Endocrine System Continued Flashcards
how is the endocrine system controlled
negative feedback systems
- increase hormone effects on target organs can inhibit further hormone release
- levels vary only within narrow, desirable range
hormone release is triggered by what two things
endocrine gland stimuli
nervous system modulation
what three stimuli does endocrine glands respond to
endocrine glands are stimulated to synthesize and release hormones in response to:
humural stimuli
neural stimuli
hormonal stimuli
hurmoral stimuli is stimulated by…
changing blood level of ions and nutrients directly stimulate secretion of hormones
whats an example of calcium in the blood for humoral stimuli
declining blood calcium concentration stimulates parathyroid glands to secrete PTH(parathyroid hormone)
-PTH causes calcium concentrations to ride, and stimulus is removed
describe neural stimuli
nerve fibers stimulate hormone release
- sympathetic nervous sytem fibers stimulate adrenal medulla to secrete catecholamines
what does hormonal stimuli stimulate
hormones stimulate other endocrine organs to release their hormones
in hormonal stimulli what does hypothalamic hormones stimulate
hypothalamic hormones stimulate release of most anterior pituitary hormones
what do anterioir pituitary hormones stimulate in hormonal stimuli
anterior pituitary hormones stimulate targets to secrete still more hormones
what occurs in hypothalamic-pituitary-target endocrine organ feedback
hormones from final target organs inhibit release of anterior pituitary hormones
what can make adjustments to the endocrine systems hormone levels
the nervous system can make adjustments to hormone levels (called modulation) when needed. It can modify stimulation or inhibition of endocrine glands. the nervous sytem can also override normal endocrine controls
whats an example of the nervous system overriding the endocrine system
under stress, hypothalamus and sympathetic nervous system override insulin to allow blood glucose levels to increase
-prepare for “fight or flight”
a target cell must have what specific sturucture?
target cells must have specific receptors to which hormone binds
ex: ACTH receptors are found only on certain cells of adrenal cortex, but thyroxin receptors are found on nearly all cells of the body
what three factors does target cell activation depend on
- blood levels of hormone
- relative number of receptors on/in target cell
- affinity(strength) of binding between receptor and hormone
up-regulation
target cells form more receptors in response to low hormone levels
down-regulation
target cells lose receptors in response to high hormone levels
what can influence the muber of receptors for that hormone
the amount of hormone can influence number of receptors for that hormone
what does down-regulation desensitize
the target cells to prevent them from overreacting to persistently high levels of hormone