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Chapter 6 Nervous System, SpecialSenses, and Endocrine System 121
Encephalitis—Inammation of the brain; may be
r
caused from poliovirus, rabies virus, West Nile virus,
and HIV
Hydrocephalus–Abnormal accumulation of cerebro-
r
spinal uid within the brain; caused by congenital
deformity, tumors, and hemorrhage
Stroke—Cerebrovascular accident (CVA); caused by
r
a blood clot that blocks blood ow to a specic area
of the brain or a ruptured blood vessel resulting in
hemorrhage; results in various levels of paralysis and
aphasia (loss of speech or communication)
Concussion—Known as mild traumatic brain injury
r
(MTBI); caused by head trauma resulting in symptoms including headache, dizziness, vomiting, and
sometimes loss of consciousness
Cerebral palsy—Caused by brain damage occurring
r
before or during the birth process; results in varying
degrees of muscular and speech disorder and paralysis
Alzheimer disease—Degeneration of the cerebral cor-
r
tex resulting in gradual intellectual impairment and
memory loss
Parkinson disease—Progressive neurologic condition;
r
causes tremors and rigidity of the limbs and joints
Case Questions
A
F
F
her? Throughout the day, she continued to get
worse and started feeling very nauseated. She
went to the college medical clinic where the
physician decided to admit her to a local hospital. He ordered a lumbar puncture and immediately started her on an antibiotic.
Alicia, ordered the spinal tap, and started her on
antibiotics?
Remember Alicia, the college student
in the case study? Were you able to
gure out what might be going on with
Why do you think the physician hospitalized
C
O
G
The nervous system is composed of both motor and sensory nerves. This section will focus on those senses that
provide us with ways to evaluate and respond to our
environment. The body has various types of receptors
that respond to the stimuli surrounding us:
r
r
r
r
THE SENSORY SYSTEM
Chemoreceptors—Allow us to detect chemicals in
solutions; receptor for taste and smell.
Photoreceptors—Respond to light; located in the retina of the eye.
Thermoreceptors—Allow us to detect changes in temperature; most are located in the skin.
Mechanoreceptors—Allow us to respond to movement
such as vibration and pressure; located in the skin; also
receptors of hearing and equilibrium in the ear.
General and Special Senses
The body has general senses that include pressure, temperature, pain, and touch. The receptors for these senses
are found in the skin and internal organs. The sense of
position is determined by receptors found in the muscles, tendons, and joints. The special senses associated
with specic areas of the body include:
Vision—Receptors are in the eye.
r
Hearing—Receptors are in the inner ear.
r
Equilibrium (balance)—Receptors are in the inner ear.
r
Taste—Receptors are in the tongue.
r
Smell—Receptors are in the upper nasal cavities.
r
The Sense of Vision
The eyes provide a window to the world. We perceive
more than half of our information from what we see.
Since the eyes are so valuable, they need structures to protect them from injury and damage. The bones surrounding the eye that form the orbits of the eyes are the rst
line of protection. Other protective structures include:
C
O
G
Since the nervous system disorders typically involve pain
and discomfort, one of the more common treatments is
the use of pain medication. A method of administration
of pain medication is to deliver it into the epidural space
of the spinal region. The injection in this area allows
the medication to diffuse into the spinal cord causing
an analgesic effect (pain relief). This method is also indicated for use during childbirth and is referred to as an
“epidural.” Physicians also use a variety of psychoactive drugs that affect the neurotransmitter activity in the
brain. They are used to treat depression, anxiety, and
obsessive–compulsive disorder.
TREATING THE NERVOUS
SYSTEM
Eyelids—Upper and lower lids protect the front of the
r
eye, lubricating the eye each time you blink.
Eyelashes and eyebrows—These structures help keep
r
foreign matter out of the eye catching dust and debris
before it can get to the eye.
Lacrimal glands—Produce tears that bathe the eye
r
and help wash away foreign materials; the lacrimal
apparatus is the entire structure that includes the
glands and nasolacrimal ducts that cause the tears to
run into the nose when there is overproduction.
Conjunctiva—Lines the inner eyelid and the white of
r
the eye (sclera); provides a layer of lubricating mucus
to protect the eye.
