What percentage of total body surface area (TBSA) is represented by the head of an adult according to the rule of nines?

Rationale:

A. Vasoconstriction of the afferent arteriole reduces blood flow into the glomerulus, which lowers glomerular filtration rate (GFR). A reduced GFR results in less filtrate formation, leading to oliguria (decreased urine output). This is a common physiologic response in conditions such as hypovolemia or acute kidney injury, where the body attempts to conserve fluid.

B. Constriction of the afferent arteriole decreases hydrostatic pressure within the glomerular capillaries, lowering filtration pressure. Glomerular pressure would actually decrease, not increase, in this scenario.

C. Increased filtrate production is incorrect. Reduced blood flow into the glomerulus decreases the amount of plasma filtered across the glomerular membrane, so filtrate production declines rather than increases.

D. Increased blood urea nitrogen (BUN) clearance is incorrect. When GFR decreases, the kidneys filter less urea, leading to elevated BUN levels in the blood. Clearance of BUN is reduced, not increased, during afferent arteriole vasoconstriction.

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.