What is the main responsibility of erythrocytes (RBCs) in the body?

Rationale:

A. Chronic venous insufficiency is incorrect. Chronic venous insufficiency typically causes bilateral leg edema, skin changes (hyperpigmentation), and venous stasis ulcers, rather than sudden unilateral redness and swelling. It develops gradually due to venous valve incompetence, not an acute obstruction.

B. Deep vein thrombosis (DVT) is correct. DVT occurs when a blood clot forms in a deep vein, commonly in the lower extremities. Classic manifestations include unilateral swelling, redness, warmth, and pain in the affected leg. The swelling is often asymmetric, distinguishing it from systemic causes of edema. DVT is a medical emergency due to the risk of pulmonary embolism if the clot dislodges and travels to the lungs.

C. Peripheral artery disease (PAD) is incorrect. PAD primarily causes ischemic symptoms, such as pain with exertion (intermittent claudication), cool extremities, and weak pulses, rather than acute unilateral swelling and redness. PAD results from arterial obstruction, not venous blockage.

D. Intermittent claudication is incorrect. Intermittent claudication is a symptom of PAD, characterized by exercise-induced leg pain that resolves with rest, without acute redness or unilateral swelling. It reflects muscle ischemia, not venous obstruction.

Rationale:

A. Very low-density lipoprotein (VLDL) is incorrect. VLDL is considered a “bad” lipoprotein because it carries triglycerides from the liver to peripheral tissues and can contribute to plaque formation in arteries. Elevated VLDL levels increase the risk of atherosclerosis and cardiovascular disease.

B. High-density lipoproteins (HDL) is correct. HDL is referred to as “good cholesterol” because it transports excess cholesterol from peripheral tissues back to the liver for excretion or recycling. High levels of HDL are associated with reduced risk of atherosclerosis and cardiovascular events. HDL also has anti-inflammatory and antioxidant properties, providing additional protection to blood vessels.

C. Intermediate-density lipoproteins (IDL) is incorrect. IDL is a transitional lipoprotein formed during the metabolism of VLDL to LDL. It is considered atherogenic, meaning it can contribute to plaque buildup, and is not classified as “good cholesterol.”

D. Low-density lipoproteins (LDL) is incorrect. LDL is commonly referred to as “bad cholesterol” because it transports cholesterol from the liver to peripheral tissues, where it can deposit in the arterial walls and lead to atherosclerosis, heart attacks, and strokes.