Which of the following is the area of the brain that contains the medulla, pons, and midbrain?

a. Sodium: Correct. Sodium (Na⁺) is the primary extracellular cation and plays a crucial role in maintaining osmotic pressure and fluid balance in the body.

b. Magnesium: Magnesium (Mg²⁺) is important for many cellular functions but is not a major contributor to osmotic pressure compared to sodium.

c. Calcium: Calcium (Ca²⁺) is vital for bone health and cellular processes but does not primarily influence osmotic pressure.

d. Potassium: Potassium (K⁺) is the main intracellular cation and affects cell function, but sodium has a more significant role in osmotic pressure regulation.

a. AB positive: Individuals with AB positive blood are universal recipients. They have A and B antigens on their red blood cells but no antibodies (anti-A or anti-B) in their plasma. Therefore, their body will not reject blood types A, B, AB, or Rh positive or negative.

b. A positive: Individuals with A positive blood can only receive A positive or O positive blood. Their plasma contains anti-B antibodies, which would attack blood types B and AB.

c. B negative: Individuals with B negative blood can receive B negative or O negative blood. Their plasma contains anti-A antibodies, which would attack blood types A and AB. The Rh factor is another compatibility consideration, but the question specifies positive.

d. O negative: Individuals with O negative blood are universal donors but not universal recipients. Their red blood cells lack A and B antigens, so they can be donated to anyone. However, their plasma contains anti-A and anti-B antibodies, so they can only receive O negative blood.