Structural Basis Of Kidney Function

Question 1

What are the 3 components of the filtration barrier in the renal corpuscles?

Answer 1

1) Fenestrated endothelium
2) Basal lamina
3) Filtration slits between feet of podocytes

Question 2

Structural adaptations of the PCT?

Answer 2

Many mitochondria for active reabsorption
Brush border to maximise SA
Many vesicles containing the materials reabsorbed

Question 3

Why does there appear to be more PCT than DCT and what is the actual ratio of the two?

Answer 3

PCT is longer to cope with greater reabsorption needs

1:1

Question 4

Describe structural features of PCT and adaptations

Answer 4

Cuboidal
Water-permeable loose tight junctions
Max SA by - brush border, interdigitarions of lateral membrane
Contains AQPs for water reabsorption
Many mitochondria for active reabsorption high metabolic demand

Question 5

Outline what’s reabsorbed at the PCT and how

Answer 5

Na+, water, anions,glucose and amino acids, small proteins

Anions and water follow Na+
Glucose and amino acids use sodium cotransporters
Small proteins reabsorbed via endocytosis

Question 6

Outline the countercurrent multiplier mechanism in the loop of henle

Answer 6

The descending limb of the loop of henle is water permeable and ion impermeable. The ascending limb is water impermeable and ion permeable.
The ascending limb pumps out ions into the renal medulla ECF. Water flows out of the descending limb by osmosis. Therefore the tubular fluid in the loop of henle appears to be saltier and so the ascending limb pumps out even more ions and the process repeats cycilically until you get very hypo-osmotic tubular fluid and very hyoerosmotic ECF in the renal medulla

Question 7

What are the cell types in the descending and ascending limb?

Answer 7

Descending limb - squamous

Ascending limb -cuboidal

Question 8

Why does the ascending limb of the loop of henle have lots of mitochondria?

Answer 8

Because its actively transporting lots of ions out into the renal medulla which gives it a high metabolic requirement

Question 9

Describe the structure and function of the DCT

Answer 9

No brush border
Fewer mitochondria
Invaginations with many ion pumps
Water impermeable usually unless ADH inserts AQPs into it
Aldosterone adjusts conc of sodium, potassium, hydrogen and ammonia ions
Macula densa - sensitive to NaCl

Question 10

What does the Macula densa do and where is it?

Answer 10

It’s part of the juxtaglomerular apparatus at the DCT
Sensitive to NaCl - signals to cause the following responses when NaCl is low:
1) Decreases resistance to blood flow in afferent arterioles to raise glomerular hydrostatic pressure and return GFR to normal
2) Increases renin releases from juxtaglomerular cells of the afferent and efferent arterioles which store renin to increase blood pressure to improve GFR as mentioned above

Question 11

Outline the main function of the collecting tubule

Answer 11

Determines the concentration of the urine as there is movement of water down its concentration gradient into the extracellular fluid of the salt renal medulla and this into the capillaries
If aquaporins are switched on, water will be reabsorbed, creating concentrated urine and vice versa

Question 12

How does ADH act on the collecting tubule?

Answer 12

Inserts AQP2 on the apical membrane of the collecting tubule (already AQP3 at rest on vasolateral membrane) so allows water reabsorption by water moving into the collecting tubule via apical membrane and out via the vasolateral membrane into the perirubukar capillaries via the vasolateral membrane using the driving force of the salty renal medulla osmotic gradient

Question 13

2 thing the ascending limb of medulla affects?

Answer 13

Increases saltiness of renal medulla to increase the reabsorption of water at the descending limb and at the collecting tubule

Question 14

Does water reabsorption occur at the descending limb of the loop of henle?

Answer 14

Yes, by passive osmosis ibto perirubukar capillaries driven by gradient created by salty renal medulla created by the ascending limb

Question 15

Where does water reabsorbed at the collecting tubule drain?

Answer 15

Drains into the minor calyx at the papilla of the medullary pyramid

Question 16

Why does the cortex have a granular, disorganised structure?

Answer 16

Because of the glomeruli within it with twisted glomerular structures

Question 17

Why does the medulla have a striated structure?

Answer 17

Straight tubules cause this

Question 18

What are the vasa recta?

Answer 18

Mesh of blood vessels surrounding the loop of henle

Question 19

Describe the role of the juxtaglomerular with BP in haemorrhage and hypertension and renal stenosis?

Answer 19

.....
Detects BP
Secretes renin
Upregulates AT2
Vasoconstriction, upregulates ADH and aldosterone to preserve CO in haemorrhage, and in renal stenosis the kidney thinks BP has dropped but it hasn't so this response is chronic causing chronic HTN

The reverse mechanisms occur in HTN to reduce BP