Which epithelial membranes line the body cavities and cover organs that lie in them, that are not open to the exterior of the body?

A. For fluid balance: Lipids do not play a direct role in maintaining fluid balance; electrolytes and plasma proteins like albumin regulate this function.

B. As a component of the myelin sheath: Lipids, particularly phospholipids and cholesterol, are essential for forming the myelin sheath, which insulates nerve fibers and facilitates efficient nerve conduction.

C. Component of hemoglobin: Hemoglobin is composed of iron and protein (globin chains), not lipids.

D. As a component of the cell membrane: Cell membranes are composed of a lipid bilayer (phospholipids and cholesterol), which helps maintain structural integrity and fluidity.

E. As an energy source: Lipids provide a concentrated energy source, yielding 9 kcal per gram, which is more than carbohydrates (4 kcal/g).

A. The pain receptors in the dermis have been destroyed: Third-degree burns penetrate the entire dermis and often destroy nerve endings, reducing the ability to feel pain at the site of injury.

B. The melanin within the skin acts as a pain reliever: Melanin is responsible for skin pigmentation and does not have analgesic properties.

C. The burn site has not yet become infected: The presence or absence of infection does not determine pain perception in third-degree burns.

D. He is immobile and not moving the injured site: While movement may exacerbate pain, third-degree burns often result in reduced pain due to nerve destruction.