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3 - Urinary > deck_1460742 > Flashcards

deck_1460742 Flashcards

1
Q

How much K+ is found in the body?

A

3500 mmol

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2
Q

How is the K+ distributed through the body?

A

98% in the intracellular fluid 2% in the extracellular fluid

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3
Q

How are the concentrations of K+ in different body compartments maintained?

A

Na-K-ATPase pump

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4
Q

Why is K+ regulation important?

A
  1. K+ determine the resting membrane potential and any changes have significant effects on the excitability of cardiac and neuromuscular tissues, which will effect their functions. 2. Intracellular K+ levels are important for cell functione.g. Cell volume and growth, DNA/protein synthesis, enzyme function
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5
Q

What are the mechanisms for controlling K+ levels?

A

External balance adapts excretion to match the K+ intake and regulates the total potassium contentInternal balance regulates the [K+] in the ECF.

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6
Q

Describe the external balance of K+ and its characteristics

A

Kidneys adjust excretion to match intakeIs slower to act – 6-12 hoursIs responsible of K+ levels in the long term

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7
Q

Describe the internal balance of K+ and its characteristics

A

Has an immediate effectResponsible for moment to moment controlShifts the K+ from the ICF to the ECF

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8
Q

Describe the events of K+ following a meal

A

Intestine and colon absorb K+ directlySubstantial amount of K+ enters the ECF80% of ingested K+ moves into the cellsKidneys begin to excrete K+ after a slight delay Excretion is complete in 6-12 hours

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9
Q

What channels control the internal balance of K+?

A
  1. Movement of K+ from ECF into cells by Na-K-ATPase2. Movement of K+ out of cells to the ECF by K+ channels (determine K+ permeability of the cell membrane)
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10
Q

What three factors promote the uptake of K+ into cells?

A

HormonesAlkalosisIncreased [K+] in the ECF

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11
Q

What are the three hormones that promote the uptake of K+ into cells?

A

InsulinAldosteroneCatecholamines

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12
Q

Describe the effect of insulin on [K+] in the blood

A

K+ in the blood stimulates insulin secretionInsulin promotes the uptake of K+ into muscle and liver cells via Na-K-ATPase

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13
Q

Describe the effect of aldosterone on [K+] in the blood

A

K+ in the blood stimulates aldosterone secretion which in turn stimulate the excretion of K+ by Na-K-ATPase by increasing transcription of Na-K-ATPase

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14
Q

What factors promote the shift of K+ out of the cells and into the ECF?

A
  1. Low ECF [K+]2. Exercise3. Cell lysis4. Increase in ECF osmolality/tonicity5. Acidosis and alkalosis
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15
Q

What affect does exercise have on the [K+]?

A

During skeletal muscle contraction, there is a net release of K+ in the recover period of APPlasma [K+] increases proportionally with the amount of exercise doneNon-contracting tissues take up excess K+ (prevents hyperkalaemia)Increase secretion of catecholamines increase K+ uptake in other cells

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16
Q

What can causes cell lysis?

A

Trauma to skeletal muscle, causing muscle cell necrosis (Rhabdomyolysis)Intravascular haemolysisCancer chemotherapy

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17
Q

How does plasma tonicity cause K+ to move out of cells?

A

Water moves into cells from ECFCauses an increase in [K+] in the ICFK+ leaves down its concentration gradient

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18
Q

What effects does acidosis have on the [K+]?

A

Causes H+ to move into cells which cause K+ to move out of the cell causing hyperkalaemia

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19
Q

What effects does alkalosis have on the [K+]?

A

Causes H+ to move out of cells, which causes K+ to move into the cells causing hypokalaemia

20
Q

Where is K+ reabsorbed in the kidney?

A

PCTThick ascending limbIntercalated cells of DCTIntercalated cells of cortical collecting ductIntercalated cells of medullary collecting duct

21
Q

Where is K+ secreted from in the kidney?How much K+ is secreted?

A

Principal cells of the DCT and the cortical collecting duct20%

22
Q

How much reabsorption occurs at the different parts of the kidney?

A

Most at PCT – 67%TAL – 20%Others – 10-12%

23
Q

What can a very low K+ lead to?

A

Inability of kidney to form concentrated urineIncreased tendency to develop metabolic alkalosisEnhancement of renal ammonium excretion

24
Q

What and an increase [K+] in the ECF do to the cell membrane?

