Download The Endocrine System

The Endocrine System
• Hormones are
substances secreted by
cells that act to regulate
the activity of other cells
in the body.
– Hormones affect all cells in
the body and are made and
secreted by endocrine
glands.
• Endocrine glands are
ductless organs that
secret hormones either
into the bloodstream or
the fluid around cells.
• The endocrine glands can be found
through out the body and are collectively
known as the endocrine system.
• Endocrine glands, such as the pancreas,
can also be exocrine glands.
– Exocrine glands secrete substances through
ducts to specific locations inside and outside
the body.
The Endocrine System
Types of Hormones
• Hormones can be grouped into two types based
on their structure. Hormones can either be
amino acid-based hormones or steroid
hormones.
– Amino acid based-hormones are made of amino
acids, either a single modified amino acid or a protein
made of 3-200 amino acids, and are water soluble.
– Steroid hormones are lipid hormones that the body
makes from cholesterol and are fat soluble.
• Similar to steroid hormones are thyroid hormones.
• Regardless of which type of hormone is being
activated, all hormones affect only their target
cells.
– Target cells are specific cells to which a hormone
travels to produce a specific effect.
– On the target cells are receptors. Receptors are
proteins that bind to specific signal molecules, such
as hormones, that cause a cell to respond.
• Amino acid-based hormones
– Amino acid-based hormones bind to receptor proteins
on the cell membrane and are called first
messengers.
– Second messengers are then activated. A second
messenger is a molecule that initiates changes
inside a cell in response to the binding of a specific
substance to a receptor on the outside of a cell.
• Changes to the cell through enzyme action then occur in a
cascade fashion.
• Steroid and Thyroid Hormones
– Steroid and thyroid hormones are similar because
they are both fat soluble.
– Because these hormones are fat soluble they can
pass through the cell membrane.
– Thus, these hormones can enter their target cells
and bind directly to receptor sites in the cytoplasm or
nucleus and directly activate enzymes.
• Two other types of chemical messengers that
are classified as hormones are neuropeptides
and prostaglandins.
– Neuropeptides are hormones secreted by the
nervous system and tend to affect many cells near the
nerve cells that release them.
– Prostaglandins are modified fatty acids that are
secreted by most cells and tend to accumulate in
areas where tissues are disturbed or injured.
The Hypothalamus
The Pituitary
Hypothalamus and Pituitary Gland
• Two organs, the hypothalamus and the
pituitary gland, control the initial release of
many hormones for the endocrine system.
– The hypothalamus is the area of the brain
that coordinates many activities of the
nervous and endocrine systems.
• The hypothalamus
secretes:
• 1. ADH = Antidiuretic
Hormone=stimulates
reabsorption of water in
the body.
• 2. Oxytocin- Used during
childbirth to bring on labor
contractions.
• The nerve cells in the hypothalamus that secrete
hormones are called neurosecretory cells.
– These cells secrete two types of hormones to the
pituitary gland.
• Releasing hormones stimulate the anterior pituitary to make
and secrete hormones.
• Release-inhibiting hormones inhibit production and secretion
of anterior-pituitary hormones.
The Pituitary Gland
• 1. Known as the master gland. Controls
all other glands.
• 2. It is stimulated by hormones from the
hypothalamus to target other glands.
• 3. It secretes:
– A.
– B.
– C.
– D.
– E.
GH= Growth Hormone
ACTH= Adrenocorticotrophic Hormone
FSH= Follicle Stimulating Hormone
LH=Luteinizing Hormone
TSH=Thyroid Stimulating Hormone
Acromegaly
• Widening of bones
The Thyroid
The Thyroid Gland
• The thyroid gland is
located near the larynx
and helps maintain a
normal heart rate, blood
pressure, and body
temperature by
increasing or decreasing
cellular metabolic rates.
• It secretes thyroxine.
• The thyroid gland is also
important for
development.
Goiter
• Abnormal thyroid activity can result in
hypothyroidism or hyperthyroidism.
• Overproduction of thyroid hormones is called
hyperthyroidism and can have symptoms that
vary from overactivity to high body temperature.
• A deficiency in a thyroid hormone is known as
hypothyroidism and can have symptoms that
vary from weight gain to retardation.
The Adrenal Gland Video
The Adrenal Gland
• Humans have an adrenal
gland located above each
kidney. Each adrenal gland
has an inner core, the medulla,
and an outer core, also called
the cortex.
• The medulla and the cortex
function as separate endocrine
glands.
– The medulla is controlled by
the nervous system, and the
cortex is controlled by the
anterior pituitary.
Cushing’s Syndrome -11month old
baby
Cushing’s Syndrome
• Adrenal Medulla
– The adrenal medulla secretes the hormones that
stimulate a “flight-or-fight” response to a stress.
– In this response, the hormones epinephrine, also
called adrenaline, and norepinephrine are released.
• These hormones increases heart rate, blood pressure, blood
glucose levels, and blood flow into the heart and lungs so the
body can respond to the initial stress.
• Adrenal Cortex
– In the presence of some stresses the pituitary
gland will secrete the adrenocorticotropic
hormone (ACTH).
– This hormone stimulates the adrenal cortex to
produce the hormone cortisol.
• Cortisol promotes the production of glucose from
proteins to help cells make usable energy.
