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• 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.