Nephron workshop

Question 1

What are the possible causes of reduced nephron numbers?

Answer 1

Normal ageing
Renal injury
Renal injury

Question 2

Describe juxtamedullary nephrons

Answer 2

Long
Adapted to resorb lots of water back into blood
Ideal for animals that need to retain water e.g., desert animals
Ability to make concentrated urine is associated with higher percentage of juxtamedullary nephrons

Question 3

Describe the renal corpuscle

Answer 3

ball of capillaries (glomerulus) where blood flows and is filtered towards a double walled capsule (Bowman’s capsule)

Question 4

Describe the glomerulus

Answer 4

Acts as a sieve to filter blood and create a filtrate
Formed by an afferent arteriole that divides into looping capillaries
Intraglomerular mesangial cells and matrix occupy spaces between capillary loops
Afferent arterioles enter at vascular pole
Ultrafiltrate is created and enters Bowman’s capsule at the urinary pole

Question 5

Describe the Bowman’s capsule

Answer 5

Cup shaped
2 layers separated by the urinary space (where the filtrate is collected)
Inner layer (visceral layer) is made up of podocytes that play a role in filtration

Question 6

Describe the function of the cells of the Bowman’s capsule

Answer 6

Podocytes have foot-like processes that interdigitate with other podocytes to make a layer that spreads out to cover glomerular endothelial cells and intraglomerular mesangial cells with a glomerular basement membrane inbetween
Mesangial cells keep the glomerular basement membrane ‘clean’ for filtration by having cytoplasmic projections that extend between the endothelial cells and GBM for phagocytosis of debris

Question 7

Label the histology of the renal filter

Answer 7

Question 8

How does the glomerulus act as a filter?

Answer 8

Endothelial cells have large fenestrations (pores) which allow passage of small molecules
There is also a charge-barrier as the material that makes up the pores is -ve
Blood cells and most proteins are too large

Question 9

What 3 layers does blood in the glomerular capillary get filtered through?

Answer 9

Endothelial cells of glomerulus
Glomerular basement membrane
Podocytes of visceral layer of Bowman’s capsule

Question 10

Describe the podocytes of the visceral layer of the Bowman’s capsule

Answer 10

Podocytes don’t completely cover the glomerular basement membrane - some gaps
Spaces between foot projections (filtration slits) which block small molecules due to -ve membrane within slit

Question 11

What is the juxtaglomerular apparatus (JGA)

Answer 11

Region at the vascular pole of the glomerulus made of 3 cell types:
- juxtaglomerular cells
- macula densa cells
- extraglomerular mesangial cells

Question 12

Describe the juxtaglomerular cells

Answer 12

Modified smooth muscle cells in wall of the afferent arteriole which contain renin granules

Question 13

Describe the macula densa cells

Answer 13

Specialised epithelial cells in wall of ascending limb of LoH and distal tubule
Sits close to afferent and efferent arterioles
Detect changes luminal NaCl conc
Signal changes in arteriolar resistance to affect blood flow to glomerulus
Signals release of renin

Question 14

Describe extraglomerular mesangial cells

Answer 14

bridge the afferent and efferent arterioles and the macula densa cells to help coordinate messages and effects of juxtaglomerular apparatus

Question 15

Describe the anatomy of the proximal convoluted tubule

Answer 15

Coiled
Cuboidal epithelial cells
Apical intercellular tight junctions (stop molecule leakage, allows passage of water and small ions)
Microvilli increase SA
Lots of mitochondria

Question 16

Describe the anatomy of the LoH

Answer 16

Descend into medulla and ascend into cortex
Thin descending and ascending limbs - flatter cells (simple squamous cells), no microvilli
Thick ascending and descending limb - simple cuboidal epithelium

Question 17

Describe the anatomy of the distal convoluted tubule

Answer 17

Shorter
less developed microvilli
lots of basolateral interdigitations and more mitochondria

Question 18

Describe the anatomy of the collecting duct

Answer 18

3 sections:
- cortical collecting duct
- outer medullary collecting duct
- inner medullary collecting duct

Question 19

What marker is used to measure GFR?

Answer 19

creatinine as it is not reabsorbed, all is secreted