Tissue Regeneration and Development

Regeneration of Tissues

• Epithelial tissue (skin and mucous membranes) and fibrous connective tissues and bone regenerate easily.
• Skeletal muscle regenerates poorly.
• Cardiac muscle and nervous tissue within the brain and spinal cord are replaced largely with scar tissue.

Developmental Aspects of Cells and Tissues

• Growth through cell division continues through puberty.
• Cell populations exposed to friction (such as epithelium) replace lost cells throughout life.
• Connective tissue remains mitotic and forms repair (scar) tissue.
• Muscle tissue becomes amitotic by the end of puberty, except for some exceptions.
• Nervous tissue becomes amitotic shortly after birth.
• Injury can severely handicap amitotic tissues.

Aging and Neoplasms

• The cause of aging is unknown, but chemical and physical insults, as well as genetic programming, have been proposed as possible causes.
• Neoplasms, both benign and cancerous, represent abnormal cell masses in which normal controls on cell division are not working.
• Hyperplasia (increase in size) of a tissue or organ may occur when tissue is strongly stimulated or irritated.
• Atrophy (decrease in size) of a tissue or organ occurs when the organ is no longer stimulated normally.

Glands of the Integumentary System

• Sebaceous (oil) glands are found throughout the entire body except for palms and soles, and produce sebum by holocrine secretion to oil and lubricate.
• Sweat glands are found on the entire skin surface except for nipples and part of external genitalia, and help prevent overheating, producing 500 cc to 12 l/day.