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 epidermis. This is the outermost layer of your skin. There are three sub-layers within the epidermis itself: the outer stratum corneum, the middle squamous cell layer, and the bottom basal cell layer.The stratum corneum is the visible part of the epidermis and is actually a layer of dead skin cells immediately on the skin's surface.This layer uses a protein called keratin to form a tough barrier between the outside world and the more vulnerable cells inside the skin and body. Keratinocytes or squamous cells are in the middle layer of the epidermis and produce keratin, the protein that forms the protective outer layer. 2  Keratin also is used to produce hair and nails.