The document provides an overview of the endocrine system, including: - The endocrine system is composed of ductless glands that secrete hormones directly into the bloodstream to regulate bodily functions like metabolism and growth. - The major glands are the pituitary, thyroid, parathyroid, adrenal, pancreas, ovaries/testes, thymus, and pineal glands. - Common endocrine disorders affect hormone balance and can cause symptoms ranging from fatigue and weight changes to neurological or organ issues depending on the gland impacted.

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OVERVIEW OF ENDOCRINE
SYSTEM

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Anatomy and physiology of the endocrine system
Endocrine glands and hormones
Glands can be divided into two broad categories: exocrine and endocrine. Exocrine
glands secrete through a series of ducts (sebaceous and sudoriferous glands of the skin). Their
secretions are protective and functional. Endocrine glands are ductless; they release their
secretions directly into the bloodstream. Their secretions have a regulatory function.
The endocrine system is composed of a series of ductless glands whose work is closely related
to the nervous system. Both systems control homeostasis through communication within the
systems. The endocrine system communicates more slowly through the use of hormones, which
are chemical messengers that travel through the bloodstream to their target organ. When the
hormone reaches its target, a metabolic change occurs.
The total weight of all the endocrine glands is less than half a pound, yet they have a powerful
influence. The slightest change in hormonal levels can upset the metabolic balance of the entire
body. Hormones can increase or decrease a normal body process by affecting a target organ. Too
much or too little of a given hormone can affect other hormones, and for this reason they are
somewhat interrelated. The endocrine glands (Figure 11-1) have a generalized effect on the
patient’s metabolism, growth, development, reproduction, and many other bodily activities.
FIGURE 11-1 Location of the endocrine glands in the female and male bodies. Thymus gland is
shown at maximal size at puberty.
The amount of hormonal release is controlled by a negative feedback (a decrease in function
in response to stimuli) system. Information is constantly being exchanged between the target

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organ and the pituitary gland via the bloodstream regarding the effect of the hormone on the
target organ.
Pituitary gland
The pea-sized pituitary gland (hypophysis) is one of the most powerful glands in the body. It
has been called the “master gland” because, through the negative feedback system, it controls the
other endocrine glands. It works closely with the hypothalamus of the brain and is located in the
cranial cavity in a small saddlelike depression in the sphenoid bone. It is divided into two
segments, the anterior pituitary (adenohypophysis) and the posterior
pituitary (neurohypophysis). Each segment has specialized hormones. The hypothalamus
actually produces the hormones of the posterior pituitary and releases them for storage in the
posterior pituitary gland; they are released from here as a result of nerve impulses received from
the hypothalamus.
Anterior pituitary gland
Six major hormones are secreted by the anterior pituitary gland; the hormones make up about
75% of the gland’s total weight. Five hormones are called tropic hormones, because they are
responsible for the stimulation of other endocrine glands. Prolactin, the remaining hormone,
causes the mammary glands to produce milk. These hormones and their functions are shown
in Figures 11-2 and 11-3.

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FIGURE 11-2 Pituitary hormones. Principal anterior and posterior pituitary hormones and their
target organs.
FIGURE 11-3 Names and functions of anterior pituitary hormones.
Posterior pituitary gland
Two hormones are released by the posterior pituitary when the hypothalamus stimulates their
release. They are oxytocin and antidiuretic hormone (ADH) (see Figure 11-2). Oxytocin
promotes the release of milk and stimulates uterine contractions during labor. ADH, also called
vasopressin, causes the kidneys to conserve water by decreasing the amount of urine produced.

