Blood capillaries consist of which of the following combination of components?
Endothelium and a thin layer of connective tissue
Endothelium and a thin layer of muscle fibers
Endothelium and a thin layer of both connective tissue and muscle fibers
Endothelium only
Blood capillaries are composed of a single layer of endothelial cells. The endothelium serves as a selectively permeable barrier, allowing the exchange of substances such as oxygen, nutrients, and waste products between the blood and surrounding tissues. There is no additional layer of connective tissue or muscle fibers present in the structure of blood capillaries.Hence, the correct answer is option 4.