important role is to regulate the movement of materials into and out of cells. The phospholipid bilayer structure (fluid mosaic model) with specific membrane. proteins accounts for the selective permeability of the membrane and passive. and active transport mechanisms.
Structure of Blood Vessels a) Three distinct layers or tunics form the walls of blood vessels: ---The tunica interna (tunica intima) is the innermost layer.It contains the endothelium which is a continuation of the endocardial lining of the heart.tructure of Blood Vessels a) Three distinct layers or tunics form the walls of blood vessels: ---The tunica interna (tunica intima) is the innermost layer.
The tunica interna is the innermost lining of the blood vessel. It is lined by endothelium, which is almost always simple squamous epithelium, and its underlying connective tissue. In arteries a layer of elastic tissue called the internal elastic membrane marks the outer boundary of the tunica interna.2.rteries sometimes have an outer layer of elastic tissue called the external elastic membrane. When present this marks the boundary between the tunica media and tunica externa. 3. Tunica externa a.k.a. tunica adventitia. The tunica externa is the connective tissue that forms the outermost layer of the vessel.