Question

During urine formation, which of the following processes create high osmotic pressure in the uriniferous tubule?

• A. Active $N{a}^{+}$ absorption, followed by absorption of $C{l}^{-}$
• B. Active $C{l}^{-}$ absorption, followed by absorption of $N{a}^{+}$
• C. Active secretion of $N{a}^{+}$ into efferent arteriole followed by absorption of $C{l}^{-}$ into efferent renal arteriole
• D. Active secretion of $C{l}^{-}$ and absorption of $N{a}^{+}$ into efferent renal arteriole

Answer 1

The correct option is A Active $N{a}^{+}$ absorption, followed by absorption of $C{l}^{-}$

• Active sodium absorption is followed by the absorption of chlorine. Sodium is the positively charged electrolyte in extracellular body fluid. The amount of sodium in the fluid influences its volume, which in turn determines blood volume and blood pressure.
• Most of the sodium is reabsorbed in the form of sodium bicarbonate and sodium chloride.
• About 70% of the sodium reabsorption occurs in the proximal convoluted tubule. When sodium ion moves, water follows. The movement of water balances the osmotic pressure within or across the tubule walls, which maintains extracellular fluid volume.
• The fluid entering the late proximal tubule has been depleted of the essential substances. As bicarbonate being negatively charged was reabsorbed initially with sodium, chloride ion has been left behind in the tubule.
• Due to the extensive reabsorption of water in the early part of the tubule, chloride ions are highly concentrated and get reabsorbed.
  So, the correct option is A.