Interstitial fluid enters capillaries at the venular end through the action of:

Correct Answer: B

Rationale: At the venular end, colloid osmotic pressure (about 25 mmHg, due to plasma proteins) exceeds the lower hydrostatic pressure (about 15 mmHg), pulling interstitial fluid back into the capillary. Capillary pores facilitate this, but the driving force is osmotic.

Correct Answer: A

Rationale: The foramen ovale is a fetal opening between the right and left atria, allowing blood to bypass the lungs. It normally closes after birth. The ductus arteriosus connects pulmonary artery to aorta, ligamentum arteriosum is its remnant, and Tetralogy of Fallot is a different defect.

Correct Answer: D

Rationale: Normal RBC count is 4.5-5.9 million/mm³ (men) or 4.0-5.2 million/mm³ (women). 3.8 million/mm³ is below normal (assuming male; still low for female), indicating anemia. Thrombocytes are normal (150,000-450,000), hematocrit 43% is normal (38-50%), and hemoglobin 17 g/dL is normal.

Correct Answer: B

Rationale: In adults, RBC production (erythropoiesis) occurs in red bone marrow of flat bones (sternum, skull, vertebrae) and proximal ends of long bones. The femur’s shaft in adults is mostly yellow marrow, not active in erythropoiesis.

Correct Answer: C

Rationale: The carotid sinus baroreceptors detect increased pressure, triggering a reflex via the vagus nerve (parasympathetic) to slow heart rate (bradycardia) and reduce blood pressure. Hypercapnia (high CO₂) and hyperpnea (increased breathing) are unrelated, and tachycardia would counter the response.