AP BIOLOGY: HUMAN BODY
SYSTEMS
Endocrine System
Renira Rugnath
ENDOCRINE SYSTEM
Function: The Endocrine System is in
charge of body processes that happen
slowly, such as cell growth.
Purpose: to secrete hormones, or signal
molecules released by glands
◦The endocrine system is a collection of glands
that secrete chemical messages we call
hormones.
◦These signals are passed through the blood to
arrive at a target organ, which has cells
possessing the appropriate receptor.
◦Exocrine glands (not part of the endocrine
system) secrete products that are passed outside
the body.
◦Sweat glands, salivary glands, and digestive
glands are examples of exocrine glands
◦ The major glands that make up the human endocrine
system are the hypothalamus, pituitary, thyroid,
parathyroids, adrenals, pineal body, and the reproductive
glands, which include the ovaries and testes. The pancreas
is also part of this hormone-secreting system, even though
it is also associated with the digestive system because it
also produces and secretes digestive enzymes.
◦ Although the endocrine glands are the body's main
hormone producers, some non-endocrine organs — such
as the brain, heart, lungs, kidneys, liver, thymus, skin, and
placenta — also produce and release hormones.
Parts of the Endocrine
System
Endocrine
Glands
◦ Exocrine glands are duct
glands that produce a
substance which travels
through small tube-like ducts.
Its secretions are transported
in the ducts directly to an
organ or the body surface.
Exocrine glands include
sweat and oil glands of the
skin, intestinal glands, and
salivary glands in the mouth.
Exocrine
Glands
◦ Unlike exocrine glands,
endocrine glands are
ductless glands. They secrete
hormones directly into the
bloodstream, which then
travel to the target organs.
Hormones help regulate
metabolism, water and
electrolyte concentrations in
cells, growth, development,
and the reproductive cycles.
◦ The production and secretion of pituitary
hormones can be influenced by factors such
as emotions and seasonal changes. To
accomplish this, the hypothalamus relays
information sensed by the brain (such as
environmental temperature, light exposure
patterns, and feelings) to the pituitary.
The Pituitary Gland
◦ The tiny pituitary gland is divided into two parts: the
anterior lobe and the posterior lobe. The anterior
lobe regulates the activity of the thyroid, adrenals,
and reproductive glands. Among the hormones it
produces are:
•growth hormone, which stimulates the growth of
The Hypothalamus
bone and other body tissues and plays a role in the
◦ The hypothalamus, a collection of specialized body's handling of nutrients and minerals
cells that is located in the lower central part of •prolactin, which activates milk production in
the brain, is the primary link between the
women who are breastfeeding
endocrine and nervous systems. Nerve cells in •thyrotropin, which stimulates the thyroid gland to
the hypothalamus control the pituitary gland
produce thyroid hormones
by producing chemicals that either stimulate or
suppress hormone secretions from the pituitary. •corticotropin, which stimulates the adrenal gland to
produce certain hormones
◦ The pituitary also secretes endorphins, chemicals that
act on the nervous system to reduce sensitivity to pain.
In addition, the pituitary secretes hormones that signal
the ovaries and testes to make sex hormones. The
pituitary gland also controls ovulation and the
menstrual cycle in women.
◦ The posterior lobe of the pituitary releases antidiuretic
hormone, which helps control body water balance
through its effect on the kidneys and urine output; and
oxytocin, which triggers the contractions of the uterus
that occur during labor.
Thyroids
◦ The thyroid, located in the front part of
the lower neck, is shaped like a bow tie or
butterfly and produces the thyroid
hormones thyroxin and triiodothyronine.
These hormones control the rate at which
cells burn fuels from food to produce
energy. As the level of thyroid hormones
increases in the bloodstream, so does the
speed at which chemical reactions occur
in the body.
◦ Thyroid hormones also play a key role in
bone growth and the development of the
brain and nervous system in children. The
production and release of thyroid
hormones is controlled by thyrotrophin,
which is secreted by the pituitary gland.
Parathyroids
◦ Attached to the thyroid are four tiny
glands that function together called
the parathyroids. They release
parathyroid hormone, which regulates
the level of calcium in the blood with
the help of calcitonin, which is
produced in the thyroid.