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ADH/vasopressin also causes constriction of the arterioles in the body and a pressor effect,
which results in increased blood pressure.
Thyroid gland
The thyroid gland is butterfly shaped, with one lobe lying on either side of the trachea just
below the larynx (Figure 11-4). The lobes are connected by the isthmus. The gland is very
vascular and receives approximately 80 to 120 mL of blood per minute.
FIGURE 11-4 Thyroid and parathyroid glands. Note their relations to each other and to the
larynx and trachea.
The thyroid gland secretes the hormones thyroxine (T4) and triiodothyronine (T3). Adequate
oral intake of iodine is necessary for the formation of thyroid hormones. These hormones
regulate three main functions: (1) growth and development, (2) metabolism, and (3) activity of
the nervous system. Their function is controlled by the release of thyroid-stimulating hormone
(TSH) from the pituitary gland.
Calcitonin is a hormone also released by the thyroid gland. It decreases blood calcium levels
by causing calcium to be stored in the bones.
Parathyroid glands
The four parathyroid glands are located on the posterior surface of the thyroid gland and
secrete parathyroid hormone (PTH, parathormone). As an antagonist to calcitonin from the
thyroid, PTH tends to increase the concentration of calcium in the blood. It also regulates the
amount of phosphorus in the blood.

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The delicate balance of calcium in the blood is extremely important for normal body function.
When calcium blood levels are low, the nerve cells become excited and stimulate the muscles
with too many impulses, resulting in spasms (tetany). When blood calcium levels are
abnormally high, heart function becomes impaired; this can result in death. Under the influence
of PTH, two changes occur in the kidneys: It increases the reabsorption of calcium and
magnesium from the kidney tubules and accelerates the elimination of phosphorus in the urine.
Adrenal glands
The adrenal glands (suprarenal glands) are small, yellow masses that lie atop the kidneys. Both
glands contain an outer section, the adrenal cortex, and a smaller inner section, the adrenal
medulla (Figure 11-5).
FIGURE 11-5 Structure of the adrenal gland. The zona glomerulosa of the cortex secretes
abundant amounts of glucocorticoids, chiefly cortisol. The zona reticularis secretes minute
amounts of sex hormones and glucocorticoids. A portion of the medulla is visible at the bottom
of the illustration.
Adrenal cortex
The adrenal cortex is divided into three separate layers. Each layer secretes a particular hormone,
called a steroid:

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• Mineralocorticoids: These are primarily involved in water and electrolyte balance and
indirectly manage blood pressure. Aldosterone, the principal mineralocorticoid, regulates
sodium and potassium levels by affecting the renal tubules. It decreases the level of
potassium and increases the level of sodium in the bloodstream. The retention of sodium
causes retention of water, which leads to an increase in blood volume and blood pressure.
• Glucocorticoids: The most important of these is cortisol, which is involved in glucose
metabolism and provides extra reserve energy in times of stress. Glucocorticoids also exhibit
antiinflammatory properties.
• Sex hormones: Androgens are male hormones and estrogens are female hormones. In the
adult the adrenal glands release a relatively small amount of these hormones, which have an
insignificant impact on the system.
Adrenal medulla
The cells composing the adrenal medulla arise from the same type of cells as the sympathetic
nervous system. Two hormones are released during times of stress: (1) epinephrine (adrenaline),
and (2) norepinephrine. They cause the heart rate and blood pressure to increase, the blood
vessels to constrict, and the liver to release glucose reserves for immediate energy. This is a
systemic preparation of the body for a “fight-or-flight” response needed in times of crisis.
Pancreas
The pancreas is an elongated gland that lies posterior to the stomach. It is an active organ,
composed of both exocrine and endocrine tissue. The endocrine tissue of the pancreas contains
more than a million tiny clusters of cells known collectively as the islets of Langerhans. These
cells secrete two major hormones. The first, insulin, is secreted by the beta cells in response to
increased levels of glucose in the blood. Insulin’s secretion pattern is a physiologic example of
negative feedback between insulin and glucose. Elevated blood glucose levels stimulate the
pancreas to secrete insulin. The stimulus for insulin secretion decreases as blood glucose levels
decrease. The homeostatic mechanism is considered negative feedback because it reverses the
change in blood glucose level. The second pancreatic hormone is glucagon, which is secreted by
the alpha cells in response to decreased levels of glucose in the blood. Insulin and glucagon play
a major role in carbohydrate, fat, and protein metabolism.
Female sex glands
Deep in the lower abdominal region, lying to the left and the right of the uterus, are two almond-
shaped ovaries, the major sex glands of the woman. At puberty the ovaries begin producing two
hormones: estrogen (responsible for the development of secondary sex characteristics, such as
axillary hair and pubic hair, and for maturation of the reproductive organs)
and progesterone (continues the preparation of the reproductive organs that was initiated by the
estrogen).

