3. Hormones are chemical substances,
secreted by cells into the extracellular
fluids, that regulate the metabolic function
of other cells in the body.
Most hormones are amino acid-based, but
some are steroids.
4. Eicosanoids are biologically active lipids
that include leukotrienes and
prostaglandins, which are released from
most cell membranes.
6. Amino acid-based hormones and
second-messenger systems
Second messengers are intracellular
molecules generated by the binding of a
hormone to a plasma membrane receptor.
Cyclic AMP is an important 2nd messenger
that mediates hormonal effects.
7. A first messenger, such as a hormone, binds
to a receptor, which prompts the G protein
to signal adenylate cyclase, which generates
cyclic AMP from ATP.
8. GTP hydrolysis provides the energy to
convert the first messenger into the second.
Protein kinases are enzymes, activated by
cAMP, that catalyze a variety of reaction
through phosphorylation.
Phosphodiesterase is an enzyme that
degrades cAMP.
9.
10.
11.
12. Phospholipase is membrane-bound enzyme
that splits PIP2 into diacylglycerol and IP3
(inositol triphosphate), which act as second
messengers.
13. IP3 triggers the release of of Ca+2 from the
ER, which may act as a third messenger by
binding to the intracellular regulatory
protein calmodulin.
15. Target cells are the tissue cells whose
activity are influenced by a particular
hormone.
Target cells respond when hormones bind to
specific protein receptors on their plasma
membranes.
16. When target cells form more receptors in
response to rising blood levels of the
affecting hormone, it is known as up-
regulation.
When prolonged exposure to high hormone
concentration desensitizes the target cells so
that the respond less vigorously to hormonal
stimulation, it is known as down-regulation.
18. Half-life is the persistence of a hormone in
the blood.
The synthesis and release of most hormones
are regulated by some type of negative
feedback system.
19. Endocrine gland stimuli
The secretion of hormones as a result of
changing blood levels of ions and nutrients
is called humoral stimulus.
The secretion of hormones as a result of
neural stimulation is called neural stimulus.
The secretion of hormones in response to
hormones produced by other endocrine
organs is known as hormonal stimulus.
20.
21. Nervous system modulation
The nervous system can also affect the
homeostasis of circulating hormones.
30. Endocrine Gland Major Hormones Target Organs Primary Effects
Adrenal cortex Glucocorticoids Liver and muscles Cortisol promotes gluconeogenesis
Mineralocorticoids Kidneys Aldosterone promotes Na+ retention,
K+ excretion
Adrenal medulla Epinephrine, Heart, bronchioles, Causes adrenergic stimulation
norepinephrine blood vessels
Heart Atrial natriuretic Kidneys Promotes excretion of Na+ in
hormone the urine
Hypothalamus Releasing & inhibiting Anterior pituitary Regulates secretion of anterior
hormone pituitary hormones
Small intestine Secretin and Stomach, liver, and Inhibits gastric motility and stimulates bile
cholecystokinin pancreas and pancreatic juice secretion
Islets of Langerhans Insulin Many organs Insulin promotes cellular uptake of glucose
and formation of glycogen and fat
Glucogon Liver and adipose Glucagon stimulates hydrolysis of
glycogen and fat
31. Endocrine Gland Major Hormones Target Organs Primary Effects
Kidneys Erythropoietin Bone marrow Stimulates red blood cell production
Ovaries Progesterone, Female repro. tract Maintains structure of reproductive tract,
estrogen & mammary glands promotes and maintains secondary sexual
characteristics
Parathyroid glands Parathyroid hormone Bone, small intestine, Increases Ca+ concentration in blood
and kidneys
Pineal gland Melatonin Hypothalamus and Anti-gonadotropic effect,
anterior pituitary affects sleep cycles
Pituitary, anterior GH, TSH, ACTH, Endocrine glands Stimulates growth and development of
FSH, LH, PRL target organs, stimulates secretion of
other hormones
Pituitary, posterior Antidiuretic hormone Kidneys and blood ADH promotes water retention and
vessels vasoconstriction
Oxytocin Uterus and Oxytocin stimulates contraction of uterus
mammary glands and mammary secretory units
32. Endocrine Gland Major Hormones Target Organs Primary Effects
Stomach Gastrin Stomach Stimulates acid secretion
Testes Testosterone Prostate and Promotes and maintains secondary
seminal vesicles sexual characteristics
Thymus Thymosin Lymph nodes Stimulates white blood cell production
Thyroid gland Thyroxin and Most organs Thyroxine and triiodothyronine promote
triiodothyronine growth and development and stimulate
basal rate of cell respiration
Calcitonin Calcitonin lowers blood calcium
and phosphate levels
