Functional histology of the kidney

Question 1

The first stage of the filter

Answer 1

Capillary fenestrations

Question 2

The second and third stage of the filter

Answer 2

Basement membrane & podocytes

Question 3

What is the filter cut off?

Answer 3

~70 kDa (albumin)

Question 4

What are the 3 layers of the glomerular filter

Answer 4

a) The cytoplasm of the capillary endothelial cell of the glomerulus
b) The thick, fused basement membrane of capillary & podocytes
c) Filtration slit membranes

Question 5

Functions of Proximal convoluted tubule

Answer 5

Reabsorption from ultrafiltrate

• 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 6

Structure of Proximal convoluted tubule

Answer 6

• Long microvilli for high surface area for reabsorption, also lytic enzymes on the surface to break down macromolecules
• Pinocytotic vesicles carrying macromolecules to lysosomes
• Many lysosomes to break down and recycle macromolecules
• Many mitochondria to fuel active transport

Question 7

The functions of Loop of Henle

Answer 7

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

Question 8

The structures of loop Henle

Answer 8

• Thin, squamous epithelium to allow passive fluxes

- A membrane of organelles

Question 9

The function of Distal convoluted tubule and thick ascending loop of Henle

Answer 9

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

Question 10

The structure of the Distal convoluted tubule

Answer 10

• Cuboidal epithelium- thicker than squamous, to reduce passive fluxes and accommodate organelles
• Few, short microvilli
• Many mitochondria to fuel active transport. these are mainly basal and can show as a pale or striped basal area in H&E - strained section

Question 11

The function of Collecting duct and collecting tubule

Answer 11

• Transport of urine to the ureter

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

Question 12

The structure of the Collecting duct and collecting tubule

Answer 12

Cuboidal to columnar epithelium, to prevent passive flux of water

Specialized dense membranes at cell contracts

Question 13

Macula densa

Answer 13

Sensing [Na+] in the DCT fluid. Signals Juxtaglomerular cells

Question 14

Juxtaglomerular cells

Answer 14

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

Question 15

Lacis cells

Answer 15

Function unknown

Question 16

Structure of ureter

Answer 16

Transitional epithelium
Densa connective tissue
Layers of smooth muscle
Adventitia

Question 17

Transitional Epithelium

Answer 17

• Specialized to be impermeable to urine
• Changes appearance on stretching
• Stratified squamous epithelium when distended, but Apical cells are biggest and have much apical cytoplasm.

Question 18

Why are urinary infections quite common?

Answer 18

Transitional epithelium highly impermeable- leukocytes of the immune system can’t readily penetrate

Question 19

Why are urinary infections more common in females?

Answer 19

The female urethra is shorter. More risk of contamination - anal region

Question 20

What prevention is needed for urinary infections?

Answer 20

Plenty of fluids