1 - Homeostasis and kidney function

Question 1

What are the 4 functions of kidney?

Answer 1

1. Regulation of electrolyte and water balance.
2. Removal of metabolic waste products from the blood and their excretion in
   the urine (creatinine from muscle metabolism, urea from protein
   metabolism and uric acid from nucleic acid metabolism).
3. Removal of foreign chemicals (drugs) from the blood and their excretion in
   the urine.
4. Secretion of hormones:
   a. Erythropoietin, which controls erythrocyte
   production;
   b. Renin, which controls formation of angiotensin, which influences blood pressure and blood volume (sodium balance);
   c. 1,25-Dihydroxyvitamine D3, which influences calcium balance

Question 2

State the functional regions of a nephron tubule from proximal to distal.

Answer 2

Bowman’s capsule > Proximal convoluted tubule >
Proximal straight tubule >
Thin descending limb of the loop of Henle > TAL of LOH > Cortical collecting tubule > Outer medullary duct, inner medullary duct

Question 3

Which part of the nephron tubule is responsible for bulk reabsorption of Na+? What channels are involved?

Answer 3

Proximal convoluted tubule;

Na+/glucose cotransporter (1:1 reabsorption together)
and
Na+/H+ ATPase
in lumen

Na+/K+ ATPase in interstitial space

Question 4

The normal renal blood flow is about 
A. 800 ml per min
B. 1000 ml per min
C. 1200 ml per min
D. 1400 ml per min;

its how many percent of the cardiac output?

Answer 4

C

25%/ 1/4

Question 5

The GFR is determined by which 3 parameters?

which is normally the major determinant of the GFR?

Answer 5

1. Hydrostatic pressure in the glomerular capillary (Pgc)
2. Hydrostatic pressure of the Bowman’s space (Pbs)
3. Plasma colloid oncotic pressure (pie gc) exerted by the proteins (mainly albumin) in the capillary plasma.

Pgc is the major determinant .

Question 6

What is the equation to derive GFR (with the 3 parameters)?

Answer 6

GFR = k [Pgc - (Pbs + pie gc)]

k is the filtration coefficient and is a constant under normal condition. In
diseases affecting the glomerulus, k falls and this contributes to a fall in GFR
in renal failure.

Question 7

Which of the following can affect GFR?

1. Compressed renal capsule
2. ureteral obstruction
3. hypoalbuminemia in liver diseases
   4 starvation

Answer 7

All of them

1 and 2 affects the Pbs

3 and 4 affects the pie gc

Question 8

State the effect of increase in afferent arteriole pressure in GFR and RPF.

Answer 8

Constriction of the afferent arteriole
reduces Pgc, hence GFR, and also RPF (due to an increase in total renal
resistance).

Question 9

State the effect of constriction of the efferent arteriole on GFR and RPF.

Answer 9

GFR increased;
RPF decreased

Constriction of the efferent arteriole retards fluid movement from the
glomerulus into the efferent arteriole, resulting in an increase in Pgc and GFR,
but because of an increase in total renal resistance produced by efferent arteriolar constriction
(the afferent and efferent arterioles contribute to a major part of the total renal resistance),

renal blood flow (Renal blood flow = Aortic
pressure/Total renal resistance) is reduced (assuming aorta pressure
unchanged).

Question 10

What is the normal GFR? (ml/min)

A. 100
B. 125
C. 145
D. 180

Answer 10

B

180L/day
but 125 ml/min

Question 11

How can the difference between amount filtered and amount reabsorbed be kept constant?

Answer 11

1. Glomerulotubular balance
   - when GFR increased, Na+ reabsorption increases
2. Autoregulation

Question 12

List 3 factors affecting autoregulation of GFR.

Answer 12

1. Stretch receptors in the afferent arteriole
2. Angiotensin II
3. Tubuloglomerular feedback

All of them takes place int he juxtaglomerular apparatus

Question 13

When and how is Angiotensin II produced?

Answer 13

low blood volume and low blood pressure.
Ang II is a potent vasoconstriction.

Renin secreted by juxtaglomerular cells at wa;; of afferent arterioles + angiotensinogen > Ang I +ACE (angiotensin converting enzyme) > Ang II

Question 14

What are the 6 effects of Ang II?

Answer 14

1. Vasoconstriction > raise blood pressure
2. Stimulates the release of aldosterone form cortex of the adrenal gland
   (to increase Na+ and water absorption)
3. Constricts efferent arteriole more than afferent, reduce RPF, increase GFR
4. Increase Na+ reabsorption by activating Na+-H+ antiporter
5. increases sensitivity of TG feedback mechanism by increasing the responsiveness of afferent arteriole to signal from macula densa
6. stimulates thirst and ADH release

Question 15

When GFR is increased, how is the tubuloglomerular feedback (TGF) work to stabilise the GFR?

Answer 15

When GFR increased, the [NaCl] increases increases, sensed by the macula densa cells around the JGA (juxtaglomerular apparatus) in the ascending limb og LOH,
release of ATP and adenosine increases, causing the constriction of afferent arteriole

Question 16

What is the effect of sympathetic stimulation on the GFR?

When is it activated?

Answer 16

Sympathetic stimulation will cause constriction of afferent arterioles more than the efferent, thus RPF and GFR reduces.

Activated in adverse conditions like hypovolemia and dehydration

*** in mild hypovolemia: efferent constricts more than afferent, GFR unchanged, RPF increases, FF increases (favours reabsorption)

Question 17

Which of the following controls the GFR? If they control GFR, how?

A. Prostaglandins
B. ADH (= AVP)
C. RAA-Axis
D. ANP (atrial natriuretic peptide)

Answer 17

A. vasodilator, dilates afferent arteriole and increases GFR.

*with NSAIDS, which are inhibitors of prostaglandins, no use

D. ANP dilates the afferent arteriole and constrict efferent arteriole

Question 18

What is the equation of GFR (by amount of substance filtered…) ?

Answer 18

GFR = Ux . V / Px

Question 19

Inulin is not used as it is tedious to infuse inulin into the body.
What is used as a clinical marker of GFR?

Where is it produced?

Answer 19

Plasma creatinine.

Produced in skeletal muscles at a constant rate.

Question 20

There are limitations to the use of creatinine clearance in the determination of glomerular filtration rate (GFR). Which of the following is an example of such limitations?

A. Creatinine is not filtered freely at the glomerulus.
B. Creatinine is actively reabsorbed by the renal tubule.
C. Creatinine is metabolised by the liver.
D. Creatinine is released at variable rates by muscles.
E. Creatinine is actively secreted by the renal tubule.

Answer 20

E.

When blood creatinine concentration is much higher than normal, as is seen in severe renal failure, the proximal tubule can secrete creatinine into the lumen via organic cation transporters. Under these circumstances, creatinine clearance can no longer reflect GFR.

Question 21

What is the clearance of X?

= rate of urinary excretion of X

Answer 21

Cx = Ux . V /Px

Question 22

The concept of clearance can be used to determine whether a substance is
reabsorbed or secreted into the lumen.

If Cx of a substance is less than that of inulin, the substance undergoes a process involving net __________ in the
tubule.

if Cx is greater than that of inulin, the secretion of X excretion
must involve net ________.

Answer 22

reabsorption;

tubular secretion

Question 23

Types of nephrons:
30% A
15% B
rest: C

Which one is involved in the countercurrent system to concentrate urine?

Answer 23

A: superficial
B: juxtamedullary
C: intermediate nephrons

B;
they have long loops of Henle