2. The body contains at least 200 distinct cell types. These cells contain essentially the same internal structures yet they vary enormously in shape and function. The human body starts as a single cell at fertilization. As this fertilized egg divides, it gives rise to trillions of cells, each built from the same blueprint

3. What is a tissue? Tissue - a group or mass of similar cells working together to perform certain common functions Four Primary Types: – Epithelium – Connective – Nervous – Muscle

4. Epithelial Tissue (ET) Epithelia are sheets of cells that function in protection, secretion, absorption, and excretion. Epithelium is composed of tightly packed cells anchored to a basement membrane. It lacks blood vessels and rapidly divides. ET are classified by cell shape and number of cell layers.

5. Classification of Epithelial Tissues

6. Connective Tissues (CT) Connective tissue is the most abundant tissue in the body. Extracellular material, a matrix, makes up the bulk of the tissue. Matrix is composed of fibers and ground substance. Connective tissue cells usually can divide.

7. CT Cell Types Mast cells or basophils release heparin, which prevents blood clotting, and histamine, which aids in the inflammatory response.

8. CT Cell Types Fibroblasts secrete protein into the matrix, usually collagen which is a fibrous protein resulting in fibers.

9. CT Cell Types Macrophages originate as white blood cells. They can move and phagocytize foreign particles.

10. CT Fibers White collagenous fibers, are made of thick threads of collagen. They are strong, flexible, and inelastic. Elastic fibers, yellow fibers, are made of bundles of elastin.

11. Muscle Tissue (MT) There are three types of muscle tissue: skeletal, smooth, and cardiac. Properties: It is contractile (muscle fibers can shorten and thicken). It is excitable.

12. NERVOUS TISSUE We will devote a whole unit to this.