Flashcards in Control Of Potasssium Deck (33):
What is maintaing the ECF k+ critical?
Because of its effect on the resting membrane potential, hence the effects of the excitability on cardiac tissue and the risk o flife threatnign arrhythmia's with hyperkalaemia and hypokalmeia
How does the ecf k+ effect the resting membrane potential?
There is a gradient for k+ to move out the cell, and this results in the resting membrane potential, and therefore it is important that this gradient is not altered in any way
How si the ecf k+ regualted?
Immediate control is regulated by hte internal balance that moves K+ between the ecf and the icf and by the renal excretion of K+
What are some of the features of the internal K+ balance?
Is a net result of movement of K+ from the ECF into cells mediated by the Na K Atpas and movement of k+ out of the cells via K+ cahnnels that help to maintain the permeability of the membrane
What are the factors that increase the K+ uptake by the cells?
Hromones suchp as inulin, aldosterone and the catechilamines, and the increased K+ in the ecf
And alkalosis causes a shift of K+ into the cells
What are some of the factors promoting the K+ shift out of the cells?
Excecise, cell l,ysos, increase in the ecf osmolarity low concentration of k+ in the ecf adn acidosis which causes the shift of K+ out of the cells
What is the effect of insulin on the uptake of potassium?
K+ in the splanchic blood increases the production of insluin, which increases the Na-K-ATPase activity and icnreases the uptake of K+ by the diffferent cells
How is the fact insulin increases potassium uptake clincally releant?
IV insulin+ dextrose is used to treat hyperkalemia
What is the effect of aldosterone on K+ uptake?
K+ in blood stimulates the uptake of aldosterone, via Na_K_ATPase
What are the infleunces of catecholamines on potassium uptake?
They act via the B2 adrenoreceptors and stimulate Na-K-Atpase and the cellular uptake of K+
What is the effect of excerice on ECF K+?
Net realease of K+ during the revecory phase of the action potential means that K+ exits the cell, and skeltal muscle damage during excerise realeases K+, and the increase in plasma K+ is proportional to the intestiny of excercies, but uptake by non contracting cells prevents a danagerous hyperkalemia- and excercise will also increase production of catecholamines which increases the uptake by the non excercisng cells
What is the affect of acidosis on ECF K+?
There is a shift of K+ into cells, and then a recroprocal shift of K+ out of cells and therefore leads to hperkalemia
What is the effect of alkalosis on ECF K+?
There is a shift of H+ out of the ells, and there is therefrore a recrpical shift ofK= into the cells, and therefore the alkosis causes hypokalemia
What is the effect of hyperkalemia on the acid base balance?
There is a shift of K+ into the cells, and therefore there is a reciprocal H+ shift out of the cell,s and therefore hyerpkalemia leads to acidosis
What is the effect of hypokalemia on the acid base status?
There is a shift of K+ out of the cell,s and therefore there is a recirpcal H+ shift into the cells, and therefore hypokalemia causes alkalosis
Where does reabsorption of K+ occur within the nephron?
K+ is reasborbed passively by paracellular diffusion in the proximal tubule (67%), in the thick asecending limb in an active proccess driven by Na_K-ATpase in the basolateral membrane, Na_K_2cl in the apical membran, about (20%0 and by the intercalacted cells of the DCT and the collecting duct
From where in the nephron is K+ secreted?
By the principal cells of the DCT and the collecting duct
What are the tubular factors that affect K+ secretion by the prinical cells of the collecting duct?
The ECF (K+) as it stimulates the Na-K-atpase, and increase the permability of the channela=s, and aldosterone which increases the secretion of revelant proteins, such as Na-K-ATPase, and the acid base status as acidosis causes a decrease in K+ secretio whereas akalsis causes a increase in K+ secretion
What are some of the limunial factors affecting the secretion of K+?
An increase distal tubular flow rate washes away the luminal K+ and therefore increase the K+ loss, and there is also increased delivery of Na to the distal tubule and therefore loss of K+
What is the pump that mediates the K+ absorption by intercalacted cells in the distal tubule?
H+-K+-ATPase within the distal tubule
What are some of the effects of a change in ECF potassium conc?
Alter the cell membrane resting potential, alters the neuromuscula excitabily, and this causes problems with cardiac conduction and automaticity, and alters the nerual function and the sketal muscle function, and results in arrythimias, cardaic arresst and muscle paralysis
What concentration of potassium in the ECF would be classed as hyperkalemia?
What can be some of the external causes of hyperkalemia?
May be due to an increased intake (but only really if there is decreased renal function), or decreased renal excretion due to acute or chronic kidney injury, drugs which block potassium excertion such as ace inhibitors, K= sparing direutics or a low aldosterone state
What are some of the internal shifts that can cause hyperkalemia?>
Diabteic ketoacidosis, where there is no insulin, plasma osmolarity and metabolic acidosis, cell lysis in muscle crush injries and timour lusis, and metabolic acidosis and excercise
What are the clincal features of meatbolic acidosis?
in the heart, altered excitability, arrythmias and hear block, gastorintestinal such as neuromuscular dysfunction and a paralytic ileus and acidosis
What are some of the ECG features of hyperkalemia?
Ventricular fibrillation, p wave absent (intraventicular block, atrial stanstill), or a prolonged PR interval and depressed segement and a high t wave, and a high t wave by itself
What is the emergency treatment for Hyperkalemia?
Reduce the K+ effect on heart by the used of IV calcium gluconate which has an immediate effect, adn shift K+ into the ICF by a glucose and insulin IV, and remove K+ via the use of dialysis
What are some of the longer term treatments?
Treat cause, via stopping medications etc, reduce intake, and measures to remove K+ such as dialysis in chronic kidney injuryu.
What are the levels of potassium in hypokalemia/
< 3.5 mmol/l
What might cause hypokalemia?
Problems of the external balance, such as excessive loss in gi complaints such as diarrhea, bulmia and vomiting, renal loss due to use of direutic drugs, osmotic diresusi and high aldosterone levels, and problmes in the internal balance causing shifts of K+ into the ICF
What are the cliniacla features of hypokalemia?
In the heart, altered excitability and arrythmias, gastrointestinal, including neruomsucular dysfunction, and a paralyitic ileus, sketal muscule includes the neruomusuclar dysfunxtion that can potentially cause muscle weakenass, and renal, unresponsive to ADH and nephrogenic pH
What is the effect of hypokalmemia on the heart?
More fast Na channels anre in the active form, and therefore the heart is more exictable