The Endocrine System
Around age 12, as they enter puberty, boys and girls start to develop striking differences in
physical appearance and behavior. Chemical messages originating from the brain and pituitary
gland markedly increase the synthesis of new messenger molecules, the sex hormones, from the
gonads. In girls, fatty tissue starts to accumulate in the breasts and hips. In boys, muscle mass
builds and they develop a deeper voice. These changes provide just a few examples of the
powerful influence of secretions from endocrine glands.
Contents:
1.
Endocrine Glands:
a)
Hypothalamus
g) Ovary
b)
Pituitary
h) Testes
c)
Thyroid
i) Pineal
d)
Parathyroid
j) Thymus
e)
Adrenal
k) Heart
f)
Pancreas
l) Kidney
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Functions:
1.
Maintain homeostasis in body fluids
a.
Salt balance, glucose balance, calcium balance
2.
Regulate metabolic rate
a.
Rate of protein synthesis
b.
Rate of bone modeling
3.
Regulate growth and onset of puberty and menopause
4.
Regulate gametogenesis
5.
Regulate pregnancy, childbirth and milk production
1. Endocrine glands vs. exocrine glands
All glands of the body derive from embryonic extoderm
exocrine:
Glands secrete into a duct  onto surface of skin or into a hollow organ.
Ex) sweat gland, oil gland, salivary gland, tear gland, stomach
acid.
endocrine:
Glands secrete into blood or interstitial fluid. NO DUCT!
Ex) hormones
2. Endocrine regulation vs. nervous regulation
Sometimes, the line separating nervous and endocrine systems is fuzzy.
Ex) some neurons secrete hormones
One endocrine gland is made of neurons
-Often combined into neuro-endocrine system
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nervous system
endocrine system
a) Uses electrochemical messages
a) uses chemical messages in
blood
(hormones)
b) Fast acting but short-lived
b) slow acting but long-lived
c) affects: 3 types of muscles and glands
c) affects: metabolic rate of
cells
(action potentials)
3. Hormones
Chemical messengers that are sent from one group of cells through body
fluids to influence the activity of a second group of cells.
Another example of a chemical messenger-neurotransmitter
About 50 hormones in the human body
Hormones are powerful chemicals and work in relatively low
concentrations
Basal Level = the lowest concentration of a hormone in body fluids
a) chemical types of hormones
1) Steroid
ex: testosterone
2) polypeptide/ protein ex: insulin
3) biogenic amine
ex: epinephrine (adrenaline)
4) flcosonoids
ex: prostaglandins
b) target cells
Virtually all cells in body are exposed to circulating hormones but only certain cells
respond to a given hormone. These are TARGET CELLS.
Target cells have specific receptors. These are located
a)
on the surface of cell membranes
b)
inside target cells
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Once a hormone binds to a receptor, it alters the activity within the target cell.
It alters the rate of an existing metabolic process
Ex: increase/decrease rate of cell division
Ex: increase/decrease synthesis and secretion of a material.
4. Control of endocrine secretion
a) negative feedback
Feedback that causes the original stimulus to decline or end
The response of the target cells reverses the original imbalance back into
homeostasis.
Low [Ca] in blood
imbalance
[Ca] level normal
Stimulates the release of
Parathyroid hormone
Increases [Ca] level in blood
homeostasis reestablished
travels in blood
Target Cells: Osteoclasts
(break down bone tissue)
b) nervous stimulation
In most all cases, the ANS controls the release of hormones as a motor
response within a reflex arc.
Ex: stimulates adrenal gland to secrete epinephrine and norepinephrine
stimulates kidney to secrete renin
5. Endocrine glands:
a) hypothalamus
a region of the brain within the diencephalon
secretes several hormones whose functions are to control the release of
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other hormones called RELEASING hormones
Ex: growth hormone releasing hormone
Function: stimulates the release of growth hormone
b) anterior pituitary gland
Pituitary gland is located immediately inferior to the diencephalon.
 nick-named: master gland
 Anterior pituitary comprises 75% of entire gland. Secretes 7
hormones
 Ex: growth hormone. Function: stiumulate growth and increases
metabolic rate.
