Download Endocrinology_2

Ashlee Black
Kelsey Hunter
Melanie O’Bar
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Composed of cells, tissues, and organs (collectively
called endocrine glands) that secrete hormones. As
the hormones diffuse into the bloodstream they act
on target cells.
The glands of the endocrine system should not be
confused with paracrine secretions, which affect
neighboring cells, autocrine secretions, which affect
only the secreting cell itself, or exocrine glands,
which secrete outside the body through ducts or
tubes that lead to the skin surface.
Only target cells will respond to a hormone.
Endocrine glands help regulate metabolic processes,
control rates of certain chemical reactions, help
regulate water and electrolyte balances, and aid in
diffusion of substances across membranes.
Reproduction, development, and growth.
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The major endocrine glands are the pituitary glands,
thyroid gland, parathyroid glands, adrenal glands,
pancreas, pineal gland, thymus gland, and reproductive
glands (ovaries and testes).
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Pituitary glands: located at the base of the brain and attached to the
hypothalamus. It has an anterior and posterior lobe.
The posterior pituitary gland releases hormones when nerve impulses from
the hypothalamus signal the axon ends of the neurosecretory cells of the
posterior gland. “Releasing hormones” from the hypothalamus control the
secretion from the anterior gland. The hormones travel through a capillary
network associated with the hypothalamus. These capillaries merge to form
the hypophyseal portal veins, which pass down the pituitary stalk and arise
into a capillary network in the anterior gland. Via this pathway the
hypothalamus releases substances that the blood carries to the anterior
pituitary.
Hormones of the anterior pituitary: growth hormone (GH) stimulates cells to
increase in size and divide more frequently, prolactin (PRL) stimulates and
sustains the production of milk after childbirth, thyroid-stimulating hormone
(TSH) controls thyroid gland secretions, adenocorticotropic hormone (ACTH)
controls the manufacture and secretion of certain hormones from the cortex
of the adrenal gland, follicle-stimulating hormone (FSH), luteinizing
hormone (LH).
Hormones of the posterior pituitary (composed mostly of nerve fibers and
neuroglial cells): antidiuretic hormone (ADH) decreases urine formation by
reducing the volume of water the kidneys excrete, thus it regulates the
water concentration of body fluids. Oxytocin (OT) contracts smooth muscles
in the uterine wall and stimulates contractions in later stages of childbirth.
It also controls the lactation process.
Thyroid gland: located just below the larynx on
either side and in front of the trachea.
 Hormones: thyroxine and triiodothyronine. Have
similar actions but T3 is five times more potent.
They help regulate the metabolism of carbs,
lipids, and proteins and increase the rate at
which cells release energy from carbs, the rate
of protein synthesis, and stimulate breakdown
and mobilization of lipids. Calcitonin regulates
the concentrations of blood calcium and
phosphate ions. Blood concentration of calcium
ions regulates its release and as the
concentration increases so does the secretion of
calcitonin.
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 Parathyroid:
located on the posterior surface
of the thyroid gland, there are 4 glands- a
superior and inferior gland for each of the
thyroid’s lateral lobes.
 Hormones: parathyroid hormone (PTH)
increases blood calcium concentration and
decreases blood phosphate ion
concentration. It affects the bones, kidneys,
and intestine.
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Calcitonin and PTH maintain stable blood calcium
concentration.
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Adrenal glands: closely associated with the kidneys, a gland
is atop each kidney and is embedded in the adipose tissue
that encloses the kidney.
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Hormones: epinephrine (adrenaline) and norepinephrine
(noradrenaline) increase heart rate, force of cardiac muscle
contraction, breathing rate, and blood glucose level,
elevate blood pressure, and decrease digestive activity.
 Aldosterone helps regulate the concentration of mineral
electrolytes, causes the kidney to conserve sodium ions
and excrete potassium ions. By conserving the sodium, the
hormone stimulates water retention helping to maintain
blood volume and blood pressure.
 Cortisol (hydrocortisone) affects glucose metabolism, it
also influences protein and lipid metabolism.
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Pancreas: located near the small intestine and gallbladder.
