Glomerular Filtration Rate

Question 1

Describe the arterial supply of the kidney - name all the arteries

Answer 1

Renal artery

Segmental arteries

Interlobar arteries

Arcuate arteries

Interlobular arteries

Afferent arterioles

Efferent arterioles

Question 2

What do the efferent arterioles become

Answer 2

Become either the peritubular capillaries or the vasa recta

Question 3

What are the differences between the peritubular capillaries and the vasa recta

Answer 3

Peritubular capillaries:

• Supply cortical nephrons
• Capillaries are randomly arranged

Vasa recta

• Supplies juxtamedullary nephrons
• Capillaries are straight and run parallel to the loop of Henle

Question 4

What substances are filtered by the glomerulus

Answer 4

Water

Salts

Glucose

Urea

Question 5

What forms the filtration barrier - name and describe the layers

Answer 5

Capillary endothelial layer - have fenestrations which allow particles and fluid through

Basement membrane - has glycoproteins in it which carry a -ve charge -> repells proteins (all -vely charged)

Podocytes - has filtration slits between pedicels to allow filtrate to pass through

Question 6

What pressures are found at the glomeulus

Answer 6

P_GC - hydrostatic pressure in the capillary

P_BC - hydrostatic pressure in Bowman’s capsule

π_GC - oncotic pressure in glomerulus

Question 7

How is P_GC formed

Answer 7

Hydrostatic pressure in the capillary is formed due to the AA diameter being larger than the EA diameter

This causes there to be a build up of fluid in the glomerulus which increases the hydrostatic pressure and forces fluid out

Question 8

How is the P_GC regulated

Answer 8

By autoregulation and by TG-feedback

Question 9

Describe how P_GC is regulated

Answer 9

An increase in BP results in the AA constricting to keep GFR unchanged - increased BP increases amount of fluid in the glomerulus -> want to stop this happening

A decrease in BP results in the AA dilating to keep GFR unchanged by allowing more fluid in

Question 10

How does autoregulation increase the GFR

Answer 10

Constrict efferent arteriole - less blood able to leave glomerulus -> increased hydrostatic pressure -> increased GFR

Dilate afferent arteriole - more blood enters glomerulus so increases hydrostatic pressure -> increases GFR

Question 11

How does autoregulation decrease GFR

Answer 11

Constriction of the AA - less blood enters glomerulus so hydrostatic pressure decreases so GFR decreases

Dilation of EA - more blood leaves glomerulus so hydrostatic pressure decreases so GFR decreases

Question 12

What is the tubular glomerular feedback

Answer 12

Further autoregulation of the GFR

It links the NaCl concentrations at the macula densa with control of renal arteriolar resistance

Question 13

Describe what happens if there is an increase in [NaCl] in the DCT

Answer 13

Increased [NaCl] means more NaCl enters the macula densa cells via NKCC2 from the DCT

This causes increased ATP production which is converted to adenosine which is released and binds to A1 GPCRs on smooth muscle cells to cause production of:

• Gi - inhibits adenylyl cyclase
• Go - increases intracellular [Ca] which causes additional vasoconstriction in the AA -> decreases GFR

Question 14

What is the macula densa’s response if there is a decreased [NaCl]

Answer 14

Macula densa cells release prostaglandins which cause vasodilation of the AA

Question 15

What happens to the GFR during sleep

Answer 15

During sleep the AA constricts while the EA dilates to cause a decrease in the GFR