There are numerous muscles attached to the eyeball
that allow the eyeball to move up, down, side to side,
122 Section II Anatomy and Physiology
and in a circular eld. The eye also requires a variety of
nerves to supply specic functions including the optic
nerve that carries visual impulses from the photoreceptors in the eye to the brain.
The Eyeball
The eyeball has many structures and layers including the:
Sclera—Outermost layer of the eyeball that is referred
r
to as the white of the eye
Cornea—The transparent, colorless, anterior portion
r
of the sclera; the window of the eye
Choroid—The middle, vascular layer; contains mela-
r
nin, which absorbs light rays to reduce sun glare
Ciliary muscle and suspensory ligaments—Control
r
the shape of the lens.
Iris—Colored ring-like portion of the eye that con-
r
trols the size of the pupil.
Pupil—Opening in the center of the iris that becomes
r
larger or smaller allowing more or less light to enter
the eye, called dilation.
Sclera
Retina—Nerve layer of the inner part of the eyeball;
r
contains the rods and cones.
Rods and cones—Found in the retinal layer; rods
r
allow differentiation of shades of gray and dim light,
cones allow us to see color, and when there is a deciency in the cones, a person could be color-blind.
Aqueous humor—A watery uid that lls the eyeball
r
anterior to the lens and helps maintain the cornea’s
convex curve.
Vitreous body—A soft jelly-like substance that lls
r
the space behind the lens; helps maintain the shape
of the eyeball.
Lens—A clear, circular structure made of an elastic
r
material capable of changing shape to accommodate
vision.
Optic disk—Where the optic nerve connects with the
r
retina, called the blind spot.
Fovea centralis—Area on the retina close to the optic
r
disk where there is the most acute, sharp vision.
See Figure 6-8, a detailed image of the eye and the
internal structures.
Suspensory
ligaments
Fovea
centralis
Retinal artery
and vein
Optic nerve
Choroid
Retina
Optic disk
(blind spot)
Retinal vein
Vitreous body
Aqueous
humor
Cor
nea
Pupil
Iris
Lens
Ciliary
muscle
Conjunctival
sac
Retinal artery
Optic nerve
Figure 6-8 Structures of the
eyeball. (Reprinted from Cohen
BJ. Memmler’s The Human Body
in Health and Disease. 13th ed.
Philadelphia, PA: Wolters Kluwer;
2014.)
Chapter 6 Nervous System, SpecialSenses, and Endocrine System 123
The Process of Vision
There are many structures that the light must pass through
and changes in the eye structures that take place in order
for us to see. The light rays are bent and changed through
a process called refraction. As light rays go through the
cornea, lens, and uids of the eye, the rays bend and are
able to focus on the retina. Another process required for
vision is accommodation, which is the ability of the lens to
change shape and become thicker or thinner. This provides
the vision for far and near distances. The ciliary muscle
contracts and relaxes to allow the change in the lens.
Problems with the Eye and Vision
There are numerous problems that can occur with the
eye and its structures that affect the function of the eye
and ability to see images properly. Some of the physical
problems that affect the eye include:
Conjunctivitis—Inammation of the conjunctiva;
r
caused from irritant or pathogen; an acute, contagious type caused by bacteria is referred to as pinkeye.
Corneal abrasion—Injury to the cornea causing
r
scratches.
Enucleation—Eyeball removed through surgical pro-
r
cedure; may be result of severe injury to the eyeball.
Cataract—Cloudiness of the lens causing gradual loss
r
of vision; requires surgical replacement of the lens.
Glaucoma—Excessive pressure of the aqueous humor;
r
leads to destruction of some of the optic nerve bers.
Retinopathy—Disease of the retina resulting in dam-
r
age to the blood vessels of the choroid layer; may be
directly related to diabetes (diabetic retinopathy)
Retinal detachment—The retina separates from the
r
choroid layer; requires surgical repair and if untreated
will result in blindness.
Macular degeneration—Deterioration of the fovea
r
centralis region of the retina causing gradual vision
loss; typically age related.
Figure 6-9 is a photo of a healthy retina. The blood
vessels are normal.
