Hypothalamus-posterior pituitary Flashcards by Audrey Bocabarteille

what types of neurons are found in hypothalamus reaching posterior pituitary

magnicellular neurons

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what is the particularity of the magnicellular neurons

they extend axons to posterior pituitary gland

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which are the 2 hormones of the posterior pituitary

oxytocin and vasopressin

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which magnicellular neurons release oxytocin

paraventricular nucleus PVN which contains both magnicellular and parvicellular neurons

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which magnicellular neuron releases Vasopressin/ADH/AVP?

supraoptic nucleus SON (80-90% neurons produce AVP

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ADH

antidiuretic hormone

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AVP

arginine vasopressin

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Oxytocin and AVP are made up of .. AA, making them …

9 AA - nanopeptides

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in which chromosome are AVP and OXT genes found in humans

chromosome 20

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what is the difference between OXT and AVP

their nucleotide sequence varies by 2 AA

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what is the difference between LVP and AVP

LVP - lysine vasopressin found in pigs
AVP - arginine vasopressin in humans
=> both at position 8

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structure of AVP and OXT

ring structure connection AA at position 1 and 6 due to di-sulfide bridges between 2 cysteine

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when are the pro hormones of OXT and AVP cleaved?

as vesicles/granules traverse through the axons

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storage of OXT and AVP is enough for ….. days

30-50 days

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Function of ADH/AVP

regulation of water retention and thirst - primary regulator of blood osmolality
> water retention by kidney + contraction of blood vessels (arterioles)

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function of oxytocin

contraction of smooth muscles cells - myoepithelial cells of the alveoli in lungs and smooth muscle cells of the uterus during labor

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vasopressin/antidiuretic hormone are names derived from 2 physiologic systems regulated which are?

osmotic

2. pressure/volume

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what are the different receptors used by AVP/ADH

V1a/b and V2

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where are V1a receptors found and what are their respective functions

vascular smooth muscle - vasoconstriction, myocardial hypertrophy
platelets - platelet aggregation
hepatocytes - glycogenolysis
myometrium - uterine contraction

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where are V1b receptors found and what’s their function

anterior pituitary - ACTH release (regulates CRH signaling)

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where are V2 receptors found and what are their respective functions?

basolateral membrane collecting tubule - insertion of AQP2 water channels into apical membrane, induction of AQP2 synthesis
vascular smooth muscle - vasodilation

vasopressin receptor signaling via V2 receptor

cAMP - PKA: insertion of aquaporin 2 channels on plasma membrane thorough which water can pass through

vasopressin receptor signaling via V1a and V1b receptors

V1a: vascular and uterine smooth muscle contraction or exocytosis
V1b: anterior pituitary - release of ACTH
GPCR - Gq - PLC - IP3 - increase in calcium concentration in cytoplasm

how does the regulation of osmolality work?

involves osmostat in hypothalamus

sensation of osmotic pressure
osmoreceptors most sensitive to sodium - detect osmotic changes in blood
> end result: control/conservation of water

osmolarity vs osmolality

number of solutes in 1L vs number of solutes in 1kg

which hormones regulate blood pressure and blood volume?

vasopressin, renin-angiotensin system and aldosterone

how to the osmoreceptors found in the hypothalamus detect osmotic changes in blood

via circumventricular organ OVLT

what is the normal blood osmotic pressure?

280 to 295 mOsm/kg H2o

what happens under hypotonic conditions

solute concentration inside the cell is lower than normal due to actual concentration or due to increased solvent volume

what happens under hypertonic conditions

more souls present due to actual increase or decrease in volume itself

mechanism for correction of low blood pressure by vasopressin

vasopressin from posterior pituitary acts on smooth muscle causing vasoconstriction + at kidney level, increase water retention by binding on receptors on distal tubule cells activating GPCR - cAMP pathway and insertion of aquaporins which increases blood volume => vascular constriction and increased blood volume => increased blood pressure

what is thirst and what triggers it?

defense mechanism to replace water lost through urine, respiration, and perspiration triggered by changes in osmolality/volume - usually hypovolemia [low blood volume] and decreased BP

AVP is more sensitive to ... than ....

osmolality than volume/pressure

how is oxytocin release regulated?

regulated by suckling stimulus

oxytocin regulates ... of milk under the influence of ....

ejection of milk under the influence of prolactin

oxytocin can be produced elsewhere than in pituitary, where?

ovaries (corpus luteum) - involved in luteolysis | and in uterus in some species

how is lactation/milk ejection done

secretion of oxytocin stimulated by suckling or tactile stimuli - oxytocin receptors on myoepithelial cells causing contraction when binding

other function of oxytocin

contraction of smooth muscle around uterus during parturition/birth - as pregnancy comes to an end, myometrium becomes sensitive to oxytocin as oxytocin receptor concentration increases

how is the uterus maintained relaxed during pregnancy

by progesterone and relaxin

uterine contraction by oxytocin co-occurs with ....

prostaglandin F2a

mechanism of action of oxytocin

- binds to GPCR - PLC - IP3 - cytoplasmic [calcium] increases - MLCK - smooth muscle contraction

what can high levels of oxytocin be associated with?

with more socially positive behaviour - monogamy or help female raise the young ones

what are the causes of diabetes insipidus

- lack of vasopressin - lack of response to vasopressin in kidney - receptor defect or aquaporin defect - rapid metabolism of vasopressin - pregnancy [transient diabetes insipidus]

what is diabetes insipidus

excretion of large volume of urine diabetes) that is hypotonic, dilute and tasteless (insipid)

osmotic pressure and blood volume causing vascular constriction or dilation also requires .... sensitive to pressure change

baroreceptors located in arch or aorta in carotid arteries

AVP is released after .... decrease in volume and .... decrease in pressure

8% and 5%

what is vasoconstriction

increased contraction of circular smooth muscle in the arteriolar wall, which leads to increased resistance and decreased flow through the vessel

what is vasodilation

decreased contraction of circular smooth muscle in the arteriolar wall which leads to decreased resistance and increased flow through the vessel

what causes vasoconstriction

- increased myogenic activity - increased oxygen - decreased CO2 - increases sympathetic stimulation, VASOPRESSIN, angiotensin 2. cold

what causes vasodilation

- decreased myogenic activity - decreased oxygen - increase in CO2 - decreased sympathetic stimulation, histamine release, heat