The endocrine system is made up of glands that secrete hormones directly into the bloodstream to regulate bodily functions. The major glands include the pituitary, thyroid, parathyroid, adrenal, pancreas and reproductive glands. Hormones regulate metabolism, growth and development, tissue function, sexual function, pregnancy and lactation. Gland secretions are regulated by feedback mechanisms involving the hypothalamus and pituitary. The endocrine system maintains homeostasis through synthesis and secretion of hormones which target distant organs and cells.

1. Endocrine System
Endocrine System
od
pophysis)
pophysis)
retion
s
During Exercise
ng Exercise
ctrolyte Balance

2. ductless glands called endocrine glands that secrete chemical messengers called hormones into the bloodstream or in the extrac
made and secreted by one cell that travels through the circulatory system or the extracellular fluid to affect the activities of cells
onment in the body (the optimum biochemical environment)
es
wth and development.
igates sexual reproduction, including gametogenesis, coitus, fertilization, fetal growth and development and nourishment of the n
ural functions and
rmones and
ones and exocrine
o produce
ells of the small
and heart

3. Nervous System Endocrine System
Neurons release neurotransmitters Endocrine cells release hormones
A neurotransmitter acts on specific cell right next to it.
Hormones travel to another nearby cell or act on cell in another part of
the body.
Neurotransmitters have their effects within
milliseconds.
Hormones take minutes or days to have their effects.
The effects of neurotransmitters are short-lived. The effects of hormones can last hours, days, or years.
Performs short term crisis management Regulates long term ongoing metabolic function
Neurotransmitter acts on specific cell right next to it.
Hormone can travel to another nearby cell or it can act on another part
of the body.
Note, however that these two systems coordinate their activities: certain parts of the
nervous system stimulate or inhibit the release of hormones (e.g. hypothalamus) and
in turn, certain hormones can stimulate or inhibit the flow of nerve impulses.
The nervous system modifies the stimulation of endocrine glands and their negative
feedback mechanisms. The nervous system can override normal endocrine controls

4. reted by cells into the extracellular fluids
tion of other cells
m seconds to hours
cts
nly activate cells referred to as target cells
fic receptors to which the hormone binds.
acellular or located on the plasma membrane.
tors:
ormone
eceptors on the target cell
eptors for the hormone
form more receptors in response to the hormone
lls lose receptors in response to the hormone
ore of the following cellular changes in target cells
meability

5. me systems
modified from the amino acid called tyrosine. They include the thyroid hormones and the hormones of the adrenal medulla (epi
oluble.
hains of amino acids that vary in size from 3 amino acids (TRH) to 191 amino acids (GH). These hormones are water soluble.
t are steroids (e.g. estrogen and testosterone) and fatty acids derivatives (e.g. prostaglandins). These hormones are lipid soluble.
rget cell in 1 of 2 ways:
volves regulatory G proteins)
ptide, and fatty acid-derived hormones work)
n-linked receptor on the cell membrane; t he hormone acts as a first messenger.2. The binding of the hormone to the G protein-lin
cond messenger than activates or inactivates enzymes in the cell
l help you understand how hormones that bind to G protein-linked receptors on the surface of the cell activate second messenger
mones work)
rmones pass directly through the cell membrane of target cells.
oplasm or in the nucleus. (Thyroid hormones also bind to receptors in the mitochondria.)
toplasm, the hormone-receptor complex then enters the nucleus.
ctly either turn genes “on” or turn genes “off.” That is they either cause the gene to start making a protein by transcription and tra
tochondria increase the rate of ATP production in the cell.