 Ex: prolactin. Function: initiate milk production during
pregnancy.
c) posterior pituitary gland
Posterior pituitary comprises 25% of entire gland.
* neurons secrete these hormones. There are 2.
* Oxytocin. Function: allows milk secretion & contracts smooth muscles
of the uterus
* Antidiuretic hormone: Function: decrease urine production to conserve
water
(Diaretic – increases urine production)
QUIZ 1
d) thyroid gland
Located in anterior neck just anterior to larynx and trachea. Secretes 2
hormones:
 thyroxine – regulates rate of general metabolism.
 calcitonin – decreases calcium level in blood.
e) parathyroid gland
Located on posterior sie of thyroid gland
Consists of 4 small patches of tissue. Secretes 1 hormone.
 Parathyroid hormone- increases calcium level in blood.
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f) adrenal cortex
Adrenal galnd is located at superior end of each kidney
 outer (superficial) region is the CORTEX.
 The cortex secretes 5 hormones.
o Aldosterone – increases Sodium level in blood
o Cortisol – increases activity of immune system. Increases
resistance to stress
g) adrenal medulla
Inner (deep) region of adrenal gland
Made entirely of sympathetic postganglionic neurons.
Secretes 2 hormones
 epinephrine and norepinephrine
o Function increase HR, RR, BP, etc…
h) pancreas
Located in abdominal cavity. Contains both endocrine and exocrine
cells. Secretes 4 hormones
 ex: insulin – decrease glucose level in blood.
 Glucagon – increase glucose level in blood.
i) ovaries
Female reproductive organs that produce gametes via meiosis.
Secretes 4 hormones.
 estrogen-regulates menstrual cycle & produces secondary sex
characteristics
 progesterone – regulates pregnancy
j) testes
Male reproductive organs that produce gametes via meiosis.
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Secrete 2 hormones
 testosterone – regulates sperm production & produces secondary
sex characteristics.
 Inhibin – inhibits the release of menstrual cycle hormones
k) pineal
A small rounded gland located in midbrain region. Secretes 1 hormone.
 Melatonin – controls body’s internal clock. Affects: jet lag,
insomnia.
l) thymus
A small mass of tissue located anterior to heart. Secretes 4 hormones.
 thymosin – promotes maturity of T-Cells.
m) heart
A large muscular organ in thoracic cavity. Secretes one hormone.
 Atrial matriuretic peptide – decreases blood pressure
n) kidneys
2 large bean-shaped organs located on posterior wall of abdominal
cavity. Secretes 2 hormones.
 renin(combined with another hormone) regulates blood pressure
 erythropoietin – regulates production of new blood cells in red
bone marrow.
6. Disorders of the endocrine system
a) diabetes mellitus
A group of related disorders that all result in hyperglycemia (high level
of glucose in blood and/or in urine)
Two varieties
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Type I - juvenile onset diabetes. Insulin dependant diabetes. Insulin
producing cells in pancreas are destroyed by body’s own immune
system.
Type II – Adult onset diabetes. Target cells loose ability to respond to
insulin.
http://www.thevisualmd.com/health_centers/nutrition_and_metabolism_health/type_2_diabetes/type_2_diabetes_video
b) diabetes insipidus
An under-secretion of ADH from posterior pituitary.
Symptoms: production of large volumes of urine, excessive thirst,
dehydration. Associated with cases of bed-wetting in children.
Treatment: replace ADH via injection or nasal spray
c) acromegaly
An over-secretion of growth hormone in adulthood.
Symptoms: thickening of facial bones, large hands and feet. Usually
caused by tumor of pituitary.
Treatment: Surgical removal of tumor but symptoms not reversible.
http://www.clas.ufl.edu/users/krigbaum/ANT4468/ANT4468/Human%20Growth%20Hormone.htm
d) goiter
A pronounced enlargement of thyroid gland. Increased size due to a
lack of iodine in diet.
Iodine needed in assembly line to manufacture thyroxine. Accumulation
of intermediary compounds. Treatment: add iodine to diet (iodized salt)
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