Kidney function & Diuretics

Question 1

What is filtered from the blood at the Bowmans capsule via ultrafiltration

Answer 1

Salts, glucose, most small molecules

Question 2

What 6 things are actively pumped back into the plasma at the proximal convoluted tubule

Answer 2

Water
Sodium
Potassium
Bicarbonate
Phosphate
Glucose

Question 3

How are glucose and sodium pumped back into plasma at the PCT

Answer 3

Using sodium / glucose co transporters e.g. SGLT2

Question 4

What enzyme is responsible for producing bicarbonate (HCO3-) into the plasma, and excreting H+ into the urine at the PCT

Answer 4

Carbonic anhydrase

Question 5

How much Na+ and water is reabsorbed at the PCT

Answer 5

65% of both

Question 6

What is the basic 2 stage process of water and electrolyte reabsorbtion the occurs in the Loop of Henle “counter-current mechanism”

Answer 6

1. Na+, K+ and Cl- actively pumped out of ascending limb into IS fluid
2. Water drawn through osmosis (through aquaporins) into IS fluid by high conc of salts. Water quickly passes into vasa recta blood vessels and plasma. This draws salts in from IS fluid via osmosis.

Question 7

What percentage of water and Na+ is reabsorbed at the LOH

Answer 7

20% H2O

25% Na+

Question 8

What 2 ions are exchanged at the Distal convoluted tubule to maintain salt balance

Answer 8

Na reabsorbed into plasma, in exchange for K+ excreted in urine.

Question 9

What is the kidney natural response to detecting hyperkalaemia

Answer 9

Renin is produced - increases Na+ reabsorption to plasma, - increases K+ extretion in urine.

Question 10

PTH acts on the DCT to increase the reabsorption of what?

Answer 10

Ca++ - DCT is the main site of reabsorption in the kidney.

Question 11

What is the basic process of responding to dehydration involving the hypothalamus, pituitary and kidney collecting duct

Answer 11

1. Plasma increase in osmolality detected at Hypothalamus.
2. Stimulates “thirst” sensation and production of ADH (vasopressin) from post. pituitary.
3. ADH acts to open aquaporins at collecting duct - increases H2O reabsorption into plasma, therefore decr. urine production.

Question 12

Where is the site of action of mannitol - how does it act as a diuretic

Answer 12

PCT - purely osmotic effect, draws H2O into tubule through increase osmotic pressure (think mannitol - similar to mannose - sugar - big molecule)

Question 13

Mannitol draws water from cells into plasma / IS fluid, what other conditions / pathology can be treated with it?

Answer 13

For reducing intracranial / intra ocular pressure

Also in haemolysis and rhabdomylosis (why?)

Question 14

Give 2 examples of loop diurectics (act on LOH)

Answer 14

Furosemide / Bumetonide

Question 15

1. How do loop diuretics work
2. How does this relate to their side effects
3. Random other SE of loop diuretics

Answer 15

1. Block Na / K / Cl co transporter, - increase osmololality of urine - retains water in urine.
2. Hypokalaemia (Na is able to reabsorb into blood later on but K+ relies on transport) - metabolic acidosis (K+ and H+ ions go hand in hand)
3. Ototoxicity

Question 16

Are loop diuretics quick or slow acting

Answer 16

Relatively quick - 30mins IV, 60 mins oral

Question 17

Where to thiazide - diuretics act, give 3 examples

Answer 17

Indapamide, bedroflumethiazide, metalozone

Act at distal convoluted tubule (DCT)

Question 18

How do thiazide diuretics work - relate this to their potential initial SE

Answer 18

Block Na reuptake into plasma, increasing urine osmolality so drawing out more water in urine.
Can cause hyponatraemia as excreting more Na+

Question 19

Why do thiazide-diuretics also cause hypokalaemia

Answer 19

Initially they increase urine Na+ , but further down tubule this high level of Na+ reabsorbs into plasma, K+ is exchanged for this into urine so get low K+ plasma levels.

Question 20

Other than hyponatraemia and hypokalaemia what other SE of 2 things is caused by thiazides

Answer 20

Hyper calcaemia
Increased urate (avoid in gout)

Question 21

Give 2 examples of potassium sparing diuretics, where and how do they work, how can this lead to a SE

Answer 21

Spironolactone, Eplerenone
Aldosterone receptor blockers - prevent aldosterone (mineralocorticoid produced by adrenal gland) acting on kidney. Therefore salt re-absorption into plasma is stopped, so have high urine Na+ levels - water drawn out via osmosis, but means get incr. plasma K+ levels - hyperkalaemia SE (also metab acidosis as K+ and H+ go hand in hand).

Question 22

How long does spironolactone and eplerenone take to work

Answer 22

Days