6. l help you understand how hormones that bind to intracellular receptors (activate second messengers) work.
od
ood in two forms – free or bound
ne are attached to plasma proteins
d
g hormone reflect:
emoval from the body
m the blood by:
ed by negative feedback systems
ithin a narrow desirable range
nd released in response to humoral, neural, and hormonal stimuli

7. d in
blood
2+
ates
ds to
yroid
e and
ved

8. etic
s
la
d in response to hormones produced by other endocrine organs
mones stimulate the anterior pituitary to release hormones. The pituitary hormones then stimulate other target organs to secrete s

11. in the diencephalon, inferior to the thalamus.
euroglial cells.
ormones:
anterior pituitary gland to release a specific hormone (e.g. GRH-GH)

12. anterior pituitary gland to not release a specific hormone (e.g. GRIH-GH)
also called vasopressin)
e conserves body water by reducing the loss of water in urine.
s the collecting ducts of the kidneys to reabsorb more water and constrict blood vessels, which leads to higher blood pressure and
dration.
h muscle of the uterus to contract, inducing labor.
pithelial cells of the breasts to contract which releases milk from breasts when nursing.
behavior.
s muscle contractions in the prostate gland to release semen during sexual activity
hormones made by the hypothalamus reach the anterior lobe of the pituitary gland DIRECTLY by a special set of blood vessels
tidiuretic hormone (ADH) and oxytocin in the cell bodies of neurons and then the hormones are transported down the axons wh
r pituitary gland The posterior pituitary gland stores and later releases the hormones as needed.
elationship of the hypothalamus to the anterior and posterior pituitary glands and on the relationship of the hormones made in th
hormones) to the anterior and posterior pituitary glands.

13. cretes nine major hormones
posterior lobe (neural tissue) receives, stores, and releases hormones (oxytocin and antidiuretic hormone) made in the hypothala
a axons.
anterior lobe, made up of glandular tissue. Synthesizes and secretes a number of hormones.
easing hormones to the anterior pituitary that stimulates the synthesis and release of hormones from the anterior pituitary gland
s inhibiting hormones that shut off the synthesis and release of hormones from the anterior pituitary gland
nine important peptide (protein) hormones
ind to membrane receptors and use cyclic AMP as a second messenger

15. ry Gland (Adenohypophysis)
totropin)
matotropic cells of the anterior lobe
s, but target bone and skeletal muscle
and other tissues to secrete insulin-like growth factor I (IGF-I or somatomedin)
iferation of chondrocytes (cartilage cells), resulting in bone growth.
rowth, replication, and protein synthesis through release of IGF-I.
es lipolysis to encourage the use of fats for fuel and inhibits glucose uptake
alamic hormones regulate GH
mone–releasing hormone (GHRH) stimulates GH release
mone–inhibiting hormone (GHIH or somatostatin ) inhibits GH release

16. (TSH or Thryotropin)
d gland (target cells) where it stimulates the release of thyroid hormones in response to low temperatures, stress, and pregnancy
g hormone (TRH) from the hypothalamus promotes the release of TSH
of thyroid hormones act on the pituitary and hypothalamus to block the release of TSH
(ACTH or Corticotropin)
l gland (target cells) where it stimulates the release of corticosteroids (such as cortisol) in the adrenal cortex.
ng hormone (CRH) from the hypothalamus promotes the release of ACTH in a daily rhythm
factors such as fever, hypoglycemia, and stressors can trigger the release of CRH
FSH)
s (target cells) and stimulates sperm or egg cell production and maturation and estrogen secretion
ing hormone (GnRH) from the hypothalamus promotes the release of FSH during and after puberty
s in females (target cells) and stimulates ovulation, maturation of follicles (together with FSH) and stimulates the corpus luteum
o the testes (target cells) to stimulate secretion of testosterone.
o as interstitial cell-stimulating hormone (ICSH)
l help you to understand how GnRH, FSH, and LH are involved in the female reproductive cycle.
mary glands (target cells) and stimulates the development of mammary glands to produce milk.
ink prolactin influences the sensitivity of cells in the testes (interstitial cells) to the effects of luteinizing hormone (LH)
ormone (PRH) from the hypothalamus stimulates the release of prolactin
hormone (PIH) from the hypothalamus inhibits the release of prolactin
ward the end of pregnancy, suckling stimulates PRH release and encourages continued milk production
Gland (Neurohypophysis)
ns axons from neurons in the hypothalmus
r vasopressin)
the supraoptic nucleus in the hypothalamus
g ducts of the kidneys to reabsorb more water and constrict blood vessels, which leads to higher blood pressure and thus counters
reasons
cribes how the hypothalamus releases antidiuretic hormone (ADH or vasopressin) which then acts on other organs to have its ef

17. mone.
the paraventricular nucleus of the hypothalmus
h muscle of the uterus to contract, inducing labor
pithelial cells of the breasts to contract which releases milk from breasts when nursing.
behavior.
s muscle contractions in the prostate gland to release semen during sexual activity.

