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McHenry Western Lake County EMS System
Paramedic, EMT-B and PHRN
Optional Continuing Education
December 2014
Overview of the Endocrine System
The endocrine system consists of hormone-producing glands that control basic body functions.
The hormones may affect one or several organs throughout the body: depending on hormone
type, they influence metabolism, growth, and sexual development. Many of the hormones
produced by the endocrine glands interact with each other to maintain the homeostatic balance.
The amount of hormones produced by each gland is regulated by complex feedback loops.
Abnormal over- or underproduction of the hormones has numerous effects that can result in
endocrine disorders.
The following glands make up the endocrine system:
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Pituitary Gland
Hypothalmus
Thymus
Pineal Gland
Testes
Ovaries
Thyroid
Adrenal Glands
Parathyroid
Pancreas
Regulation of Hormones
Secretion of hormones is regulated by a system of sensing elements possessing the means to
detect need for both increased and decreased secretion. The particular sensing network, feedback
elements, and network of control responses are unique for each hormone. Hormonal pathways
maintain homeostasis, and adjustments in secretion usually result in changes that will help
maintain the status quo. In addition, secretion and activity of a particular hormone may be
adjusted upward or downward in response to challenges such as chronic stress, disease, or
change in nutritional status.
For example, for the hormones that are regulated by the pituitary gland, a signal is sent from the
hypothalamus to the pituitary gland in the form of a “releasing hormone.” This causes the
pituitary to secrete a “stimulating hormone” into the circulation. The stimulating hormone then
signals the target gland to secrete its hormone. As the level of this hormone increases in the
circulation, the hypothalamus and the pituitary gland recognize the increased level of the
hormone and decrease secretion of the releasing hormone and the stimulating hormone, which in
turn slows the secretion by the target gland. This feedback system results in stable blood
concentrations of the hormones that are regulated by the pituitary gland.
Another example: An insulin-dependent diabetic took his insulin this morning, but because he
was feeling nauseated, he didn’t eat anything. As a result, the patient’s circulating blood sugar
has moved from the vascular space into the cells of his body to be used as energy. As the sugar
is utilized, and no additional sugar is added to the body in the form of food, the cells of the body
soon become starved for glucose. The sugar-poor cells send a message via the afferent pathway
to the brain that they need sugar. The brain in turn sends a message to the endocrine system via
the efferent pathway that the cells of the body need sugar. The message results in the release of
the hormone glucagon, which converts glycogen, amino acids and lactic acid to glucose and
temporarily raises the blood sugar in an attempt to meet the demands of the cells. In this
example the set point is the normal “random” blood glucose level. The receptors are the cells of
the body, the control center is the brain, and the effectors are the endocrine system. (glucagon).
Hypothalamus
The hypothalamus is located in the lower part of the brain. It influences water balance, sleep,
temperature, appetite and blood pressure.
It secretes hormones that either stimulate or suppress the release of hormones in the pituitary
gland. Five of these hormones are releasing hormones, which are secreted into arteries, thereby
allowing them to directly influence the pituitary gland. Once they reach the pituitary gland, the
releasing hormones signal secretion of stimulating hormones. Two of the hormones are
inhibitory hormones that suppress the release of other pituitary hormones.
Pituitary Gland
The pituitary gland is located at the base of the brain. It controls many functions of the other
endocrine glands earning it the name “Master Gland.”
The pituitary gland produces several hormones. The front part of it, commonly called the anterior
pituitary, produces the following types of hormones:
-Growth hormone: This hormone promotes growth in childhood. For adults, it helps to maintain
healthy muscle and bone mass.
-Prolactin: In women, it stimulates milk production. In males, low levels are linked to sexual
problems; however, most males make no use of the hormone.
-Adrenocorticotropic: This hormone promotes the production of cortisol, which helps to reduce
stress, maintain healthy blood pressure and more.
-Thyroid-stimulating hormone: Just as the name implies, this hormone helps to regulate the
body's thyroid, which is crucial in maintaining a healthy metabolism.
-Luteinizing hormone: In women, this hormone regulates estrogen. In men, it regulates
testosterone.
-Follicle-stimulating hormone: Found in both men and women. It stimulates the releasing of
eggs in women and helps ensure the normal function of sperm production in men.
The back part of the pituitary gland is called the posterior pituitary. It produces the following two
hormones:
-Oxytocin: This hormone causes pregnant women to start having contractions at the appropriate
time and also promotes milk flow in nursing mothers.
-Antidiuretic hormone: Commonly referred to as vasopressin, this hormone helps to regulate
water balance in the body.
Thymus
The thymus is found in the mediastinum, just above the heart. It produces T-lymphocytes, which
are white blood cells that fight infections and destroy abnormal cells.
Pineal Gland
The pineal gland is located in the middle of the brain. It secretes melatonin at night and
serotonin during the day. These help regulate the sleep and wake cycles of the body. Both
hormones are believed to be connected to mood as well.
