The sigmoid is part of the:

A. Nothing, it's just a pass through to the next structure: The stomach plays a critical role in digestion through mixing and secretion of gastric juices.

B. Gastric juices mix with the food and the stomach muscles squeeze it: This process forms chyme through mechanical (squeezing) and chemical (acid/enzymes) digestion.

C. The food moves quickly into the small intestine: Food stays in the stomach for a period of time for processing before gradually passing into the small intestine.

D. The food is completely digested and is absorbed by tiny blood vessels in the walls of the stomach: Most digestion and nutrient absorption occur in the small intestine, not the stomach.

A. Causes Na⁺ excretion: Aldosterone promotes sodium reabsorption, not excretion, to increase blood volume and pressure.

B. Depletes blood volume: Aldosterone increases blood volume by retaining sodium and water.

C. Causes K⁺ reabsorption: Aldosterone promotes potassium excretion, not reabsorption.

D. Causes Na⁺ and water reabsorption: Aldosterone acts on the renal tubules to reabsorb sodium, which draws water back into circulation, increasing blood volume.