4. Functions
The endocrine system influences almost every cell,
organ, and function of our bodies. The endocrine
system is instrumental in regulating mood, growth and
development, tissue function, metabolism, and sexual
function and reproductive processes.
In general, the endocrine system is in charge of body
processes that happen slowly, such as cell growth.
Faster processes like breathing and body movement
are controlled by the nervous system. But even though
the nervous system and endocrine system are separate
systems, they often work together to help the body
function properly.
5. Hormones
• The foundations of the endocrine system are the
hormones and glands. As the body's chemical
messengers, hormones transfer information and
instructions from one set of cells to another.
Many different hormones move through the
bloodstream, but each type of hormone is
designed to affect only certain cells.There are
three general classes (groups) of hormones.
These are classified into three groups by chemical
structure, not function.
9. -
1) Steroid hormones including prostaglandins
which function especially in a variety of
female functions (aspirin inhibits synthesis of
prostaglandins, some of which cause
“cramps”) and the sex hormones all of which
are lipids made from cholesterol,
2) Amino acid derivatives (like epinephrine)
which are derived from amino acids, especially
tyrosine, and
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3) Peptide hormones (like insulin) which is the
most numerous/diverse group of hormones.
A gland is a group of cells that produces and
secretes, or gives off, chemicals. A gland
selects and removes materials from the blood,
processes them, and secretes the finished
chemical product for use somewhere in the
body.
11. Exocrine Glands
Some types of glands release their secretions in
specific areas. For instance, exocrine glands, such
as the sweat and salivary glands, release
secretions in the skin or inside the mouth.
Mammary glands, lacrimal glands, gastric glands,
sebaceous glands, mucous glands are also
exocrine glands. Endocrine glands, on the other
hand, release more than 20 major hormones
directly into the bloodstream where they can be
transported to cells in other parts of the body.
12. Endocrine Glands
The major glands that make up the human endocrine system
include the:
1. Hypothalamus
2. Pituitary gland (hypophysis)
3. Thyroid gland
4. Parathyroid glands
5. Thymus
6. Adrenal glands
7. Pancreas
8. Pineal gland (epiphysis)
9. Reproductive glands (which include the ovaries and
testes)
16. Hypothalamus
The hypothalamus, a collection of specialized
cells that is located in the lower central part of
the brain, is the main link between the
endocrine and nervous systems. Nerve cells in
the hypothalamus control the pituitary gland
by producing chemicals that either stimulate
or suppress hormone secretions from the
pituitary.
18. The Pituitary Gland
The pituitary gland is located at the base of the human
brain. It is suspended from the hypothalamus, to which
it is connected by a short stem. The gland consists of
two parts: the anterior lobe (adenohypophysis) and the
posterior lobe (neurohypophysis).
The anterior lobe secretes at least seven hormones.
One hormone, the human growth hormone (HGH),
promotes body growth by accelerating protein
synthesis. This hormone is also known
as somatotropin. A deficiency of the hormone results
in dwarfism; an oversecretion results in gigantism.
20. Another hormone of the anterior pituitary is
prolactin, also called lactogenic hormone (LH).
This hormone promotes breast development and
milk secretion in females. A third hormone is
thyroid-stimulating hormone (TSH). The function
of TSH is to control secretions of hormones from
the thyroid gland. A fourth hormone is
adrenocorticotropic hormone (ACTH). This
hormone controls the secretion of hormones
from the adrenal glands.
22. -
There are three more hormones produced in the anterior
lobe of the pituitary gland. The first is follicle-stimulating
hormone (FSH). In females, FSH stimulates the
development of a follicle, which contains the egg cell; in
males, the hormone stimulates sperm production. The next
hormone is luteinizing hormone (LH). In females, LH
completes the maturation of the follicle and stimulates the
formation of the corpus luteum, which temporarily secretes
female hormones. In males, LH is interstitial cell-stimulating
hormone (ICSH), which stimulates the production of male
hormones in the testes. The final hormone is melanocyte-
stimulating hormone (MSH), which stimulates production
of the pigment melanin.
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The posterior pituitary gland manufactures two
hormones that are produced in the
neurosecretory cells in the hypothalamus, and
pass into the neurohypophysis through the axons
of these cells. When they are needed they are
released. The first hormone is antidiuretic
hormone (ADH). This hormone stimulates water
reabsorption in the kidneys. It is also
called vasopressin. The second hormone is
oxytocin, which stimulates contractions in the
muscles of the uterus during birth.
24. The Thyroid Gland
The thyroid, located in the front part of the lower
neck, is shaped like a bow tie or butterfly and
produces the thyroid hormones thyroxine and
triiodothyronine. These hormones control the
rate at which cells burn fuels from food to
produce energy. Thyroid hormones affect three
fundamental physiologic processes: cellular
differentiation, growth, and metabolism.
