Which of the following cations makes an important contribution to osmotic pressure?

a. Mouth: The mouth is primarily responsible for the mechanical breakdown of food and the beginning of starch digestion via salivary amylase, but it is not a major site of nutrient absorption.

b. Small intestine: The small intestine is the primary site for nutrient absorption. The majority of carbohydrates, proteins, fats, vitamins, and minerals are absorbed here through its extensive surface area provided by villi and microvilli.

c. Large intestine: The large intestine primarily absorbs water and electrolytes. It is not a major site for nutrient absorption.

d. Stomach: The stomach is mainly involved in the mechanical and chemical breakdown of food, particularly proteins, but only a small amount of nutrients (e.g., alcohol, some drugs) are absorbed here.

a. Decreased blood pressure due to increased blood viscosity: Increased viscosity makes blood flow more difficult, raising blood pressure, not lowering it.

b. Increased blood pressure due to decreased blood viscosity: Decreased viscosity would make blood flow easier, potentially lowering blood pressure, not raising it.

c. Decreased blood pressure due to decreased blood viscosity: Same error in reasoning as b.

d. Increased blood pressure due to increased blood viscosity: Red blood cells are the main components of blood that affect its viscosity (thickness). An increased concentration of red blood cells (erythrocytosis) makes the blood more viscous. Thicker blood increases resistance to flow within blood vessels, making the heart work harder to pump blood, which can lead to increased blood pressure.