Human Anatomy and
Physiology
Endocrinology
Overview
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Nervous system
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electrochemical impulses regulate muscles
and glands
quick response
Endocrine system
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influences metabolism via chemical messages
prolonged response
Endocrine versus exocrine glands
Endocrine glands
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Major glands
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Other glands
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Pituitary, thyroid, parathyroid, adrenal, pineal and
thymus glands
Pancreas, gonads
Organs/tissues producing hormones
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Adipose tissue, intestine, stomach, kidneys, heart
Hormones
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Steroidal
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Gonads, adrenal glands
Amino acid based
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Works by a secondary messenger system
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Cyclic AMP : cAMP signaling mechanism
PIP-Calcium signaling mechanism
cAMP components
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Receptor, G protein, adenylate cyclase, cAMP, protein
kinase
Cyclic AMP signaling
Cyclic AMP signaling
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Steps
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First messenger
GDP displaced by GTP
Activation of G-protein
Activation of adenylate cyclase
Hydrolysis of GTP to GDP
Inactivation of G-protein
Second messenger cAMP from ATP
Activation of protein kinase
Activation of metabolism
PIP calcium signaling
PIP calcium signaling
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Steps
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First messenger
GDP displaced by GTP
Activation of G-protein
Activation of phospholipase
Hydrolysis of GTP to GDP
Inactivation of G-protein
Phospholipase splits PIP2 into DAG and IP3
DAG and IP3 act as secondary messengers
DAG activates protein kinases, IP3 triggers Ca++ release
from ER
Ca++ activates channels on plasma membrane or binds
to calmodulin which activates metabolism
Steroidal hormones
Steroidal hormones
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Steps
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Diffuse into cell and enter nucleus
Bind to receptors to form receptor complexes
Complexes bind to DNA
Production of mRNA
mRNA + ribosomes make proteins
Proteins include enzymes that stimulate
metabolism
Hormones
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Hormones travel in blood free or bound to
protein carriers
Blood hormone concentration decreases
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Degraded by target organs
Removal by kidneys and liver
Half-life (seconds to 30 min.)
Hormone release
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Three major stimuli
1. Humoral
 Ca++ lowering causes PTH release
2. Neural
 SNS stimulates adrenal gland to release epinephrine
3. Hormonal (common)
 Hypothalamus releases hormones that cause pituitary to
release other hormones (e.g. GnRH to FSH)
Growth hormone
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Site of release
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Target organ
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All body organs especially bones and skeletal
muscle
Stimulation
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Anterior pituitary
Primarily in adolescence, low levels of GH
Feedback mechanism
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High levels of GH, hyperglycemia, obesity
Thyroid hormone precursors
Hypothermia
TRH
TSH
T3 & T4
Increase in metabolism
& body temperature
Thyroid hormone
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Stimulation
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Falling levels of T3 (triiodothyronine) and T4
(thyroxine). TH raise BMR and heat production
Feedback mechanism
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Increase in BMR and body heat (i.e., exercise)
Parathyroid hormone
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Site of release
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Target organ
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Bone, intestine, kidneys
Stimulation
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Parathyroid glands
Falling Ca++ blood levels
Feedback mechanism
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Increase in Ca++ blood levels
Parathyroid hormone
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Ca++ needed for nerve impulses, muscle contraction and blood
clotting
Adrenocorticotropic hormone
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Site of release
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Target organ
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Adrenal cortex (glucocorticoids)
Stimulation
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Anterior pituitary
Stress (i.e., fever, hypoglycemia)
cortisol
Feedback mechanism
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Increase levels of blood glucocorticoids
Adrenal gland hormones
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Mineralocorticoids (aldosterone)
Site of release
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Target organ
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Kidneys
Stimulation
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Adrenal cortex
Decrease in blood volume, pressure, Na+ level
Feedback mechanism
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Increase in blood volume, pressure, Na+ level
Adrenal gland hormones
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Epinephrine and norepinephrine
Site of release
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Target organ
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Heart, vasculature, bronchioles
Stimulation
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Adrenal medulla
Sympathetic nervous system (SNS)
Feedback mechanism
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None. SNS stimulation decreases when
needed
Pancreatic hormones
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Insulin and glucagon
Meal
( plasma glucose)
Starvation
( plasma glucose)
insulin from
pancreas
glucose
uptake
into cells
plasma
glucose
glucagon
glycogen
from
(skeletal
plasma
pancreas
muscle,
liver)
glucose
converted
to glucose
Other hormones
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Renal
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Arginine vasopressin (antidiuretic hormone - ADH)
Reproduction
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Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Oxytocin