5.6 Tissue Modification, Aging, and Tissue Transplant (Vocabulary)

Hypertrophy: increase in size of existing cells; number of cells remains constant; example: skeletal muscle with long-term rigorous exercise.
Hyperplasia: increase in cell number; example: callus formation on the palm.
Atrophy: shrinkage due to decreased cell size or cell number; aging (senile atrophy) or disuse atrophy; disuse (e.g., bedridden or cast) can be reversed with therapy.
Metaplasia: mature epithelium changes to a different mature epithelium; smokers often show metaplastic changes in tracheal epithelium; quitting can revert to original pseudostratified ciliated columnar epithelium.
Dysplasia: abnormal tissue development; precancerous potential; may revert to original tissue or progress to cancer; closely monitored.
Neoplasia: uncontrolled tissue growth; neoplasms can be benign or malignant; malignant neoplasms invade local tissues and may metastasize; commonly called cancer; often linked to DNA damage from environment or genetics.
Necrosis: tissue death from irreversible damage; inflammatory response usually occurs.
Gangrene: necrosis with tissue decay; forms include:
- Intestinal gangrene: from lost blood supply due to obstruction or volvulus.
- Dry gangrene: desiccated, sharply demarcated, often from constricted vessels (e.g., frostbite).
- Wet gangrene: bacterial infection with tissue, loss of blood/oxygen; foul pus.
- Gas gangrene: usually muscle tissue infection by Clostridium; gas bubbles produced, crackling sound on movement.

All tissues change with age; proper nutrition, good health, adequate circulation, and few wounds promote continued function.
With aging: epithelia thin; connective tissue loses pliability; collagen declines; tissue repair slower.
Bones become brittle; muscle and nervous tissue atrophy.
Accelerating factors: poor diet, circulation problems, chronic alcohol use, smoking.
Cumulative minor damage can lead to major health problems.

Grafting = surgical transplant of healthy tissue to replace diseased/damaged tissue; four types: 4 autograft, syngeneic (isograft), allograft, xenograft (heterograft).
Autograft: from one site to another in the same individual; common for skin grafts; no rejection since it is self-tissue; feasibility limited by tissue availability.
Syngeneic (isograft): from a genetically identical person (identical twin); minimal rejection.
Allograft: from a genetically different person; risk of rejection; immunosuppressants required; closer genetic match reduces rejection; used for tissues and organs.
Xenograft (heterograft): from an animal to a human; higher rejection risk; examples include porcine/cattle tissues; 2022 milestone: genetically modified pig heart transplanted in a human with limited survival but ongoing progress.