The Posterior Pituatory Gland

Question 1

Two main nuclei in the posterior pituitary

Answer 1

Paraventricular nucleus

Supraoptic nucleus

Question 2

Two hormones produced in the hypothalamus

Answer 2

Vasopressin and oxytocin

Travel to terminals and are released from here

Question 3

Vasopressin

Answer 3

Antidiuretic hormone – controls water secretion into urine

Primarily from supraoptic nuclei

Peptide hormone

Plasma binding protein

Life is 5-10 mins

Neurophysin II (nicotine stimulated)

Question 4

Oxytocin

Answer 4

expression of milk from the glands of the breasts to the nipples; promotes onset of labour

Primarily from paraventricular nuclei

Peptide hormone

5-10 mins lifetime

Neurophysin I- oestrogen stimulated

Question 5

Production, transport and secretion of vasopressin

Answer 5

On slide

Question 6

Regulating water balance

Answer 6

Water is ingested so fluids in body are diluted, reducing plasma osmolality
This causes increase in cellular hydration
So body feels that it doesn’t need to drink anymore so thirst decreases
No need for vasopressin so this decreases
So water intake decreases
As vasopressin is not being secreted anymore, more fluids are gonna be secreted in the kidneys (increase in renal water excretion)
This is the action of ADH, vasopressin

Opposite in low water levels

Question 7

Graph

Answer 7

As plasma osmolality increases, AVP goes up

As AVP goes up, more water is reabsorbed from kidneys and the urine osmolality is going to go up As all the water from urine is being removed, so concentrated urine produced

Question 8

Where does vasopressin act?

Answer 8

Collecting tubule of the nephron

Question 9

Vasopressin: mechanism of action

Answer 9

Vasopressin is secreted and travels to the collecting tubule where it binds to the membrane receptor

Receptor (V2) activates cAMP second messenger system

CAMP causes ACP2 water receptors to be produced
Cell inserts ACP2 water pores into apical membrane

Water is reabsorbed by osmosis into the blood

On slide

Question 10

Vasopressin receptors

Answer 10

Table

Question 11

Osmoreceptors and Baroreceptors regulate ADH release

Answer 11

Vasopressin reaches the kidney in two ways: osmoreceptors and baroreceptors

Question 12

Osmoreceptors

Answer 12

Detect the change in osmolality

Found in the hypothalamus

Question 13

Baroreceptors

Answer 13

These detect changes in pressure in the vascular system- eg when in shock

This also stimulates ADH release

Found in the carotid sinus or aortic arch

When you’re in shock AVP (vasopressin) is released so you retain as much fluid as possible, as don’t wanna lose anymore fluids when in shock

Slide 20

Question 14

Interplay between AVP and salt and water physiology

Answer 14

If blood volume goes down, central venous pressure goes down
Atrial detects this which then influences how much Na and fluids are being excreted
ADH will then not be secreted

When blood vol goes down, ADH will be secreted

Question 15

Dehydration

Answer 15

Slide 22

Question 16

What is osmolality?

Answer 16

Concentration of particles per kilo of fluid

size of particle not important, number is important - i.e one molecule of larger protein albumin same effect as Na+

sodium, potassium, chloride, bicarbonate, urea and glucose present at high enough concentrations to affect osmolality

alcohol, methanol, polyethylene glycol or mannitol-
exogenous solutes that may affect osmolality

Question 17

Plasma osmolality can be approx calculated

Answer 17

Slide 23

Question 18

Osmotic control of AVP release

Answer 18

AVP is released at a threshold

As osmolality increases, AVP is released

Question 19

Relationship of plasma AVP concentration and urine concentration

Answer 19

The more vasopressin is secreted, the more concentration of the urine osmolality because water is being absorbed from the kidneys

Same thing happens in correlation with thirst

Question 20

Loss of relationship between plasma osmolality and vasopressin

Answer 20

Drinking rapidly suppresses vasopressin release and thirst.

In pregnancy osmotic threshold for VP release and thirst is decreased.

Plasma VP concentrations increase with age (also thirst blunting, decreased renal concentrating ability, decreased fluid intake).