H, K, Ca & Mg

Question 1

Why does the kidney try to conserve all/generate excess bicarb?

Answer 1

For every bicarb lost in urine an H+ is generated

Therefore need to re-absorb all bicarb before we can excrete excess H+

Question 2

Acidosis and alkalosis, which can we withstand better?

Answer 2

Alkalosis

Question 3

The pH is 6.7 at the end of the PCT, why?

Answer 3

Re-absorption of bicarb

Question 4

The pH in the CD can vary between 4.5-8, why such a large range?

Answer 4

pH will reflex how much acid needed to maintain serum pH

Question 5

How is the acid-base balance effected in vomiting?

Answer 5

Loss of H+

Loss of K+

Metabolic alkalosis

Question 6

How is the acid-base balance effected in diarrhoea?

Answer 6

Loss of K+

Loss of bicarb

Metabolic acidosis

Question 7

K+ intake from food (and therefore serum levels) can be quite high, how is death prevented?

Answer 7

K+ uptake into cells (quick)

K+ excretion in urine (6-8hrs)

Question 8

What 3 things increase the activity of Na/K ATPase? (Decreasing extracellular [K])

Answer 8

K+ conc in plasma

Insulin

Noradrenaline effect on beta2-adrenoceptors

Question 9

How is K+ excreted?

Answer 9

Small amounts in faeces and sweat

800 mmol by normal kidneys

Question 10

What factors increase K+ secretion?

Answer 10

Increased intracellular [K+] = larger gradient (raised by aldosterone)

Increased electro-ve lumen = large pull for K+ (raised by aldosterone)

Increased permeability of the luminal mem (raised by aldosterone)

Decreased luminal [K+]

Question 11

What is hypokalaemias effect on membrane potential?

Answer 11

Bigger gradient between intracellular and extracellular compartment

Depolarisation lead to increased excitability

Risk of arrhythmias

Question 12

What is hyperkalaemias effect on membrane potential?

Answer 12

Smaller gradient between intracellular and extracellular compartment

Decreased membrane excitability

Risk of cardiac arrhythmias

Question 13

Outline the symptoms of hypokalaemia

Answer 13

Weakness

Polyuria = low K causes ADH resistance

Constipation = smooth muscle dysfunction

Arrhythmias

U wave on ECG

Question 14

What are the causes of hypokalaemia?

Answer 14

Reduced dietary intake

Increased entry into cells = met alkalosis, increased beta-adrenergic activity

Increased GI loss = vomiting, diarrhoea

Increased urine loss = increased aldosterone, increased urine flow, renal tubular acidosis

Question 15

Ca reabsorption is under what kind of control?

Answer 15

Hormonal and vitD

Question 16

What inhibits the precipitation of Ca and therefore the formation of stones?

Answer 16

Magnesium

Question 17

What happens in the presence to hypercalcaemia?

Answer 17

Activation of Ca sensing receptors

Decreased PTH and increased calcitonin release =
1) increased renal excretion

2) less active vit D = decreased calcitriol synthesis = decreased mobilisation of Ca from skeleton and soft tissues

= normal plasma Ca

Question 18

What happens in the presence of hypocalcaemia?

Answer 18

Inactivation of Ca sensing receptors

Increased in PTH release =

1) decreased in renal excretion
2) more active vit D = increase in calcitriol synthesis = increased mobilisation of Ca from skeleton and soft tissue

= normal plasma Ca

Question 19

What part of the tubules is under PTH and vit D control?

Answer 19

DCT

Question 20

What are the symptoms of hypocalcaemia?

Answer 20

Paraesthesia = pins and needles

Tetany

Laryngospasm

Reduced myocardial contractility

Memory loss

Confusion

Hallucination

Question 21

Outline the causes of hypocalcaemia?

Answer 21

Vit D def

Lack of PTH

Reduced intake

Malabsorption

Hypomagneasaemia = interferes with PTH

Question 22

Outline the functions of magnesium

Answer 22

Intracellular signalling

Cofactor for protein and DNS synthesis

Control of neural activity in the brain

Cardiac excitability

Neuromuscular transmission

Osteoblast proliferation and bone strength

Question 23

In the tubule where does the majority of magnesium reabsorption take place?

Answer 23

TAL 50-70%

Question 24

Name some causes of hypomagnesaemia

Answer 24

Malnutrition

Prolonged fasting

IV feeding

Loop diuretics

Thiazide diuretics

Question 25

What symptoms occur with hypomagnesaemia?

Answer 25

Fatigue

Muscle spasms

Anxiety

Headache

Cardiac dysrhythmias

Tetany

Seizures

Hypocalaemia