Posterior Pituitary Flashcards
What nuclei in the posterior pituitary are responsible for which hormones?
Supraoptic -> ADH
Paraventricular -> OT
What is the structure of pituitary hormones?
Nonapeptide (9AA) -> forms ring with disulfide bridge
Functions of oxytocin: (3)
contract smooth muscle cells:
- myoepithelial cells of alveoli (milk letdown)
- uterus contraction during labor/menstruation
- emotional effects? (love, bonding)
ADH functions (2):
water retention by kidney
blood vessel contraction
What are alternative names for ADH?
vasopressin/arginine vasopressin
What 2 systems/balances does arginine vasopressin regulate?
osmotic balance
pressure-volume
What receptors are associated with vasopressin, and what are the downstream functions?
V1a -> constrict/contract
V1b -> ACTH release
V2 -> synth/insert AQP2 to resorb more water in kidneys
What tissues have V1a receptors?
vasc. smooth muscle
platelets
hepatocytes
myometrium
What tissue has V1b receptors?
anterior pituitary
What tissues have V2 receptors?
basolateral membrane collecting tubule (renal system)
vasc. endothelium
vasc. smooth muscle
True/False: Vasopressin can cause either vasoconstriction or vasodilation, depending on the receptor type
True; V1a can cause constriction; V2 causes dilation
What is the detection system for osmolarity? How does it work?
osmostat; cells swell/shrink in response to tonicity of surrounding fluid
What is the basic mechanisms of the body to control osmolarity? (2)
control water levels (conserve or excrete more)
regulate Na plasma levels
What is the detection system for Na concentration in plasma? What system regulates it?
pressure-volume (baroreceptors)
renin-angiotensin system/aldosterone (complicated)
describe how osmotic changes trigger the osmostat cells:
changes 1% or more will trigger:
too dilute -> cell expands in hypotonic fluid -> no vasopressin
too concentrated -> cell contracts -> stretch cytoskeleton and pulls on membrane protein to affect potential (signal neurons to make VP)
When the body is in a hypertonic state, ____ intake will increase, ____ intake will decrease, ____ retention will increase, and ____ excretion increases.
water
Na
water
Na
If there is no vasopressin, what type of urine is produced?
very dilute
Give an example of a osmoreceptor:
VR-OAC (vanilloid receptor-related osmotically activated channel)
How does the stretch/shrink of the osmoreceptor cause downstream signalling?
membrane signal proteins linked to cytoskeleton; shrink/stretch will stretch cytoskeleton and ‘pull’ on membrane protein to affect membrane potential -> sends signal
What hormone corrects low blood pressure?
ADH (vasopressin)
What factors stimulate vasopressin? (4)
Angiotensin II
hyperosmolarity
decreased atrial receptor firing
sympathetic stimulation
How does vasopressin achieve increased arterial pressure? (2)
water retention (greater blood volume) vasoconstriction
Describe the path of water in renal filtration/urine formation
- enter through afferent arteriole
- bowman’s capsule (filtered through) -> glomerulus
- proximal tubule
- some re-enters bloodstream (peritubular capillaries); some keeps going to distal tubule/collecting duct (exits body)
Insertion of more _____ channels allows for water to re-enter the ____ from the ____.
AQP2
bloodstream
proximal tubule
Vasopressin uses a ____ receptor
GPRC - cAMP
What happens to the water channels when the vasopressin signal stops?
endocytosis; brought inside cell
What is the difference beteween AQP2 and AQP3?
AQP2 is vasopressin dependent (allow for fluid to pass into tubular cell membrane)
AQP3 always present (allows fluid to pass from cell back into blood)
Why is vasopressin also known as ADH?
due to its ‘antidiuresis’ function (produce concentrated urine and decrease urine output)
What are unavoidable routes of water loss? (2)
urine production (remove catabolites, metabolites, toxic substances)
insensible loss (sweat, breathing, etc)
What is the purpose of thirst? What are its triggers? (2)
defense mechanism against dehydration
caused by changes in osmolarity or volume
True/False: Thirst plays the largest role in regulating fluid levels
False; usually changes in osmolarity too small to trigger thirst
(regulated by water excretion)
What happens to body fluid levels in pregnancy, and why?
