TEM of capillary at junction of three thyroid follicles. Specimen from cat. Capillaries are the smallest of a body's blood vessels (and lymph vessels) that make up the microcirculation. Their endothelial linings are only one cell layer thick. These microvessels connect arterioles and venules, and they help to enable the exchange of water, oxygen, carbon dioxide, and many other nutrients and waste substances between the blood and the tissues surrounding them. The thyroid gland is one of the largest endocrine glands in the body, and consists of two connected lobes. Magnification @ 6500x, 5x7 print.