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Lecture notes of 5 pages for the course Foundations Of Biomedical, Behavioural And Social Sciences For Medicine 2020/21 at UoS (YR 2 CONTENT)
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Potassium Homeostasis:Potassium-needed for maintainance of cell function
Ionic imbalance of K+ and Na+ conc intracellularly and extracellularly
Maintained by the Na+/k+ ATPase pump at REST
Pumps 3Na+ out 2K+ in
Potassium channels-K+ out of the cell
Higher K+ conc inside than outside
Most K+ held in cells
Little in ECF
Hyperkalaemia- failure to remove ingested K+ from ECF
Hypokalaemia- loss of K+ from ECF
Normal plasma potassium: 3.5-5.0mm/L
Excretion of K+ from kidneys= K+ regulation
Re-distribution of K+ ECF and ICF-first line defence
Regulation of K+ ECF and ICF=internal K+ balance
Cells-overflow site in hyperkalaemia
Source of K+ in hypokalaemia
Factors regulating K+ into and out of skeletal muscle:
Insulin-shifts K+ into cells until kidney exretes K+ load
Catecholamines-adrenaline
Factors increasing K+uptake into cells:
Insulin
Aldosterone- excess=hypokalaemia deficient=hyperkalaemia
B-adrenergic stimulation-(carecholaimnes)- movement from ECF-ICF
Beta blockers- hyperkalaemia-prevent uptake into cells
Metabolic alkalosis- decreases K+ ECF
Factors that decrease K+ uptake into cells:
Metabolic acidosis
Cell lysis-severe muscle injury/red blood cell injury-hyperkalaemia
, Strenuous activity- hyperkalaemia-releases potassium from skeletal muscle
Increased ECF osmolarity-causes redistribution of potassium
Due to osmotic flow out of cells
K+ diffuses out of cells
Increasing ECF K+ conc
Acid-base transport:
Na+-H+
Na in needs to be removed by Na+ K+ ATP ase pump
K+ uptake-greater when this transport pahway activated
HCO3 and H+ - Acidosis with acidemia
Decrease in ECF- HCO3
Inhibition of Na+ and HCO3
Fall in intracellular Na+
Therefore, reduced Na+/K+ ATPase activity
Acidosis with acidemia:
CL-HCO3 exchange
Decrease in extracellular HCO3- = increase inward movement of CL-
Inclused K+ effluex by K+ Cl- cotransport
Renal potassium excretion:
Determined by 3 sums
Rate of filtation
Rate of reabsorption
Rate of secretion
Most reabsorption in the Proximal convolunted tubule and the loop of henle (thick
ascending limb)
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