Renal System (Test 3)

Question 1

How does the renin-angiotensin system regulate aldosterone secretion?

Answer 1

When blood volume is low, juxtaglomerular cells in the kidneys secrete renin directly into circulation. Plasma renin then carries out the conversion of angiotensinogen released by the liver to angiotensin I. Angiotensin I is subsequently converted to angiotensin II. Angiotensin II stimulates the secretion of aldosterone from the adrenal cortex

Question 2

What is the renal clearance of a substance (X) that is filtered and secreted but not reabsorbed equivalent to? Example?

Answer 2

Renal plasma flow. Para aminohippurate (PAH)

Question 3

What factors are primarily responsible for the whole kidney phenomenon of renal autoregulation?

Answer 3

The intrinsic myogenic response of preglomerular arterioles and the tubuloglomerular feedback mechanism

Question 4

What is the renal clearance of a substance (X) that is filtered but not secreted or reabsorbed equivalent to?

Answer 4

Glomerular filtration rate (GFR). Creatinine is filtered but not secreted or reabsorbed

Question 5

How do you calculate GFR from creatinine clearance?

Answer 5

GFR = Clearance of creatinine = (urine creatinine concentration X urine flow rate)/plasma creatinine concentration

Question 6

What is the effect of angiotensin II on the renal vascular resistance?

Answer 6

Increase

Question 7

The following data were obtained in order to assess renal function in a patient weighing 70kg and diagnosed with hypertension (150/95 mm Hg). The subject was adequately hydrated to increase urine flow. What are his GFR and filtration fraction? The normal GFR in both kidneys in adults is 120 mL/min. The filtration fraction is normally about 20%.

• plasma inulin- .2mg/ml
• urine inulin- 8mg/ml
• plasma PAH .04 mg/ml
• urine PAH 6mg/ml
• urine flow 1.5ml/min

Answer 7

GFR (60 mL/min) is approximately half of normal with filtration fraction (24%) greater than normal. (Note, Clearance of PAH underestimates RBF by 10%)

Question 8

What is the effect of increased sympathetic stimulation on renal function?

Answer 8

Decrease both renal blood flow and GFR.

Question 9

How do renal arteriole changes regulate GFR?

Answer 9

GFR will be increased as dilation of the afferent arteriole and constriction of the efferent arteriole

Question 10

Following an acute increase in renal arterial pressure, what kidney response would be expected under normal conditions?

Answer 10

An increase in afferent arteriolar resistance with minimal steady state changes in renal blood flow and GFR.

Question 11

Assume that arterial pressure does not change, what is the effect of a decrease in afferent arteriolar resistance on the GFR?

Answer 11

Increase in GFR.

Question 12

If a substance X is freely filtered and not metabolized, but has a clearance greater than that of inulin, what can be concluded about that substance X?

Answer 12

Substance X is secreted into the tubular fluid.

Question 13

What is the function of kidney?

Answer 13

Regulation of electrolytes balance. Also net production of glucose under stress conditions such as starvation, net production of hormones, excretion of foreign chemicals from the blood.

Question 14

What are the major resistance vessels in the kidney?

Answer 14

Arterioles.

Question 15

What is the mechanism of Na transport in proximal tubule?

Answer 15

Na transport involves Na/K-ATPase (primary active transport) on the basolaleral membrane and cotransport (secondary active transport) on the apical membrane.

Question 16

If a substance X is freely filtered and not metabolized or synthesized, and has a clearance less than that of inulin, what can be concluded about that substance X?

Answer 16

Substance X undergoes net reabsorption by the tubules.

Question 17

What is ultrafiltration in kidney?

Answer 17

The high capillary pressure forces small molecules such as water, glucose, amino acids, sodium chloride and urea through the filter, from the blood in the glomerular capsule across the basement membrane of the Bowman’s capsule and into the nephron. This type of high pressure filtration is ultrafiltration. The fluid formed in this way is called glomerular filtrate. The ultra filtrate is essentially devoid of high molecular weight proteins.

