Hypothalamus and Pituitary Flashcards
What is the hypothalamus composed of and what do they do?
composed of neurons
neurons secrete chemical signals that regulate the pituitary
What is the difference between the anterior and posterior pituitary?
anterior is the true endocrine gland, posterior is neural tissue, not a gland
What is Rathke’s pouch?
neural tissue that protrudes and pinches off to form the anterior pituitary
How does the posterior pituitary form? What is the intermediate pituitary?
the neural tissue from the anterior pituitary remains connected to the brain to form the posterior
intermediate form between the two, unknown function
What is the median eminance?
interphase between neural tissues of hypothalamus and the peripheral endocrine system of the pituitary
Why is the median eminence important?
Critical communication link between anterior and posterior
What is the hypophyseal portal system?
path by which the chemical signals from the hypothalamus travel to regulate the function of anterior pituitary
2 capillary beds
What does the portal system do?
ensures high concentration of signal enters anterior pituitary for strong and efficient release
What is the portal system capillary route?
heart - artery - capillary bed - another capillary bed
What is a feedback loop? (2)
how the body maintains the appropriate amounts of chemical signals or hormones at each level
sets “targets” of concentrations necessary for proper functioning
What activates the physiological process?
GnRH release
What is the feedback loop? (4 questions)
did the stimulus have an effect?
was the appropriate substance released?
was the correct amount released?
did it have an effect?
What is positive feedback?
the release of GnRH stimulates the release of FSH and LH, does not stop until target level is reached
When does positive feedback stop?
when target is reached (switches to negative feedback)
What is negative feedback?
decrease in the release of GnRH to stop the release of FSH and LH
What is GnRH?
Gonadotropin releasing hormone
What does GnRH do?
bind to receptors to activate synthesis and release of gonadotropins
maintain ovary and testes
generate LH surge necessary for ovulation
What kind of secretion does LH do?
cyclic surge (it’s infrequent)
What does the surge center contain (2)?
preoptic nucleus (pon), anterior hypothalamic area (aha)
What is the other name for the basal hypothalamus (arc?)
tonic center
What are the 2 cycles of secretion?
tonic (pulsatile) and cyclic surge
What is tonic secretion?
continuance release, (maintenance), burst of hormones released (pulsatile)
What type of secretion does GnRH have?
pulsatile
What is cyclic surge secretion?
surge of increased secretion, caused by stimulation of GnRH neurons
When does cyclic surge secretion happen?
during cyclin (menstrual or estrus) just prior to ovulation
What types of neurons regulate GnRH?
KNDy and kissipeptin
What does leptin do?
regulate energy balance
What other factors regulate GnRH?
gonadal steroids, glucose, leptin
What is induced ovulation? What animals use it?
ovulation after mating
rabbits, cats, ferrets, camel
What happens in induced ovulation?
sensory nerves in vagina and uterus are activated after mating, generate signal regulating GnRH to increase the release of LH surge
How does seasonal reproduction work?
controlled by melatonin from pineal gland
short day (less light) = more melatonin which shows an either increase or decrease in GnRH
What are some examples of seasonal breeders?
bird, sheep, horse
What are the importance of the alpha and beta subunits of a hormone?
alpha is common to all hormones, abundant
beta is unique to each hormone, what the receptors look for, low abundance
What does LH do? (3)
induce ovulation, promote CL development, regulate gonadal steroids by theca and granulosa/leydig
What does FSH do?
stimulate growth of ovarian follicules, fetal gonads and number of receptors
What hormone is made in the posterior pituitary?
oxytocin
