Sodium Balance Flashcards
Total amount of sodium in the ECF represents a balance between 2 factors
- Sodium ion uptake across the digestive epithelium. Enters ECF through diffusion and carrier-mediated transport.
- Sodium ion excretion by the kidneys and other sites. Losses are primarily excreted in urine and perspiration. Kidneys are the most important site of sodium regulation.
A person in sodium balance typically gains and losses
48-144 mEq (1.1 - 3.3g) of Na+ each day
When sodium gains are higher than losses
The total sodium content of the ECF increases
When sodium losses exceed gains
The sodium content decreases.
A change in the sodium content of the ECF does not produce a change in the sodium concentration.
What happens when sodium intake or output changes
A corresponding gain or loss of water tends to keep the sodium concentration constant.
What happens if you consume large amounts of salt without adequate fluid
- The plasma sodium concentration increases temporarily
- Fluid will exit the ICF, increasing ECF volume and decrease Na concentration
- The secretion of ADH Restricts water loss and stimulates thirst .
- Due to the inhibition of water receptors in the pharynx, ADH Secretion begins before sodium absorption occurs.
- ADH secretion rate increases more after sodium absorption, due to Osmo receptors stimulation.
What happens when sodium losses exceed gains
- Osmoreceptors in hypothalamus inhibited
- As soon as the osmotic concentration of the ECF decreases by 2% or more, ADH secretion decreases so thirst is suppressed and water losses by the kidneys increase.
- Water loss decreases ECF volume
- Increased sodium levels in ECF. Returns to normal.
The net result is that homeostatic mechanisms can monitor ECF volume indirectly by
Monitoring blood pressure
The receptors involved are the baroreceptors at the
Carotid sinus
Aortic sinus
Right atrium
If the ECF volume is inadequate, both blood volume and blood pressure decreased, and
- Endocrine response: The renin-angiotensin-aldosterone system is activated.
- In response, losses of water and sodium are decreased, and gains of water and sodium are increased.
- The net result is that ECF volume increases.
If the ECF volume becomes abnormally large
- Increased venous return ; increased blood volume and atrial distention.
- Natriuretic peptides released by cardiac muscle cells. ANP and BNP
- Increased sodium loss in urine; Increased water loss in urine; Decrease thirst. Inhibition of ADH, aldosterone, epinephrine, and norepinephrine release.
- Decreased blood volume. Decreased blood pressure
- Decreasing ECF volume
