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Endocrine System
AAIMT©
Endocrine System Documentation
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Revised: August 23, 2005
ENDOCRINE SYSTEM
The endocrine system is closely related to the nervous system in its functioning. This system,
like the nervous, helps to coordinate and regulate the activities of cells, tissues and organs of the
body and maintain homeostasis. While the nervous system is general, has a rapid effect, the
actions of the endocrine system are generally slow and go on for long periods of time.
In contrast to exocrine glands whose secretions are transported through ducts to their respective
destinations, endocrine glands are ductless. The endocrine glands secrete biologically active
chemicals called hormones directly into the blood. Many endocrine glands are discrete organs
whose primary functions are the production and secretion of hormones. The pancreas functions
as both an exocrine and an endocrine gland; the endocrine portion of the pancreas is composed of
microscopic structures called the pancreatic islets, or islets of Langerhans. The concept of the
endocrine system, however, must be extended beyond these organs. In recent years, it has been
discovered that many other organs in the body secrete hormones. When these hormones can be
demonstrated to have significant physiological functions, the organs that produce them may be
categorized as endocrine glands, although they serve other functions as well. A partial list of the
endocrine glands should include the heart, liver, hypothalamus, and kidneys.
Hormones affect the metabolism of their target organs and help regulate total body metabolism,
growth and reproduction.
As the body begins to experience the changes of puberty, the nervous and endocrine systems
begin to impact bodily functions. Changes in the brain and pituitary gland help us evolve from
adolescents to teens and then to adults.
The word endocrine describes the cells, tissues, and organs that secrete hormones into the body.
Both the nervous and endocrine systems work together to control homeostasis by way of
electrical impulses and chemical messengers. Neurons tend to act over short distances within a
few milliseconds while hormones can take up to several hours or more to bring about their
responses.
These two systems coordinate their activities like an interlocking supersystem. Certain portions
of the nervous system stimulate or inhibit the release of hormones; meanwhile hormones are very
capable of stimulating or inhibiting the transmission of nerve impulses.
In this partnership the endocrine system is primarily involved with physiologic function. We’ll
come back to this later in this document.
The product of endocrine glands is hormones. Hormones are chemical messengers of the body:
made primarily from proteins and steroids. They have an effect on target organs and cells.
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Primary Mechanisms of Endocrine Disease
The endocrine system can be affected by numerous diseases. They usually will present
themselves as tumors or other abnormalities due to glands secreting too much or too little of their
hormones.
Production/secretion of too little hormone is called hyposecretion, and production/secretion of
too much is called hypersecretion. It could be any number of mechanisms in place to cause either
of these conditions to exist.
Hypersecretion – tumors could cause an abnormal increase in numbers of endocrine tissue cells
which causes an increase in hormone secretions. Another cause could be autoimmunity caused
by the immune system ill-functioning. Another could be the failure of the feedback mechanisms
that regulate secretion.
Hyposecretion – this could be because of tissue death caused by a blockage or failure of blood
supply, or because of abnormal operation of regulatory feedback loops. Possibly abnormalities of
immune function could cause this as well.
The Major Glands of the Endocrine System
Hypothalamus – this is the link between the body/mind and nerve/endocrine function. It resides
in the brain. Its main purpose is homeostasis. Example: it affects blood pressure, body
temperature, and fluid and electrolyte balance
The hypothalamus has a primary influence over the pituitary gland, which in turn, controls other
endocrine glands by way of hormones. It does this by secreting hormones with either a releasing
or inhibiting affect on the pituitary hormones.
Pathologic Conditions of the Hypothalamus:
• Psychosocial dwarfism, failure-to-thrive syndrome and delayed tissue healing (all of
which result from stress, emotional disorders and deprivation) can result from
suppression of hypothalamic release of growth hormone.
Pituitary – this is the so called “master gland.” It is situated beneath the hypothalamus in the
brain and is made up of two lobes, the anterior and posterior. This is at about eye level. Many
people believe that this is actually the third eye. Others believe it is actually a different gland that
deserves this title of the third eye, the pineal gland.
The pituitary secretes hormones that regulate growth, fluid balance and lactation. It is a source of
what is known as tropic hormones which are hormones that have a stimulating effect on other
endocrine glands.
There is a difference between the two lobes of the pituitary. The posterior lobe is not considered
a true endocrine gland as it only stores and releases hormones. It does not synthesize them as
well. It secretes two major hormones. The larger anterior lobe secretes six major hormones.