Adrenal Glands
◦ Each kidney has an adrenal gland
located above it. The adrenal gland is
divided into an inner medulla and an
outer cortex. The medulla synthesizes
amine hormones, the cortex secretes
steroid hormones. The adrenal medulla
consists of modified neurons that secrete
two hormones: epinephrine and
norepinephrine. Stimulation of the cortex
by the sympathetic nervous system
causes release of hormones into the
blood to initiate the "fight or flight"
response.
◦ The adrenal cortex produces several steroid hormones
in three classes: mineralocorticoids, glucocorticoids,
and sex hormones. Mineralocorticoids maintain
electrolyte balance. Glucocorticoids produce a longterm, slow response to stress by raising blood glucose
levels through the breakdown of fats and proteins; they
also suppress the immune response and inhibit the
inflammatory response.
The Gonads
◦ The gonads are the main source of sex hormones. In
males, they are located in the scrotum. Male gonads, or
testes, secrete hormones called androgens, the most
important of which is testosterone. These hormones
regulate body changes associated with sexual
development, including enlargement of the penis, the
growth spurt that occurs during puberty, and the
appearance of other male secondary sex characteristics
such as deepening of the voice, growth of facial and
pubic hair, and the increase in muscle growth and
strength. Working with hormones from the pituitary gland,
testosterone also supports the production of sperm by the
testes.
The Pineal Glands
◦ The female gonads, the ovaries, are located in the pelvis.
They produce eggs and secrete the female hormones
estrogen and progesterone. Estrogen is involved in the
◦ The pineal body, also called the pineal
development of female sexual features such as breast
gland, is located in the middle of the brain.
growth, the accumulation of body fat around the hips and It secretes melatonin, a hormone that may
thighs, and the growth spurt that occurs during puberty.
help regulate the wake-sleep cycle.
Both estrogen and progesterone are also involved in
pregnancy and the regulation of the menstrual cycle.
Pancreas
◦ The pancreas contains exocrine cells that secrete digestive
enzymes into the small intestine and clusters of endocrine
cells (the pancreatic islets). The islets secrete the hormones
insulin and glucagon, which regulate blood glucose levels.
◦ After a meal, blood glucose levels rise, prompting the
release of insulin, which causes cells to take up glucose,
and liver and skeletal muscle cells to form the
carbohydrate glycogen. As glucose levels in the blood fall,
further insulin production is inhibited. Glucagon causes the
breakdown of glycogen into glucose, which in turn is
released into the blood to maintain glucose levels within a
homeostatic range. Glucagon production is stimulated
when blood glucose levels fall, and inhibited when they
rise.
◦ Diabetes results from inadequate levels of insulin.
Type I diabetes is characterized by inadequate
levels of insulin secretion, often due to a genetic
cause. Type II usually develops in adults from both
genetic and environmental causes. Loss of
response of targets to insulin rather than lack of
insulin causes this type of diabetes. Diabetes causes
impairment in the functioning of the eyes,
circulatory system, nervous system, and failure of
the kidneys. Diabetes is the second leading cause
of blindness in the US. Treatments involve daily
injections of insulin, monitoring of blood glucose
levels and a controlled diet.
 Integumentary System: By releasing hormones to activate the skin cells/glands
Muscular System: One way the endocrine system works with the muscles is
through the release of glucose. When your muscles need energy, a signal will
be sent to your brain to release more insulin from your pancreas, which will
create more energy to be available for use. Glycogen will be pumped out by
your liver if you are in need of energy stores. Also read more about the fight or
flight response.
Relationships
Skeletal System: The thyroid in the endocrine system produces the hormone
calcitonin. Calcitonin decreases the concentration of calcium in the blood by
acting with bone to inhibit its breakdown. The less bone that is reabsorbed the
less calcium moves into the blood. So the level of calcium in the blood
decreases. On the other hand, the parathyroid secretes parathyroid hormone
which increases the concentration of calcium in the blood. The PTH stimulates
the osteoclasts to increase the breakdown of bone. Cells in our bodies are very
sensitive to changing amounts of calcium in the blood. With too much or too
little calcium in the blood cells do not function correctly and for example the
heart could stop.
