deck_1460742 Flashcards
(47 cards)
How much K+ is found in the body?
3500 mmol
How is the K+ distributed through the body?
98% in the intracellular fluid 2% in the extracellular fluid
How are the concentrations of K+ in different body compartments maintained?
Na-K-ATPase pump
Why is K+ regulation important?
- 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
What are the mechanisms for controlling K+ levels?
External balance adapts excretion to match the K+ intake and regulates the total potassium contentInternal balance regulates the [K+] in the ECF.
Describe the external balance of K+ and its characteristics
Kidneys adjust excretion to match intakeIs slower to act – 6-12 hoursIs responsible of K+ levels in the long term
Describe the internal balance of K+ and its characteristics
Has an immediate effectResponsible for moment to moment controlShifts the K+ from the ICF to the ECF
Describe the events of K+ following a meal
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
What channels control the internal balance of K+?
- 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)
What three factors promote the uptake of K+ into cells?
HormonesAlkalosisIncreased [K+] in the ECF
What are the three hormones that promote the uptake of K+ into cells?
InsulinAldosteroneCatecholamines
Describe the effect of insulin on [K+] in the blood
K+ in the blood stimulates insulin secretionInsulin promotes the uptake of K+ into muscle and liver cells via Na-K-ATPase
Describe the effect of aldosterone on [K+] in the blood
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
What factors promote the shift of K+ out of the cells and into the ECF?
- Low ECF [K+]2. Exercise3. Cell lysis4. Increase in ECF osmolality/tonicity5. Acidosis and alkalosis
What affect does exercise have on the [K+]?
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
What can causes cell lysis?
Trauma to skeletal muscle, causing muscle cell necrosis (Rhabdomyolysis)Intravascular haemolysisCancer chemotherapy
How does plasma tonicity cause K+ to move out of cells?
Water moves into cells from ECFCauses an increase in [K+] in the ICFK+ leaves down its concentration gradient
What effects does acidosis have on the [K+]?
Causes H+ to move into cells which cause K+ to move out of the cell causing hyperkalaemia
What effects does alkalosis have on the [K+]?
Causes H+ to move out of cells, which causes K+ to move into the cells causing hypokalaemia
Where is K+ reabsorbed in the kidney?
PCTThick ascending limbIntercalated cells of DCTIntercalated cells of cortical collecting ductIntercalated cells of medullary collecting duct
Where is K+ secreted from in the kidney?How much K+ is secreted?
Principal cells of the DCT and the cortical collecting duct20%
How much reabsorption occurs at the different parts of the kidney?
Most at PCT – 67%TAL – 20%Others – 10-12%
What can a very low K+ lead to?
Inability of kidney to form concentrated urineIncreased tendency to develop metabolic alkalosisEnhancement of renal ammonium excretion
What and an increase [K+] in the ECF do to the cell membrane?
Depolarises the cell membrane
