4. Posterior Pituitary and its hormones Flashcards
Where are posterior pituitary hormones synthesised?
They are synthesised in the para-ventricular nuclei (PVN) and supra-optic nuclei (SON) in the hypothalamus.
Name 2 hormones secreted from the posterior pituitary.
- Oxytocin
- ADH
Give 2 functions of oxytocin.
- Milk secretion/release
- Make smooth muscle cells around the glands in the breast - Uterine contraction during labor
Where is oxytocin stored before its release into the blood?
Herring bodies
- Small dilations at the end of the axons in the posterior pituitary
Role of oxytocin during labor
- Positive feedback cycle of cervix dilation + oxytocin release
- Periodic contraction of the muscular layer of the uterus
Role of oxytocin during breastfeeding
The Neuroendocrine reflex:
- Suckling of the breast
- Tactile receptors in the nipple respond
- Signal to hypothalamus
- Oxytocin release in pulses
- Oxytocin binds to oxytocin receptors on myoepithelial cells
- Stimulates milk ejection - in a pulsatile pumping manner
Another name of ADH
Arginine Vasopressin = AVP = ADH
State 3 functions of ADH.
- Prevents making too much urine
- Vasoconstriction
- Increases blood pressure
Where is ADH produced in the posterior pituitary?
Supraoptic nuclei in the anterior hypothalamus
Where is ADH stored before its release into the blood?
Herring bodies
- Small dilations at the end of the axons in the posterior pituitary
Name 3 ways in which ADH release is stimulated.
- Osmoreceptors in the SON in the anterior hypothalamus
(day to day) - Baroreceptors in the CVS
(in emergency) - Angiotensin II
What are the units for osmolality?
mOsmol/Kg.
What is the primary cation in ICF?
K+.
What is the primary cation in the ECF?
Na+.
what are the primary anions in the ECF?
Cl- and HCO3-.
Describe the ADH pathway.
- Osmoreceptors in the SON in the anterior hypothalamus sense changes in blood osmolarity
- High blood osmolarity -> H2O moves out of these cells by osmosis via AQP-4 -> causing these cells to shrink
- Osmoreceptors fire more APs
- Signals the hypothalamus to trigger:
1) The thirst response (get some water!)
2) ADH production - ADH release from posterior pituitary
- ADH acts on vasopressin receptor 2 (AVPR2) on the basolateral membrane of the principal cells of the DCT + collecting ducts of the nephrons in the kidneys
- Binding of ADH + AVPR2 -> cAMP production
- Increased cAMP causes:
1) More AQP-2 produced
2) Already-made AQP-2 in vesicles fuse with apical membrane - Allows H2O to move from the lumen of the tubules to the interstitium and back into circulation
- Returns plasma osmolarity to a normal level
Role of the kidneys in ADH production
↓↓ blood pressure
↓
Angiotensinogen
↓ Renin
Angiotensin I
↓ ACE
Angiotensin II
↓
Stimulates hypothalamus to produce more ADH
↓
ADH production:
1) Acts on V1 receptors on smooth muscle cells
- Vasoconstriction of arterioles
2) Acts on V2 receptors on principle cells in DCT + collecting duct
- Increased no. of AQP2 -> Reabsorption of H2O from the urine
↓
↑↑ blood pressure
