Integration of salt and water

Question 1

ECV detection

Answer 1

Cardiovascular, baroreceptors, stretch receptors

Renal: macula densa, senses NaCl reabsorption

Question 2

Stimulation for renin release

Answer 2

Increases SNS

Decreased distal flow

Question 3

Juxtaglomerular apparatus

Answer 3

Macula densa situated between afferent and efferent arterioles
Ring of cells in the TAL

Question 4

Renin

Answer 4

Release by cells of afferent arteriole, enzyme that causes sodium retention by kidneys and fluid expansion
Decrease: increased delivery of Cl-, increased GFR; ATP/ adenosine; expansion of afferent
Increase: increases sympathetic nerve activity, decrease in ECV

Question 5

Renin-angiotensin-aldosterone

Answer 5

Renin is a protease, released when ECV falls
Conversion of angiotensin from liver -> angiotensin I
Converted to angiotensin II in lungs
Angiotensin II (active hormone) acts on hypothalamus to increase ADH release, thirst,
- stimulate adrenal glands to release aldosterone (increases Na absorption)
Increases water reabsorption

Question 6

Angiotensin II action (5 main)

Answer 6

Causes aldosterone release from adrenal cortex which:

Arteriolar vasoconstrictor: (efferent>afferent), increases GFR

PCT: stimulates NHE, more H+ into lumen and more NaCl and bicarb absorbed

• also heightened sensitivity of the macula densa to flow rate
• stimulates thirst and ADH release

Question 7

Effects of volume expansion

Answer 7

Less renin release
More ANP
Increase cellular cGMP
Vasodilation, more GFR, less reabsorption so more water excreted

Question 8

control of osmolarity

Answer 8

blood osmotic potential detected by osmoreceptors in hypothalamus
more ADH release, synthesised in hypothalamus and secreted from posterior pituitary
- increased water potential

Question 9

other ADH actions

Answer 9

stimulate NKCC on TAL
vasoconstrictor, especially efferent arteriole
activates urea carriers in CD

Question 10

ECV

Answer 10

volume of plasma circulating in tissues 
detected by volume sensors 
cardio = altered sympathetic discharge 
baro = carotid sinus, aortic arch 
stretch = atria/pulmonary circulation
pressure receptors in renal afferent arterioles

Question 11

aldosterone antagonists

Answer 11

spironolactone

decreases na+ reabsorption

Question 12

aldosterone action

Answer 12

• Stimulates Na+ reabsorption
• acts at principle cells in collecting duct
• steroid hormone
• Increases sympathetic activity
• Increase Na+/Cl- reabsorption and K+ excretion
• H2O retention