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AP 17 Endocrine Part 3 - Hormone Control
chapter 17 endocrine system part 3 hormone control
Terms in this set (22)
Most Hormones Controlled by?
negative feedback system
3 Regulations of Hormone Secretion Rate
Most hormones not secreted at constant rate and regulated by 1) action of substance other than hormone on an endocrine gland (ex: glucose), 2) neural control of endocrine gland (ex: stress), 3) control of secretory activity of one endocrine gland by hormone or neurohormone secreted by another endocrine (ex: thyroid)
3 Types of Stimuli That Control Hormone Release
Humoral Stimuli, Neural Stimuli, Hormonal Stimuli
Humoral Stimuli - Secretion
Blood-born molecules (molecules that circulate in blood) can directly stimulate the release of some hormones. These hormones sensitive to blood levels of particular substances, such as glucose, calcium or sodium.
Control by Humoral Stimuli
When blood levels of a particular molecule changes, the hormone is released in response to the molecule's concentration. Ex - long distance runner not having to urinate up to 12hrs after race due to high level of blood-solute concentration, Calcium released from bone w/low blood calcium, elevated blood lucose simulates insulin by pancreas
Neural Stimuli to Endocrine Gland - Secretion
involves neural stimulus of endocrine glands; Following action potentials, neurons release a neurotransmitter into the synapse with the cells that produce the hormone; when stimulus is no longer present, neural stimulation declines and secretion decreases.
Neural Stimuli Directly to Blood - Secretion
some neurons secrete chemical messengers directly to blood when they are stimulated, making them hormones (neuropeptides) which can stimulate hormone secretion from other endocrine cells and are called releasing hormones (usually reserved for hormones from hypothalamus)
chemical messengers from neurons that are secreted directly into blood when they are stimulated - some can stimulate hormone secretion from other endocrine cells (releasing hormones)
Control by Neural Stimuli
ex -in response to stimuli (stress/excercise), sympathetic division of ANS stimulates the adrenal gland ot secrete epinephrine and norepinephrine, which help body respond to stimulus (elevated heart rate, increased blood flow)
Hormonal Stimuli - Secretion
occurs when a hormone is secreted that, in turn, stimulates the secretion of other hormones. Most common are tropic hormones (produced in anterior pituitary). Many tropic hormones are prt of complex process in which releasing hormone from hupothalamus stimulates the release of tropic hormone from pituitary. Pituitary tropic travels to 3rd endocrine to and stimulates release of 3rd hormone
produced in anterior pituitary; Many tropic hormones are prt of complex process in which releasing hormone from hupothalamus stimulates the release of tropic hormone from pituitary. Pituitary tropic travels to 3rd endocrine to and stimulates release of 3rd hormone
Control of Hormonal Stimuli
ex - hormones from hypothalamus and anterior pituitary regulate the secretion of thyroid hormones from thyroid gland
Are Hormones Stimulatory or Inhibitory?
Humoral Stimuli - Inhibition of Hormone Release
when a hormone's rlease is sensitive to presence of a humoral stimulus, there exists a companion hormone whose release is inhibited by the same humoral stimulus. Usually, companion hormone's effects oppose and counteract the secreted hormones action. ex - to raise blood pressureeeee, adrenal cortex secretes aldosterone, if blood pressure goes up, atria of heart secrete atrial natriuretic peptide. So ANP and aldosterone work together to maintain homeostasis.
Neural Stimuli - Inhbition of Hormone Release
Neurons inhibit just as often as they stimulate. If inhibitory target endocrine gland does not secrete its hormone. Hormones from hypothalamus that prevent secretion of tropic hormones from pituitary glands are called inhibiting hormones
Hormones from hypothalamus that prevent secretion of tropic hormones from pituitary glands
Hormonal Stimuli - Inhibition of Hormone Release
some hormones prevent scretion of other hormones, which is common mode of hormone regulation. ex - thyroid hormones can control their own blood levels by inhibiting their pituitary tropic hormone. Without the original stimulus, less thyroid hormone is released
Regulation of Blood Hormone Levels
Negative Feedback (most hormone regulation), Positive Feedback
Negative Feedback System
Most hormones regulation - hormone's secretion is inhibited by the hormone itself once blood levels have reached a certain point and there is adequate hormone to activate target cell. - Self limiting system - ex - Thyroid hormones inhibit secretion of TRH from hypothalamus and TSH from anterior pituitary
Negative Feedback System Picture
ex - production of T3 & T4
Positive Feedback System
when stimulated by tropic hormone, promote synthesis and secretion of tropic hormone in addition to stimulating target cell. In turn, this stimulates further secretion of original hormone. - Self propagating system - Ex - Prolonged estrogen stimulation promotes release of LH; Oxytocin released during childbirth
Positive Feedback System Picture
ex - Pitosin with uterin contractions, contraction actually produces more pitosin until contractions stop
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