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The placenta is a temporary endocrine gland that forms and functions during pregnancy.
During this time the ovaries become inactive and the placenta releases the estrogen and
progesterone needed to maintain the pregnancy. (For a more in-depth discussion,
Male sex glands
Suspended outside the body in the scrotum, a saclike structure, are the two oval sex glands
called the testes. They release the hormone testosterone, which is responsible for the
development of the male secondary sex characteristics, including axillary, pubic, and facial hair;
maturation of the reproductive organs; deepening of the voice; and development of muscle and
bone mass. Testosterone is necessary for sperm formation.
Thymus gland
The thymus gland lies in the upper thorax, posterior to the sternum. It produces the
hormone thymosin, which plays an active role in the immune system. T lymphocytes (a type of
white blood cell) are stimulated to carry out immune reactions to certain types of antigens. The
thymus gland programs this information into the T lymphocytes in utero and during the first few
months of life.
Pineal gland
The pineal gland is a small, cone-shaped gland located in the roof of the third ventricle of the
brain. It secretes the hormone melatonin, which seems to inhibit reproductive activities by
inhibiting the gonadotropic hormones. This is particularly important in preventing the sexual
maturation of the child’s body until adulthood. It is thought to induce sleep, may affect mood,
and has an impact on menstrual cycles.
ENDOCRINE DISORDERS
Introduction
Endocrine disorders are diseases related to the endocrine glands of the body. The endocrine
system produces hormones, which are chemical signals sent out, or secreted, through the
bloodstream. Hormones help the body regulate processes, such as appetite, breathing, growth,
fluid balance, feminization and virilisation, and weight control.
The endocrine system consists of several glands, including the pituitary gland and hypothalamus
in the brain, adrenal glands in the kidneys, and thyroid in the neck, as well as the pancreas,
ovaries and testes. The stomach, liver and intestines also secrete hormones related to digestion.
Most common endocrine disorders are related to improper functioning of the pancreas and the
pituitary, thyroid and adrenal glands.
Common endocrine disorders include
Diabetes mellitus,

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Acromegaly (overproduction of growth hormone),
Addison’s disease (decreased production of hormones by the adrenal glands),
Cushing’s syndrome (high cortisol levels for extended periods of time),
Graves’ disease (type of hyperthyroidism resulting in excessive thyroid hormone production),
Hashimoto’s thyroiditis (autoimmune disease resulting in hypothyroidism and low production of
thyroid hormone),
hyperthyroidism (overactive thyroid),
hypothyroidism (underactive thyroid), and prolactinoma (overproduction of prolactin by the
pituitary gland). These disorders often have widespread symptoms, affect multiple parts of the
body, and can range in severity from mild to very severe. Treatments depend on the specific
disorder but often focus on adjusting hormone balance using synthetic hormones.
Modern treatment is generally quite effective for endocrine disorders, and severe consequences
of endocrine dysfunction are rare. However, untreated endocrine disorders can have widespread
complications throughout the body.
While endocrine disorders do not usually require hospitalization, in some cases they may lead to
severe symptoms.
Seek prompt medical care if you are being treated for endocrine disorders and have persistent
bothersome symptoms, as they may indicate a more serious condition.
Symptoms
What are the symptoms of endocrine disorders?
The symptoms of endocrine disorders can range from mild or even nonexistent to serious and
affecting your entire body and overall feeling of well-being. Specific symptoms depend on the
specific part of the endocrine system affected.
Common symptoms of diabetes
Diabetes mellitus is the most common endocrine disorder and occurs when the pancreas either
does not produce sufficient insulin or the body cannot use the available insulin. Symptoms of
both type 1 and type 2 diabetes include:
• Excessive thirst or hunger
• Fatigue
• Frequent urination
• Nausea and vomiting
• Unexplained weight loss or gain
• Vision changes
Common symptoms of acromegaly
Acromegaly is a disorder in which the pituitary gland overproduces growth hormone. This leads
to symptoms of overgrowth, especially of the hands and feet. Symptoms of acromegaly include:

