vestibulocochlear nerve innervates the hair cell receptors of the
inner ear. It carries vestibular information to the brain from the
semicircular canals, utricle, and saccule providing the sense of
balance. It also carries information from the cochlea providing thesense of hearing. This cranial nerve branches into the Vestibular
branch (balance) and the cochlear branch (hearing). The cochlear
fibers originate from the spiral ganglion. It is pure sensory nerve
fiber.
Cranial nerve IX: Glossopharyngeal nerve
The glossopharyngeal nerve innervates the pharynx (upper part of
the throat), the soft palate and the posterior one-third of the
tongue. It carries sensory information (touch, temperature, and
pressure) from the pharynx and soft palate. It carries taste
sensation from the taste buds on the posterior one third of the
tongue. It provides somatic motor innervation to the throat muscles
involved in swallowing. It provides visceral motor innervation to the
salivary glands. This cranial nerve also supplies the carotid sinus and
reflex control to the heart . It is composed of both sensory and
motor axons and originates from the nucleus ambiguous in thereticular formation of the medulla.
Cranial nerve X: Vagus nerve
The vagus nerve consists of many rootlets that come off of the
brainstem just behind the glossopharyngeal nerve. The branchial
motor component originates from the nucleus ambiguous in the
reticular formation of the medulla. The visceral component
originates from the dorsal motor nucleus of the vagus located in the
floor of the fourth ventricle in the rostral medulla and in the central
grey matt er of the caudal medulla. It is the longest cranial nerve
innervating many structures in the throat, including the muscles of
the vocal cords, thorax and abdominal cavity. It provides sensory information (touch,
temperature and pressure) from the external auditory meatus (ear canal) and a portion of the
external ear. It carries taste sensation from taste buds in the pharynx. It also provides sensory
information from the esophagus, respiratory tract, and abdominal viscera (stomach, intestines,
liver, etc.). It provides visceral motor innervation to the heart, stomach, intestines, and
gallbladder. It is part of the ANS, the parasympathetic branch. It is composed of both sensory
and motor axons. Other parasympathetic ganglia include CN III , CN VII and CN IX .
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Cranial nerve XI: Spinal Accessory nerve
The spinal accessory nerve has two branches. The cranial branch
provides somatic motor innervation to some of the muscles in the
throat involved in swallowing. This cranial branch is accessory to CN
X, originating in the caudal nucleus ambiguous, with the fibers of the cranial root traveling the same extracranial path as the
branchial motor component of the vagus nerve. The spinal branch
provides somatic motor innervation to the trapezius muscles,
providing muscle movement for the upper shoulders head and
neck. It is pure motor nerve fiber.
Cranial nerve XII: Hypoglossal nerve
The hypoglossal nerve provides somatic motor innervation to the muscles of the tongue. This
pure motor nerve originates from the hypoglossal nucleus located in the tegmentum of the
medulla.
Circle of Willis
The Circle of Willis (also called Willis' Circle, cerebral arterial circle, arterial Circle of
Willis, and Willis Polygon) is a circle of arteries that supply blood to
the brain.
Components
The Circle of Willis comprises the following arteries
y Anterior cerebral artery (left and right)
y Anterior communicating artery
y Internal carotid artery (left and right)
y Posterior cerebral artery (left and right)
y Posterior communicating artery (left and right)
The left and right internal carotid arteries arise from the right and left
common carotid arteries.
The posterior communicating artery is given off as a branch of the internal carotid artery just
before it divides into its terminal branches - the anterior and middle cerebral arteries. The anterior
cerebral artery forms the anterolateral portion of the Circle of Willis, while the middle cerebral
artery does not contribute to the circle.
The right and left posterior cerebral arteries arise from the basilar artery, which is formed by the
left and right vertebral arteries. The vertebral arteries arise from the subclavian arteries.
The anterior communicating artery connects the two anterior cerebral arteries and could be said to
arise from either the left or right side.
All arteries involved give off cortical and central branches. The central branches supply the interior
of the Circle of Willis, more specifically, the Interpeduncular fossa. The cortical branches are named
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Like kidney beans, the bodys kidneys are dark red in color and have a shape in which
one side is convex, or rounded, and the other is concave, or indented. The kidneys of adult
humans are about 10 to 13 cm (4 to 5 in) long and about 5 to 7.5 cm (2 to 3 in) wideabout the
size of a computer mouse.
The kidneys lie against the rear wall of the abdomen, on either side of the spine. They
are situated below the middle of the back, beneath the liver on the right and the spleen on the
left. Each kidney is encased in a transparent, fibrous membrane called a renal capsule, which
helps protect it against trauma and infection. The concave part of the kidney attaches to two of
the bodys crucial blood vesselsthe renal artery and the renal veinand the ureter, a tubelike
structure that carries urine to the bladder. (Rod R. Seeley et. al, Essentials of Anatomy and
Physiology 5th edition, McGraw-Hill Int. NY 10020 2005)
A primary function of kidneys is the removal of poisonous wastes from the blood. Chief
among these wastes are the nitrogen-containing compounds urea and uric acid, which result
from the breakdown of proteins and nucleic acids. Life-threatening illnesses occur when too
many of these waste products accumulate in the bloodstream. Fortunately, a healthy kidney
can easily rid the body of these substances.
