1. Structural Basis of Kidney Function

Question 1

What is function of kidneys?

Answer 1

1) Production of urine:
Filtration of blood plasma
Selective reabsorption
Tubular secretions of some components
Concentration of urine as neccessary
2) It is sensitive to body needs via hormones, nerves
3) It has endocrine function - signals to the rest of the body (Renin, erythropoietin, 1,25-OH vitamin D)

Question 2

Which tissue in the kidney has the greatest blood supply?

Answer 2

The cortex - where ultra filtration occurs

Question 3

In acute trauma to the kidney which part of the kidney is most likely going to die?

Answer 3

The ends of the medulla - it is not as well perfused so you get acute tubular necrosis.

Question 4

How can you diagnose acute tubular necrosis?

Answer 4

You can see it in the urine

Question 5

Where does the urine collect?

Answer 5

In the renal pelvis down into the ureter

Question 6

Why does the cortex have a granular irregular structure?

Answer 6

It has lots of glomeruli

Question 7

Why does the medulla have a striated structure?

Answer 7

It is made up of the long tubules of the nephron

Question 8

What are the 5 stages of urine production in the kidney?

Answer 8

Filtration
Reabsorption
Creation of hyper-osmotic extracellular fluid
Adjustment of ion content of urine
Concentration of urine

Question 9

Where is the site of ultrafiltration?

Answer 9

Glomerulus

Question 10

What is the molecular weight of substances that are filtered?

Answer 10

<50,000

Question 11

How the pressure build up in the glomerulus?

Answer 11

The afferent arteriole has a wider diameter than the efferent arteriole

Question 12

What are the three layers of the capillaries of the glomerulus/filtration barrier?

Answer 12

Fenestrated (leaky) endothelium, Basement membrane (modified for filtration) and podocytes (with feet for filtration)

Question 13

What makes up the renal corpuscle?

Answer 13

Bowman’s capsule, glomerulus (consists of capillaries) and podocytes

Question 14

What are the two poles of the renal corpsucle?

Answer 14

Urinary and vascular pole

Question 15

Where does the urinary pole of the corpuscle drain?

Answer 15

Into the PCT

Question 16

Where is most of the substances reabsorbed?

Answer 16

PCT

Question 17

What is absorbed in the PCT?

Answer 17

Ions, water, glucose, amino acids, small proteins

Question 18

What is the structure of the PCT?

Answer 18

Lots of mitochondria, brushed border, vesicles, cuboidal epithelium, sealed with tight junctions, aquaporins

Question 19

What are the functions of the PCT?

Answer 19

Reabsorption of 70% of the glomerular filtrate

1) Na+ uptake by basolateral Na+ pump
2) Water and anions follow Na+
3) Glucose uptake by Na+/glucose co-transporter
4) Amino acid uptake by Na+/aminoacid co-transporter
5) Protein uptake by endocytosis

Question 20

Why does the PCT appear more than the DCT?

Answer 20

There appears to be more PCT than DCT because it has to reabsorb more hence is longer

Question 21

Where does the creation of a hyperosmotic extracellular fluid occur?

Answer 21

At the loop of henle and with the vasa recta (blood vessels) using a counter current system

Question 22

Where does the loop of henle run?

Answer 22

down into the medulla

Question 23

What is the function of the ascending limb of the loop of henle?

Answer 23

It actively pumps Na+ and Cl+ out of the tubular fluid. It is impermeable to water

Question 24

What is the function of the descending limb of the loop of henle?

Answer 24

It has aquaporins so passive diffusion of water can occur (osmosis)

Question 25

What is the function of the vasa recter?

Answer 25

It is arranged in loop of henle, takes away water and sodium ions

Question 26

How does the loop of henle function to create a hyperosmotic extracellular fluid?

Answer 26

The ascending limb actively pumps Na+ ions into the extracellular fluid creating a hyperosmotic extracellular fluid. Water in the descending limb then diffuses into the extracellular fluid by osmosis through aquaporins. The end result is a hypo-osmotic tubular fluid and hyper-osmotic extracellular fluid. Creates a hyperosmolar medulla

Question 27

Where does the adjustment of the ion content of urine occur?

Answer 27

In the DCT - controls levels of Na+, K+, H+ and NH4+

Question 28

What is the structure of the DCT?

Answer 28

Controlled by vasopressin, Aldosterone (with controls the ions). It has cuboidal epithelium with lateral membrane indigitations with Na+ pumps. Lots of large mitochondria and also specialised macular densa cells.

Question 29

Where does the concentration of urine occur?

Answer 29

At the collecting tubules - Water will move by osmosis into the extracellular fluid if there are high levels of ADH which increase the number of aquaporins in the collecting tubules

Question 30

What does the rate of water movement in the collecting duct dependent on?

Answer 30

Levels of aquaporin 2 in the apical membrane and aquaporin 3 in the basal membrane

Question 31

Where does the glomerular fluid drain into?

Answer 31

Minor calyx at papilla of medullary pyramid

Question 32

What is the function of the macular densa of the DCT?

Answer 32

They can sense the sodium chloride concentration - stimulate the juxtoglomerular cells

Question 33

What are the juxtoglomerular cells?

Answer 33

They surround the afferent arterioles and sense pressure - they can release renin (controls BP via angiotensin) = increasing aldosterone + vasoconstriction