Functional histology of the kidney

Question 1

How does homeostasis of plasma composition occur?

Answer 1

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

Question 2

How does homeostasis of blood pressure occur?

Answer 2

→ Through the enzyme renin

Question 3

How does homeostasis of RBC content occur?

Answer 3

→ secretion of EPO

Question 4

How much of the cardiac output do the kidneys receive?

Answer 4

→ 25%

Question 5

What happens at the nephron?

Answer 5

→ blood is filtered at the molecular level (dialysis) to produce urine, while retaining cells and large proteins

Question 6

How many nephrons are there in each kidney?

Answer 6

→ About 1 million

Question 7

What is the glomerulus the site of?

Answer 7

→ site of ultrafiltration

Question 8

What is ultrafiltration?

Answer 8

→Filtration/dialysis of blood through an extremely fine molecular filter
→A knot of capillaries

Question 9

What capillaries are there in the glomerulus?

Answer 9

→ fenestrated capillaries

Question 10

What happens during nephrotic syndrome?

Answer 10

→Glomerular basement membranes become damaged and more leaky

→So proteins are lost in the urine (proteinuria)

Question 11

What happens to glomeruli during high pressure?

Answer 11

→Some glomeruli are destroyed and replaced by masses of clear “hyaline” material (H)

Question 12

What is the function of the renal tubule?

Answer 12

→ adjust the composition of the ultrafiltrate, to recover nutrients, water etc, and to regulate plasma composition

Question 13

What is the function of the proximal convoluted tubule?

Answer 13

Reabsorption from the ultrafiltrate

By active transport across the membrane into the cell
→Small molecules like Na+, glucose and amino acids

By pinocytosis: macromolecules, especially proteins
→These are broken down in lysosomes and returned to the blood

By passive flux
→Water, Cl-

Question 14

What is the structure of the PCT?

Answer 14

→Long microvilli
→For high surface are for reabsorption
→Many mitochondria to fuel active transport
→Seen especially near the basolateral sodium pumps

Question 15

What enzymes does the PCT have and what is this for?

Answer 15

→Lytic enzymes on the surface to break down macromolecules

→Has many lysosomes to break down and recycle macromolecules

Question 16

What is the function of the loop of Henle?

Answer 16

→Reabsorption of water and salts from the filtrate

→Passive flux across the epithelium, by osmosis & concentration gradients

Question 17

What is the function of epithelial cells in the loop of Henle?

Answer 17

→Thin, squamous epithelium to allow passive fluxes

A minimum of organelles

Question 18

What is the function of the distal convoluted tubule?

Answer 18

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

Question 19

What is the structure of the DCT?

Answer 19

→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 20

What is the function of the collecting ducts?

Answer 20

→Transport of urine to ureter

→Water homeostasis, passive reabsorption of water, regulated through epithelial permeability

Question 21

What is the structure of the collecting ducts?

Answer 21

→Cuboidal to columnar epithelium
→To prevent passive flux of water (and urea etc)
→Specialised dense membranes at cell contacts (RED)
→Function is unclear – probably also helping to prevent passive flux

Question 22

As you go down the collecting duct what happens to the cells?

Answer 22

→cells get taller and taller

→ more impermeable to the water crossing them

Question 23

Where is the juxtaglomerular apparatus found?

Answer 23

→Is found where the DCT loops back to meet arterioles of the same nephron

Question 24

What does the macula densa do?

Answer 24

→Senses [Na+] in the DCT fluid

→Signals to the juxtaglomerular cells

Question 25

What do the juxtaglomerular cells release?

Answer 25

→Release renin

→More release of renin in response to lower [Na+] in DCT

Question 26

What does renin indirectly increase?

Answer 26

→Renin indirectly increases vascular tone and sodium resorption

Question 27

What are Lacis cells also known as?

Answer 27

→ extraglomerular mesangial cells

Question 28

What is transitional epithelium?

Answer 28

→special stratified epithelium, found only in ureters and bladder

Question 29

What is the transitional epithelium specialized for?

Answer 29

→Specialised to be impermeable to urine

Question 30

When does the transitional epithelium change appearance?

Answer 30

→It changes appearance on stretching

Question 31

What is transitional epithelium similar to?

Answer 31

→It is similar to stratified squamous epithelium (SSE) when distended

Question 32

What cells are the bigger in the transitional epithelium

?

Answer 32

→But apical cells are the biggest and have a lot of apical cytoplasm
→In SSE, basal cells are the biggest, and apical cells are very flat

Question 33

What cells are biggest in stratified squamous epithelium?

Answer 33

→In SSE, basal cells are the biggest, and apical cells are very flat

Question 34

What is present in the apical cells of epithelium?

Answer 34

→There are plaques of specialised (urine-resistant) plasma membrane in the apical cells of transitional epithelium

Question 35

What do the rigid membrane patches in apical cells in the TE do?

Answer 35

→These impermeable, rigid membrane patches (plaques) protect apical cells from toxic urine

Question 36

What happens to the rigid membrane patches when the bladder is empty?

Answer 36

→rigid plaques are invaginated
→ forming pits and vesicles in the cell
→ allowing the cell surface are to decrease

Question 37

Why are urinary infections quite common?

Answer 37

→Transitional epithelium is highly impermeable

→The leukocytes of the immune system cannot readily penetrate

Question 38

Why are urinary infections common in women?

Answer 38

→The female urethra is shorter
→More risk of contamination
E.g. from anal region

Question 39

How do you prevent urinary infections?

Answer 39

→ Drinking water