Urinary: Glomerular Filtration

Question 1

How does the kidney deal with glucose, amino acids and bicarbonate?

Answer 1

• 100% of the glucose, AA and bicarbonate are reabsorbed
• 99% of water and Na+, Cl- are reabsorbed
• only a few wast products are not recovered

Question 2

What are the functions of the kidney?

Answer 2

• regulation of concentrations of substances in the ECF
• excretion of waste products
• endocrine: synthesis of renin, prostaglandins
• metabolism: active form of vit D, catabolism of insulin

Question 3

How many litres of ECF do the kidneys filter each day?

How much urine is produced?

Answer 3

Filter 180L/day

1.5L of urine produced per day

Question 4

What is the role of the PCT?

Answer 4

ISOSMOTIC REABSORPTION (major site of reab)

• reabsorbs 67% of Na+ and water
• 80-90% of K+
• 90% bicarb
• all glucose and AA

The reabsorbed material leave by peritubular capillaries

Question 5

What is the role of the loop of henle?

Answer 5

Some reabsorption of salts

Major function is to create gradient of increasing osmolarity in the medulla using counter-current multiplication.

Question 6

What is the role of the DCT?

Answer 6

Major site of VARIABLE reabsorption of electrolytes and water - fluid leaving LoH is hypotonic.
Removes more Na+ and Cl- and actively secretes H+ –> water may or may not follow.

Question 7

What is renal plasma flow?

Answer 7

Not all the blood that goes to the glomerulus is filtered - the plasma is filtered (55% of blood) but the haematocrit isnt (45% of blood).

Therefore renal plasma flow is 0.55 x 1.1L/min (renal blood flow) = 605ml/min of plasma

Question 8

What are the 2 types of nephrons?

Answer 8

Cortical Nephrons: (90%)
Short with tangled peritubular capillaries

Juxtamedullary Nephrons: (10%)
Long with golmerulus next to medullary border
Have vasa recta running parallel with LoH but flow in different direction.

Question 9

What percentage of blood is filtered?

Answer 9

Only 20%, the other 80% flows through unchanged (however has haematocrit from 20% added meaning an increase in velocity and oncotic pressure)

Question 10

What are the layers of the filtration barrier?

Answer 10

1. Capillary Endothelium - water salts and glucose can pass through, filtrate moves between cells
2. Basement membrane - acellular layer of collagen and glycoproteins (have a neg charge so repel proteins)
3. Podocyte layer - forms filtration slits

Question 11

What are the 3 forces creating a net filtration pressure/

Answer 11

Favouring filtration:
The large hydrostatic pressure in the capillary

Opposing filtration:
Oncotic pressure in the capillary drawing water in
Hydrostatic pressure in the bowmans capsule

Question 12

What are the autoregulatory mechanisms to maintain the hydrostatic pressure in the capillary?

Answer 12

1. Myogenic response (maintains GFR when BP is within physiological limits)
2. Tubular Glomerular feedback

Question 13

Outline the myogenic response to maintain GFR

Answer 13

Myogenic response maintains GFR when BP is within physiological limits

Increase hydrostatic pressure:

• Decreasing afferent resistance
• Increasing efferent resistance

Decrease hydrostatic pressure:
- Increasing afferent resistance

Question 14

Outline the tubular-glomerular feedback to maintain GFR

Answer 14

Relies on the distal tubule nestling between the AA and EA. Macula densa cells detect changes to NaCl conc

If NaCl conc increases:

• GFR needs to decrease
• macula densa release adEnosine to vasodilate EA

If NaCl conc decreases:

• GFR needs to increase
• macula densa release prostAglandins to vasodilate AA

Question 15

Outline the different types of sodium channels in the apical membrane of the nephron

Answer 15

PCT: Na-H antiporter and Na-Glucose cotransporter
LoH: Na-K-2Cl symporter
Early DT: Na-Cl symporter
Late DT and CD: ENaC

Question 16

How is glucose reabsorbed in the PCT?

Answer 16

The Na-Glucose cotransporter (SGLUT) reabsorbs 1 glucose with 2 sodium. The glucose leaves the basolateral side by facilitated diffusion.

If the transport maximum of the plasma is exceeded then excess glucose is spilled over into the urine - glycosuria resulting in polyuria (water follows)

Question 17

What substances are secreted into the tubular fluid?

Answer 17

Protons
Potassium
Organic anions and cations (many drugs are secreted this way)

Question 18

What is the mechanism of organic cation secretion in the PCT?

Answer 18

Na-K-ATPase on apical keeps Na low
Therefore Na - H antiporter works to lower H conc
Therefore a H - Cation antiporter secretes cations