Endocrine System
Endocrine vs Exocrine
Endo = within
Exo = out Crine = to secrete
 Exocrine glands (sweat, sebaceous,
digestive) secrete products through ducts
into body cavities or onto body surfaces
 Endocrine glands are small, inconspicuous,
ductless tissues that deposit products into the
interstitial tissues that bathe the cells.
Hormonal Actions
Regulate the metabolic function of other cells in
the body
 Reproduction
 Growth and Development
 Mobility of body defenses
 Maintenance of blood electrolyte,
water and nutrient balance
 Regulation of cellular metabolism
 Energy balance
Chemistry of Hormones

Body produces a large variety of hormones
 Classified chemically as:
A) Amino acid based
1) Makes up the majority
2) Can be simple AA derivatives or long polymers
B) Steroids
1) derived from cholesterol
2) only gonadal and adrenocortical hormones
C) Prostaglandins/Eicosanoids
1) Derived from lipids
2) Leukotrienes
3) Protaglandins
Endocrine System
 Focuses on the hormonal control of the body
 Integrates with nervous system to maintain
homeostasis
Nerves
Endocrine
Gland
stimulus received
Stimulus received
Muscle/Gland
Activity
Increase in
metabolic
activity in most
body cells
Endocrine Hormones
Steroid Hormone Signaling
Amino Acid-Based Hormone
Action: cAMP Second Messenger
Second Messenger Mechanisms
 Cyclic AMP
Hormone binds
to its receptor on
the Target cell
membrane
cAMP now triggers
cascade reactions to
activate protein kinase,
which can catalyze
hundreds of reactions
GTP in the
cytoplasm
binds
to and “turns
on” the G-protein
Receptor
changes shape
and binds
to an inactive
G-protein
Activated
Adenylate Cyclase
generates the second
messenger cAMP
from ATP
Activated G-protein
moves along the
membrane; binds and
activates the enzyme
Adenylate Cyclase
ATP = Adenocine Triphosphate
How Hormones work?
1. Hormones signal a cell by binding to specific
receptors on or in the cell
2. lock and key
3. alter chemical rxns in target cell (ex. Initiate
synthesis of new protein)
4. different hormones can work togethersynergism
5. different hormones can have opposite effectantagonism
Prostaglandins
 lipid molecules that are similar to, but do
not meet usually definition of, a hormone
 A through I
 secreted by seminal vesicles, kidneys,
lungs, iris, brain, thymus
 varied functions. Ex:
–
–
PGE- regulate HCL secretion in stomach
PGF- cause uterus contractions; induce labor
Prostaglandins
Hormone Interaction at Target Cells
 Multiple hormones acting upon target
cells simultaneously = varied results
Permissiveness = one hormone depends upon
another in order to have full effect (reproductive
hormones need thyroid hormones)
Synergism = More than one hormone amplifies
the desired effect (glucagon and epinephrine cause
liver to release glucose)
Anatgonism = One hormone opposes the action
of another
(insulin and glucagon produce opposite effects on blood
glucose levels)
Control of Hormone Release
 Humoral Stimuli
– Respond to blood levels of ions and nutrients
• Aldosterone (Kidney)
• Insulin (Pancreas)
 Neural Stimuli
– Respond to innervation
• Sympathetic nervous system releases Epinephrine
and Norepinephrine during stress
 Hormonal Stimuli
– Respond to release of other hormones
Endocrine Organs & Hormones
Overview of the hypothalamic-pituitary
system
The pituitary gland (Hypophysis)
1. “master gland”
2. stalk- infundibulum
3. 2 parts:
1. adenohypophysis
(anterior pituitary)secretes GH, TSH,
PRL, LH, FSH, MSHactually controlled by
hypothalamus’
releasing hormones
(ex. GnRH)
2. neurohypophysis
(posterior pituitary)secretes ADH and OT
hangs from diencephalon
Pituitary Gland
Posterior
pituitary:
axons from
hypothalamus
Oxytocin &
ADH
Pineal Body

Pineal Body- part of
diencephalon
–
–
biological clocksleeping; female
reproductive cycle
secretes melatonininduces sleep;
secretion inhibited
by sunlight
Thyroid Gland: Master of metabolism
 below larynx
 secretes Thyroid
hormones
– T4
– T3
– Calcitonin, CT
Thyroid Glands
Cell Type
Hormone
Regulator
Target Tissue
Function
Follicular cells
Thyroid Hormones (T3,T4)
TSH
all tissues
Regulates basal metabolic rate
and has important influences
on growth and maturation.
Parafollicular cells
Calcitonin
Calcitonin
Bone
Regulates blood Ca++ levels in
concert with parathyroid hormone.
Calcitonin lowers Ca++ by
inhibiting decalcification of bone.
Parathyroid Gland
Parathyroid Glands- 4 or 5;
posterior surface of thyroid;
secrete PTH
Acts on:
 Bone: increases blood calcium by inhibiting osteoblast
deposition of calcium and stimulating osteoclast removal of
calcium.
 Kidney: increases blood calcium by increasing calcium ion
reabsorption by kidney tubular cells; inhibits reabsorption of
phosphate ion from the glomerular filtrate
 Small intestine: increases the absorption of calcium from
the small intestine
Calcium regulation
 PTH - increases
blood calcium by
taking in out of
bones, kidney, and
small intestine
 Calcitonin decreases blood
calcium by
stimulating uptake
into bone
Parathyroid Hormone & Ca2+
Adrenal Glands (aka suprarenal)
top of kidneys;
secrete corticosteroids
which are divided
into:
1. Mineralocorticoidaldosterone
2. glucocorticoidscortisol; cortisone
3. gonadocorticoidsandrogens
What’s this stress mess?
The Endocrine Pancreas


–
–
–
–
The endocrine pancreas is
formed by the Islets of
Langerhans that are
scattered throughout the
exocrine tissue.
Secretes the following:
glucagon
Insulin
Somatostatin
pancreatic polypeptide
Islets of Langerhans
A sweet battle: Insulin vs. Glucagon
What happens when there is no
insulin?
Miscellaneous structures that
produce hormones
Placenta- secretes hCG
2. thymus- thymosin and thymopoietin
3. gastric & intestinal mucosa- gastrin, secretin
4. heart- ANH
1.