Testes
Found in men, this gland produces testosterone, which promotes the growth of the penis as a
male gets older as well as facial and body hair. It also deepens the voice of a male at a certain
age. Other functions of testosterone include:
- Maintaining sex drive
- Promoting production of sperm
- Maintaining healthy levels of muscle and bone mass
Ovaries
Found in women, this gland produces both estrogen and progesterone, which promote the
development of breasts. They also help a woman maintain healthy menstrual periods
Thyroid
The thyroid gland is located in the lower portion of the anterior neck and is the largest endocrine
gland. The thyroid plays an important role in the body’s metabolis. It secretes thyroxin,
triiodothyronine, calcitonin, which affect metabolism, body heat and bone growth. Calcitonin
antagonizes the action of parathyroid hormone.
Parathyroid
The parathyroid gland consists of small pea-shaped glands that are located on the surface of the
thyroid gland. Typically, there are four glands. They release parathyroid hormone, which plays
a role in regulating calcium levels in the blood and bone metabolism.
Adrenal
The adrenal glands are located on top of the kidneys. Adrenal glands work in conjunction with
the hypothalamus and pituitary gland. They secrete glucocorticoids (cortisol and corticosterone),
which affects metabolism. It also secretes androgen hormone and aldosterone, which affect
blood pressure and saline balance. It secretes epinephrine and norepinephrine.
Pancreas
The pancreas is located toward the posterior portion of the upper abdomen, behind the stomach.
It has both exocrine and endocrine functions. The exocrine pancreas secretes digestive enzymes
through ducts that empty into the duodenum to help with digestion of food and nutrients. The
endocrine pancreas secretes insulin and glucagon. The alpha cells of the pancreas secrete
glucagon, and the beta cells secrete insulin.
Endocrine-related Organs
Several organs play a major role in helping the endocrine system to work well. Although these
organs are not glands themselves, they do produce, store, and send out hormones that help the
body to function properly and maintain a healthy balance.
Placenta
Besides providing a connection between mother and fetus, the placenta is a special endocrine
organ. It produces hormones that are similar to those produced elsewhere in the body. Human
chorionic gonadotropin (hCG), estrogens, and progesterone are among the most important of
these because they help maintain a normal pregnancy and prepare a woman's breasts for milk
production and breastfeeding.
In a normal pregnancy, hCG stimulates the ovary to produce estrogens and progestins and helps
stimulate normal development of the fetal genitals. The estrogens in the placenta stimulate breast
development, promote normal labor, and help produce a steady rise in prolactin. The progestins
stimulate breast development and help reduce uterine muscle contractions until the baby has
fully developed. Human placental lactogen increases the amount of blood glucose and lipids
(fatty substances) circulating in the mother's blood to ensure there is a food source for the
developing baby.
Skin, Liver, and Kidneys
The skin, liver and kidneys work together to synthesize 1,25-diydroxyvitamin D (calcitriol), the
active form of vitamin D, which helps maintain normal levels of calcium and phosphorus in the
blood. In the skin, a molecule made from cholesterol is converted to vitamin D by exposure to
ultraviolet rays from the sun. Vitamin D undergoes further chemical changes, first in the liver
and then in the kidneys, to become calcitriol. Calcitriol acts on the intestine, kidneys, and bones
to maintain normal levels of blood calcium and phosphorus.
Stomach and Small Intestine
The digestive tract is the largest endocrine-related organ system in the body. It makes and
secretes several different types of hormones that play a role in the body's metabolism. Gherlin
and leptin are two hormones that have been shown to regulate appetite and may be important in
obesity and weight disorders.
McHenry Western Lake County EMS System
Paramedic, EMT-B and PHRN
Optional Continuing Education
December 2014
Overview of the Endocrine System
Post Test
Name: _______________________ (Please Print)
Date: _______________________
Match the gland and its function:
Answer
Gland
Hypothalamus
Pituitary
Thyroid
Parathyroid
Adrenal
Pineal
Testes
Ovaries
Thymus
Pancreas
Function
A. Produces both estrogen and progesterone.
B. Produces T-lymphocytes, which are white blood cells
that fight infections and destroy abnormal cells.
C. Secretes hormones that stimulate or suppress the
release of hormones in the pituitary gland.
D. Secretes insulin and glucagon.
E. Secretes hormone that affects calcium levels in the
blood.
F. Produces testosterone.
G. The “master gland” Release hormones that control
many of the functions of other endocrine glands.
H. Secretes thyroxin, triiodothyronine and calcitonin ,
which affect metabolism, body heat and bone growth.
I. Produces melatonin and serotonin, affecting sleep
patterns and moods.
J. Secretes glucocorticoids (cortisol and corticosterone),
which affects metabolism. Also secretes aldosterone,
which affects blood pressure. In addition secretes
epinephrine and Norepinephrine.