In addition to cleaning the blood, the kidneys perform several other essential functions.
One such activity is regulation of the amount of water contained in the blood. This process is
influenced by antidiuretic hormone (ADH), also called vasopressin, which is produced in the
hypothalamus (a part of the brain that regulates many internal functions) and stored in the
nearby pituitary gland. Receptors in the brain monitor the bloods water concentration. When
the amount of salt and other substances in the blood becomes too high, the pituitary gland
releases ADH into the bloodstream. When it enters the kidney, ADH makes the walls of the
renal tubules and collecting ducts more permeable to water, so that more water is reabsorbed
into the bloodstream. (Rod R. Seeley et. al, Essentials of Anatomy and Physiology 5th edition,
McGraw-Hill Int. NY 10020 2005)
The hormone aldosterone, produced by the adrenal glands, interacts with the kidneys
to regulate the bloods sodium and potassium content. High amounts of aldosterone cause the
nephrons to reabsorb more sodium ions, more water, and fewer potassium ions; low levels of
aldosterone have the reverse effect. The kidneys responses to aldosterone help keep the
bloods salt levels within the narrow range that is best for crucial physiological activities. (Rod R.
Seeley et. al, Essentials of Anatomy and Physiology 5th edition, McGraw-Hill Int. NY 10020
2005)
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Aldosterone also helps regulate blood pressure. When blood pressure starts to fall, the
kidney releases an enzyme (a specialized protein) called renin, which converts a blood protein
into the hormone angiotensin. This hormone causes blood vessels to constrict, resulting in a
rise in blood pressure. Angiotensin then induces the adrenal glands to release aldosterone,
which promotes sodium and water to be reabsorbed, further increasing blood volume and
blood pressure.
The kidney also adjusts the body's acid-base balance to prevent such blood disorders as
acidosis and alkalosis, both of which impair the functioning of the central nervous system. If the
blood is too acidic, meaning that there is an excess of hydrogen ions, the kidney moves these
ions to the urine through the process of tubular secretion. An additional function of the kidney
is the processing of vitamin D; the kidney converts this vitamin to an active form that stimulates
bone development. (Rod R. Seeley et. al, Essentials of Anatomy and Physiology 5th edition,
McGraw-Hill Int. NY 10020 2005)
Several hormones are produced in the kidney. One of these, erythropoietin, influences
the production of red blood cells in the bone marrow. When the kidney detects that the
number of red blood cells in the body is declining, it secretes erythropoietin. This hormone
travels in the bloodstream to the bone marrow, stimulating the production and release of more
red cells. (Rod R. Seeley et. al, Essentials of Anatomy and Physiology 5th edition, McGraw-Hill
Int. NY 10020 2005)
The Respiratory System
The respiratory system generally includes tubes, such as the
bronchi, used to carry air to the lungs, where gas exchange
takes place. A diaphragm pulls air in and pushes it out.
Respiratory systems of various types are found in a wide variety
of organisms. Even trees have respiratory systems.
In humans, the respiratory system consists of the
airways, the lungs, and the respiratory muscles that mediate the
movement of air into and out of the body. Within the alveolar
system of the lungs, molecules of oxygen and carbon dioxideare passively exchanged, by diffusion, between the gaseous
environment and the blood. Thus, the respiratory system facilitates oxygenation of the blood
with a concomitant removal of carbon dioxide and other gaseous metabolic wastes from the
circulation. The system also helps to maintain the acid-base balance of the body through the
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efficient removal of carbon dioxide from the blood. (Rod R. Seeley et. al, Essentials of Anatomy
and Physiology 5th edition, McGraw-Hill Int. NY 10020 2005)
Mechanics of Breathing
To take a breath in, the external intercostal muscles contract, moving the ribcage up and
out. Thediaphragm moves down at the same time, creating negative pressure within the
thorax. The lungs are held to the thoracic wall by the pleural membranes, and so expand
outwards as well. This creates negative pressure within the lungs, and so air rushes in through
the upper and lower airways.
Expiration is mainly due to the natural elasticity of the lungs, which tend to collapse if
they are not held against the thoracic wall. This is the mechanism behind lung collapse if there
is air in the pleural space (pneumothorax). (Rod R. Seeley et. al, Essentials of Anatomy and
Physiology 5th edition, McGraw-Hill Int. NY 10020 2005)
Physiology of Gas Exchange
Each branch of the bronchial tree eventually sub-divides to form very narrow terminal
bronchioles, which terminate in the alveoli. There are many millions of alveoli in each lung, and
these are the areas responsible for gaseous exchange, presenting a massive surface area for
exchange to occur over.
Each alveolus is very closely associated with a network of capillaries containing
deoxygenated blood from the pulmonary artery. The capillary and alveolar walls are very thin,
allowing
rapid exchange of gases by passive diffusion along concentration gradients.
CO2 movesinto the alveolus as the concentration is much lower in the alveolus than in
the blood, and O2 moves out of the alveolus as the continuous flow of blood through the
capillaries prevents saturation of the blood with O2 and allows maximal transfer across the
membrane. (Rod R. Seeley et. al, Essentials of Anatomy and Physiology 5th edition, McGraw-Hill
Int. NY 10020 2005)