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A common pathological disorder concerning the tunica externa is scurvy, also known as vitamin C deficiency. Scurvy occurs because vitamin C is essential for the synthesis of collagen, and without it, the faulty collagen cannot maintain the vein walls and rupture, leading to a multitude of problems.
External lamina is a structure similar to basal lamina that surrounds the sarcolemma of muscle cells. It is secreted by myocytes and consists primarily of Collagen type IV, laminin and perlecan (heparan sulfate proteoglycan). Nerve cells, including perineurial cells and Schwann cells also have an external lamina-like protective coating. [1]
The tunica intima of muscular arteries features a thin subendothelial layer and a prominent internal elastic lamina, while the media may contain up to 40 layers of large smooth muscle cells interspersed with a variable number of elastic lamellae, depending on the vessel size. Only the larger muscular arteries possess an external elastic lamina.
Small vessels like vasa vasorum and vasa nervorum are particularly susceptible to external mechanical compression, [10] and thus are involved in pathogenesis of peripheral vascular and nerve diseases. A tear in vasa vasorum situated in tunica media layer of aorta may start pathologic cascade of events leading to aortic dissection. [4]
The tunica media is made up of smooth muscle cells, elastic tissue and collagen.It lies between the tunica intima on the inside and the tunica externa on the outside.. The middle coat (tunica media) is distinguished from the inner (tunica intima) by its color and by the transverse arrangement of its fibers.
This tissue covers all organismal surfaces that come in contact with the external environment such as the skin, the airways, and the digestive tract. It serves functions of protection, secretion, and absorption, and is separated from other tissues below by a basal lamina. The connective tissue and the muscular are derived from the mesoderm.
The tunica intima (Neo-Latin "inner coat"), or intima for short, is the innermost tunica (layer) of an artery or vein.It is made up of one layer of endothelial cells (and macrophages in areas of disturbed blood flow), [1] [2] and is supported by an internal elastic lamina.
Muscle cells are grouped into muscle fascicles by enveloping perimysium connective tissue. [1] Fascicles are bundled together by epimysium connective tissue. [1] Muscle fascicles typically only contain one type of muscle cell (either type I fibres or type II fibres), but can contain a mixture of both types.