Functional Histology of the Kidney

Question 1

How is plasma composition maintained?

Answer 1

By regulated excretion of water, ions and organic waste products into urine.

Question 2

How is blood pressure maintained?

Answer 2

Through the enzyme renin.

Question 3

How is RBC content maintained?

Answer 3

Through the secretion of erythropoietin.

Question 4

How much of the cardiac output do the kidneys receive?

Answer 4

25%

Question 5

What does high blood pressure do?

Answer 5

It destroys glomeruli and they are replaced by masses of clear ‘hyaline’ material.

Question 6

What is the function of the proximal convoluted tubule?

Answer 6

Reabsorption from the ultrafiltrate

Question 7

How does reabsorption occur in the PCT?

Answer 7

• By active transport across the membrane into cell: small molecules like Na+, glucose, amino acids
• By pinocytosis: macromolecules, especially proteins. These broken down in lysosomes and returned to the blood.
• By passive flux: water, Cl-

Question 8

What is the structure of the PCT epithelial cells?

Answer 8

• Long microvilli for a high surface area for reabsorption, also lytic enzymes on the surface to break down macromolecules
• Many lysosomes to break down 
and recycle macromolecules
• Many mitochondria to fuel active transport (seen especially near the basolateral sodium pumps)

Question 9

What are the functions of the (thin) Loop of Henle?

Answer 9

Reabsorption of water and salts from filtrate - passive flux across the epithelium, by osmosis & concentration gradients.

Question 10

What is the structure of the Loop of Henle?

Answer 10

• Thin, squamous epithelium to allow passive fluxes

- A minimum of organelles

Question 11

What are the functions of the DCT and the thick ascending loop of Henle?

Answer 11

Homeostasis by regulated active transport & exchange of ions
(Na+/K+, H+/HCO3-)

Question 12

What are the structures of the DCT and the thick ascending loop of Henle?

Answer 12

• Cuboidal epithelium – thicker than squamous, to reduce passive fluxes and accommodate organelles
• Few, short microvilli (unlike PCT)
• Many mitochondria to fuel active transport. These are mainly basal and can show as a pale or striped basal area in H&E-stained sections.

Question 13

What is the function of the collecting duct?

Answer 13

• Transport of urine to the ureter.

- Water homeostasis: passive reabsorption of water, regulated through epithelial permeability.

Question 14

What is the structure of the collecting duct?

Answer 14

• Cuboidal to columnar epithelium, to prevent passive flux of water (and urea etc)
• Specialized dense membranes at cell contacts [red]. 
Function unclear – probably also helping to prevent passive flux.

Question 15

What is the juxtaglomerular apparatus?

Answer 15

Where DCT loops back to meet arterioles of the same nephron.

Question 16

What does the macula densa?

Answer 16

sensing [Na+] in the DCT fluid. Appears to signal to the glomerular cells telling them how much renin to release

Question 17

What do juxtaglomerular cells do?

Answer 17

They release renin – more so in response to lower [Na+] in DCT. Renin indirectly increases vascular tone and sodium resorption.

Question 18

What do the Lacis cells do?

Answer 18

Function unknown. (Signalling between the other two?) Also called extraglomerular mesangial cells.

Question 19

What are the parts of the ureter?

Answer 19

Transitional epithelium
Dense connective tissue (lamina propria)
Layers of smooth muscle
Adventitia

Question 20

What are the properties of transitional epithelium?

Answer 20

Specialized to be impermeable to urine.
Changes appearance on stretching
Somewhat like stratified squamous epithelium (SSE) when distended, but apical cells are biggest and have much apical cytoplasm
(in SSE, basal cells are biggest, apical cells very flat).