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Anterior Lobe Hormones:
• Growth hormone (GH) – stimulates and controls growth of bone and soft tissue, and
increases glycogen synthesis and fat metabolism.
• Thyroid-stimulating hormone (TSH) – stimulates the thyroid gland to produce thyroid
hormones for metabolism regulation.
• Adrenocorticotropic hormone (ACTH) – stimulates the growth and development of the
adrenal cortex; stimulates the adrenal cortex to produce cortisol.
• Prolactin (PRL) – stimulates the production of milk in the mammary glands of the breast;
promotes breast development during pregnancy. Interestingly enough, this is found in
both men and women.
• Follicle stimulating hormone (FSH) – stimulates development of the follicle which is a
structure in the ovaries that produces eggs. It also stimulates production of sperm.
• Luteinizing hormone (LH) – this acts with FSH to develop the follicle and promotes
ovulation. It also stimulates the secretion of testosterone from the testes.
Posterior Lobe Hormones:
• Antidiuretic hormone (ADH) – this is also referred to as vasopressin. It increases water
reabsorption in the kidney to decrease urine formation.
• Oxytocin – stimulates contraction of the uterus in childbirth and the milk letdown
response causing milk ducts to release milk.
Pathologic Conditions of the Pituitary:
• Because growth hormones are released during sleep, a disrupted sleep pattern could be
the cause of fibromyalgia and other pain and fatigue syndromes, and the body could have
problems with cellular repair consequently. Therapeutic massage has been shown to have
the beneficial influence of bringing about more restful sleep patterns.
• Stress over a long period of time will generate large amounts of glucocorticoids which
are known to suppress the immune system. The use of any form of body work that
reduces stress will also help to reduce the effects of stress in the body.
Pineal - this is a small, cone-shaped gland that is attached to the upper portion of the thalamus
and encapsulated by the meninges covering the brain. It weighs only about 1/5 of a gram in a
child and begins to regress in size at about age 7. In an adult it appears to be a thickened strand
of fibrous tissue.
While there is no direct nervous system connection, it is none the less able to be innervated by
sympathetic nerve fibers. All functions of this gland have not yet been identified. This is truly the
third eye spoken about in many Eastern philosophies. These theories show it to be the gland of
inner sight or awareness.
Its major function is to secrete its principal hormone known as melatonin. During the daytime,
neural pathways from the retinas in the eyes depress the secretion of melatonin. Its secretion
occurs at night only. The pineal is involved in the regulation of circadian rhythms, including the
reproductive cycle.
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As this gland is the body’s clock, gonadal maturation begins when there is a decrease in
melatonin secretions. Excessive secretion is associated with a delay in the onset of puberty.
Secretion is highest in children of age’s one through five. This makes sense when you remember
that growth hormone is also secreted at night and also mainly active in children.
Melatonin is responsible for us being able to fall asleep, stay asleep, and sleep soundly. By the
time we reach age 50, the pineal all but stops production of melatonin. This could explain why as
we grow older we seem to sleep less. Older adults often complain that while they fall asleep
early (maybe by nine or ten PM) they are often wide awake again by three or four AM.
Pathological Conditions of the Pineal Gland:
• Not being able to fall asleep
• Not being able to stay asleep for more than a few hours
• Not sleeping soundly – waking up several times through the night
Various styles of therapeutic massage will help promote and support effective sleep patterns.
Parathyroid – this is composed of four to five tiny glands embedded in the posterior side of the
thyroid gland. It functions to secrete parathyroid hormone. This promotes calcium movement
from bone tissue and absorption from the intestines.
Pathologic Conditions of the Parathyroid Gland:
• An excess of parathyroid hormone causes too much calcium to be removed from bone
giving us weak bones.
• A deficiency of parathyroid hormone can cause hypocalcemic tetany. Symptoms include
loss of sensation, muscle twitches, uncontrolled spasm and convulsion.
• In hyperparathyroidism there will be mild to severe skeletal pain and possibly
osteoporosis. Be sure to provide appropriate referral if there has been no attempt from the
individual to discover the underlying cause of the condition.
Thyroid – this is on the trachea below the thyroid cartilage. With a right and a left lobe, it is
shaped like a “bowtie.” This gland is heavier in women than in men.
Hormones secreted:
• Thyroxine (T4) – this increases metabolic rate by way of catabolism of carbohydrates.
