Renal blood flow

Question 1

Why is renal blood flow high?

Answer 1

Haemodynamic factors:
- lots of ‘push power’ to get blood to be adequately filtered
High resistance of afferent and efferent arterioles means the hydrostatic pressure beyond them is relatively low - helps promote resorption

Question 2

What do the efferent arterioles do beyond the glomerulus in cortical nephrons?

Answer 2

Glomerulus in cortex
Short LoH (only goes a bit into medulla)
Efferent arterioles => peritubular capillaries

Question 3

What do the efferent arterioles do beyond the glomerulus in Juxtamedullary nephrons

Answer 3

Glomerulus deeper in cortex
Long LoH dives deep into medulla
Efferent arterioles form the vasa recta

Question 4

What is the vasa recta?

Answer 4

Blood vessels that follow the LoH
Important in urine concentration

Question 5

Describe the countercurrent exchange mechanism in the kidney

Answer 5

Vasa recta amplifies concentrating ability of nephron
In the ascending limb:
- ions are pumped out of LoH
- water cannot follow
- makes interstitium salty
In the descending limb:
- water moves out
- concentrating tubular fluid

Question 6

Describe the autoregulation of renal blood flow

Answer 6

Myogenic reflex:
- high BP => stretches BV => reflex vasoconstriction and reduced blood flow
Tubuloglomerular feedback:
- Rise in glomerular pressure => increased GFR => increased tubular flow rate => less time for Na and Cl reabsorption => macula densa detects higher Na/Cl => JGA releases adenosis => afferent arteriolar vasoconstriction => reduces blood flow and GFR

Question 7

What factors affect renal blood flow?

Answer 7

Autoregulation
RAAS system
Vasoactive peptides

Question 8

what are some vasoactive peptides that control renal blood flow?

Answer 8

Bradykinin
Endothelin
Vasopressin