Regulation of ECF Volume - Pt 2

Question 1

What does aldosterone promote?

Answer 1

Na+ reabsorption

Question 2

What does atrial natriuretic peptide (ANP) promote?

Answer 2

Na+ excretion

Question 3

What happens if aldosterone is given to normal subject on adequate Na diet?

Answer 3

There will be Na retention and K loss
Weight gain of 2-3kg due to Na and H2O retention
After a couple days - spontaneous diuresis occurs secondary to volume expansion although K loss persists

Question 4

Where does aldosterone cause Na reabsorption and K secretion?

Answer 4

Both at distal tubule

Question 5

What does retention of water and Na cause?

Answer 5

Volume expansion and stimulation of ANP from atrial cells

Question 6

What does stimulation of ANP from atrial cells cause?

Answer 6

Loss of Na and H2O - natriuresis
Can inhibit secretion of renin, and generally opposes the actions of angiotensin II

Question 7

Why does ANP override aldosterone on Na reabsorption?

Answer 7

Volume expansion - aldosterone escape

Question 8

What is ANP secreted by atrial cells in response to?

Answer 8

Expansion of ECF volume

Question 9

Where do natriuretic peptides act on and effects?

Answer 9

Hypothalamus - less vasopressin
Kidneys - increased GFR and decreased renin
Adrenal cortex - less aldosterone
Medulla oblongata - decreased BP

Question 10

What happens in uncontrolled DM where BG conc. levels not in control?

Answer 10

High plasma glucose level exceeds max. absorptive capacity in proximal tubule - glucose remains in tubule and exerts osmotic effects to retain H2O

Question 11

What happens when H2O is retained in the proximal tubule?

Answer 11

Na conc. in lumen is decreased as Na is present in larger volume
Na reabsorption is decreased

Question 12

How does Na gain access to proximal tubule cells?

Answer 12

Passive diffusion down a conc. gradient created by active transport out of basolateral surfaces

Question 13

What is decreased Na reabsorption effect on glucose reabsorption?

Answer 13

Decreased as shares the same symport as Na

Question 14

What happens in descending limb of Henle if excess glucose and Na?

Answer 14

Reduced movement of H2O into interstitium as osmotic effect to retain H2O
Fluid is then not as concentrated

Question 15

What does less concentrated fluid in the ascending limb lead to?

Answer 15

NaCl pumps are gradient limited so medullary interstitium is much less - reduction in H2O and NaCl reabsorbed in loop of Henle

Question 16

What happens to the interstitial gradient in loop of Henle during uncontrolled DM?

Answer 16

Gradually abolished
Then large volume of NaCl and H2O delivered to distal tubule

Question 17

Under normal conditions, what does a large volume of NaCl and H2O delivered to distal tubule mean?

Answer 17

Excess ECF volumes and therefore need to get rid of NaCl and H2O

Question 18

What happens when macula densa detects high rate of delivery of NaCl?

Answer 18

Renin secretion will be suppressed and Na reabsorption at distal tubule will be decreased
So normal response accelerates the uncontrolled DM problem

Question 19

What is normal reabsorption of NaCl and H2O in renal tubule?

Answer 19

65-75% NaCl and H2O reabsorbed in proximal tubule
15-20% in loop of Henle
5-20% from distal tubule to collecting duct

Question 20

What is the osmotic diuresis of uncontrolled DM?

Answer 20

Decreased reabsorption of NaCl and H2O in proximal tubule, loop of Henle, and distal tubule
Wrecks interstitial gradient so decreased ability of ADH to conserve H2O
So excrete 6-8l of urine a day

Question 21

What can osmotic diuresis lead to?

Answer 21

Hypovolaemia

Question 22

What happens when a large isotonic urine amount is excreted?

Answer 22

Decreased plasma volume
Which stimulates ADH release via baroreceptors but not effective

Question 23

Why is ADH not effective in uncontrolled DM?

Answer 23

Interstitial gradient has run down

Question 24

What are the results of uncontrolled DM?

Answer 24

Severe salt and water depletion
Raging thirst
Then hypotension can lead to hyperglycaemic coma

Question 25

What cause a hyperglycaemic coma?

Answer 25

Inadequate BF to brain

Question 26

What can any solute in tubule lead to?

Answer 26

Osmotic diuresis - NaCl or urea

Question 27

What does the active transport mechanism that operates on luminal surface of think ascending loop of Henle?

Answer 27

K+ ions as well as NaCl
Na+-K+-2Cl- co transporter

Question 28

What can loop diuretics also cause?

Answer 28

K+ ion wasting