• Triiodonthyronine (T3) – together with Thyroxine, they regulate the rate of growth of an
individual.
• Calcitonin – this lowers blood calcium levels by inhibiting the release of calcium from
bone tissue.
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Pathologic Conditions of the Thyroid Gland:
• Hyperthyroidism is the second most common endocrine disorder after diabetes and it
most often affects women. Mostly caused by autoimmune dysfunction, the symptoms
would include increased metabolic rate, excessive sweating, weight loss, fatigue,
nervousness, loose stools, tachycardia (an unusually rapid heart rate of over 100 beats per
minute), warm moist skin, hand tremor and hyperactivity. This can mimic manicdepression and usually there is a goiter (an enlarged thyroid gland).
• Grave’s Disease is another form of hyperthyroidism and will include a goiter along with
abnormal eyeball protrusion resulting from excess fluid behind the eye. This runs in
families, is associated with autoimmune problems, and is most common in women
between 20 and 40 years of age.
• Hypothyroidism – can actually result from treatment of hyperthyroidism by radioactive
iodine, overdosing of antithyroid medication, or partial or complete thyroidectomy.
Symptoms would include weakness, fatigue, lower metabolic rate, constipation,
hoarseness, bradycardia (abnormally slow heart rate), skin dryness, weight gain to the
point of obesity, sluggishness and slowed mental function with psychotic behavior.
• If thyroid hormones are absent in a fetus or during infancy, it can result in cretinism
(dwarfism with mental retardation).
Thymus – this is located deep to the sternum, between the lungs at the level of T-4 & T-5. This
produces T-cells (thymus-dependant cells) which are specialized lymphocytes used in body
immunity. This gland is large in children, providing some evidence that its production of
hormones may slow down with age.
Hormones Secreted:
• Thymosin – this stimulates the t-cells in the body that have already been produced.
Adrenal – this is a pair of pyramid shaped glands, each on top of a kidney. Sometimes referred to
as the suprarenal glands. Each consists of an inner portion called the medulla, and an outer layer
called the cortex.
Adrenal Cortex – this secretes three major glucose producing hormones derived from
cholesterol. ACTH from the pituitary gland, which receives its messages from the hypothalamus,
stimulates the release of these three hormones.
Hormones secreted:
• Cortisol – this is released in response to stress. It increases blood sugar levels, fatty acid
immobilization and immunosupression.
• Aldosterone – this helps regulate blood pressure by promoting sodium uptake and
potassium secretion by the kidneys.
• Sex hormones – these regulate sexual development and sex drive. They are as follows:
• Testosterone – causes masculinization.
• Estrogens – causes feminization.
• Progesterone – another feminization hormone
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Adrenal Medulla – the tissue structure in this portion is similar to nerve tissue and functions as
part of the sympathetic nervous system.
Hormones secreted:
• Epinephrine – sometimes called adrenaline, produces a sympathetic response of fight or
flight, or an alarm response to stress. This can cause an increase in heart rate.
• Norepinephrine – sometimes called noradrenalin, produces a sympathetic response
slightly less intense than that produced by epinephrine. Affects peripheral
vasoconstriction, raising blood pressure.
Studies have shown that various methods of therapeutic massage can help dissipate the
concentration of adrenal medulla hormones while reducing cortisol levels. This promotes
improved sleep, better digestion, increased immune function and improved tissue repair. This all
supports the body to return to a state of homeostasis.
Ovaries – these are the female gonads located in the pelvic cavity that produce sex hormones
identical to those of the adrenal cortex. Because this is their primary function, they secrete larger
amounts than the adrenal cortex and secrete them in a cyclical way to regulate the menstrual
cycle, support pregnancy, and prepare for lactation.
Hormones secreted:
• Estrogen – this regulates menstrual changes and sex drive. It is responsible for the
development of secondary sexual organs (mammary glands, vagina and the uterine
tubes), and the distribution of fat.
• Progesterone – this prepares the uterus for implantation of a fertilized egg and prevents
spontaneous abortion by preserving the lining of the uterus.
Testes – these are the male gonads located in the pelvic cavity that produce sex hormones
identical to those of the adrenal cortex. Again, like in the ovaries, they secrete larger amounts.
Hormones secreted:
• Testosterone – this is the main male hormone. This regulates the production of sperm
cells in the testes and the development of the penis and accessory glands. It also causes
development of body and facial hair, a deeper voice and larger muscles and bones than in
females.