Hormones: Glucagon stimulates the liver to break down
glycogen and certain noncarbs such as amino acids, into
glucose, raising blood sugar concentration. Insulin
stimulates the liver to form glycogen from glucose and
inhibits the conversion of noncarbs into glucose.
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Pineal Gland: located between the brain’s hemispheres; secretes
the hormone melatonin in response to light conditions outside
the body. In the dark, nerve impulses from the eyes decrease and
melatonin increases. (Circadian rhythms)
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Thymus Gland: located posterior to the sternum and between
the lungs; shrinks with age. It secretes hormones called
thymosins which affect the production and differentiation of
leukocytes (WBCs!).
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main types: steroid and nonsteroid.
 Steroid hormones are from cholesterol and
made of rings of carbon and hydrogen with
some oxygen atoms.
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They are insoluble in water but soluble in lipids.
B/c lipids are the bulk of cell membranes,
steroidal hormones diffuse into cells easily and
may enter any cell in the body.
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What happens when a steroid enters a target
cell?
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The lipid-soluble hormone diffuses through the
membrane.
It binds to a specific protein molecule - the receptor
for the hormone.
The resulting unit binds within the nucleus to certain
areas of the cell’s DNA and activates transcription of
specific genes into mRNA molecules.
The mRNAs leave the nucleus and enter the
cytoplasm.
The mRNA molecules then associate with ribosomes to
direct the synthesis of specific proteins.
The new proteins then carry out the effects
associated with the specific hormone.
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Examples of steroid hormones:
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GnRH- produced by the hypothalamus, “tells” the pituitary to
make FSH & LH
FSH- follicle stimulation hormone; aids in egg and sperm
development. Made by the pituitary gland and is under the
control of GnRH levels.
LH- luteinizing hormone, tells the gonads to either release
estrogen or testosterone.
Progesterone- it is secreted by the corpus luteum and by the
placenta and is responsible for preparing the body for
pregnancy and, if pregnancy occurs, maintaining it until birth
(thickens the uterine lining).
Estrogen- secreted by ovaries, develops eggs and is responsible
for the secondary sexual characteristics in females. Targets
female reproductive organs.
Testosterone- helps sperm develop; responsible for the
secondary sexual characteristics in males. Targets male
reproductive organs.
Thyroxine- thyroid gland, metabolic rate increased.
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Nonsteroid Hormones: these are amines, peptides or
proteins synthesized from amino acids. Glycoproteins are
also included though they are formed from protein and
carbs. They are insoluble in lipids.
How do they work?
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Usually bind receptors in target cell membranes.
Each of the receptors is a protein with a binding and activity
site.
A hormone molecule delivers its message to a target cell by
joining with the binding site of its receptor.
This junction stimulates the activity site to interact with other
membrane proteins.
This action may alter the function of transport membranes or
enzymes thereby changing concentrations of other cellular
components.
The hormone that induces this entire process is called a “first
messenger” while the biochemicals in the cell that start the
changes in response to the hormone’s binding are called
“second messengers.”
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Examples of Nonsteroid Hormones:
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ADH- “tells” the kidney to reabsorb more water. Made by
hypothalamus
Angiotensin- makes the kidney reabsorb more NaCl and water.
Lowers blood pressure
Aldosterone- absorbs Na+ and water. Produced by adrenal gland, it
increases blood pressure (adrenaline)
Glucagon- increases glucose levels in the blood, by hydrolyzing
glycogen in the liver. It is produced by the pancreas. Targets liver
Insulin- decreases glucose levels in the blood, by storing glucose as
glycogen in the liver. Produced by the pancreas. Targets liver
Calcitonin- produced by the thyroid, it decreases Ca+ levels in the
blood by storing Ca+ in bone and allowing the kidney to urinate
more Ca+ out.
PTH- parathyroid hormone, produced by the parathyroid. This
increases blood Ca+ levels by accessing stored Ca+ in bone and
telling the kidney to reabsorb (keep) more Ca+ ions.
Adrenaline- produced by the adrenal glands. Acts as the “fight” or
“flight” hormone. Targets liver, heart, etc.
Oxytocin- produced by the hypothalamus, released by the
posterior pituitary gland. It causes uterine contractions during
labor.