Potassium

Examples of Potassium in the following topics:

• Potassium Balance Regulation

  • Potassium is predominantly an intracellular ion .
  • In an unprocessed diet potassium is much more plentiful than sodium.
  • If there is a high potassium intake, eg. 100 mmol, this would potentially increase the extracellular K+ level two times before the kidney could excrete the extra potassium.
  • The body buffers the extra potassium by equilibrating it within the cells.
  • A high plasma potassium increases aldosterone secretion and this increases the potassium loss from the body, restoring balance.

• The Action Potential and Propagation

  • The repolarization or falling phase is caused by the slow closing of sodium channels and the opening of voltage-gated potassium channels.
  • As the sodium ion entry declines, the slow voltage-gated potassium channels open and potassium ions rush out of the cell.
  • Hyperpolarization is a phase where some potassium channels remain open and sodium channels reset.
  • A period of increased potassium permeability results in excessive potassium efflux before the potassium channels close.

• Diuretics

  • There are three types of diuretics: thiazide, loop and potassium-sparing.
  • This results in several effects including bicarbonate retention in the urine, potassium retention in urine and decreased sodium absorption.
  • These are diuretics which do not promote the secretion of potassium into the urine; thus, potassium is spared and not lost as much as in other diuretics.
  • The term "potassium-sparing" refers to an effect rather than a mechanism or location; nonetheless, the term almost always refers to two specific classes that have their effect at similar locations: Aldosterone antagonists: spironolactone, which is a competitive antagonist of aldosterone.
  • A similar agent is potassium canreonate.

• Resting Membrane Potentials

  • The three ions that appear in this equation are potassium (K+), sodium (Na+), and chloride (Cl−).
  • In most animal cells, the permeability to potassium is much higher in the resting state than the permeability to sodium.
  • Consequently, the resting potential is usually close to the potassium reversal potential.

• Postsynaptic Potentials and Their Integration at the Synapse

  • Sodium and potassium diffuse simultaneously but in opposite directions.
  • Since the electrochemical gradient of sodium is steeper than that of potassium, a net depolarization occurs.
  • Most inhibitory neurotransmitters hyperbolize the postsynaptic membrane by making it more permeable to potassium or chloride.

• Adrenal Cortex

  • Aldosterone exerts its effects on the distal convoluted tubule and collecting duct of the kidney where it causes increased reabsorption of sodium and increased excretion of both potassium (by principal cells) and hydrogen ions (by intercalated cells of the collecting duct).
  • Aldosterone is secreted in response to high extracellular potassium levels, low extracellular sodium levels, and low fluid levels and blood volume.

• Body Fluid Composition

  • In contrast to extracellular fluid, cytosol has a high concentration of potassium ions and a low concentration of sodium ions.
  • The reason for these specific sodium and potassium ion concentrations are Na+/K ATPase pumps, which facilitate the active transport of these ions.
  • The cations include: sodium (Na+ = 136-145 mEq/L), potassium (K+ = 3.5-5.5 mEq/L) and calcium (Ca2+ = 8.4-10.5 mEq/L).

• Sodium, Electrolytes, and Fluid Balance

  • The most serious electrolyte disturbances involve abnormalities in the levels of sodium, potassium, and/or calcium.
  • For example, during heavy exercise electrolytes are lost in sweat, particularly sodium and potassium, and sweating can increase the need for electrolyte (salt) replacement.

• Regulation of Water Output

  • This causes greatly increased reabsorption of sodium and water (which follows sodium osmotically by cotransport) while causing the secretion of potassium into urine.
  • Aldosterone therefore increases water reabsorption, however it involves an exchange of sodium and potassium, which ADH reabsoption regulation does not involve.

• Dialysis

  • When healthy, the kidneys maintain the body's internal equilibrium of water and minerals (sodium, potassium, chloride, calcium, phosphorus, magnesium, sulfate).
  • The concentrations of solutes (for example potassium, phosphorus, and urea) are undesirably high in the blood, but low or absent in the dialysis solution; constant replacement of the dialysate ensures that the concentration of undesired solutes is kept low on this side of the membrane.
  • The dialysis solution has levels of minerals like potassium and calcium that are similar to their natural concentration in healthy blood.