The Gonad Video
The Gonads
• Gonads are the gamete-producing organs that
also produce a group of steroid sex hormones.
– Gonads, ovaries in females and the testes in males,
are regulated by sex hormones, which begin
production at puberty.
• Puberty is the adolescent stage during which
the sex organs mature and secondary sex
characteristics appear.
• The production of sex hormones is stimulated by
the release of two hormones by the pituitary.
– The first hormone is luteinizing hormone (LH). This
hormone stimulates ovulation and the release of
progesterone in females and the release of androgens,
such as testosterone, in males.
– The second hormone is follicle-stimulating hormone
(FSH). This hormone stimulates the growth and maturation
of the ovarian follicles in females and
sperm production in males.
The Pancreas Video
The Pancreas
• The pancreas contains both exocrine and
endocrine cells. The endocrine cells are called
islets of Langerhans.
• These cells secrete hormones that regulate the
level of sugar in the blood. The hormone insulin
is one of the hormones produced.
– Insulin lowers the blood sugar level by stimulating
body cells to store glucose or use it for energy.
• A condition called diabetes mellitus occurs when cells
are unable to obtain glucose from the blood. This results
in a high glucose level in the blood
• There are two types of diabetes: Type I and Type II.
– Type I occurs when immune cells attack and destroy the islet of
Langerhans cells.
– Type II occurs when cells don’t have sufficient insulin levels or
when the organism’s cells have become less responsive.
• A condition called hypoglycemia occurs
when excessive insulin is stored and not
properly delivered to body cells.
• This leads to a lowered blood glucose
concentration, which can cause such
symptoms as overactivity and dizziness.
Other Glands
• There are several other glands in the endocrine
system, including thymus gland, the pineal gland
and the parathyroid glands.
• Thymus Gland
– The thymus gland is located beneath the sternum and
plays a role in the development of the immune system
by secreting thymosin.
• This amino acid-based hormone stimulates formation of T
cells.
Thymus Video
• Pineal Gland
– The pineal gland is
located near the base
of the brain and helps
regulate sleep patterns
by secreting
melatonin.
Pineal Gland Video
• Parathyroid Gland
– The parathyroid glands is
made up of four glands
embedded in the two
thyroid glands.
• These glands secrete the
parathyroid hormone,
(calcitonin) which
stimulates the transfer of
calcium ions from the
bones to the blood.
The Parathyroids
• Digestive Cells
– Some of the digestive organs also act as endocrine
cells by secreting a variety of hormones that control
digestive processes. Two hormones that are secreted
are gastrin and secretin.
• Gastrin is released by the stomach when food is eaten.
• Secretin is released by the small intestine and helps
stimulates the release of various digestive fluids from the
pancreas.
• The endocrine system plays an important role in
the maintenance of a stable internal
environment, or homeostasis.
• Maintenance of homeostasis is controlled by
feedback mechanisms. A feedback mechanism
is one in which the last step in a series of events
controls the first.
• Feedback mechanisms can be either negative or
positive.
• Negative Feedback
– When the final step in
a series of events
inhibits the initial
signal in the series it is
called negative
feedback.
– An example of
negative feedback is
the regulation of
thyroid hormones.
Negative Feedback
Positive Feedback
Positive feedback occurs when
the release of an initial hormone
stimulates release or production of
other hormones or substances.
An example of positive feedback is
the stimulation and increase in
luteinizing hormone by estrogen.
• Antagonistic Hormones
– Antagonistic hormones work together in
pairs to regulate the levels of critical
substances.
– Example: Both glucagon and insulin regulate
blood sugar levels.
Quiz
1.What are the chemical messengers of the
endocrine system called?
A. neurons
B. hormones
C. blood cells
D. carbohydrates
• Answer
• D. Hormones
2.
X and Y are hormones. X stimulates
the secretion of Y, which exerts negative
feedback on the cells that secrete X.
Suppose the level of Y decreases. What
should happen immediately afterwards?
F. Less X is secreted.
G. More X is secreted.
H. Secretion of Y stops.
J. Secretion of X stops.
• Answer
• G. More X is secreted
3.Endocrine glands
A. function only after puberty.
B. function only before puberty.
C. release products through ducts.
D. release products into the bloodstream.
• Answer
• D. Release products into the bloodstream
4. What happens after food
is eaten?
F. Blood glucose levels
increase.
G. Blood glucose levels
decrease.
H. Blood glucose levels
remain the same.
J. Blood glucose levels
decrease then increase.
• Answer
• F. Blood glucose increases
5. Which hormones are
primarily responsible for
the changes in blood
glucose levels about 2
hours after food is eaten?
A. insulin
B. estrogen and
progesterone
C. epinephrine and
norepinephrine
D. aldosterone and
parathyroid hormones
• Answer
• A. insulin
6.Neurotransmitters : nervous system ::
hormones :
F. feedback system
G. endocrine system
H. circulatory system
J. respiratory system
• Answer
• G. Endocrine system
7. Thyroid stimulating hormone (TSH) is a
hormone that stimulates the release of the
thyroid hormones from the thyroid gland. At
what time would you expect thyroid
hormone levels to be at their lowest?
A. 0 hours
B. 4 hours
C. 8 hours
D. 12 hours
• Answer
• D. 12 hours