Vision Disorders
There are also many conditions that cause problems
with the ability to see properly. These conditions
include:
Night blindness—Difculty seeing in dim light; due
r
to vitamin A deciency that provides nutrient to the
pigment found in the rods
Hyperopia—Farsightedness, able to see things at a
r
distance (far away) but not things up close (near)
Myopia—Nearsightedness, able to see things close by
r
(near) but not things far away at a distance
Presbyopia—Age-related loss of elasticity in the lens
r
causing inability to properly focus on objects
Astigmatism—Caused by irregularity in the curvature
r
of the cornea or lens; causes distorted vision; may be
found in people with myopia or hyperopia
Strabismus—Condition involving the eye muscles not
r
allowing the eyes to move properly but may cause
appearance of cross eyed, the eyes converge toward
the nose
See Figure 6-10 to see how the images are not properly reected on the retina with conditions like myopia
and hyperopia. Corrective lenses are required to allow
the rays to properly converge on the retina.
Treatment of Eye Conditions
An ophthalmologist is a medical doctor who specializes in the treatment of eye conditions. This doctor
is trained to perform eye surgery, prescribe medications for the eye, and perform basic eye examinations.
Many people see an optometrist who is not a medical
doctor and can examine the eye for visual problems
that require corrective lenses. The optician is a trained
Fovea
centralis
(in macula
lutea)
Blood vessels
Optic disk
Retina
Figure 6-9
(Reprinted from Cohen
BJ. Memmler’s The Human
Body in Health and Disease.
13thed. Philadelphia, PA:
Wolters Kluwer; 2014.)
A healthy retina.
124 Section II Anatomy and Physiology
A
B
Hyperopia
(farsightedness)
Myopia
(nearsightedness)
Corrected
Corrected
Convex
lens
Concave
Lens
Figure 6-10 Refraction errors caused
by (A) myopia (nearsightedness) with
concave corrective lens. Hyperopia
(B) (farsightedness) with convex
corrective lens. (Reprinted from
Cohen BJ. Memmler’s The Human
Body in Health and Disease. 13thed.
Philadelphia, PA: Wolters Kluwer;
2014.)
person who can make lenses and t eyeglasses. They
also instruct in the use of contact lenses. The main
instrument used to examine the eyes is an ophthalmoscope. It is used to visualize the back of the eye,
the retina. A tonometer is a device used to measure
the intraocular pressure to rule out glaucoma. Laser
surgical procedures are used to correct vision problems including nearsightedness, farsightedness, and
astigmatism.
C
O
G
THE EAR
The ear is the sense organ responsible for hearing and
equilibrium (balance). There are three specic areas of
the ear, the outer, middle, and inner ear.
Outer Ear
The external portion of the ear that you can see is called
the pinna or auricle. The shape of the pinna allows
sound waves to be captured and directed into the ear.
The external auditory canal is the tube entrance into the
ear. It is visible from the outside and extends into the
eardrum. Ceruminous glands are located in the canal
and secrete a substance called cerumen (earwax). At the
end of the external auditory canal is the tympanic membrane, or eardrum. This structure separates the outer
ear from the middle ear. The eardrum vibrates when the
sound waves enter the ear.
The eustachian tube (auditory tube) connects the middle
ear with the pharynx (throat). This tube equalizes pressure within the ear.
Inner Ear
The inner ear is the most complicated part of the ear.
It contains the structures that help maintain our equilibrium and balance and serve as a pathway sending
impulses to the brain where they are interpreted into
sounds (hearing). The inner ear has been described as
a labyrinth because of its complex structure. There are
three divisions of the inner ear, the vestibule and semicircular canals that contain receptors for equilibrium and
the cochlea where the receptors for hearing are located.
Within the labyrinth are two uids, perilymph in the
outer portion and endolymph in the inner portion. These
uids are necessary to transmit the sensory impulses.
Figure 6-11 is a diagram of the ear showing the divi-
sions of the outer, middle, and inner ear.
The Process of Hearing
Hearing starts as the sound waves enter the external
auditory canal. The waves vibrate the eardrum which
activates the ossicles to move. The movement now
stimulates the structures within the inner ear triggering the structures to convert the sound waves into nerve
impulses, which now travel to the brain through the vestibulocochlear nerve.
