1. Histology
Histology : is the study of the tissues of the body and how these tissues are arranged to constitute organs.
Tissues have two interacting components:
Cells .
Extracellular matrix (ECM).which is consist of many kinds of macromolecules.
The (ECM) function :
Supports the cells and the fluids that transports nutrients to the cells .
Carries away their catabolites and secretory products.

2. Types of Tissue
Despite its complexity, the human body is composed of only four basic types of tissue:
Epithelial tissue.
Connective tissue.
Muscular tissue.
Nervous tissue.
1. Epithelial tissue
it is a tissue in which cells are bound tightly together structurally and functionally to form a sheetlike or tubular structure with little extracellular material between the cells

3. All epithelial cells in contact with connective tissue at basal surfaces which referred as the Basement membrane which is a thin extacellular layer of specialized proteins , its components:
Attach epithelia to connective tissue.
Regulate (filter) substances passing from connective tissue to epithelia.
Guide tissue during regeneration after injury.

4. Functions of epithelial tissue
Covering.
Lining.
Protecting surfaces.
Absorption Ex. Intestinal lining
Secretion Ex. Parenchymal cells of glands
Specific cells of certain epithelia may be contractile or specialized sensory cells Ex1. Taste buds
Ex2. Olfactory epithelium
Because epithelial cells line all external and internal surfaces of the body, all substances that enter or leave tissues and organs must cross an epithelium.
Ex. Epidermis