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.
A rhytid, (riâ²tid), is a wrinkle in the skin. The skin is composed of three layers: the epidermis, the dermis, and subcutaneous fat. The epidermis, the top layer of the skin, produces melanin, which gives the skin its color. It also protects the skin, with special cells known as keratinocytes, against environmental toxins.