Pancreas – this is a long, slender gland located deep to the stomach. It is a “dual” gland in that it
is both exocrine and endocrine. While its enzymes aid in digestion, it also produces hormones.
There are islands of cells called the islets of Langerhans interspersed within the exocrine gland
tissues. It is these islets that produce the hormones.
Hormones secreted:
• Insulin – this hormone is produced by the beta cells of the islets. It lowers the blood sugar
levels by promoting glucose uptake by the cells.
• Glucagon – this hormone is produced by the alpha cells of the islets. It increases blood
sugar levels by releasing glucose from glycogen stored in the liver.
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Pathological conditions of the pancreas:
• Benign tumors will occasionally cause high insulin levels.
• More often though, high insulin levels occur in diabetic people who take insulin without
eating properly. This result is called insulin reaction (too much insulin).
• If more glucose enters the blood, glucose levels fall causing hypoglycemia (low blood
sugar). Symptoms will be confusion and weakness. True hypoglycemia is rare, usually
this is caused by improper diet.
• A hypofunction disorder would be diabetes. This is caused by the pancreas not producing
enough insulin or stopping insulin production. Now cells will not absorb glucose causing
incr3eased amount to remain in the blood stream – hyperglycemia. Huge amounts of
water will accompany the glucose through the kidneys as it is a diuretic. This is how the
excess is released in the urine. Symptoms are dehydration, high blood sugar, and coma
induced by acidosis depressing the cerebral cortex. At this point the breathing rate will
increase.
Differences between endocrine and exocrine glands:
The endocrine glands are ductless and secrete hormones directly into the blood stream or
diffuse them into nearby tissues. The exocrine glands have ducts and secrete their products
directly into ducts that open to specific areas.
General characteristics and function of endocrine glands:
• Helps regulate metabolic processes
• Regulates chemical make-up of extracellular fluid
• Helps transport substances through membranes
• Helps regulate water and electrolyte balances – homeostasis
• Plays a role in the integration of growth and development
• Plays a role in the reproductive process
Hormones:
• Definition – an organic substance secreted by a cell that effects the function of another
cell
• Are released into extracellular spaces
• The physiological action is restricted to the target cell
• Target cells or receptor cells are specific only to the hormone meant for it
Controls of hormonal secretions:
• Negative feedback system – this is thy typical regulatory system. It works like all other
negative feedback systems in the body. An example would be a thermostat in the room. If
you set the temperature at 65 with the heat on, when the thermostat reads a temperature
of below 65, it will start the furnace. If the air conditioning is on and the thermostat reads
a temperature of above 65, it starts the air conditioning unit.
•
Nerve control – if you remember, a chemical found in a synapse is called a
neurotransmitter. When this same chemical is found in the bloodstream or a tissue, it is
called a hormone. Neurotransmitters act on adjacent cells, where hormones may travel
long distances in the body before they reach their target cells. The main differences
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between the endocrine system and the nervous system control are speed and duration of
effect. The nervous system is fast acting with a short duration of effect, where the
endocrine system is slow acting with a long duration of effect. This gives us a balance of
control, with the nervous system responding quickly and the endocrine system taking
over to sustain a response.
•
Stress – because the major repair and energy restoring mechanisms of the body are
supported most effectively in the parasympathetic pattern and because most energy is
expended and tissue damage created during fight-or-flight activity, we can begin to see
the importance of supporting parasympathetic function to allow sufficient time for
restoration and repair of the body. A general rule of thumb is that for every 15 minutes of
stressful activity, the body requires about 45 minutes of parasympathetic balancing time.
Actually in a healthy person, 25% of the day involves stressful activity with
parasympathetic restoration processes making up another 25%. The other 50% of the
time is taken up with both actions taking place at the same time.
Dysfunction will result when stress dominates – a demanding lifestyle will create
dysfunction.
The endocrine system secretes hormones that regulate body functions. Stress will affect
this system in a number of ways:
•
Stress causes the hypothalamus to release hormones to activate the fight-or-flight
response of the sympathetic division of the autonomic nervous system. This causes
increased levels of glucose in the bloodstream, increased heart and breathing rate, higher
blood pressure and more blood to flow to the muscles and nervous systems.
•
Prolonged stress may cause constant secretion of fight-or-flight inducing hormones
which, in turn, will decrease immunity, cause gastrointestinal ulcers, and increase blood
pressure.
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