Elastic fibers (or yellow fibers) are bundles of proteins (elastin) found in extracellular matrix of connective tissue and produced by fibroblasts and smooth muscle cells in arteries.These fibers can stretch up to 1.5 times their length, and snap back to their original length when relaxed.he elastic fiber is formed from the elastic microfibril (consisting of numerous proteins such as microfibrillar-associated glycoproteins, fibrillin, fibullin, and the elastin receptor) and amorphous elastin.
Venous, Arterial, and Capillary Blood Specimens. Venous Blood. Venous blood is deoxygenated blood that flows from tiny capillary blood vessels within the tissues into progressively larger veins to the right side of the heart.Venous blood is the specimen of choice for most routine laboratory tests.apillary Blood. Capillary blood is obtained from capillary beds that consist of the smallest veins (venules) and arteries (arterioles) of the circulatory system. The venules and arterioles join together in capillary beds forming a mixture of venous and arterial blood.
Capillaries are where fluids, gasses, nutrients, and wastes are exchanged between the blood and body tissues by diffusion. Capillary walls contain small pores that allow certain substances to pass into and out of the blood vessel.hese structures are located between arterioles and capillaries and contain muscle fibers that allow them to contract. When the sphincters are open, blood flows freely to the capillary beds of body tissue. When the sphincters are closed, blood is not allowed to flow through the capillary beds.