Because sodium is the major osmotically active ion in the extracellular fluid (ECF), total body sodium content determines ECF volume. Deficiency or excess of total body sodium content causes ECF volume depletion Volume Depletion Volume depletion, or extracellular fluid (ECF) volume contraction, occurs as a result of loss of total body sodium. Causes include vomiting, excessive sweating, diarrhea, burns, diuretic use... read more or volume overload Volume Overload Volume overload generally refers to expansion of the extracellular fluid (ECF) volume. ECF volume expansion typically occurs in heart failure, kidney failure, nephrotic syndrome, and cirrhosis... read more . Serum sodium concentration does not necessarily reflect total body sodium. (See also Water and Sodium Balance Water and Sodium Balance Body fluid volume and electrolyte concentration are normally maintained within very narrow limits despite wide variations in dietary intake, metabolic activity, and environmental stresses. Homeostasis... read more .)
Dietary intake and renal excretion regulate total body sodium content. When total sodium content and ECF volume are low, the kidneys increase sodium conservation. When total sodium content and ECF volume are high, sodium excretion (natriuresis) increases so that volume decreases.
Renal sodium excretion can be adjusted widely to match sodium intake. Renal sodium excretion requires delivery of sodium to the kidneys and so depends on renal blood flow and glomerular filtration rate (GFR). Thus, inadequate sodium excretion may be secondary to decreased renal blood flow, as in chronic kidney disease Chronic Kidney Disease Chronic kidney disease (CKD) is long-standing, progressive deterioration of renal function. Symptoms develop slowly and in advanced stages include anorexia, nausea, vomiting, stomatitis, dysgeusia... read more 
or heart failure Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular (LV) failure causes shortness of breath and fatigue, and right ventricular (RV) failure causes peripheral and abdominal... read more 
.
Renin-angiotensin-aldosterone axis
The renin-angiotensin-aldosterone axis is the main regulatory mechanism of renal sodium excretion. In volume-depleted states, GFR and chloride delivery to the distal nephrons decreases, causing release of renin. Renin cleaves angiotensinogen (renin substrate) to form angiotensin I. Angiotensin-converting enzyme (ACE) then cleaves angiotensin I to angiotensin II. Angiotensin II does the following:
Increases sodium retention by decreasing the filtered load of sodium and enhancing proximal tubular sodium reabsorption
Increases blood pressure (has pressor activity)
Increases thirst
Directly impairs water excretion
Stimulates the adrenal cortex to secrete aldosterone, which increases sodium reabsorption via multiple renal mechanisms
Angiotensin I can also be transformed to angiotensin III, which stimulates aldosterone release as much as angiotensin II but has much less pressor activity. Aldosterone release is also stimulated by hyperkalemia Hyperkalemia Hyperkalemia is a serum potassium concentration > 5.5 mEq/L (> 5.5 mmol/L), usually resulting from decreased renal potassium excretion or abnormal movement of potassium out of cells. There... read more .
Other natriuretic factors
Several other natriuretic factors have been identified, including atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and a C-type natriuretic peptide (CNP).
ANP is secreted by cardiac atrial tissue. Concentration increases in response to ECF volume overload (eg, heart failure Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular (LV) failure causes shortness of breath and fatigue, and right ventricular (RV) failure causes peripheral and abdominal... read more , chronic kidney disease Chronic Kidney Disease Chronic kidney disease (CKD) is long-standing, progressive deterioration of renal function. Symptoms develop slowly and in advanced stages include anorexia, nausea, vomiting, stomatitis, dysgeusia... read more , cirrhosis Cirrhosis Cirrhosis is a late stage of hepatic fibrosis that has resulted in widespread distortion of normal hepatic architecture. Cirrhosis is characterized by regenerative nodules surrounded by dense... read more with ascites) and primary aldosteronism Primary Aldosteronism Primary aldosteronism is aldosteronism caused by autonomous production of aldosterone by the adrenal cortex (due to hyperplasia, adenoma, or carcinoma). Symptoms and signs include episodic weakness... read more and in some patients with primary hypertension Hypertension Hypertension is sustained elevation of resting systolic blood pressure (≥ 130 mm Hg), diastolic blood pressure (≥ 80 mm Hg), or both. Hypertension with no known cause (primary; formerly, essential... read more 
. Decreases have occurred in the subset of patients with nephrotic syndrome who have presumed ECF volume contraction. High concentrations increase sodium excretion and increase GFR even when blood pressure is low.
BNP is synthesized mainly in the atria and left ventricle and has similar triggers and effects to ANP. BNP assays are readily available. High BNP concentration is used to diagnose volume overload.
CNP, in contrast to ANP and BNP, is primarily vasodilatory.
Sodium depletion and excess
Sodium depletion requires inadequate sodium intake plus abnormal losses from the skin, gastrointestinal tract, or kidneys (defective renal sodium conservation). Defective renal sodium conservation may be caused by primary renal disease, adrenal insufficiency Secondary Adrenal Insufficiency Secondary adrenal insufficiency is adrenal hypofunction due to a lack of adrenocorticotropic hormone (ACTH). Symptoms are the same as for Addison disease and include fatigue, weakness, weight... read more , or diuretic therapy.
Sodium overload requires higher sodium intake than excretion; however, because normal kidneys can excrete large amounts of sodium, sodium overload generally reflects defective regulation of renal blood flow and sodium excretion (eg, as occurs in heart failure Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular (LV) failure causes shortness of breath and fatigue, and right ventricular (RV) failure causes peripheral and abdominal... read more , cirrhosis Cirrhosis Cirrhosis is a late stage of hepatic fibrosis that has resulted in widespread distortion of normal hepatic architecture. Cirrhosis is characterized by regenerative nodules surrounded by dense... read more , or chronic kidney disease Chronic Kidney Disease Chronic kidney disease (CKD) is long-standing, progressive deterioration of renal function. Symptoms develop slowly and in advanced stages include anorexia, nausea, vomiting, stomatitis, dysgeusia... read more ).
Drugs Mentioned In This Article
| Drug Name | Select Trade |
|---|---|
angiotensin ii |
GIAPREZA |
