緩い結合組織

Adults have three types of loose connective tissue: areolar, adipose, and reticular. Areolar tissue contains a loose meshwork of collagen, elastic, and reticular fibers with scattered cells. Adipose tissue comprises fat cells called adipocytes for energy storage. Reticular tissue consists of fine, branched reticular fibers and fibroblasts that provide a supporting framework in lymphatic organs.

Areolar tissue forms a loose meshwork that directly connects epithelial cells to underlying tissues, such as connecting the epidermis to the muscle beneath the skin. It also forms a protective covering around lymphatic and blood vessels. This arrangement allows areolar tissue to fill spaces between muscle fibers and support organs in the abdominal cavity.

White adipose tissue is the most abundant type in adults and primarily stores lipids while providing insulation and mechanical protection, especially around the kidneys and eyes. Brown adipose tissue is more common in infants and contains many mitochondria that metabolize stored fat to release heat rather than produce ATP. Adults have reduced brown fat, mainly in the neck and clavicular regions.

Loose connective tissue absorbs shock and binds tissues together. It allows water, salts, and nutrients to diffuse into embedded cells and adjacent tissues. The tissue also provides structural support, forms protective coverings around blood and lymph vessels, and fills spaces between organs and muscle fibers throughout the body.

Reticular tissue comprises fine, branched reticular fibers and fibroblasts that create a mesh-like, supportive framework. Reticular cells produce the reticular fibers that form the network to which other cells attach. This structure provides essential support in lymphatic organs such as lymph nodes, spleen, tonsils, and bone marrow.

Loose connective tissue consists of loosely arranged fibers and a few cells suspended in a dense ground substance. It contains collagen, elastic, and reticular fibers combined with interstitial fluid. The tissue includes various cell types such as fibroblasts, adipocytes, macrophages, and mast cells distributed in a random, web-like fashion.

In embryos, loose connective tissue appears under the skin as mesenchymal tissue and in the umbilical cord as mucoid connective tissue. In adults, loose connective tissue is the most abundant type of connective tissue and is found between many organs, beneath epithelia, around blood and lymph vessels, and throughout the body as areolar, adipose, and reticular tissues.