Physiology 6- control of body fluid volume and osmolarity

Question 1

What is ADH secretion from the hypothalamus stimulated by?

Answer 1

Water deficit (i.e. ECF is too concentrated/hypertonic)

Question 2

What other stimulus can lead to ADH secretion and why is this less important than hypothalamic stimulatory mechanisms?

Answer 2

Activation of left atrial stretch receptors (due to low blood volume)- requires very large changes in blood volume

Question 3

How is the amount of sodium that is a) filtered and b) reabsorbed controlled?

Answer 3

a) regulation of glomerular filtration rate- e.g. fall in sodium leads to fall in blood pressure; activation of sympathetic system leads to constriction of the afferent arteriole, causing decreased GFR b) renin-angiotensin-aldosterone system

Question 4

What is aldosterobe secreted in response to?

Answer 4

Falling Na/ rising K in the ECF Activation of the RAAS

Question 5

What are the three stimuli for the secretion of renin from the juxtaglomerular apparatus?

Answer 5

1. Decreased pressure in the afferent arteriole 2. Decreased NaCl concentration in the blood (macula densa cells) 3. Sympathetic innervation of the JGA (as a result of reduced MABP)

Question 6

What is thought to cause the salt and water retention seen in heart failure patients?

Answer 6

Inappropriate RAAS activation due to falling CO and MABP

Question 7

What is ANP released in response to, and what are it’s effects?

Answer 7

Increased fluid volume within the heart; causes excretion of sodium and thus water Also- causes arteriolar dilatation and inhibits the sympathetic nervous system

Question 8

Answer 8

Question 9

Answer 9