• 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

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

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.

Classification of Epithelial Tissues

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.

CT Cell Types

• Mast cells or basophils release heparin, which prevents blood clotting, and histamine, which aids in the inflammatory response.

CT Cell Types

• Fibroblasts secrete protein into the matrix, usually collagen which is a fibrous protein resulting in fibers.

CT Cell Types

• Macrophages originate as white blood cells. They can move and phagocytize foreign particles.

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.

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.

NERVOUS TISSUE

We will devote a whole unit to this.