Nervous System: The endocrine system is responsible for the regulation of hormones in the
body. It works with nervous system by stimulating the brain to release hormone to stimulate
glands like thyroid glands to secrete thyroid hormones. They also work together to maintain
homeostasis.
Digestive System: When we digest carbohydrates, they are transformed into sugars. The
pancreas, part of the endocrine system, produces the hormone insulin to regulate how fast
the sugars are broken down; therefore, insulin regulates the amount of sugar in the blood in
a certain amount of time (the blood glucose level).
 Cardiovascular System: The cardiovascular system consists of the heart and blood vessels,
from the largest veins and arteries down to the smallest capillaries. It also circulates
hormones that are released by the endocrine system--a system of glands--throughout the
body. Hormones function by producing their effects only when they attach to a suitable
target receptor. Even though hormones circulate freely throughout the cardiovascular
system, aside from the target receptors, the rest of the body's systems are essentially
unaffected by their presence. The following 10 kinds of glands form the endocrine system.
All secrete their hormones into the cardiovascular system at large.
Lymphatic System: The endocrine system releases cortisol with can make substances that
increase your immunity.
Respiratory System: Both the endocrine and respiratory systems
are dependent on each other. For example, there are certain
hormones like adrenalin, which is released by the adrenal glands,
which help to stimulate the respiratory activity. Also, some
endocrine hormones have an effect on the dilation of the alveoli,
or the respiratory passages. This can affect the amount of oxygen
that the lungs absorb.
Urinary System: The endocrine system (specifically pituitary gland
and adrenal gland (cortex)) secrete hormones (ADH - antidiuretic
hormone & aldosterone) which cause the kidneys to reabsorb salt.
This, in turn, causes the kidneys to increase water re-absorption. All
of this increases blood volume, which increases blood pressure.
 Reproductive System: The endocrine system sends out hormones
which control your fertility and periods after puberty, so the
endocrine system really controls the reproduction system.
animals with well-developed nervous and circulatory
systems have an endocrine system. Most of the similarities among
the endocrine systems of crustaceans, arthropods, and
vertebrates are examples of convergent evolution. The vertebrate
endocrine system consists of glands (pituitary, thyroid, adrenal),
and diffuse cell groups scattered in epithelial tissues.
More than fifty different hormones are secreted. Endocrine
glands arise during development for all three embryologic tissue
layers (endoderm, mesoderm, ectoderm). The type of endocrine
product is determined by which tissue layer a gland originated in.
Glands of ectodermal and endodermal origin produce peptide
and amine hormones; mesodermal-origin glands secrete
hormones based on lipids.
Evolutionary Development
 Most
There is much more but that is a start.....
Hormones!
Homeostatic conditions also vary across the body - for example, a
high acidic level must be maintained in the stomach, this level is
maintained by the hormone Gastrin, which is released when the
stomach is stretched by food, this hormone targets the production
of HCl (Hydrochloric Acid) in the stomach
Homeostasis
In order to answer this question we must all understand what the
organs are that make up the endocrine system. The hypothalamus
is the master control found in the brain at the base of the optic
chiasm. The hypothalamus releases a hormone in the pituitary
gland, controls the balance of water, sleep, temperature, appetite,
blood pressure and such.
Another, possibly the most important homeostatic condition is water, which
can be maintained by the hormone ADH (anti-diuretic hormone) which
controls how permeable the distal convoluted tubules and collecting tubules
are, the increase of permeability makes the water that would usually go
straight into the urine go back into the body, this lowers water loss and
increases urine concentration. this hormone is only released when the body is
dehydrated, but when the body has too much, this is removed from the body
and most of the water that would be reabsorbed into the body is just removed
in the urine.
Hormones send messages to different organs and organ system to turn on/off
speed up/slow down activities of those tissues
This is the main way we maintain homeostasis actually, since the endocrine
system releases chemicals known as hormones. These hormones are sent via
the blood to specific spots in the body to control things like blood sugar, heart
rate, etc.
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