Which type of "proper" connective tissue is loosely packed and surrounds blood vessels?

The correct choice is areolar connective tissue, which is indeed characterized by its loosely packed structure. Areolar tissue is a type of loose connective tissue that provides a flexible and supportive framework for various organs and tissues throughout the body. Its composition allows it to easily fill spaces between organs and tissues, making it particularly effective in surrounding blood vessels, nerves, and muscles.

The loose arrangement of collagen and elastin fibers in areolar tissue contributes to its ability to stretch and accommodate movement, while its gel-like matrix helps facilitate the exchange of nutrients and waste between blood vessels and surrounding cells. This property is essential for supplying oxygen and nutrients to tissues and removing metabolic wastes.

In contrast, other types of connective tissue, such as dense irregular and dense regular connective tissue, contain tightly packed fibers that provide strength and support but are less suited for cushioning and flexibility. Dense irregular tissue is designed to withstand forces applied in multiple directions, while dense regular tissue is aligned in a parallel fashion, primarily providing tensile strength in one direction. Reticular connective tissue, though it features a network of fibers, is more specialized for forming internal scaffolding in organs such as the liver, spleen, and lymph nodes rather than serving as a loose connective structure around blood vessels.