Question 18

What is the fluid’s osmotic and pH conditions at the end of kidney proximal tubule?

Answer 18

The fluid’s iso-osmotic but its pH is lower than that of plasma.

Question 19

How is water transported in the proximal tubule?

Answer 19

Passive reaborption.

Question 20

In what segment of the loop of Henle is Na-K-2Cl an important electroneutral co-transporter?

Answer 20

In the ascending segment (thick), Na, K, and Cl are actively transported out of lumen by Na-K-2Cl symporter. The drugs inhibit Na-K-2Cl co-transporter are called “loop diuretics”, which are commonly used as antihypertensive.

Question 21

What protein located at the apical membrane of the Principal cells is responsible for re-absorbing Na+ in the collecting duct? What blocks this protein?

Answer 21

The epithelial Na channel (ENaC). It is blocked by amiloride.

Question 22

Why is NH3/NH4+ an effective renal buffer?

Answer 22

Its acid-base reaction has a high pKa.

Question 23

What is the function of Na-K ATPase in the proximal tubule?

Answer 23

Na+ re-absorption. Na-K ATPase is located at the basolateral membrane; it maintains low intracellular Na. Digoxin inhibits Na-K ATPase.

Question 24

What are the locations where HCO3- is reabsorbed?

Answer 24

Proximal tubule, thick ascending limb, distal tubule, collecting duct. No HCO3- is secreted in urine.

Question 25

What locations are HCO3- reabsorbed in?

Answer 25

Proximal tubule, thick ascending limb, distal tubule, collecting duct. No HCO3- is secreted in urine.

Question 26

Where are most of the glucose and amino acids re-absorbed?

Answer 26

Proximal tubule.

Question 27

What is the secretion of H+ in the proximal tubule primarily associated with?

Answer 27

Re-absorption of HCO3-. The H+ secretion is mediated by Na+-H+ exchanger.

Question 28

How does kidney use HCO3- to regulate acid-base balance?

Answer 28

Re-absorbing filtered HCO3- and generating new HCO3-.

Question 29

What happens in primary metabolic acidosis?

Answer 29

Metabolic acidosis is diagnosed with low blood pH (body produces too much acid, pH < 7.35) and low bicarbonate (the inability of the body to form bicarbonate in the kidney, HCO3-< 24 mmol/L). There is a net increase in titratable acids (e.g. phosphoric acid, sulfuric acid).

Question 30

How do you diagnose primary metabolic acidosis?

Answer 30

Metabolic acidosis is diagnosed by low plasma HCO3- (less than 24 mmol/L).

Question 31

In response to metabolic acidosis, what changes in NH4+ will occur?

Answer 31

Secretion of NH4+ into tubular lumen.

Question 32

What cells of the collecting duct are associated with H+ secretion in the kidney?

Answer 32

Alpha intercalated cells.

Question 33

In what locations is HCO3- reabsorbed in?

Answer 33

Proximal tubule, thick ascending limb, distal tubule, collecting duct. No HCO3- is secreted in urine.

Question 34

Does an increase in GFR provide pathophysiological evidence for increases in glomerular permeability to large molecules?

Answer 34

No. An increase in urine albumin excretion will provide such evidence.

Question 35

What are the criteria required for the substance used to measure renal clearance using the clearance technique?

Answer 35

Be readily filtered across glomerular capillaries; not be reabsorbed by the tubules; not be secreted by the tubules; not be metabolized or synthesized by tubules.

Question 36

Where is most of the glucose and amino acids re-absorbed?

Answer 36

Proximal tubule.

Question 37

What is the change in the kidney production of NH3/NH4+ during acidosis?

Answer 37

increases

Question 38

How is HCO3- re-absorption achieved?

