Tissue Modification: Hypertrophy and Hyperplasia

Tissue Modification

• Tissues can change in size, form, or number of cells in response to stimuli.
• Hypertrophy: Increase in cell size without an increase in cell number, e.g., skeletal muscle cells during rigorous exercise.
• Hyperplasia: Increase in cell number, such as callus formation on the skin.
• Atrophy: Shrinkage of tissue due to reduced cell size or number; can be due to aging (senile atrophy) or lack of use (disuse atrophy).
• Metaplasia: Transformation of one mature epithelium type to another due to environmental stressors, e.g., smokers experiencing changes in tracheal epithelium.

Dysplasia

• Abnormal development of tissue which may reverse or progress to cancer.
• Example: Cervical dysplasia linked to human papillomavirus exposure.

Neoplasia

• Uncontrolled tissue growth leading to tumors; can be benign (localized) or malignant (cancerous, invasive, and may spread).

Necrosis

• Tissue death resulting from irreversible damage, often accompanied by inflammation.
• Example: Gangrene.

Mortality and Morbidity

• Malignant cell proliferation can impair normal organ function leading to morbidity (disease affliction) and mortality (susceptibility to death).

Stem Cells

• Undifferentiated, immature cells capable of division and differentiation into specialized cells.
• Two key characteristics: Self-renewal (ability to produce new stem cells) and Potency (ability to differentiate into various cells).
• Levels of potency include:
  • Totipotent: Can differentiate into any cell type (zygote stage).
  • Pluripotent: Derived from totipotent cells, can form most cell types except placental structures (stem cells in the blastocyst).
  • Multipotent: Limited differentiation potential, e.g., blood cell formation from marrow.
  • Unipotent: Can differentiate into one cell type, e.g., epithelial stem cells.

Differences Between Embryonic and Adult Stem Cells

• Embryonic Stem Cells:
  • Derived from zygote and blastocyst.
  • Exhibit highest potency level.
• Adult Stem Cells:
  • Found in postnatal organisms.
  • Generally multipotent or unipotent with lower potency than embryonic cells.

Harvesting Stem Cells

• Embryonic Stem Cells harvested from blastocysts, often from in vitro fertilization procedures.
• Adult Stem Cells extracted from tissues like red bone marrow; have limited potency affecting treatment options.

Gangrene

• Necrosis of soft tissues due to obstructed blood supply, commonly affecting limbs and extremities.
• Treatment involves tissue removal, blood supply restoration, and antibiotics.
• Forms of gangrene include:
  • Dry Gangrene: Tissue shrinks and desiccates due to restricted blood flow from cold exposure.
  • Wet Gangrene: Resulting from bacterial infection of necrotic tissues.
  • Gas Gangrene: Caused by Clostridium bacteria, creating gas bubbles in muscle tissue.

Necrotizing Fasciitis

• Severe tissue necrosis from bacterial infection (often Streptococcus A), known as flesh-eating bacteria.
• Symptoms include severe pain, fever, swelling; requires aggressive antibiotic treatment and surgical intervention.

Aging of Tissues

• As individuals age, tissues undergo structural and functional changes, leading to decreased efficiency in cellular support and repair.
• Common aging effects include:
  • Thinning of epithelia.
  • Decreased connective tissue pliability and resilience.
  • Decline in collagen levels affecting repair duration.
  • Increased brittleness of bones, muscle, and nervous tissue atrophy.
  • Poor nutrition and health accelerates tissue decline.

Grafting

• Surgical transplantation of healthy tissue to replace damaged areas.
• Types of grafts:
  • Autograft: Tissue transplanted from one site to another on the same individual.
  • Syngenetic Graft: Tissue from a genetically identical individual (e.g., identical twins).
  • Allograft: Tissue from one person to another with genetic differences.
  • Heterograft: Tissue from a different species.