L2 - Hypothalamus and Posterior Pituitary Flashcards
What general processes are regulated by the hypothalamus?
Pituitary functions, autonomic processes, behavioral processes, and rhythmic events
What are the two types of neurons that are important in mediating the endocrine functions of the hypothalamus?
Magnocelluar and parvocellular neurons
What are the functions of the magnocellular neurons within the hypothalamus? In which nuclei are they primarily located?
Magnocellular neurons are primarily located within the supraoptic and paraventricular nuclei- they synthesize oxytocin and arginine-vasopressin
What is the hypothalamo-hypophysial tract?
The bridge-like structure formed by the unmyelinated axons of magnocellular neurons that project from the hypothalamus through the median eminence and ends in the posterior pituitary
What is the function of parvocellular neurons of the hypothalamus? To where do they project?
Parvocellular neurons project to the median eminence and release hypophysiotropic hormones that control anterior pituitary function
What broad classes of stimuli does the hypothalamus use to drive patterns of hormone release?
Environmental, neural, and hormonal
How is circadian rhythm generated?
The rhythm is generated by the photo-neuro-endocrine system which consists of the retina, hypothalamic suprachiasmatic nucleus, and the pineal gland through release of melatonin
Which hormones are released by hypothalamic magnocellular neurons? What do they regulate (generally)?
Oxytocin (parturition and lactation) and arginine vasopressin (water balance)
How are oxytocin and ADH packaged and released?
Synthesized as the preprohormone and is post-translationally cleaved and modified, before it is packaged into secretory granules with the cleaved neurophysins
What are neurophysins? What is their apparent function?
By-products of post-translational prohormone processing; appears to play an important role in transport of AVP from cell bodies to their final release from the posterior pituitary
What is the structural difference between Oxytocin and ADH?
Two amino acids are different
What are the main 3 target organs of oxytocin?
Lactating breast, term-pregnant uterus, brain
What uterine stimulus triggers release of oxytocin? What is the effect?
Stretch of the cervix by the fetus near the end of gestation or forceful contractions of the uterus; produces rhythmic smooth muscle contractions
What mammary stimulus triggers release of oxytocin? What is the effect?
Suckling of the lactating breast; contraction of myoepithelial cells–> ejection of milk
By what mechanisms is the pregnant uterus sensitized to oxytocin?
Increase in oxytocin receptors, increase in gap junctions, and increase in prostaglandin synthesis (simulator of uterine contraction)
What is Pitocin? What is it used for?
Synthetic analog of oxytocin that is used to induce labor or stimulate force of uterine contractions
What is the signaling pathway evoked by binding of oxytocin to its GPCR?
Activation of phospholipase C, producing increase in DAG and IP3, which increases cytosolic calcium, which binds to calmodulin, activating PKC, activating myosin light chain kinase, increasing myosin ATPase activity and smooth muscle contraction
What are the receptors for AVP and in what tissues are they found? What are the physiologic effects?
V1 (GPCR alpha q): Smooth muscle; V2 (alpha s): Kidney; V3- brain; conserves water and vasoconstriction
How does AVP conserve water? What is the signaling cascade responsible for eliciting the effect?
AVP increases water re-absorption by stimulating the insertion of aquaporins into the cell membrane of principle cells of the collecting ducts of the kidney; AVP binds to the V2 receptor and activates adenylyl cyclase, leading to PKA activation which activates aquaporin 2 to be inserted into the apical membrane
Which aquaporin(s) is/are under AVP regulation? Where are those aquaporins expressed?
Only AQP2 exclusively located in collecting ducts of the kidney
How does AVP mediate vasoconstriction?
ADH binds to V1 receptors in vasculature, which is an GPCR with an alpha q subunit– activates phospholipase C –> increased calcium–> myosin light chain kinase is activated
What stimuli evoke the release of ADH? Which stimuli is more potent?
Either an increase in plasma osmolarity (dehydration) or a decrease in blood volume/ pressure; more sensitive to changes in osmolarity
How does dehydration stimulate ADH release?
Dehydration produces loss of intracellular water from hypothalamic osmoreceptors, which causes cell shrinkage and decreases magnocellular neuron inhibition
How does decreased blood pressure stimulate ADH release?
Decreases in blood pressure decrease the firing rate of the baroreceptors, whose signal is transmitted by CN IX and X. the reduced stimulation decreases the inhibition of AVP release
