SEM image, 1,200X (photo courtesy of N. P. Omelianenko). In loose connective tissue, the framework of fibers and fibrils is characterized by a chaotic orientation of its structures. It includes:

• collagen fibers #1, #2, #3, #4, which are convoluted and of varying thickness; they consist of collagen fibrils forming a longitudinal relief on the surface of fibers
• elastic fibers #1, #2 are not so convoluted, their surface is smooth
• a network of fine collagen fibrils #1, #2 binding collagen fibers together.

TEM image, 60,000X (photo courtesy of N. P. Omelianenko). An ultrafine section stained by ruthenium red reveals a macromolecular meshwork of proteoglycans in the amorphous matrix of intercellular substance, as well as around elastic fibers, around separate collagen fibrils and between collagen fibril groups (the last ones form collagen fibers).

TEM image, 10,000X. The transverse section of an elastic fiber shows peripheral and central fibrils, which are constituted by fibrillin, and an amorphous core of elastin.
In collagen fibers, separate collagen fibrils are bound into aggregates with the help of proteoglycans.

There is a nearly dormant fibroblast beside the fibers. Its cytoplasm contains some cisterns of endoplasmic reticulum, Golgi apparatus, and mitochondria.