In which part of the respiratory system does gaseous exchange take place?

Correct Answer: A

Rationale: Gaseous exchange occurs in the alveoli, tiny air sacs in the lungs where oxygen diffuses into the blood and carbon dioxide exits, facilitated by their thin walls and vast surface area surrounded by capillaries. The pharynx conducts air but lacks exchange surfaces. The larynx manages airflow and sound, not diffusion. The trachea transports air to the lungs, lined with cilia and mucus for filtering, not gas exchange. Alveoli's unique structure thin, moist, and capillary-rich optimizes this process, driven by concentration gradients, making them the respiratory system's exchange hub. This distinction is vital for understanding respiration's purpose: delivering oxygen to tissues and removing waste, a cornerstone of pulmonary physiology and clinical respiratory care.

Correct Answer: B

Rationale: The heart's apex, its lower tip, points left of the midline, typically at the fifth intercostal space, reflecting its leftward tilt in the chest about two-thirds lie left of the sternum. Midline alignment is rare, as is rightward pointing (dextrocardia, a congenital anomaly). Gender doesn't alter this orientation is consistent. This leftward apex, formed by the left ventricle, aligns with the heart's pumping role, detectable in pulse checks, a key anatomical feature in physical exams and imaging, distinguishing normal from pathological positioning.

Correct Answer: A

Rationale: Ventricular contraction (systole) forces blood into arteries the left ventricle into the aorta, the right into the pulmonary trunk via semilunar valves, initiating circulation. Capillaries receive blood later, after arterioles. Veins return blood to the heart, not from ventricles. Atrioventricular valves (tricuspid, mitral) close during systole, preventing backflow into atria, not directing outflow. This arterial ejection, driven by ventricular pressure, is the heart's pumping essence, key in cardiac cycle dynamics and assessing output in heart failure.

Correct Answer: B

Rationale: Systole is the cardiac cycle phase when a chamber (atria or ventricles) contracts, raising pressure to eject blood ventricular systole pushes blood into the aorta/pulmonary trunk. Filling occurs during diastole, when chambers relax and fill. Repolarization is an electrical event, not a mechanical phase. Diastole is relaxation, opposite to contraction. Systole's pressure rise, peaking at ~120 mmHg in the left ventricle, drives circulation, a core concept in the cardiac cycle, critical in understanding blood flow dynamics and conditions like systolic dysfunction.

Correct Answer: A

Rationale: The foramen ovale, an atrial septal opening in fetuses, allows blood to flow from the right atrium to the left, bypassing lungs oxygen comes from the placenta via umbilical veins. Ventricular shunting isn't its role (ductus arteriosus does that). It's not a vena cava valve or aortic backflow preventer. This shunt, closing post-birth (fossa ovalis), optimizes fetal circulation, key in congenital defects like ASD where it persists, affecting oxygenation.