Middle Ear
The middle ear is the space between the outer and inner
ear where the ossicles are located. These are three little
bones that vibrate and amplify the sound waves. The
bones are the
anvil shaped, and stapes that looks like a stirrup.
malleus, shaped like a hammer, incus
Equilibrium and Balance
The receptors for equilibrium and balance are located in
the vestibule and the semicircular canals. These receptors are ciliated hair cells that respond to the changes in
the position of the head generating nerve impulses that
are sent to the brain for interpretation.
Chapter 6 Nervous System, SpecialSenses, and Endocrine System 125
Figure 6-11 Three divisions of the ear: outer, middle, and inner. (Reprinted from Cohen BJ. Memmler’s
TheHuman Body in Health and Disease. 13th ed. Philadelphia, PA: Wolters Kluwer; 2014.)
Vertigo—Sensation of spinning or that the environment
Disorders of the Ear
Disorders of the ear include infection, hearing loss, and
disturbances in equilibrium. Some of the more common
disorders include:
Ceruminosis—Impacted ear wax; a buildup of cerumen
r
that becomes hardened in the external auditory canal.
To treat this condition, the wax is softened, using warm
water or medication, and is rinsed out of the canal.
Otitis media—Infection and inammation of the middle
r
ear; caused by bacteria or virus and may be a complication of a cold or u. Figure 6-12 is a photo of an eardrum that is inamed and bulging due to otitis media.
Otitis externa—Inammation of the external auditory
r
canal usually due to bacteria or fungus; also common
among swimmers when the canal stays damp with
water, known as swimmer’s ear.
Conductive hearing loss—Varying levels of deafness
r
due to inability of the sound waves to travel through
the ear. A simple problem might be blockage such as
a buildup of earwax not allowing the sound waves to
travel past the blocked area. Otosclerosis is a hereditary problem caused when the stapes does not vibrate
allowing the sound waves to be conducted.
Sensorineural hearing loss—Loss of hearing due to the
r
inability of the nerve to properly transmit the impulses
to the brain; may be due to excessive use of headphones playing loud music and noises; problems with
the cochlea may also cause this type of hearing loss
Presbycusis—An age-related hearing loss, begins with
r
loss of high-pitched sounds
r
is spinning; caused by stimulation of the receptors that
affect the equilibrium and balance; alcohol consumption, certain drugs, and low blood pressure may contribute to the feeling of dizziness or light-headedness.
Treating Ear Conditions
As mentioned earlier, ear wax removal is a way to relive a
blockage that may have caused some conduction hearing
Otitis media
Figure 6-12 A bulging eardrum caused by otitis media.
(Reprinted from Kronenberger J, Ledbetter J. Lippincott
Williams & Wilkins’ Comprehensive Medical Assisting.
5th ed. Philadelphia, PA: Wolters Kluwer; 2016.) (From
Moore KL, Dalley AF II. Clinical Oriented Anatomy. 4th ed.
Baltimore, MD: Lippincott Williams & Wilkins; 1999.)
126 Section II Anatomy and Physiology
loss. There are several surgical procedures used to relieve
ear conditions. A myringotomy, an incision into the tympanic membrane, is a procedure used to relieve pressure
in the middle ear due to buildup of pus or uid. A longer
effect for this condition is to place a tympanostomy tube
into the eardrum. This allows the pressure to equalize in
the middle ear preventing further damage. When there is a
problem with the cochlea, a cochlear implant may correct
the problem allowing the person to hear certain sounds.
C
O
G
SENSE OF TASTE
ANDSMELL
Gustation is the sense of taste. The tongue has taste buds
located in specic areas that allow us to differentiate
ve basic tastes. These tastes include sweet (sugar), salty
(sodium), sour, bitter, and umami (savory). Olfaction is
the sense of smell. The receptor cells are in the nasal
cavity. The olfactory nerve delivers impulses to the brain
where we can interpret over 10,000 different smells. The
sense of taste is closely related to the ability to smell.
This is why when you have a cold or stuffy nose, you
cannot taste food.
temperature, position, and pain. The sense of touch
relies on receptors primarily located in the skin and
hair follicles. The sense of pressure responds to sensory receptors located in the subcutaneous tissues.
