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
how do hormones circulate in blood
either free or bound.
- steroids and thyroid hormone are attached to plasma proteins
- all others circulate w/o barriers
what does the concentration of circulating hormone reflect
rate of release
speed at which it is inactivated and removed from body
how can hormones be removed from blood
by degrading enzymes, kidneys, or liver
whats half life
time required fro level of hormone in blood level to decrease by half
-varies anywhere from fraction of a minute to a week depending on hormone
describe the three different response times
- some responses are immediate
- some, especially steroid, can take hours to days
- some are inactive until they enter target cells
the durcaion of response times for hormones are usually
limited.
- ranges from 10 secs. to several hours
- effects may dissappear rapidly as blodd levels drop, but some may persist for hours at low levels
what is half-life, onset and duraction of hormone activity dependent on
whether the hormone is water or lipid soluble
can multipule hormones act on the same target at the same time?
yes
permissiveness
one hormone can’t exert it effects w/o another hormone being present
ex: reproductive hormones need thyroid hormone to have effect
synergism
more than one hormone produces same effect son target cell, causing amplification
ex: glucagon and epinephrine both cause liver to release glucose
antagonism
one or more hormones oppos(s) action of another hormone
ex: INSULIN AND GLUCAGON
what does the posterior pituitary consists of
axon terminals of neuron form hypothalamic neurons
- paraventricular neurons produce oxytocin
- supraoptic neurons produce antidiuretic hormone (ADH)
Oxytocin and ADH
-each composed of nine amino acids
almost identical but differ in two amino acids
describe 4 things about oxytocin
- stong stimulant of uterine contractions released during childbirth
- also acts as hormonal trigger for milk ejection
- both are positive feedback mechanisms
- acts as neurotransmitter in brain. uses PIP2 calcium second messenger system
describe antiduretic hormone
- hypothalamus contains osmoreceptors that monitor solute concentrations
- if concentration too high, posterior pituitary triggered to secrete ADH
- targets kidney tubules t reabsorb mor ewater to inhibit or prevent urine formation
- release also triggered by pain, low BP, and drugs
- inhibited by alcohol, diuretics
- high concentrations cause vasoconstriction, so also called vasopressin
describe anterior pituitary hormones
-All 6 hormones are peptide hormones
-all but growth hormone activate target cells via cAMP second-messenger system
all but teo are tropic hormones(tropins) that regulate secretion of other hormones
name the tropic hormones
thyroid stimulating hormone(TSH)- tropic
Adrenocorticotropic hormone(ACTH)-Tropic
Follicle-stimulating hormone(FSH)-tropic
Lutenizing hormone(LH)-tropic
what are the two hormones that aren’t tropins
growth hormone
prolactin
what are the indirect actions on growth
GH triggers liver, skeletal muscle, and bone to produce insulin like growth factors ICFs
what do IGFs then stimulate
cellular uptake of nutrients used to synthesize DNA and proteins needed for cell division
-formation of collagen and deposition of bone matrix
what does GH stimulate most cells
what does GH stimulate most cells to enlarge an ddivide, but major targets are bone and skeletal muscle
describe the regulation of secretion
GH release or inhibition chiefly regulate by hypothalamic hormones on somatotropic cells
describe growth-hormone releasing hormone(GHRH)
stimulate GH release
-triggered by low blood GH or glucose, or high amino-acid levels
Growth hormone-inhibiting hormone (GHIH)
(somatostatin)
inhibits release
-triggered by increase in GH and IGF levels
-ghrelin (hunger hormone) also stimulate GH release
describe Regulation of secretion
GH release or inhibition chiefly regulated by hypothalamic hormones on somatotropic cells
growth hormone-releasing hormone (GHRH)
stimulates GH release
triggered by low blood GH or glucose, or high amino acid levels
growth hormone-inhibiting hormone (GHIH)
(somatostatin) inhibits release
- triggered by increase in GH and IGF levels
what does ghrelin(hunger hormone) stimulate
GH release
What is hypersecretion of GH usually caused by
anterior pituitary tumor.
-in children results in gigantism