A

Depolarises the cell membrane

25
Q

What does a decreased [K+] in the ECF do to the cell membrane?

A

Hyperpolarises the cell membrane

26
Q

Describe the characteristics of K+ secretion from principal cells

A

Is a passive process (driven by electrochemical gradient of K+ between principal cell and lumen)Na+ is reabsorbed through ENaC which drives K+ out of the cell through a separate K+ channelIs driven by Na-K-ATPase in the basolateral lumen

27
Q

What factors affect K+ secretion?

A

Aldosterone levelsECF [K+]Acid base status of the bloodIncrease distal tubular flow rate causes an increase K+ lossIncrease Na delivery to distal tubule causes more K+ loss

28
Q

Describe the absorption of K+ in the distal tubules and the collecting duct

A

K+ is absorbed by intercalated cellsIs an active processMediate by H+ K+ ATPase in the apical membrane

29
Q

What is the result of poor perfusion of a kidney due to renal artery stenosis on K+ levels?

A

Causes hypokalaemia– the poor perfusion activate the RAAS which increases the amount of aldosterone which will increase the amount of K+ excretion

30
Q

Why can Cushing’s Syndrome cause hypokalaemia?

A

Increased levels of glucocorticoids in the blood can bind to mineralocorticoid receptors and mimic their physiological actions

31
Q

What can be given to patient in order to reduce plasma K+ levels?

A

Insulin promotes the uptake go K+ into cells

32
Q

What is the main effect of changes to the [K+]?

A

Alters the cell membrane resting potentialAffects neuromuscular excitability- problems with cardiac conduction and pacemaker automaticity- affects neuronal function- alter skeletal and smooth muscle function

33
Q

What are the main clinical effects of altered [K+]?

A

ArrhythmiasCardiac ArrestMuscle paralysis

34
Q

What are some causes of Hyperkalaemia?

A

Increased intake of K+– renal dysfunction or inappropriate K+ IV dosesInadequate renal excretionInternal shifts in [K+]

35
Q

What are some things that could causes inadequate urinary excretion of K+?

A

Acute renal injuryChronic renal injuryReduced aldosterone

36
Q

What are some things that could cause the internal [K+] to change?

A

DIabetic ketoacidosisMetabolic acidosisCell lysis

37
Q

What are the main effects of hyperkalaemia?

A

Heart issues – arrhytmias and heart blockGastro intestinal (paralytic ileus due to neuromuscular dysfunction)Acidosis

38
Q

What effect does hyperkalaemia have on cardiac tissue?

A

It increases the resting membrane potential, therefore depolarising the cell– Fast Na channels remain in the active forms the heart is less excitable

39
Q

What are the ECG changes that you see in hyperkalaemia?

A
  1. Tall T waves2. Prolonged PR interval Depresses ST segmentTall T waves3. Widening of QRS complex4. Ventricular fibrillation(get more of these as the serum K+ levels increase)
40
Q

What is the emergency treatment for hyperkalaemia?

A

Reduce the effect the K+ is having on the heart– IV calcium gluconateShift K+ into the intracellular fluid – Glucose and insulin IV– Nebulised beta agonists (salbutamol)Remove excess K+– Dialysis

41
Q

What are the longer term treatment for hyperkalaemia?

A

Treat causesReduce intakeTake measures to remove excess K+

42
Q

What is the measure that defines hypokalaemia?

A

[K+]

43
Q

What are some causes of hypokalaemia?

A

Excessive loss of K+– diarrhoea, vomiting– diuretic drugs, osmotic diuresis in diabetes, high aldosterone levelsShifts of K+ into the ICF– metabolic alkalosis

44
Q

What affect does hypokalaemia have on the resting cell membrane potential?

A

Cell membrane is more hyper polarised so there are more fast Na channels in an active form and the heart is more excitable

45
Q

What are the clinical features of hypokalaemia?

A

ArrhythmiasParalytic ileusMuscle weaknessCD cells are unresponsive to ADH –> nephrogenic diabetes insipidus

46
Q

What are the ECG changes that you will see in someone with hypokalaemia?

A

Low T waveHigh U waveLow ST segment

47
Q

What is the treatment for hypokalaemia?

A

Treat the causePotassium replacement with IV or orallyPotassum sparing diuretic if it is due to an increased mineralocorticoid activity (blocks aldosterone action on principal cells)

3 - Urinary (39 decks)

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