Thyroxine production depends on the availability
of iodine.
26. -
The production and release of thyroid hormones is
controlled by thyrotropin, which is secreted by
the pituitary gland. The more thyroid hormone
there is in a person's bloodstream, the faster
chemical reactions occur in the body.
The thyroid gland also produces another hormone
called calcitonin, and the parathyroid glands
secrete parathyroid hormone. Parathyroid
hormone and calcitonin participate in control of
calcium and phosphorus homeostasis and have
significant effects on bone physiology.
27. The Parathyroid Glands
The parathyroid glands are located on the
posterior surfaces of the thyroid gland. They
are tiny masses of glandular tissue that
produce parathyroid hormone, also
called parathormone. Parathyroid hormone
regulates calcium metabolism in the body by
increasing calcium reabsorption in the
kidneys, and by increasing the uptake of
calcium from the digestive system.
29. The Thymus Gland
The thymus is a gland that forms part of the immune system. It is
situated in the upper part of the chest, behind the breastbone, and
is made up of two lobes that join in front of the trachea. Each lobe
is made of lymphoid tissue, consisting of tightly packed white blood
cells and fat. The thymus enlarges from about the 12th week of
gestation until puberty, when it begins to shrink. It
secretes thymosins, which influence the development of the T-
lymphocytes of the immune system. Its function is to transform
lymphocytes (white blood cells developed in the bone marrow) into
T-cells (cells developed in the thymus). These cells are then
transported to various lymph glands, where they play an important
part in fighting infections and disease. Swelling of lymph glands and
fever are a signal that immune cells are multiplying to fight off
invaders of the body: bacteria, fungi, viruses or parasites.
31. The Adrenal (Suprarenal) Glands
• The adrenal glands are two pyramid-shaped glands lying
atop the kidneys. The adrenal glands consist of an outer
portion, the cortex, and an inner portion, the medulla.
• The adrenal cortex secretes a family of steroids
called corticosteroids. The two main types of steroid
hormones are mineralocorticoids and glucocorticoids.
Mineralocorticoids, such as aldosterone, control mineral
metabolism in the body. They accelerate mineral
reabsorption in the kidney. Mineralocorticoid secretion is
regulated by ACTH from the pituitary gland.
Glucocorticoids, such as cortisol and cortisone, control
glucose metabolism and protein synthesis in the body.
Glucocorticoids are also anti-inflammatory agents.
33. Adrenal Medulla
The adrenal medulla produces two
hormones: epinephrine (adrenaline) and
norepinephrine (noradrenaline). Epinephrine
increases heart rate, blood pressure, and the
blood supply to skeletal muscle. Epinephrine
functions in stressful situations to promote the
fight–flight response. Norepinephrine intensifies
the effects of epinephrine. Both hormones
prolong and intensify the effects of the
sympathetic nervous system.
35. Pancreas
The pancreas is located just behind the stomach. Its
endocrine portion consists of cell clusters called the islets
of Langerhans.
The pancreas produces two hormones: insulin and glucagon.
Insulin is a protein that promotes the passage of glucose
molecules into the body cells and regulates glucose
metabolism. In the absence of insulin, glucose is removed
from the blood and excreted in the kidney, a condition
called diabetes mellitus. Diabetes mellitus is characterized
by glucose in the urine, heavy urination, excessive thirst,
and a generally sluggish body metabolism.
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The second pancreatic hormone, glucagon,
stimulates the breakdown of glycogen to
glucose in the liver. It also releases fat from
the adipose tissue so the fat can be used for
the production of carbohydrates.
The pancreas is also associated with the
digestive system because it produces and
secretes digestive enzymes (Acinar cells).
39. Pineal Gland (epiphysis)
The pineal gland is a tiny gland in the
midbrain. Its functions are largely unknown,
but it seems to regulate mating behaviors and
day–night cycles.
41. The Reproductive Glands
The gonads are the main source of sex
hormones. Both men and women have gonads. In
men the male gonads, or testes, are located in
the scrotum. They secrete hormones called
androgens, the most important of which is
testosterone. These hormones tell a boy's body
when it's time to make the changes associated
with puberty, like penis and height growth,
deepening voice, and growth in facial and pubic
hair. Working with hormones from the pituitary
gland, testosterone also tells a guy's body when
it's time to produce sperm in the testes.
43. -
A girl's gonads, the ovaries, are located in her pelvis.
They produce eggs and secrete the female hormones
estrogen and progesterone. Estrogen is involved when
a girl begins to go through puberty. During puberty, a
girl will experience breast growth, will begin to
accumulate body fat around the hips and thighs, and
will have a growth spurt. Estrogen and progesterone
are also involved in the regulation of a girl's menstrual
cycle. These hormones also play a role in pregnancy.