total body water increases 7-8L
osmostat is reset (‘normal’ range is increased) because fetus needs expanded fluid volume for growth - causes vasodilation + vasopressin action
Vasopressin levels may drop in week _______ of pregnancy. Why?
week 20-40
placenta make VASOPRESSINASE (to break down oxytocin, prevent uterine contraction)
What does excessive vasopressinase action cause?
diabetes insipidus
too little vasopressin, large volumes of water in urine
In pregnancy, the osmostat becomes (more/less) sensitive
less
By age 80, body water declines to ____ of a young adult. Why? (3)
50%
decreased kidney filtration rate, collecting duct less responsive to vasopressin, decreased dehydration response
Are elderly people susceptible to hypo or hypernatremia? why?
Both
aged system -> less responsive
Plasma osmolarity vs vasopressin levels follows a ____ relationship
linear
what is the normal physiological range of vasopressin? What happens above this range?
0.5-6pg/mL
urine osmolarity is at maximum, urine volume is at minimum (cannot change any further); but thirst will keep increasing (UNTIL YOU DIE lol)
Increased VP will increase ___ and ____, and decrease ____
thirst; urine osmolarity
urine volume
the ‘detection systems’ for controlling vasopressin release and fluid balance are located where?
osmolarity: hypothalmic osmoreceptors
pressure: left atrial volume receptors
What is the effect of alcohol on the vasopressin system?
osmoreceptors become less responsive -> less VP produced -> increased water loss -> dehydration
What is diabetes insipidus, and what are possible causes? (4)
excreting large volume of urine that is hypotonic, dilute, tasteless
- lack of VP (tumour, trauma)
- lack of VP response in kidney (receptor defect, AQP2 defect)
- VP broken down (pregnancy)
- polydipsia (drink too much water)
How is the cause of diabetes insipidus determined?
water deprivation test (to see if polydipsic)
If not, then inject with VP and see if they respond
arterial baroreceptors are located in the ____ and _____
carotid sinus
aortic arch
What is vasoconstriction
contraction of circular smooth muscle in arteriolar wall (increases resistance, decreased flow, increased pressure)
Vasopressin is released in response to a ___ decrease in volume or a ____ decrease in pressure
8%
5%
What can stimulate vasoconstriction? (5)
myogenic activity more oxygen less CO2/other metabolites sympathetic stimulation (VP, Angiotensin II) cold
What can stimulate vasodilation? (6)
less myogenic activity low O2 increased CO2/metabolites less stimulation (VP) histamine heat
Where is oxytocin synthesized in the body?
post. pit.
ovaries (corpus luteum)
*also uterus in some species
What is a stimulus that can regulate oxytocin?
suckling action (tactile response; regulated by CNS)
main functions of oxytocin:
lactation (milk let down) uterine smooth muscle contraction (birth) Affect CNS (love? bonding?) reproductive cycle (luteolysis)
What is stimulated by oxytocin for the lactation process? (2)
glandular cells in mammary alveoli (release)
myoepithelial layers in mamm. ducts (contraction)
What happens to the uterine myometrium during pregnancy? What factors control it?
relaxed during preg. (progesterone from placenta & CL, relaxin from cervix)
What changes happen to the uterine myometrium as parturition approaches?
becomes responsive to oxytocin (receptors increase)
form gap junctions (for synchronized contraction)
The main 2 hormones necessary for uterine contraction in birth:
oxytocin, prostaglandin F2
How does oxytocin function during labor?
bursts of OT secretion (pulsatile); triggered by Fergusson reflex (cervix/vagina dilation)
The oxytocin release reponse during birth is a form of ____ feedback
positive
increased stretch will feedback to cause more release
What causes changes in oxytocin responsiveness postpartum?
changes in steroid hormones during birth
increased Estradiol, decreased progesterone
What is luteolysis?
breakdown of CL if no fertilization occurs
What type of receptor is stimulated by oxytocin for luteolysis?
GPCR (Gq pathway)
What evidence suggests that oxytocin is involved in ‘bonding’ and love?
big flush of OT at birth (maternal bonding)
higher amounts of OT receptors in brains of mammals that mate for life
How might oxytocin be used therapeutically?
Can reduce stress/anxiety, improve social behaviour - part of anxiety treatment possibly?
True/False: sexual intercourse can stimulate OT release
true
