Renal Physiology

Question 1

If MAP is 160mmHg, what is the likely renal blood flow?

Answer 1

1200ml/min

Renal blood flow is 25% of cardiac output, and is maintained by autoregulation in the range 80-200mmHg

Question 2

Where is the blood supply to the renal medulla derived from?

Answer 2

Capillaries close to the boundary of the cortex and medulla loop into the medulla and form the vasa recta. These surround the Loop of Henle.

They are the only blood supply to the medulla.

Question 3

Where are the macula densa cells located?

Answer 3

The DCT

Question 4

Will autoregulation still occur in the dennervated kidney?

Answer 4

Yes

Question 5

What is renal oxygen consumption?

Answer 5

18ml/min

Question 6

How many nephrons does each kidney contain?

Answer 6

1 million each

Question 7

Which cells of the kidney have brush borders?

Answer 7

PCT cells.

Question 8

Where are there more mitochondria - the DCT or PCT?

Answer 8

The PCT is rich in mitochondria

Question 9

Do only 20% of nephrons have a LoH?

Answer 9

No, all nephrons possess a Loop of Henle. 20% will be juxtamedullary

Question 10

What size are the pores of Bowman’s capsule?

Answer 10

5nm

Question 11

What is the set up of the renal blood supply?

Answer 11

The renal arteries divide into arterioles, then capillaries, then efferent arterioles, then vasa recta

Question 12

Where does 90% of the blood entering the kidneys supply?

Answer 12

The cortex.

It has a high blood flow-500 ml/min per 100 g of tissue. It has a low arteriovenous difference of approximately 2%.

Question 13

What do PGI2 and PGE2 do?

Answer 13

Released in hypovolaemia and may cause vasodilation helping prevent the kidney from ischaemic damage

Question 14

Do NSAIDs reduce GFR under normal circumstances?

Answer 14

NSAID’s do not influence GFR under normal circumstances but can cause significant loss of function if there is effective loss of circulating volume from any cause

Question 15

At what point does symptomatic uraemia occur?

Answer 15

Symptomatic uraemia usually devlops when the GFR is about 15 ml/min

The symptoms of uraemia occur late in the loss of renal function, and are caused by retained toxic products. They are non specific and include anorexia, nausea, vomiting, lethargy, poor sleep, pruritus

Question 16

What is the normal young adult renal blood flow?

Answer 16

1200ml/min - 25% of cardiac output

Question 17

What happens to sodium in the PCT?

Answer 17

Sodium is pumped from tubular cells into the interstitium by the sodium-potassium-ATPase pump (actively reabsorbed)

Question 18

What is reabsorbed in the PCT?

Answer 18

Bicarbonate, chloride, glucose, sodium and potassium

Question 19

Is water reabsorption under control of aldosterone?

Answer 19

No, aldosterone mainly acts in the distal tubule by regulating sodioum reabsorption. Water then follows passively.

Up to 70% of filtered water is reabsorbed in the proximal convuluted tubule

Question 20

Where is ammonia produced in the nephron?

Answer 20

Ammonia is produced in tubular cells by metabolism of glutamine. Its main role is in the buffering processes promoting the excretion of hydrogen ions.

Tubular secretion of ammonia occurs in both proximal and distal tubules

Question 21

Does the kidney filter of all molecules under 5nm diameter?

Answer 21

No, glomerular filtration is partly determined by molecular size, charge and protein binding.

Question 22

What happens to proteins in the kidney?

Answer 22

In health, large molecules do not pass through the glomerular membrane. Any protein molecules that do are taken up by pinocytosis at the luminal membrane

Question 23

How much glucose is reabsorbed per day?

Answer 23

160g

99% of glucose is reabsorbed by a saturable co-transport mechanism in the proximal tubule

Question 24

What happens to hydrogen ions in the kidney?

Answer 24

Hydrogen ions are buffered intraluminally by phosphate, not bicarbonate ions.

Question 25

What is the tubular transport maximum for glucose?

Answer 25

380g/min

Question 26

What is the renal threshold for glucose?

Answer 26

11 mmol/L

Question 27

What causes renin release?

Answer 27

Renin is controlled by the macula densa and is release in response to low sodium flux.

When less filtrate reaches the macula densa, sodium concentration around the cells is reduced. This is detected by the macula densa cells and an increase in rennin secretion is triggered

Question 28

Where is renin released from?

Answer 28

Juxtaglomerular apparatus in the wall of the afferent arteriole

Question 29

How is renin release affected by hypotension, beta blockers and ADH?

Answer 29

Renin is released in response to the low cardiovascular pressures which occur in hypotension

Renin release is increased in response to beta-1-receptor stimulation

Release is decreased by antidiuretic hormone which acts to conserve sodium and water

Question 30

What does the primary active transport of Na/K do?

Answer 30

3 sodium ions are pumped outwards for 2 potassium ions inward

Question 31

In primary active transport, where is energy used?

Answer 31

In primary active transport, energy is imparted which allows the substance being transported to be moved against its electrochemical gradient

Question 32

What happens to aldosterone production if sodium chloride is ingested?

Answer 32

Sodium chloride ingestion increases plasma osmolality and will decrease aldosterone prouction.

Question 33

What effect does trauma leadning to hypovolaemia have?

Answer 33

Hypovolaemia causes renin release, and thus angiotensin II release. This causes aldosterone release, with the ultimate effect of increasing sodium and water reabsorption

Question 34

What does aldosterone do to potassium?

Answer 34

Aldosterone stimulates the production of potassium channels in the luminal membrane of the cortical collecting duct. Potassium is lost through these.

=> increases urinary potassium excretion

Question 35

What will aldosterone do to urinary sodium concentration?

Answer 35

Reduce it

Question 36

What is para amino hippuric acid?

Answer 36

PAH is 90% cleared by the kidneys from the plasma. PAH clearance is therefore used to estimate RPF (renal plasma flow). The amount of PAH still in the blood can be corrected for.

Question 37

What are the features of an ideal substance for measuring GFR?

Answer 37

• freely filtered
• neither secreted or reabsorbed
• not metabolised

eg inulin