Sodium is filtered through the glomerular barrier in the kidneys.
Here's a more detailed explanation:
The kidneys play a crucial role in regulating sodium levels in the body. This process involves filtration, reabsorption, and excretion. The initial step, filtration, occurs in the glomerulus.
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The Glomerulus: The glomerulus is a network of capillaries within the Bowman's capsule of the nephron, the functional unit of the kidney. It acts as a selective filter.
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Filtration Process: Blood enters the glomerulus under pressure. The glomerular barrier, composed of the capillary endothelium, the glomerular basement membrane, and the podocytes of the Bowman's capsule, allows water and small solutes (like sodium, chloride, glucose, amino acids, urea, etc.) to pass through into Bowman's space.
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Forms of Sodium: While sodium is filtered, it predominantly exists in a complex with chloride (sodium chloride). However, other sodium compounds like sodium hydrogen phosphate and sodium carbonate are also filtered.
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Selective Filtration: The size and charge of molecules determine whether they can pass through the glomerular barrier. Large proteins and blood cells are typically retained in the blood. Smaller molecules like sodium are freely filtered.
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Reabsorption: The vast majority of the filtered sodium is reabsorbed back into the bloodstream in the proximal tubule and other parts of the nephron, preventing significant sodium loss. This reabsorption is tightly regulated by hormones like aldosterone.
In summary, sodium, primarily as sodium chloride but also in other forms, is filtered through the glomerular barrier from the blood into the Bowman's capsule as part of the initial step in urine formation. The kidneys then fine-tune sodium levels through reabsorption and excretion.
