What happens when sodium remains in the tubular fluid as a result of ANP activity?

A. Sodium ions (Filtered): These small monovalent cations pass freely through the fenestrations and slit diaphragms of the filtration membrane. Their concentration in the initial filtrate is nearly identical to that of the plasma. This allows the tubules to later regulate their total body balance.

B. Fatty acids (Not filtered): In the plasma, long-chain fatty acids are predominantly bound to albumin for transport. Because albumin is restricted by the glomerular basement membrane and negative charge, the associated fatty acids are also excluded. They are too large or protein-bound for filtration.

C. Clotting factors (Not filtered): Most coagulation factors are large plasma proteins, such as fibrinogen, synthesized by the liver. Their high molecular weight and complex structure prevent them from passing through the glomerular sieve. The presence of such proteins in urine indicates significant glomerular pathology.

A. ADH: Arginine vasopressin is released from the posterior pituitary when baroreceptors detect a significant decrease in mean arterial pressure or blood volume. It increases the water permeability of the collecting ducts. This facilitates rapid water recovery to restore systemic hemodynamics.

B. Renin: This enzyme is secreted by the juxtaglomerular cells to initiate the angiotensin cascade. While it eventually leads to water retention via aldosterone, renin itself is a proteolytic enzyme, not a hormone that directly recovers water. It is a catalyst for the system.

C. Aldosterone: This hormone promotes water recovery indirectly by increasing the active reabsorption of sodium. While it is vital for volume expansion, its primary direct target is the sodium ion. ADH remains the primary hormone for direct, regulated water recovery via aquaporins.

D. ANP: Atrial natriuretic peptide is released in response to atrial stretch caused by high blood volume. It functions to increase the excretion of sodium and water to reduce blood pressure. It is an antagonist to the volume-conserving effects of ADH.