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• Abnormally large lips, nose or tongue
• Abnormally large or swollen hands or feet
• Altered facial bone structure
• Body and joint aches
• Deep voice
• Fatigue and weakness
• Headaches
• Overgrowth of bone and cartilage and thickening of the skin
• Sexual dysfunction, including decreased libido
• Sleep apnea
• Vision impairment
Common symptoms of Addison’s disease
Addison’s disease is characterized by decreased production of cortisol and aldosterone due to
adrenal gland damage. Common symptoms of Addison’s disease include:
• Depression
• Diarrhea
• Fatigue
• Headache
• Hyperpigmentation of the skin (bronze appearance)
• Hypoglycemia (low blood glucose)
• Loss of appetite
• Low blood pressure (hypotension)
• Missed menstrual periods
• Nausea, with or without vomiting
• Salt cravings
• Unexplained weight loss
• Weakness (loss of strength)
Common symptoms of Cushing’s syndrome
Cushing’s syndrome arises from excess cortisol, produced by the adrenal glands. Symptoms of
Cushing’s syndrome include:
• Buffalo hump (fat between the shoulder blades)
• Skin discoloration such as bruising
• Fatigue
• Feeling very thirsty
• Thinning and weakening of the bones (osteoporosis)

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• Frequent urination
• High blood sugar (hyperglycemia)
• High blood pressure (hypertension)
• Irritability and mood changes
• Obesity of the upper body
• Rounded “moon“ face
• Weakness (loss of strength)
Common symptoms of Graves’ disease
Graves’ disease is a type of hyperthyroidism resulting in excessive thyroid hormone production.
Common symptoms of Graves’ disease include:
• Bulging eyes (Graves’ ophthalmopathy)
• Diarrhea
• Difficulty sleeping
• Fatigue and weakness
• Goiter (enlargement of the thyroid gland)
• Heat intolerance
• Irregular heart rate
• Irritability and mood changes
• Rapid heart rate (tachycardia)
• Thick or red skin on the shins
• Tremors
• Unexplained weight loss
Common symptoms of Hashimoto’s thyroiditis
Hashimoto’s thyroiditis, or autoimmune thyroiditis, is a condition in which the thyroid is
targeted by the immune system, leading to hypothyroidism and low production of thyroid
hormone. Often, Hashimoto’s thyroiditis is symptomless, but symptoms can include:
• Cold intolerance
• Constipation
• Dry hair and loss of hair
• Fatigue
• Goiter (enlargement of the thyroid gland)
• Joint and muscle pain
• Missed menstrual periods
• Slowed heart rate
• Weight gain

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Common symptoms of hyperthyroidism
Hyperthyroidism is a condition characterized by an overactive thyroid gland. Common
symptoms of hyperthyroidism include:
• Diarrhea
• Difficulty sleeping
• Fatigue
• Goiter (enlargement of the thyroid gland)
• Heat intolerance
• Irritability and mood changes
• Rapid heart rate (tachycardia)
• Tremors
• Unexplained weight loss
• Weakness (loss of strength)
Common symptoms of hypothyroidism
Hypothyroidism is a condition in which the thyroid is underactive and produces too little thyroid
hormone. Often, hypothyroidism can be symptomless or very mild. Common symptoms of
hypothyroidism include:
• Cold intolerance
• Constipation
• Decreased sweat production
• Dry hair
• Fatigue
• Goiter (enlargement of the thyroid gland)
• Joint and muscle pain
• Missed menstrual periods
• Slowed heart rate
• Swollen face
• Unexplained weight gain
Common symptoms of prolactinoma
Prolactinoma arises when a dysfunctional pituitary gland makes excess prolactin hormone,
which functions in the production of breast milk. Excess prolactin can lead to symptoms such as:
• Erectile dysfunction
• Infertility
• Loss of libido
• Missed menstrual periods
• Unexplained milk production

