Elements of Renal Function

Question 1

A bit generic but… name some functions of the kidney.

8 Things listed… could be more

Answer 1

Regulate water and electrolyte balance. 
Regulate ECF volume. 
Regulate plasma osmolality.
Regulate RBC production (erythropoietin)
Regulate vascular resistance
Regulate acid-base balance (H+ ion movement)
Regulate vitamin D production (calcitriol, final form)
Gluconeogenesis

Question 2

The kidneys receive approximately what % of cardiac output?

Answer 2

20% (10% per kidney)

Question 3

Describe the two capillary networks of the kidney.

Answer 3

Two networks in series. The first are glomerular, which have high pressure (favor filtration). Second are peritubular capillaries, which are low in hydrstatic pressure that favor reabsorption.

Question 4

Where in the kidney is blood flow and perfusion higher?

Answer 4

In the cortex vs. the medulla.

Question 5

What process is carried out by the glomerulus?

Answer 5

Filtration governed by starling forces.

Question 6

What process is carried out by the Proximal tubule?

Answer 6

Reabsorption of the largest fraction of glomerular filtrate

Question 7

What process is carried out by the loop of henle?

Answer 7

Controls urine concentration.

Secretes Tamm-Horsfall glycoproteins.

Question 8

What process is carried out by the Distal tubule / collecting duct system?

Answer 8

Fine control of salt and water excretion.

Question 9

What are the three systems and receptors that the sympathetics use to increase BP in the kidneys?

Answer 9

1) Arterial resistance vessels, vasoconstriction… afferent > efferent: alpha1-adrenoreceptors
2) Juxtaglomerular granular cells, renin release + RAAS: B-1 adrenoreceptors
3) Tubular epithelial cells, Na-K ATPase, increased Na+ reabsorption: a-1 adrenoreceptors

Question 10

How do you calculate urinary excretion?

Answer 10

Urinary excretion = Amount filtered (glomerulus) - amount reabsorbed + amount secreted

Question 11

Equation for excretion rate

Answer 11

Excretion rate = [urine] * (urine output / time)

Question 12

Equation for GFR

Answer 12

[Urine]/[Plasma] * (urine output / time)

Question 13

Just study the picture of the equations…

Answer 13

Yeah…

Question 14

What is the filtration fraction of the kidneys?

Answer 14

20% of RBF (renal blood flow)

Question 15

What is the equation for filtration fraction?

What can this be used to do?

Answer 15

FF = GFR/RPF (can be used to calculate RBF pretty easily, since FF = 20% usually.

Question 16

What are two things we use to measure GFR?

Which one is better? More often used?

Answer 16

Inulin and creatinine.

Inulin is totally secreted, so it can be measured more accurately, but creatinine is more regularly used (10% is lost).

Question 17

What do we use to measure renal plasma flow?

Answer 17

PAH (para-aminohippuric acid).
RBF can be calculated.
Must be careful not to overwhelm the system.
All PAH is in the urine.