18. ecretion

19. c stimulation–from CNS
ulation–from hypothalamic trophic hormones
and stimulation–from pituitary trophic hormone
vides an example of positive and negative feedback control of the reproductive hormones.
ctice questions. Click here for even more practice questions.
ntains numerous thyroid follicles that release 2 hormones: thyroxine (T4) and triiodothyronine (T3)
e held in storage but eventually attach to thyroid binding globulins (TBG); some are attached to transthyretin or albumin
gulate metabolism; they diffuse into target cells and bind to mitochondria, thereby increasing ATP productio; they also bind to r
ation
crease protein synthesis, and promote glycolysis, gluconeogenesis, and glucose uptake
e necessary for normal growth as they stimulate release of GH from the anterior pituitary
e very important for brain development
he thyroid follicles produce calcitonin.
the concentration of calcium in the blood where most of it is stored in the bones; it stimulates osteoblast activity and inhibits ost
on.
calcium concentration in body fluids
cribes the structure of the thyroid gland, how thyroid hormones are made, the functions of calcitonin and thyroid hormones, and

20. ds are four or so masses of tissue embedded posteriorly in each lateral mass of the thyroid gland
ne (PTH) is the most important endocrine regulator of calcium and phosphorus concentration in extracellular fluid
e effect of calcitonin.

21. oclasts which increases blood calcium levels.
tion of Ca+2 from kidneys so it is not excreted in the urine
hesis of calcitriol (hormone made in the kidney which the active form of Vitamin D which increases Ca+2 absorption from sma
cribes the structure of the parathyroid glands, the function of parathyroid hormones, and the effects of hypo- and hyperparathyro

22. re located superior to each kidney.
as a pyramid shape.
as an inner medulla and outer cortex:

23. over 30 different steroid hormones (collectively called corticosteroids)
as 3 regions (zones) that each make a major type of hormones:
rone)
e kidneys to reabsorb sodium if blood pressure drops
es (eliminates) potassium
nes help you to cope with stress
eases the level of sugar in the blood by stimulating the production of glucose from fats and proteins (gluconeogenesis)

24. s swelling
s, cortisol inhibits the immune system.
gluconeogenesis, mobilization of free fatty acids, glucose sparing. Also acts as an anti-inflammatory agent
one, estrogens, and progesterone )
gland also makes small amts of the sex hormones (mostly androgens (testosterone) and lesser amounts of estrogens and progester
certain what role these hormones play; but know that when over secreted they can cause problems
s epinephrine and norepinephrine when stimulated by sympathetic neurons of the autonomic nervous system (ANS)
d norepinephrine contribute to the bodies' "fight or flight" response, just like the sympathetic nervous system.
effects as direct stimulation by the sympathetic NS (increase heart rate, breathing rate, blood flow to skeletal muscles, and conce
onger lasting
milar to epinephrine, but it is less effective in the conversion of glycogen to glucose.
ne
hrine
bes adrenal gland structure and hormones,

25. wer curvature of the small intestine (duodenum)
ns both exocrine and endocrine cells
secretes digestive enzymes into the duodenum via the pancreatic duct
n has clusters of endocrine cells within the pancreas called pancreatic islets or Islets of Langerhans

26. ecrete glucagon
rete insulin
the levels of glucose in the blood by stimulating the liver to breakdown glycogen into glucose during fasting or starvation
d glucose by increasing the rate of glucose uptake and utilization
d glucose by increasing the rates of glycogen breakdown and glucose manufacture by the liver
cribes pancreas structure and hormones.

28. This material is based upon work supported by the Nursing, Allied
Health and Other Health-related Educational Grant Program, a grant
program funded with proceeds of the State’s Tobacco Lawsuit
Settlement and administered by the Texas Higher Education
Coordinating Board.