sodium

Examples of sodium in the following topics:

• Sodium Balance Regulation

  • The body has potent sodium retaining mechanisms and even if a person is on five mmol Na+/day they can maintain sodium balance.
  • Sodium is lost through the kidneys, sweat, and feces.
  • In states of sodium excess aldosterone levels decrease.
  • When aldosterone has been activated to retain sodium the plasma sodium tends to rise.
  • In states of sodium depletion, aldosterone levels increase, and in states of sodium excess, aldosterone levels decrease.

• The Action Potential and Propagation

  • The depolarization, also called the rising phase, is caused when positively charged sodium ions (Na+) suddenly rush through open voltage gated sodium channels into a neuron.
  • As additional sodium rushes in, the membrane potential actually reverses its polarity.  
  • As a result, the membrane permeability to sodium declines to resting levels.
  • The hyper polarization is a phase where some potassium channels remain open, and sodium channels reset.
  • The period from the opening of the sodium channels until the sodium channels begin to reset is called the absolute refractory period.

• 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.
  • There are three types of dehydration: hypotonic or hyponatremic (primarily a loss of electrolytes, sodium in particular), hypertonic or hypernatremic (primarily a loss of water), and isotonic or isonatremic (equal loss of water and electrolytes).
  • Physiologically, and despite the name, dehydration does not simply mean loss of water, as both water and solutes (mainly sodium) are usually lost in roughly equal quantities as to how they exist in blood plasma.

• Diuretics

  • Diuretics alleviate the symptoms of these diseases by causing sodium and water loss through the urine.
  • This is huge when compared to normal renal sodium reabsorption which leaves only about 0.4% of filtered sodium in the urine.
  • Loop diuretics, such as furosemide, inhibit the body's ability to reabsorb sodium at the ascending loop in the nephron, which leads to an excretion of water in the urine, whereas water normally follows sodium back into the extracellular fluid.
  • Aldosterone normally adds sodium channels in the principal cells of the collecting duct and late distal tubule of the nephron.
  • Spironolactone prevents aldosterone from entering the principal cells, preventing sodium reabsorption.

• Body Fluid Composition

  • In contrast to extracellular fluid, cytosol has a high concentration of potassium ions and a low concentration of sodium 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).
  • Some of the electrolytes present in the transcellular fluid are sodium ions, chloride ions and bicarbonate ions.

• Regulation of Water Output

  • Among other actions, this causes renal tubules (i.e. the distal convoluted tubules and the cortical collecting ducts) to reabsorb more sodium and water from the urine.
  • Potassium is secreted into the tubule in exchange for the sodium, which is reabsorbed.
  • This hormone stimulates the reabsorption of sodium ions from distal tubules and collecting ducts.
  • Water in the tubular lumen follows the sodium reabsorption osmotically.

• 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.

• Potassium Balance Regulation

  • In an unprocessed diet potassium is much more plentiful than sodium.
  • It is present as an organic salt while sodium is added as NaCl.

• 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.

• Postsynaptic Potentials and Their Integration at the Synapse

  • Unlike the action potential in axonal membrane, chemically gated ion channels open on postsynaptic membranes and sodium and potassium diffuse simultaneously but in opposite directions.
  • Since the electrochemical gradient of sodium is steeper than potassium, so a net depolarization occurs.