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Serious symptoms that might indicate a life-threatening condition
In some cases, endocrine disorders can be life threatening. Seek immediate medical care if you,
or someone you are with, have any of these serious symptoms that might indicate a life-
threatening condition including:
• Confusion or loss of consciousness for even a brief moment
• Dangerously low blood pressure (extreme hypotension)
• Dangerously slow heart rate
• Dehydration
• Depression or anxiety
• Difficulty breathing
• Eye problems, including dryness, irritation, pressure, pain or bulging
• Severe fatigue or weakness
• Severe, unexplained headache
• Severe vomiting and diarrhea
• Sleep disturbances
Causes
What causes endocrine disorders?
Endocrine disorders arise because of problems with the glands of the endocrine system. Of the
many potential endocrine disorders, some of the most common relate to problems with the
pancreas or with the pituitary, thyroid, or adrenal glands.
Causes of endocrine disorders
A number of factors are believed to cause endocrine disorders. Types and causes of endocrine
disorders include:
• Acromegaly, an overproduction of growth hormone, and prolactinoma, an
overproduction of prolactin hormone, resulting from damage to the pituitary gland
• Addison’s disease and Cushing’s syndrome, disorders relating to changes in levels of
hormones produced by the adrenal glands
• Diabetes mellitus, which arises when the pancreas does not produce sufficient insulin
or when the body cannot respond to the insulin that is present
• Environmental or nutritional factors, such as a lack of iodine in hypothyroidism, which
can affect hormone production
• Genetic factors, which may play a role in endocrine disorders, especially with diabetes
and other disorders, such as autoimmune thyroiditis, or Hashimoto’s thyroiditis

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• Hyperthyroidism (overactive thyroid), hypothyroidism (underactive thyroid), Graves’
disease (a type of hyperthyroidism resulting in excessive thyroid hormone production),
and Hashimoto’s thyroiditis (autoimmune disease resulting in hypothyroidism), all
resulting from problems with the thyroid gland
• Tumors, since the underlying cause of the endocrine disorder can be linked to a growth
or tumor of the gland
In many cases, the exact cause of a particular endocrine disorder is not known. Often, hormones
interact with each other, so symptoms of a particular endocrine disorder may be nonspecific. It is
important to seek medical evaluation if you believe you may have an endocrine disorder, as
direct assessment of hormone levels may help find and fix the underlying cause of hormone
imbalance.
What are the risk factors for endocrine disorders?
A number of factors increase the risk of developing endocrine disorders. Not all people with risk
factors will develop endocrine disorders. Risk factors for endocrine disorders include:
• Elevated cholesterol levels
• Family history of endocrine disorder
• Inactivity
• Personal history of autoimmune disorders, such as diabetes
• Poor diet
• Pregnancy (in cases such as hyperthyroidism)
• Recent surgery, trauma, infection, or serious injury
Reducing your risk of endocrine disorders
While many endocrine disorders are inherited or arise for unknown reasons, some may be
related to modifiable lifestyle factors. You may be able to lower your risk of certain endocrine
disorders, such as hypothyroidism, by:
• Eating a balanced, healthy diet
• Living a healthy lifestyle, including regular physical activity
Treatments
How are endocrine disorders treated?
In many cases, endocrine disorders may be symptomless or mild enough to not require
treatment. Symptoms can arise from excess hormone production or a hormone deficiency. When
symptoms of endocrine disorders are bothersome, they can generally be treated by correcting the
hormone imbalance. This is often done by means of synthetic hormone administration. In cases
such as prolactinoma, where a noncancerous tumor is responsible for symptoms, surgery

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or radiation therapy may be used. Often, diagnosis and treatment of the underlying cause of the
endocrine disorder will resolve the symptoms.
What are the potential complications of endocrine disorders?
While most endocrine disorders are mild and slow to progress, certain endocrine disorders can
lead to complications over time as unbalanced hormonal signaling affects normal body
processes. In cases of Addison’s disease and hypothyroidism in particular, acute attacks or crises
can have serious complications. Diabetes can also have potentially life-threatening
complications. Complications of untreated or poorly controlled endocrine disorders can be
serious, even life threatening in some cases. You can help minimize your risk of serious
complications by following the treatment plan you and your health care professional design
specifically for you. Complications of certain endocrine disorders include:
• Anxiety or insomnia (in many thyroid conditions)
• Coma (in hypothyroidism)
• Depression (in many thyroid conditions)
• Heart disease
• Nerve damage
• Organ damage or failure
• Poor quality of life