The ability to sense temperature is due to the free
nerve endings that are found in the skin. They respond
to varying degrees of heat and cold. Our internal
temperature is adjusted by the brain’s hypothalamus according to the temperature of the blood. The
sense of position, knowing whether we are upright or
horizontal, is determined by the receptors known as
proprioceptors.
Pain is a sense associated with the nerve endings
found in the skin, muscles, joints, and internal organs.
The pain may vary from mild to severe. Sometimes
stimulants from allergic substances cause these nerve
endings to be irritated causing mild to intense itching,
which also might become painful. Pain relief might
include analgesic medications, such as narcotic and
nonnarcotic preparations. Endorphins are natural
chemicals released from the brain and are associated
with pain control. These chemicals are released during exercise, body massage, and electrical stimulation
therapy.
C
O
G
THE OTHER SENSES
The other senses are not specic to a single organ or
location but have receptors spread throughout the
body. These include receptors for touch, pressure,
Pineal
Pituitary
(hypophysis)
Thyroid
Parathyroids
(posterior)
Adrenals
Pancreatic
islets
Ovaries
Testes
C
O
G
THE ENDOCRINE SYSTEM
The endocrine system consists of a group of glands that
secrete hormones. Figure 6-13 shows the location of the
endocrine glands in the body.
Figure 6-13 Glands of the endocrine
system. (Reprinted from Cohen BJ. Memmler’s
The Human Body in Health and Disease.
13thed.Philadelphia, PA: Wolters Kluwer; 2014.)
Chapter 6 Nervous System, SpecialSenses, and Endocrine System 127
Each gland specializes in a specic function and
secretes a hormone, a regulatory substance. The endocrine system works with the nervous system coordinating functions throughout the body. The endocrine glands
secrete their hormones directly into the bloodstream
where the hormones travel to the target tissue, the tissue
and cells that respond to that hormone. The action of
the endocrine glands and the release of their hormones
are stimulated by the process of negative feedback. An
example is the release of insulin when the blood sugar
increases. A hormone may be released following a rhythmic pattern such as how the hormones are released in
the female based on the menstrual cycle. Each gland will
be introduced listing the hormone(s) produced and their
function.
The Pituitary
This gland, also called the hypophysis, is situated
beneath the brain and connects with the hypothalamus. The pituitary is divided into anterior and posterior lobes. Each lobe secretes specic hormones that
target organs throughout the body. See Figure6-14
diagram of the anterior and posterior pituitary with
all the hormones produced within the pituitary
gland.
Anterior Pituitary
Hormones produced and released by the hypothalamus
stimulate the anterior pituitary to release the hormones
it produces. The anterior pituitary is referred to as the
Internal-external stimuli
Neurotransmitters
Hypothalamus
Releasing hormones
secreted
Hormones feed back
to anterior pituitary
and hypothalamus
Thyroid
Thyroid hormones
Adrenocorticosteroids
Estrogen
Anterior pituitary
Adrenal
Progesterone
TSH
ACTH
Ovary
Portal system
FSH
LH
Testes
FSH
LH
GH
ADH
Oxytocin
Infundibulum
Bone and
soft tissues
Posterior pituitary
Oxytocin
ADH
PRL
Breast
Uterus
Kidney
Breast
Testosterone
Figure 6-14 Pituitary gland hormones secreted and the organs they affect. (Reprinted from Cohen BJ. Memmler’s
The Human Body in Health and Disease. 13th ed. Philadelphia, PA: Wolters Kluwer; 2014.)
128 Section II Anatomy and Physiology
master gland because it releases hormones that affect
many other glands in the body including the thyroid,
gonads, and adrenal glands. The hormones produced by
the anterior pituitary include:
Growth hormone (GH)—Somatotropin, promotes
r
growth in the body, specically size and height during youth
Thyroid-stimulating hormone (TSH)—Stimulates
r
the thyroid gland in the neck to produce thyroid
hormones
Adrenocorticotropic hormone (ACTH)—Stimulates
r
hormone production in the adrenal glands, specically the outer layer called the cortex
Prolactin hormone (PRL)—Stimulates milk produc-
r
tion in the breasts
Follicle-stimulating hormone (FSH)—Stimulates the
r
ovary causing development of the follicles, the place
where the eggs mature, and also stimulates the testes
for the development of sperm cells
Luteinizing hormone (LH)—Causes ovulation in
r
women and promotes production of progesterone in
females and testosterone in males
Posterior Pituitary
The posterior pituitary only secretes two hormones;
however, they are very critical to the function of the
organs they stimulate. The hormones include:
Antidiuretic hormone (ADH)—Stimulates the kid-
r
neys to reabsorb water that is lost through the ltration process
Oxytocin—Stimulates contraction of the uterus dur-
r
ing childbirth and the contraction of the mammary
glands to cause milk ejection
Hypothalamus
Low level of thyroid
hormones stimulates
release of TSH
Anterior
pituitary
Stimulates
Inhibits
Thyroid
gland
Figure 6-15 Thyroid-stimulating hormone secreted
by the pituitary gland stimulates the functioning of the
thyroid gland. (Reprinted from Cohen BJ. Memmler’s
The Human Body in Health and Disease. 13th ed.