Answer 38

Binding with H+ ion to form H2O and CO2, which then diffuse into brush border cells to form new HCO3- and H+ catalyzed by carbonic anhydrase. H+-ATPase and Na+/H+ exchange will transport H+ to lumen. HCO3- will diffuse into the blood. Blocking of carbonic anhydrase will decrease HCO3- reaborption and H+ secretion.

Question 39

What is the effect of antidiuretic hormone (ADH) on the kidney?

Answer 39

Increase permeability of the distal tubule and collecting duct to water.

Question 40

How does kidney use HCO - to regulate acid-base balance?

Answer 40

Re-absorbing filtered HCO3- and generating new HCO3-.

Question 41

Does the fluid in early distal tubule have the lowest osmolarity or highest during excessive water loss?

Answer 41

Yes. Like the thick ascending limb, cells of the early distal tubule are impermeable to water and water reabsorption cannot follow solute reabsorption. Here, the osmolarity of tubular fluid becomes even more dilute, as low as 80 mOsm/L. When the plasma osmolarity increased (i.e water deprivation), the osmoreceptor stimulates secretion of ADH from posterior pituitary gland. ADH works at later distal tubule and collecting ducts to increase the reabsorption of water, thus increases urine osmolarity.

Question 42

What is the difference between respiratory and metabolic acidosis?

Answer 42

pH is depended upon the ratio of [HCO3-]/[CO2] in the blood. Respiratory acidosis is resulted from increasing CO2, whereas the metabolic acidosis is resulted from decreasing HCO3-. Both will lower the pH. The metabolic acidosis may be compensated by increasing ventilation, which lowers the CO2.

Question 43

What is the major extracellular buffer system in human body?

Answer 43

CO2/ HCO3- buffer system.

Question 44

Why is the movement of solute preferential over water movement in the ascending segment of the loop of Henle?

Answer 44

Because the thin ascending limb is not permeable to water.

Question 45

How does the osmolarity of the filtrate change in the loop of Henle?

Answer 45

The isotonic fluid from the loop looses water to the higher concentration outside the loop and increases in tonicity until it reaches its maximum at the bottom of the loop. The filtration will be then diluted in the ascending loop.

Question 46

What is the overall effect of aldosterone?

Answer 46

The overall effect of aldosterone is to increase reabsorption of ions and water in the kidney – increasing blood volume and, therefore, increasing blood pressure. Aldosterone stimulates sodium reabsorption and potassium excretion. It stimulates the activity of aquaporins (water channel) and the expression of apical Na+ channel (ENaC) in the collecting duct.

Question 47

What is the effect of blood pressure on aldosterone secretion?

Answer 47

Low blood pressure stimulates aldosterone secretion. The adrenal gland is stimulated by the stretch receptors which are sensitive to low blood pressure to release aldosterone, This will return blood pressure toward normal.

Question 48

Can you calculate glomerular filtration coefficient from glomerular filtration rate?

Answer 48

Yes, filtration coefficient Kf = GFR /( Pg – Pb –πg)
Glomerular Filtration Rate = Kf (Glomerular capillary hydrostatic pressure - Proximal tubule hydrostatic pressure - Glomerular capillary colloid osmotic pressure)

Question 49

What are thiazides?

Answer 49

Thiazides are diuretics commonly used for treating hypertension; the function of thiazides is to block Na-Cl cotransporter in the distal convoluted tubule (DCT).

Question 50

Does the fluid in early distal tubule have the lowest osmolarity during excessive water loss?

Answer 50

Yes. Like the thick ascending limb, cells of the early distal tubule are impermeable to water and water reabsorption cannot follow solute reabsorption. Here, the osmolarity of tubular fluid becomes even more dilute, as low as 80 mOsm/L. When the plasma osmolarity increased (i.e water deprivation), the osmoreceptor stimulates secretion of ADH from posterior pituitary gland. ADH works at later distal tubule and collecting ducts to increase the reabsorption of water, thus increases urine osmolarity.