Lecture 22: Homeostasis

Question 1

A good sensor for osmotic signal

Answer 1

Lamina terminalis, in particular the OVLT and SFO

Question 2

How do OVLT and SFO cells react to osmolality?

Answer 2

Stretch receptors on these cells are linked to the intracellular scaffold proteins such that a change in volume changes conductance

Question 3

What happens if OVLT neurons sense increased ECF osmolality?

Answer 3

Stretch receptors on the OVLT and SOF cells are linked to the intracellular scaffold proteins such that a change in volume changes conductance.
OVLT neurons increase their action potential firing in response to increased ECF osmolality.
↑ ECF osmolality - water leaves the cell, cell shrinks. Stretch receptors activity increases, causing a change in the scaffold proteins which cause a sodium channel to open (↑conductance) and the neurons fire.

Question 4

Mechanism of vasopressin

Answer 4

Vasopressin circulates in the blood
V2 metabotropic receptor located on the collecting ducts of the kidney
When vasopressin binds, the trimeric g protein assembles
Gαs interacts with adenylyl cyclase to stimulate the production of cGMP
The production of cGMP leads to a chain of intracellular events which lead to the increased production and insertion of aquaporins into the cell membrane of the collecting ducts
AQP are water channel pores, increase ability of water to cross from the lumen (urine) through the cell and out into the blood

Question 5

How do OVLT affect vasopressin release?

Answer 5

Vasopressinergic magnocellular neurons in the hypothalamus receive an input from the osmosensitive neurons in the OVLT that then regulate vasopressin secretion to maintain constant osmolality