Endocrinology 4- Posterior Pituitary and HPL Axis Flashcards
what part of the pituitary are ADH/AVP and oxytocin released from
posterior
What kind of pituitary cells are avp/adh and oxytocin released from
the modified neurons branching from the hypothalams (neurohypophysial tract)
What kinds of hormones are AVP and Oxytocin
Peptide hormones
How are all peptide hormones structured at first?
They are preprohormones (signal + copeptides hormones)
What neurophysin is packaged with AVP
II
What neurophysin is pckaged with Oxytocin
I
Where are the cell bodies for the posterior pituitary gland
Paraventricular nucleus and supraoptic nucleus (PVN and SON)
What are the hypothalamic cells that project to both anterior and posterior pituiary and what is the hormone they release
PVN; AVP
Of the AVP that is released from median eminance and posterior pituitary which is the side that regulates body osmolarity
The posterior pituiary ones
Roles of AVP
Osmolarity
Stress response
How is AVP going to be released? What is the signal?
Released from docked points at end of neuron - as osmolarity grows, ICF is drawn out into blood - this shrinks osoreceptor neurons and relieves inhibitory input to AVP neurons, because axons of inhibitory neurons are literally pulled away by shrinking.
Therefore –
Mean arterial pressure drops –> decreases stretch response on baroreceptors –> increased sympathetic tone increases sensitivity and moves curve to left – you need a hemorrhage for this to happen –> avp targets kidney, you get increased water absorption and rescue of blood pressure
Targets of AVP
Vasculature
Kidney
How does AVP target vasculature
V1 receptor on smooth muscle cells, binds quickly and causes contraction of vasculature which increases vascular resistance and thus blood pressure
How does AVP affect the kidney
Binds to V2 receptor (specific receptor to kidney) – AVP binds, and inroduces intracellular signaling cascade. phosphorylates Aquaporin 2 channels and lets it move to lumenal side so this can let water cme through and passively go out into basalateral membrane (so we reabsorb water) – this will retain blood and thus increase blood pressure
Diabetes insipidus 2 main etiologies
Decreased AVP release and decreased renal responsiveness to AVP
What is the most common reason for diabetes insipidus
Decreased AVP release - this is a hypothalamic or pituitary defect “central” due to trauma, cancer, or infectious disease
What are peripheral reasons for diabetes insipidus?
Decreased renal responsiveness to avp such as a genetic x linked mutation in AVP receptor type 2, or Acquired decreased renal responsivness due to lithium treatment or hypokalemia. In this case, AVP levels are normal or slightly elevated
why are AVP levels normal or slightly elevated in acquired diabetes insipidus
Body isn’t responding to normal AVP –> make more
Clinical presentation of diabetes insipidus
Polyuria, polydipsia, hypernatremia, and NO GLuCoSE IN URINE
If a patient is suspected to have diabetes insipidus but has normal AVP what might this mean
Nephrogenic diabetes insipidus
If a pt is thought to have diabetes insipidus but has low AVP what might this mean
Central diabetes insipidus
How can you test to determine if someone has central or peripheral diabetes insipidus
Artificially alter osmolality with a saline injection and measure AVP response
SIADH
Syndrome of inappropriate ADH
Primary clinical presentation of SIADH
Hyponatremia (low sodium in plasma), but no edema
Etiology of SIADH
Central (pituitary)
CNS disorders (lesions, infections, trauma)
lung disease (infections)
extrapituitary tumors that secreteAVP
Aldosterone deficiency (which will cause low blood volume and trigger AVP release despite low plasma osmolarity
Are most sIADH cases central (pituitary)
no
What does oxytocin do to smooth muscles
make them contract like AVP
What is special about oxytocin (what kind of cycle is it involved in)
positive feedback loops with breastfeeding and yeeting baby at end of pregnancy
Parturition and oxytocin
Contraction of baby –> more oxytocin –> go more until baby is out
Suckling and oxytocin
suckling –> oxytocin–> milk ejection –> suckling –> oxytocin –> milk ejection –>
(repeat until baby leaves)
Where is growth hormone release hormone made?
arcuate nucleus
