Renal Physiology

Question 1

Where is K+ reabsorbed most?

Where is it secreted?

Answer 1

Proximal tubules
65%

Secreted in distal tubules and collecting ducts

Question 2

Where is glucose removed?

Answer 2

100% glucose removed by active transport in the proximal tubule

Question 3

In the presence of hypokalaemia and metabolic alkalosis, which of K+ or H+ are retained by the kidneys and why?

Answer 3

K+ retained, H+ wasted

Question 4

In the presence of hyponatraemia, how is Na retained?

Answer 4

Retained for K+ secretion in collecting ducts

Question 5

What are the 3 renal changes associated with severe haemorrhage?

Answer 5

1. Efferent and afferent arteriole constriction
2. Enhanced filtration fractino
3. Enhanced Na retention by tubules

Question 6

What are the 3 factors that control renin secretion?

What are some triggers that increase renin secretion?

Answer 6

1. Intrarenal baroreceptors acting on the macula densa
2. Prostaglandins
3. Na content of proximal/distal tubular fluid

• decrease in ECF or Na + depletion
• Decrease in BP
• Increase in sympathetic output
• increase in prostaglandins

Question 7

What are some factors that decrease renin secretion?

Answer 7

• increased Na and Cl reabsorption across macula densa
• increased afferent arteriolar pressure
• angiotensin II (via feedback)
• vasopressin

Question 8

What are the 5 extra-renal and 3 renal effects of angiotensin II?

Answer 8

EXTRARENAL
1. Vasoconstriction
2. Aldosterone secretion from adrenal cortex
3. Decreases sensitivity of brain to baroreceptor reflex
4. Acts on circumventricular organs of brain to ↑water intake and ↑secretion of ADH release from area postrema, increases thirst from the subfornical organ and OVLT
5. NA release from sympathetic neurons
DOES NOT CROSS BLOOD BRAIN BARRIER

RENAL

1. Increases Na reabsorption
2. Efferent and Afferent arteriolar constriction
3. Constriction of mesangial cells
   - looking to decrease GFR to increase time for Na reabsorption

Question 9

What is the mechanism of action of aldosterone?

Answer 9

• Acts on P cells in the distal tubule and collecting duct to increase Na reabsorption in exchange for K and H
• increases luminal Na channels
• increases synthesis and insertion of Na/K ATPase in basolateral membrane
• works on epithelium of salivary duct, sweat glands, small/large intestine and rectum to reabsorb Na

Question 10

What is the mechanism of action of loop diuretics?

Answer 10

Inhibit Na-K-2CL cotransporter in thick ascending loop of Henle

Question 11

What is the mechanism of action of thiazide diuretics?

Answer 11

Inhibit Na-Cl co-transporter in distal tubule

Question 12

What is the mechanism of action of potassium sparing diuretics?

Answer 12

Inhibit Na-K exchange in the collecting duct

By inhibiting the action of aldosterone or blocking ENaCs

Question 13

What are the key differences between renal blood flow and GFR?

Answer 13

RBF: how much blood goes into renal arteries from aorta (affected by BP)

GFR: how much is filtered into tubules (depends on other factors)

Increasing RBF increases glomerular filtration because of the increase in glomerula pressure

Question 14

What is the result of sympathetic activation to renal vessels? (2 actions)

Answer 14

1. Arteriolar vasconstriction

2. Renin release: increase circulating ANGII to intensify vasoconstriction

Question 15

What is the renorenal reflex?

Answer 15

Increase in ureteral pressure in one kidney leads to a decrease in efferent sympathetic nerve activity to the contralateral kidney –> increase in excretion of Na+ and Water

Question 16

What is the mechanism by which the macula densa senses sodium and exerts its effect on eGFR?

Answer 16

senses the Na+ and Cl- via the NaK2Cl cotransporter

• ->Increase in Na sensation increases the Na/K ATPase activity
• -> more adenosine formation, secreted from basal membrane of cells
• -> acts via adenosine receptors on macula densa cells
• -> increase release of Ca to vascular smooth muscle in afferent arterioles
• -> vasoconstriction
• -> decrease in GFR

Question 17

What are the key transport mechanisms involved in maintaining the countercurrent mechanism?

Answer 17

• high permeability of the thin descending loop to water due to aquaporins
• Na/Cl pumps in the thick ascending limb pumping solutes into the interstitium
• the relative impermeability of the thin ascending limb to water

Question 18

Describe how the following are excreted, filtered and reabsorbed?

• inulin
• glucose
• Para-amino-hippurate
• urea
• water

Answer 18

inulin: excreted as filtered
glucose: reabsorbed
PAH: completely secreted in proximal tubules
urea: filtered and partially reabsorbed
water: ~60% reabsorbed

Question 19

What is the key difference between water diuresis and osmotic diuresis?

Answer 19

1. in water diuresis amount of water reabsorbed in proximal tubule is normal, & maximal urine flow that can be produced is
   16ml/min
2. in osmotic diuresis, increased urine flow is due to decreased water reabsorption in proximal tubules & loops thus very large
   urine flows can be produced

Question 20

What percentage of body weight is total body water? How much is intracellular vs extracellular?

Answer 20

60-70% of body weight is total body water

40% ICF
20% ECF
- of this 25% vascular (5% body weight), 75% interstitial (15% body weight)

Question 21

What percentage of total body potassium is exchangeable?

What percentage of total body sodium is exchangeable?

Answer 21

90% of potassium

70% sodium

Question 22

Which of the following has a higher concentration in plasma, which in interstitial fluid?
Na
Mg
Protein
Chloride

Answer 22

Na, Mg and protein higher intravascular
Chloride higher in interstitium

Chloride used to balance out negative charge of anionic protein held inside vasculature : Gibbs Donnan effect