Lecture 18 - Renal Physiology: Potassium & Magnesium

Question 1

Key roles of the kidney?

Answer 1

elimination of waste products, control of fluid balance, control of minerals, regulate acid-base balance, produce hormones

Question 2

Mg Physiology?

Answer 2

bone formation, cofactor in copious amounts of reactions, regulation of vascular tone, cardiac rhythm, platelet-activated thrombosis

Question 3

Mg Absorption?

Answer 3

10-20% PCT, 60-70% thich ascending LoH, 10% DCT

Question 4

Mg reabsorption - LoH?

Answer 4

active transport through Claudin 16-19 receptors

Question 5

Assessments of Mg?

Answer 5

serum Mg, red cell Mg, 24hr excretion, Mg retention test, isotope analysis

Question 6

Symptom of hypomagnesaemia?

Answer 6

fatigue, cramps, tetany spasm, numbness, seizures, arrhythmias

Question 7

Causes of hypomagnesaemia?

Answer 7

common condition; diet, malabsorption and loss, hyperaldosteronism, diabetes, SIADH, renal loss

Question 8

Hypomagnesaemia treatment?

Answer 8

typically oral magnesium, otherwise IV magnesium sulphate

Question 9

Causes of hypermagnesaemia?

Answer 9

advanced CKD, excessive magnesium salt or drugs, Iatrogenic

Question 10

Internal balance of K?

Answer 10

buffered by movement of K into or out of skeletal muscles regulated by insulin and catecholamines

Question 11

pH and K?

Answer 11

acidosis leads to K efflux (as well as hyperglycaemia), alkalosis vice versa

Question 12

K reabsorption?

Answer 12

60% PCT, 30% thick ascending LoH, variable in collecting ducts

Question 13

Symptoms of hypokalaemia?

Answer 13

muscle weakness, paralysis, cardiac conduction abnormalities, cramps, constipation

Question 14

Hypokalaemic Periodic Paralysis?

Answer 14

inherited (rare) or thyrotoxic origin, abnormal K channels, triggered by high carbs (insulin) or SNS activation (stress), excessive K influx -> weakness

Question 15

K losses - renal?

Answer 15

hyperaldosteronism, licorice, diuretics, renal tubular acidosis

Question 16

K losses - gut?

Answer 16

vomiting, diarrhoea, laxatives, ileostomy

Question 17

Conns syndrome?

Answer 17

adrenal adenoma, secretes aldosterone -> hypertension and hyperkalaemia

Question 18

Symptoms of hyperkalaemia?

Answer 18

fatigue, paraesthesia, nausea, dyspnoea, palpitations

Question 19

Heart attack?

Answer 19

hyperkalaemia -> ventricular fibrillation -> cardiac arrest

Question 20

Psuedohyperkalaemia?

Answer 20

caused by haemolysis

Question 21

Causes of hyperkalaemia?

Answer 21

increased intake, disruption of cell intake (beta blockers, acidosis), decreased excretion (renal failure, hypoaldosteronism)

Question 22

Addison’s disease?

Answer 22

deficient secretion of aldosterone and cortisol, hyperpigmentation due to excessive ACTH excretion stimulating melanocytes, symptoms: lethargy, weakness, weight loss, hypotension

Question 23

Addison’s - diagnosis and treatment?

Answer 23

hyperkalaemia, hyponatraemia; use of short synacthen test; treatment: dexamethasome or fludrocortisone

Question 24

Treatment of hyperkalaemic MI?

Answer 24

stabilise AP, push K into cells, reduce K reabsorption, increase elimination, fix underlying problem

Question 25

Stabilising AP?

Answer 25

calcium, normalises membrane excitability, lasts 30min, prolongs cardiac arrest

Question 26

Beta agonists?

Answer 26

ventolin nebuliser, reduces K via influx, 30-60min to work, lasts 6 hr (combine w insulin w dextrose)

Question 27

Treating acidosis?

Answer 27

oral bicarbonate (IV if emergency)

Question 28

Reducing K absorption?

Answer 28

cation exchange products, calcium resonium

Question 29

Increasing K elimination?

Answer 29

K losing diuretic, or dialysis if already dialysis patient or Rhabdomyolysis