APHY 102 Ch 17: Endocrine System Ivy Tech
endocrinology
Study of hormones and endocrine organs
functions of the endocrine system
1. control reproduction, development and growth
2. prepare the body to combat stress
3. maintain electrolyte and water balance and blood pressure
4. maintain n...
APHY 102 Ch 17: Endocrine System Ivy Tech
endocrinology
Study of hormones and endocrine organs
functions of the endocrine system
1. control reproduction, development and growth
2. prepare the body to combat stress
3. maintain electrolyte and water balance and blood pressure
4. maintain nutrient balance (glucose)
5. regulate cell metabolism
6. increase or decrease cellular activity by changing: plasma membrane permeability, synthesis of
proteins, enzyme functions, cellular secretions, rate of cell reproduction.
characteristics of the endocrine system
includes cells, tissues, and organs that secrete hormones. These organs and tissues are scattered in
different regions of the body. Endocrine glands have no ducts so hormones are transported through
blood and lymphatic vessels.
hormones
chemical messengers produced by endocrine tissues that alter the function of target cells
target cells
tissues with receptors for specific hormone
How are hormones specific?
act on specific target cells/target organs because each hormone binds to protein receptors present
on/in its target cell. Hormone binds to proper receptor like a key in a lock.
exocrine glands
-have ducts to transport their secretion
-action: extra cellular effect (enzyme on food)
endocrine glands
-release secretion into blood or lymph vessels to travel to target cells and induce an action:
intracellular effect.
Other organs contain cells or tissues that secrete hormones
-liver (IGF)
-small intestine- (secretin, CCK)
-placenta (estrogen, progesterone, hCG)
-stomach (gastrin)
-kidneys (EPO, renin, vitamin D)
-heart (ANP)
, -adipose (leptin)
Steroid hormones
-all steroid hormones are derived from cholesterol and are lipid soluble. Ex. estrogen, progesterone,
testosterone, cortisol, aldosterone
Amino acid-based hormones
-contain amino acids, protein or glycoprotein. All are water soluble except for thyroid hormone. Ex.
insulin, glucagon, calcitonin, GH, PRL.
Amino acid-based hormones use second messenger systems
-hormone does not enter the cell but binds to a plasma membrane receptor to initiate a second
messenger system that causes enzyme activation, secretory function, and/or permeability changes.
Steroid hormones use direct activation of genes in the nucleus
-hormone enters the cell, gain access to the nucleus of the cell and form gene-hormone complex,
alter the production of specific proteins
Hydrophilic hormones
All the amino acid-based hormones except thyroid hormone (t3/T4). Use second-messenger systems
to alter cell function.
Hydrophobic hormones
All the steroid hormones and thyroid hormone (T3/T4). Alters gene expression to change target cell
function.
Humoral stimuli
Changing blood levels of ions and nutrients directly stimulate secretion of hormones. For example,
low blood Ca2+ stimulates release of parathyroid hormone and high blood Ca2+ stimulates the
release of calcitonin.
Neural stimuli
Nerve fibers stimulate hormone release. For example, sympathetic nervous system fibers stimulate
adrenal medulla to secrete epinephrine.
Hormonal stimuli
Hormones stimulate other endocrine organs to release their hormones. Hypothalamic hormones
stimulate release of most anterior pituitary hormones. Anterior pituitary hormones stimulate targets
to secrete still more hormones.
Hypothalamic-pituitary-target endocrine organ feedback loop: hormones from final target organs
inhibit release of anterior pituitary hormones.
Hormone Interactions
Most cells sensitive to more than one hormone and exhibit interactive effects.
Synergistic effects
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