functional histology of the kidney

Question 1

functions of the urinary system

Answer 1

homeostasis of:

• Plasma composition by regulated excretion of water, ions and organic waste products into urine
• Blood pressure through the enzyme renin
• RBC content through secretion of erythropoietin

Question 2

Medullary rays

anatomy of kidney on slide

Answer 2

lines within the cortex, they are part of the medulla but they extend into the cortex

Question 3

Renal corpuscle

Answer 3

bowman’s capsule and glomerulus

Question 4

glomerulus is the site of what?

Answer 4

ultrafiltration

Question 5

The basement membrane of podocytes fuses with what?

Answer 5

the basement membrane of the endothelial cells

Question 6

function of proximal convoluted tubule

Answer 6

(selective) reabsorption from the ultra filtrate

Question 7

how are molecules reabsorbed back into the bloodstream in the proximal convoluted tubule?

Answer 7

Active transport across membrane into cell: small molecules like Na+, glucose, amino acids

Pinocytosis: macromolecules, especially proteins - these are broken down in lysosomes and returned to blood

Passive flux: water, Cl-

Question 8

how is the structure of the proximal convoluted tubule adapted for its function

Answer 8

Structure:
- Long microvilli for high surface area for reabsorption, also lytic enzymes on surface to break down macromolecules

• Pinocytotic vesicles carrying macromolecules to lysosomes - they break down and recycle macromolecules
• Many mitochondria to fuel active transport (seen especially near the basolateral sodium pumps)

Question 9

Loop of henle thin limb function

Answer 9

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

Question 10

what is the structure of the thin limb of the loop of henle similar to?

Answer 10

proximal convoluted tubule

Question 11

why are the cells thin in the thin LOH limb?

Answer 11

because there is a lot of passive flux going on

Question 12

why is here a hypertonic extracellular environment in the thin LOH limb?

Answer 12

so water will flow out of the tubule

Question 13

Thin loop of Henle - epithelial cell structure

Answer 13

• Thin, squamous epithelium to allow passive fluxes

- A minimum of organelles

Question 14

functions of the distal convoluted tubule and thick ascending loop of Henle

Answer 14

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

Question 15

why is pumping ions necessary in the thick limb of the loop of henle?

Answer 15

needed to set up the hypertonic environment towards the bottom (hairpin bend)

Question 16

Distal convoluted tubule (DCT) epithelial cell structure

Answer 16

• 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 17

Collecting duct and collecting tubule function

Answer 17

• Transport of urine to ureter
• Water homeostasis: passive reabsorption of water, regulated through epithelial permeability
• the epithelium can make itself more or less permeable partly through specialized molecules on the membrane

Question 18

Collecting duct epithelial cell structure

Answer 18

• Cuboidal to columnar epithelium, to prevent passive flux of water (and urea etc)

Question 19

is the proximal or distal convoluted tubule thicker?

Answer 19

proximal

Question 20

why is the lumen clearer in the DCT?

Answer 20

because it hasn’t got as many microvilli

PCT doesn’t have much lumen

Question 21

what type of epithelium is the thin loop?

Answer 21

squamous

Question 22

what happens to the collecting duct as you go down?

Answer 22

gets taller and thicker as you go down (starts off as cuboidal)

Question 23

what is renin involved in?

Answer 23

controlling BP (indirectly increases vascular tone and sodium resorption)

Question 24

Macula densa

Answer 24

involved in sensing [Na+] in the DCT fluid. - signals to the juxtaglomerular cells

Question 25

Juxtaglomerular cells

Answer 25

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

Question 26

what supports the ureter?

Answer 26

dense connective tissue

Question 27

layers of smooth muscle in the ureter are involved in what?

Answer 27

peristalsis

Question 28

why is peristalsis needed in the ureter

Answer 28

to make sure urine flows in the right direction

Question 29

what is the name for the special stratified epithelium only found in ureters and bladder

Answer 29

Transitional epithelium

Question 30

how is transitional epithelium specialised?

Answer 30

• Specialized to be impermeable to urine
• Changes appearance on stretching (hence the name ‘transitional’
• 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)

Question 31

how are apical cells specialised to resist the toxic substances in urine?

Answer 31

the plasma membrane on these cells have rigid plaques

Distended (bladder full):
These impermeable, rigid membrane patches (plaques) protect apical cells from toxic urine

Contracted (bladder empty):
The rigid plaques are invaginated forming pits and vesicles in the cell, allowing cell surface area to decrease

Question 32

(downside of transitional epithelium)

Why are urinary infections quite common?

Answer 32

Transitional epithelium highly impermeable - leukocytes of immune system cannot readily penetrate

-usually the white blood cells can usually go all the way through the epithelium, looking for bacteria/toxic substances to defend the body against.

Question 33

Why are urinary infections more common in women?

Answer 33

Female urethra shorter. More risk of contamination, e.g. from anal region

Question 34

preventing urinary infections?

Answer 34

Plenty of fluids

-Fluids will literally wash the microorganisms away