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LCRS Endocrinology > pituitary > Flashcards

pituitary Flashcards

neurohypophysis: explain the principle features of the posterior pituitary; list the neurohypophysial hormones, recall how their chemical structures differ and explain their homeostatic control; explain the synthesis, storage, release and physiological action of these hormones and how dysregulation may present

1
Q

what is the posterior pituitary also called

A

neurohypophysis

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2
Q

neurohypophysis origin

A

downgrowth from neural tissue

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3
Q

principle features of posterior pituitary

A

very long neurones originating in hypothalamus, projecting to posterior, and releasing vasopressin and oxytocin

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4
Q

where are neuronal cell bodies located

A

in supraoptic and paraventricular nuclei

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5
Q

supraoptic neurone pathway

A

leave hypothalamic supraoptic nuclei, pass through median eminence, terminate in neurohypophysis

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6
Q

what two types of supraoptic neurone are there

A

vasopressinergic or oxytocinergic

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7
Q

sites of vesicle storage of hormones in supraoptic neurones

A

Herring bodies

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8
Q

magnocellular paraventricular neurone pathway

A

leave paraventricular nuclei, terminate in neurohypophysis

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9
Q

parvocellular neurone pathway

A

leave paraventricular nuclei, terminate in the median eminence (similar to antrerior pituitary) or other parts of the brain

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10
Q

what influences ACTH secretion, and what is the outcome

A

vasopressin and CRH influence ACTH secretion, which influences cortisol

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11
Q

what two types of paraventricular neurone are there

A

vasopressinergic or oxytocinergic

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12
Q

vasopressin and oxytocin: differences and significance

A

are nonapeptides (derived from 9 amino acids): vasopressin: Phe and Arg; oxytocin: Ile and Leu; as very similar, some overlap in functions

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13
Q

purpose of signal peptide

A

signal peptide allows pre-prohormone from cytoplasm to be recognised by Golgi

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14
Q

fate of signal peptide

A

cleaved off to leave prohormone

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15
Q

formation of hormone from prohormone

A

as vesicles move along neurone axon, enzyme splits prohormone into hormone (vasopressin or oxytocin) and other sections

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16
Q

other sections of cleaved prohormone besides vasopressin

A

neurophysin and glycopeptide

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17
Q

other sections of cleaved prohormone besides oxytocin

A

different form of neurophysin, no glycopeptide

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18
Q

neurophysin purpose

A

carrier protein which protects and carries hormone to posterior pituitary before secreted

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19
Q

name the two different vasopressin receptors

A

V1 and V2

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20
Q

V1 vasopressin receptors: intracellular response

A

intracellular calcium increase to produce cellular response

21
Q

where is V1a present

A

arterial/arteriolar smooth muscle

22
Q

V1a function

A

acts as a vasoconstrictor

23
Q

where is V1b present

A

anterior pituitary in corticotrophs

24
Q

V1b function

A

ACTH production

25
Q

V2 vasopressin receptors: intracellular response

A

increase in cAMP to produce cellular response

26
Q

where is V2 present

A

collecting duct cells

27
Q

V2 function

A

water reabsoroption as it is anti-diuretic hormone

28
Q

V2 as anti-diuretic hormone: binding to PKA

A

V2 binds to receptor → activates G protein → increases activity of adenyl cyclase → more cAMP produced → activates PKA

29
Q

V2 as anti-diuretic hormone: PKA to aquaporins

A

PKA → increase synthesis and movement of AQP2 aquaporin channels towards impermeable apical membrane → insertion → AQP3 and AQP4 on basolateral membrane allow water movement into plasma

30
Q

what mechanism allows water to pass through AQP2

A

osmotic gradient from lumen to blood

31
Q

physiological action of oxytocin: major therapeutic effects

A

uterus, mammary gland (myoepithelial cells)

32
Q

physiological action of oxytocin: minor therapeutic effects

A

cardiovascular system (vasodilation), kidney (anti-diuresis), CNS (maternal behaviour)

33
Q

oxytocin on mammary gland

A

act on breast during lactation; myeopithelial cells contract to promote milk ejection (similar to prolactin)

34
Q

oxytocin on uterus

A

act on uterus at parturition; myometrial cells contract to promote delivery of baby; rhythmic contaction to increase local prostanoid production and dilute cervix

35
Q

what is oxytocin suppresed by

A

progesterone

36
Q

what is oxytocin enhanced by

A

oestrogen

37
Q

when does the uterus become more sensitive to oxytocin

A

as weeks of gestation increase (delivery nears)

38
Q

by which mechanism does the uterus become more sensitive to oxytocin

A

positive feedback

39
Q

oxytocin on “tend and befriend” female behavioural response to stress

A

tend: protect and care for children; befriend: seek out and receive social support; inhibitory effects on endocrine stress response; more stimulated by oestrogen than testosterone

40
Q

major clinical uses of oxytocin

A

induction of labour at term, prevention treatment of post-partum haemorrhage, faciliation of milk let-down, social responsiveness e.g. autism

41
Q

control of vasopressin: increased plasma osmolarity

A

increased plasma osmolarity → osmoreceptors in hypothalamus shrink → stimulates neurones which stimulate vasopressin secretion and feeling of “thirst” → vasopressin moves down to kidney → increases water reabsorption → plasma osmolariy returns to normal range

42
Q

control of vasopressin: blood pressure

A

low arterial BP (dehydration or hemmorhage) → baroreceptor (which inhibits vasopressin release) firing rate drops → inhibition reduced → vasopressin secretion increases → acts as vasoconstricor so blood pressure restored

43
Q

control of oxytocin: milk ejection

A

neuroendocrine reflec arc same as prolactin; neural afferent (to brain) neurones; endocrine efferent (to peripheral tissue) secretion

44
Q

oxytocin dysregulation

A

not essential; parturition and milk ejection effects induced/replaced by other means

45
Q

vasopressin dysregulation: low levels

A

constant loss of water (drink and urinate a lot) which causes diabetes insipidus

46
Q

where does diabetes insipidus come from: cranial

A

lack of vasopressin production

47
Q

where does diabetes insipidus come from: nephrogenic

A

kidneys resistant to vasopressin

48
Q

signs of diabetes insipidus

A

polydipsia (increased thirst), polyuria (large volumes of urine), hyper-osmolar (very dilute) urine

49
Q

vasopressin dysregulation: excessive levels

A

caused by certain tumours; too much water reabsorbed (syndrome of inappropriate ADH)

LCRS Endocrinology (34 decks)

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