Philadelphia, PA: Wolters Kluwer; 2014.)
H
S
T
High level of thyroid
hormones inhibits
release of TSH
The Adrenal Glands
These glands are located on top of the kidneys and are
also called the suprarenal glands. The glands have an
outer layer called the cortex and the inner portion is
the medulla. Each area secretes different hormones.
Figure6-16 shows the adrenal gland location and the
two divisions, cortex and medulla.
The Thyroid Gland
This is the largest of the endocrine glands and is located
in the neck. It is shaped like a buttery with a wing on
either side of the larynx. The thyroid is stimulated to
function by the TSH produced in the anterior pituitary
gland. The thyroid produces two hormones that regulate
cell metabolism. The hormones are labeled T
(triiodo-
3
thyronine) and T4 (thyroxine). Figure 6-15 demonstrates
the connection between the pituitary gland and the thyroid gland.
The Parathyroid Glands
These are four tiny glands that are embedded in the
thyroid gland, two on each side. They secrete parathyroid hormone (PTH), which promotes calcium
release from bone tissue increasing the blood calcium
level and regulates the amount of calcium the kidneys
excrete.
Adrenal Medulla
The primary hormone produced in the adrenal medulla
is epinephrine (adrenaline). This hormone stimulates
the sympathetic nervous system and is a major chemical released for the ght-or-ight response. Some of the
effects it causes include a rise in blood pressure, heart
rate, and overall metabolic rate of body cells.
Adrenal Cortex
There are three main categories of hormones secreted by
the adrenal cortex, which are as follows:
Glucocorticoids—Maintain blood glucose levels dur-
r
ing times of stress; suppress the inammatory response
with a specic hormone called cortisol (hydrocortisone).
Mineralocorticoids—Regulate electrolyte balance
r
controlling the sodium reabsorption and potassium
secretion in the kidney; a major hormone in this
group is aldosterone.
Chapter 6 Nervous System, SpecialSenses, and Endocrine System 129
Adrenal
glands
Kidne
y
A
Adrenal cortex
Adrenal medulla
B
Figure 6-16 A. Adrenal glands located on top of the
kidneys. B. Cortex and medulla of the adrenal gland.
(Reprinted from Cohen BJ. Memmler’s The Human Body
in Health and Disease, 13th ed. Philadelphia, PA: Wolters
Kluwer; 2014.)
Androgens—Male sex hormones only secreted in small
r
amount from the adrenal gland but is also secreted in
pre- and postmenopausal women; promote bone and
muscle growth and stimulate sexual desire.
The Pancreas
The pancreas is both an exocrine and endocrine gland
located in the left upper quadrant of the abdomen. The
exocrine portion secretes pancreatic juices, through a duct,
directly into the small intestine to assist in the breakdown
of nutrients. The endocrine portion of the pancreas is found
in the islets of Langerhans. These are specialized cells that
secrete their hormone directly into the bloodstream. Insulin
is the most important hormone secreted with the major
responsibility of maintaining glucose balance. Insulin is
necessary to transport glucose into the cells where it can be
utilized for energy. Figure 6-17 demonstrates what happens
to glucose in the body when a person does not have diabetes and when someone does have it. A normal functioning
pancreas will produce insulin, which will properly transport glucose into the cells to be used as energy. In a diabetic
person, insulin production is decreased and less glucose
moved into the cells to be used. This creates the accumulation of glucose in the bloodstream that can adversely affect
other organs and structures in the body. One of the areas
affected is the retina of the eye where damage is caused to
the blood vessels that supply the retina.
