Filtration and Reabsorption

Question 1

How is plasma pH controlled?

Answer 1

Filtering/recovering hydrogen carbonate and secreting H+

Question 2

What controls the pressure within the glomerulus?

What should the pressure in glomerular capillaries be?

Answer 2

The afferent and efferent arterioles

Glomerular capillary pressure should be about 55 mmHg

Question 3

What defines the GFR?

Answer 3

The amount of blood filtered by the kidney’s glomerulus into the bowman’s capsule per unit of time

Question 4

Describe the 3 layers of the glomerulus

Answer 4

1. Endothelial cells: have pores
2. Basement Membrane: is negative to repel proteins (so you don’t pee them out)
3. Epithelial cells: have podocytes that wrap around the endothelial cells that forms filtration slits leading into the bowman’s space that leads into the PCT

Question 5

What happens if the afferent arteriole is relaxed vs contracted?

What happens when the efferent arteriole does the same?

Answer 5

Afferent arteriole…
Relaxes: Increased blood flow into the glomerulus, low resistance, GFR pressure goes up

Contracts: Decrease blood flow into the glomerulus, high resistance and GFR pressure decreases

Efferent arteriole…
Relaxes: Easier for blood to leave the glomerulus, glomerular pressure decreases

Contracts: More blood within glomerulus = higher glomerular pressure

Question 6

What two forces are constantly battling to maintain the fluid level within the glomerulus? Which one is more important?

What does the net pressure have to be to drive filtration?

Answer 6

Hydrostatic pressure: pushes fluid out of the glomerular capillaries. Hydrostatic pressure is more important as it varies with BP.

Oncotic pressure (notably albumin): keeps fluid within the glomerular capillaries (doesn’t get filtered)

Net pressure: only 10 mmHg

Question 7

What GFR indicates renal failure?

Answer 7

15ml/min or lower

Question 8

What factors regulate the afferent and efferent arterioles? Which ones are fast/slow?

Answer 8

FAST: (short term)

1. Myogenic response- Auto-regulation
2. Sympathetic response: increases the GFR

SLOW:

1. Hormones: angiotensin II, ANP and aldosterone
2. Tubulo-glomerular feedback (JGA- macula densa)

Question 9

What is the normal range of filtrate produced per minute?

Answer 9

90-125 ml/min

Question 10

Name 5 vasoconstrictors and 4 vasodilators

Answer 10

Vasoconstrictors:

1. sympathetic nerves
2. Angiotensin II
3. Endothelin
4. Renin
5. Adenosine

Vasodilators:

1. Prostaglandins
2. NO
3. Bradykinin
4. ANP (atrial natriuretic peptide)

Question 11

What’s the renal threshold? What defines glycosuria?

Answer 11

This indicates the max rate that glucose can be re-absorbed. Glycosuria is about 10mmol/L of glucose in the urine

Question 12

Where is hydrogen carbonate recovered and through which channel?

Answer 12

90% is filtered and recovered in the PCT via the Na+/H+ antiport

Question 13

What are the two parts of the Collecting Duct?

Answer 13

The cortical part: similar to the DCT

The medullary part: re-absorption of water

Question 14

Where is H+ secreted?

Answer 14

In the DCT

Question 15

What substances would you use to measure the GFR, and what is the formula?

Answer 15

Using inulin in animals or creatinine in muscles as both are neither re-absorbed or secreted in the nephron. Also take age, gender and size of person into consideration

Formula: Conc of substance (creatinine/inulin)) in urine X Volume of urine in 1 min/Conc of substance in plasma

Question 16

Explain the myogenic reflex/ auto-regulation

Answer 16

When BP ⬆, SM in afferent arterioles senses stretch and causes the elastic fibres to recoil back - protecting GFR