Endocrinology 4- Posterior Pituitary and HPL Axis

Question 1

what part of the pituitary are ADH/AVP and oxytocin released from

Answer 1

posterior

Question 2

What kind of pituitary cells are avp/adh and oxytocin released from

Answer 2

the modified neurons branching from the hypothalams (neurohypophysial tract)

Question 3

What kinds of hormones are AVP and Oxytocin

Answer 3

Peptide hormones

Question 4

How are all peptide hormones structured at first?

Answer 4

They are preprohormones (signal + copeptides hormones)

Question 5

What neurophysin is packaged with AVP

Answer 5

II

Question 6

What neurophysin is pckaged with Oxytocin

Answer 6

I

Question 7

Where are the cell bodies for the posterior pituitary gland

Answer 7

Paraventricular nucleus and supraoptic nucleus (PVN and SON)

Question 8

What are the hypothalamic cells that project to both anterior and posterior pituiary and what is the hormone they release

Answer 8

PVN; AVP

Question 9

Of the AVP that is released from median eminance and posterior pituitary which is the side that regulates body osmolarity

Answer 9

The posterior pituiary ones

Question 10

Roles of AVP

Answer 10

Osmolarity

Stress response

Question 11

How is AVP going to be released? What is the signal?

Answer 11

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

Question 12

Targets of AVP

Answer 12

Vasculature

Kidney

Question 13

How does AVP target vasculature

Answer 13

V1 receptor on smooth muscle cells, binds quickly and causes contraction of vasculature which increases vascular resistance and thus blood pressure

Question 14

How does AVP affect the kidney

Answer 14

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

Question 15

Diabetes insipidus 2 main etiologies

Answer 15

Decreased AVP release and decreased renal responsiveness to AVP

Question 16

What is the most common reason for diabetes insipidus

Answer 16

Decreased AVP release - this is a hypothalamic or pituitary defect “central” due to trauma, cancer, or infectious disease

Question 17

What are peripheral reasons for diabetes insipidus?

Answer 17

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

Question 18

why are AVP levels normal or slightly elevated in acquired diabetes insipidus

Answer 18

Body isn’t responding to normal AVP –> make more

Question 19

Clinical presentation of diabetes insipidus

Answer 19

Polyuria, polydipsia, hypernatremia, and NO GLuCoSE IN URINE

Question 20

If a patient is suspected to have diabetes insipidus but has normal AVP what might this mean

Answer 20

Nephrogenic diabetes insipidus

Question 21

If a pt is thought to have diabetes insipidus but has low AVP what might this mean

Answer 21

Central diabetes insipidus

Question 22

How can you test to determine if someone has central or peripheral diabetes insipidus

Answer 22

Artificially alter osmolality with a saline injection and measure AVP response

Question 23

SIADH

Answer 23

Syndrome of inappropriate ADH

Question 24

Primary clinical presentation of SIADH

Answer 24

Hyponatremia (low sodium in plasma), but no edema

Question 25

Etiology of SIADH

Answer 25

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

Question 26

Are most sIADH cases central (pituitary)

Answer 26

no

Question 27

What does oxytocin do to smooth muscles

Answer 27

make them contract like AVP

Question 28

What is special about oxytocin (what kind of cycle is it involved in)

Answer 28

positive feedback loops with breastfeeding and yeeting baby at end of pregnancy

Question 29

Parturition and oxytocin

Answer 29

Contraction of baby –> more oxytocin –> go more until baby is out

Question 30

Suckling and oxytocin

Answer 30

suckling –> oxytocin–> milk ejection –> suckling –> oxytocin –> milk ejection –>

(repeat until baby leaves)

Question 31

Where is growth hormone release hormone made?

Answer 31

arcuate nucleus