Examination of a patient in a supine position reveals distended jugular veins from the base of the neck to the angle of the jaw. This finding indicates:

Correct Answer: B

Rationale: Distended jugular veins in a supine position suggest increased central venous pressure (CVP), often due to right heart failure or fluid overload, as blood backs up into the venous system. Decreased venous return would collapse veins, and C and D are less directly indicated by this sign alone.

Correct Answer: C

Rationale: The aorta (Choice A) is the largest artery, distributing oxygenated blood to the body. The pulmonary vein (Choice B) returns oxygenated blood from the lungs to the heart. The renal artery (Choice D) supplies the kidneys and is significant in systemic circulation. The femoral artery (Choice C), while important, is a regional vessel supplying the leg and not classified as a 'major' vessel like the aorta or pulmonary vein in the context of the cardiovascular system’s primary structure.

Correct Answer: A

Rationale: The prenatal heart begins to pump blood around the fourth week of embryonic development. This is when the primitive heart tube forms and starts rhythmic contractions, marking the beginning of circulation in the embryo. By the fifth week, the heart becomes more structured, but pumping begins earlier.

Correct Answer: D

Rationale: Cardiac output increases during exercise, fever, and digestion due to higher metabolic demand. Stimulation of the vagus nerves (parasympathetic system) slows heart rate via acetylcholine release, reducing cardiac output, making it the exception.

Correct Answer: C

Rationale: Antidiuretic hormone (ADH) regulates blood volume by promoting water reabsorption in the kidneys, increasing plasma volume. ACTH affects cortisol, and LH is reproductive; 'osmoretic hormone' is not a standard term.