Hyponatremia results in: March 2011
Ans. B: Increased secretion of aldosterone All ion transpo processes in the late distal tubule and collecting ducts are stimulated by the steroid hormone aldosterone. This can increase the sodium reabsorption in this segment to a maximum of 2-3% of the filtered sodium loss Hyponatremia Sodium concentration in the serum is lower than normal. Sodium is the dominant extracellular cation and cannot freely cross the cell membrane. Its homeostasis is vital to the normal physiologic function of cells. Normal serum sodium levels are between 135-145 mEq/L. Hyponatremia is defined as a serum level of less than 135 mEq/ L and is considered severe when the serum level is below 125 mEq/L. In the vast majority of cases, hyponatremia occurs as a result of excess body water diluting the serum sodium and is not due to sodium deficiency. Hyponatremia is most often a complication of other medical illnesses in which excess water accumulates in the body at a higher rate than can be excreted (for example in congestive hea failure, syndrome of inappropriate antidiuretic hormone, SIADH, or polydipsia). Lack of sodium is viually never the cause of hyponatremia although it can promote hyponatremia indirectly. In paicular, sodium loss can lead to a state of volume depletion, with volume depletion serving as signal for the release of ADH (anti-diuretic hormone). As a result of ADH-stimulated water retention, blood sodium becomes diluted and hyponatremia results. Decrease in plasma sodium increases aldosterone secretion Renin-angiotensin system and direct stimulation of adrenal coex The etiology of hyponatremia can be categorized pathophysiologically in three primary ways, based on the patient's plasma osmolality. Hypeonic hyponatremia, caused by resorption of water drawn by osmols such as glucose (hyperglycemia or diabetes) or mannitol (hypeonic infusion). Isotonic hyponatremia, more commonly called "pseudohyponatremia," is caused by lab error due to hyperiglyceridemia (most common) or hyperparaproteinemia. Hypotonic hyponatremia is by far the most common type, and is often used interchangeably with "hyponatremia." (Hypotonic hyponatremia is categorized in 3 ways based on the patient's blood volume status. Each category represents a different underlying reason for the increase in ADH that led to the water retention and thence hyponatremia): - Hypervolemic hyponatremia, wherein there is decreased effective circulating volume even though total body volume is increased (by the presence of edema). The decreased effective circulating volume stimulates the release of ADH, which in turn leads to water retention. Hypervolemic hyponatremia is most commonly the result of congestive hea failure, liver failure (cirrhosis), or kidney disease (nephrotic syndrome). - Euvolemic hyponatremia, wherein the increase in ADH is secondary to either physiologic but excessive ADH release (as occurs with nausea or severe pain) or is due to inappropriate and non-physiologic secretion of ADH, i.e. syndrome of inappropriate antidiuretic hormone hypersecretion (SIADH). - Hypovolemic hyponatremia, wherein ADH secretion is stimulated by volume depletion. Chronic hyponatremia Sodium levels drop gradually over several days or weeks and symptoms and complications are typically moderate. Chronic hyponatremia is often called asymptomatic hyponatremia in clinical settings because it is thought to have no symptoms Acute hyponatremia Sodium levels drop rapidly Resulting in potentially dangerous effects, such as rapid brain swelling, which can result in coma and death.
Increased excretion of potassium
Increased secretion of aldosterone
Increased secretion of ADH
All of the above