The Ovaries
The ovaries are located in the pelvic cavity, one at the end
of each fallopian tube. The primary hormone, estrogen,
is responsible for the development of secondary, female
Type 2 Diabetes
Normal Diabetic
ancreas produces
Pancreas produces
insulin
Glucose
Figure 6-17 The normal functioning pancreas and the nonfunctioning pancreas in the diabetic person. (Image from
Shutterstock.com.)
Insulin moves
glucose to cells
More glucose
in the blood
P
less insulin
Insulin moves less
glucose to cells
130 Section II Anatomy and Physiology
sex characteristics. It also stimulates mammary gland
development and the start of the menses. Progesterone
is the other hormone produced by the ovaries. It assists
in the normal development of pregnancy.
The Testes
The testes are located in the scrotal sac of the male. The
hormone testosterone is produced as the male enters
puberty. It causes the voice to deepen, facial and body
hair to grow, and muscle to develop. Male hormones are
classied as androgens.
The Pineal Gland
This tiny gland is located behind the midbrain. It produces the hormone melatonin. More of this hormone is
produced during darker periods and less during daylight
hours. It regulates our sleep cycle.
C
O
G
With so many glands producing these regulating hormones,
you can expect to nd abnormal conditions associated
with the glands in this system. The disorders are typically
caused by overproduction of the hormone, hypersecretion,
or from underproduction of the hormone, hyposecretion.
DISORDERS OF THE
ENDOCRINE SYSTEM
Figure 6-18 Acromegaly showing enlarged extremities
and facial features. (From Willis MC. Medical Terminology:
A Programmed Learning Approach to the Language
of Health Care. Baltimore, MD: Lipppincott Williams &
Wilkins; 2002.)
swelling of the eyeballs causing an appearance of bulging
eyes. Blood tests are used to measure the levels of thyroid
hormone in the bloodstream. Treatment of hypothyroidism includes replacement hormone medication.
Parathyroid Gland Disorders
Pituitary Gland Disorders
A tumor may develop in any area of the body, but when
there is a tumor affecting the pituitary gland, it can produce numerous problems. One of these is a pituitary
tumor that stimulates overproduction of the growth hormone. This condition, developing in childhood, is called
gigantism causing the child to grow abnormally tall.
When this occurs in adults, the bones of the face, hands,
and feet enlarge. This disorder is known as acromegaly.
Figure6-18 is a photo of a person with acromegaly. Notice
the very enlarged hands and exaggerated facial features.
Thyroid Gland Disorders
Underproduction of the thyroid hormones results in
hypothyroidism, and overproduction of these hormones
results in hyperthyroidism. Since the thyroid hormones
regulate the body’s metabolism, some signs and symptoms
of hypothyroidism include a sluggish feeling, dry skin
and hair, and weight gain. Just the opposite occurs with
hyperthyroidism with symptoms that include weight loss,
rapid pulse, sweating, and nervousness. Acommon type
of hyperthyroidism is Graves’ disease. This disease causes
development of a goiter, enlargement of the thyroid gland.
Another symptom is the development of exophthalmos,
Since the parathyroid hormone affects the calcium levels
in the body, too little may cause muscle contractions or
spasms called tetany. Too much production of the hormone causes the bones to release too much calcium into
the bloodstream. With this condition, it is not uncommon for the person to develop kidney stones since the
kidneys are ltering an excessive amount of calcium.
Adrenal Cortex Disorders
Underfunctioning of the adrenal cortex causes a condition known as Addison disease. Symptoms include
weakness, loss of muscle tissue, excessive skin pigmentation, and salt and water imbalance. Overfunctioning
of the hormone cortisol results in Cushing syndrome
with very pronounced symptoms including obesity and
a round appearance to the face called “moon face.”
Pancreas Disorders
When the islets of Langerhans do not produce enough
insulin or the body is not utilizing the insulin properly, Type 2
associated with those who are overweight. It is one of the
most common endocrine disorders. Hyperglycemia is the
term that means elevated glucose in the blood, a result of
diabetes mellitus (T2DM) develops. It is