Lecture 5 - Renal Blood Supply

Question 1

How much cardiac output does the kidney receive and how much of this is involved in glomerular filtration?

Answer 1

~ 20%
~ 1.1L blood/min

Question 2

What vessels supply the kidneys?

Answer 2

Renal arteries

Question 3

What is the blood supply path to the kidney (start to end)?

Answer 3

Renal artery
Arteries
Afferent arteriole
Glomerulus - ultrafiltration
Efferent arteriole
Peritubular capillaries and vasa recta - reabsorption
Venules
Renal vein

Question 4

Label the following diagram:

Answer 4

IA - interlobular artery

AA - afferent artery

G - glomerulus

EA - efferent artery

BS - Bowman’s capsule

RT - renal tubules (surround the peritubuluar capillaries)

NB : narrower efferent

Question 5

Whats the function of the peritubular capillaries and the vasa recta?

Answer 5

Peritubular capillaries:

• Provide nutrients and oxygen to epithelial and interstitial cells
• Supply blood for reabsorption and secretion in the PCTs

Vasa recta:

• run alongside LoH, providing nutrients and oxygen to maintain gradient
• function as countercurrent exchangers which contribute to the conc of urine (can reabsorb water)

Question 6

How is the GFR regulated?

Answer 6

Extrenal mechanism

• Sympathetic and hormonal mechanism

Intrinsic mechanism

• autoregulation - altering diameters of arterioles (myogenic control)
• tubuloglomerular feedback

Question 7

What mechanisms occur when BP falls low causing GFR to decrease?

Answer 7

• Autonomic-sympathetic nervous system causes constriction
• Myogenic control - afferent and efferent arterioles diameter altered
• tubuloglomerular feedback

Question 8

What 3 body systems would detect a drop in BP and how do they react?

Answer 8

• CV system: baroreceptors in aorta detect BP and activate sympathetic NS
• Renal system: release of renin from juxtaglomerlar apparatus and aldosterone from adrenal cortex
• Neuroendocrine system: release of ADH from pituitary gland

Question 9

What range of blood pressure can the GFR be kept constant?

Answer 9

BP range of 80-180mmHg

Question 10

What would dilation and constriction of the two arterioles cause?

Answer 10

Question 11

What are the major prostanoids and what do they do?

Answer 11

Prostaglandins E2 and I2

Dilate blood vessels and lower blood pressure

Question 12

What occurs in low blood pressure states?

Answer 12

• Angiotensin II and renin released

Question 13

What effect do NSAIDs have on PG synthesis?

Answer 13

NSAIDs block COX enzymes which are needed for PG synthesis

Causes a problem in people who have vasoconstrictor stimuli such as patients who are losing blood or those with a low BP

= UNOPPOSED vasoconstriction occurs, poor renal perfusion, acute renal failure

Question 14

What regulates the afferent and efferernt arterioles?

Answer 14

• Cicrulating hormones: such as AngII are potent efferent arteriole vasoconstrictors
• Paracrine factors: released locally by kidney such as NO and PGs
  
  • afferent arteriole is more sensitive to vasodilator effect of NO
  • PGs modulate effects of vasoconstriction
• Renal sympathetic nerves: innervate afferent and efferent arterioles = constriction

Question 15

What happens if GFR increases too much?

Answer 15

Flow of filtrate increases in tubule =

less time for NaCl to be reabsorbed from filtrate =

high conc of salt reaches DCT macula densa cells =

cells feedback to afferent and efferent arterioles =

GFR decreases

Question 16

Where is most H2O reabsrobed?

Answer 16

Primarily from collecting duct, but also the descending loop of the LoH

Question 17

How is the vasa recta involved in H2O reabsorbption?

Answer 17

Allows corticomedullary interstitial hyperosmotic gradient to be made which allows water to be drawn by osmosis.

Hyperosmotic interstitium needs to be maintained for this and water needs to be carried awway

Question 18

How are vasa recta classes as countercurrent loops?

Answer 18

Blood flows in slowly and in opposite directions to the flow in the LoH

They are looped to prevent the high concentration of solutes in the medullary interstitium being washed away

For example, if you inject NaCl into fingertip, it will be washed away but you dont want this to happen to the the cortico-medullary solute gradient

Question 19

Describe the gradient between descending vasa recta and medullary interstitial fluid next to the ascending loop.

Answer 19

H2O leaves vasa recta due to high osmolality outside and solutes enter vasa recta.

This continues until plasma and medulla have similar osmolalities = Plasma equilibriates with interstitium

Question 20

Describe the gradient between ascending vasa recta and medullary interstitial fluid next to the descending loop

Answer 20

H2O enters vasa recta due to high osmolality inside and solutes lease vasa recta.

This continues until plasma and medulla have similar osmolalities = Plasma equilibriates with interstitium

Question 21

Summarise the three main functions of the vasa recta.

Answer 21

• Provides oxygenated blood to renal medullary and carry away metabolic toxins - just like normal capillaries
• Preserve cortico-medullary osmotic gradient - prevents rapid salt removal from medullary interstitium
• Remove absorbed H2O