Cell Repair and Stem Cell Concepts

Section 1: General Concepts

• Definition of repair: Replacement of damaged tissue, either by scar tissue (repair) or new healthy tissue (regeneration).
• Repair types:
  • Regeneration: Replacement with new healthy tissue.
  • Fibrosis: Replacement with connective tissue.
• Permanent cell types: Surface epithelium, liver cells, and nerve cells
• Non-permanent cell types: Fibroblasts

Section 2: Stem Cells

• Stem cell characteristics:

  • Self-renewal: Ability to replicate itself
  • Multilineage potential: Ability to differentiate into various cell types
  • Short-term viability: (Not a characteristic)
  • Asymmetric replication: Dividing into one stem cell and one differentiated cell.

• Embryonic stem cell types:

  • Totipotent: Capable of developing into any cell type, including extraembryonic tissues.
  • Pluripotent: Capable of developing into any cell type within the embryo.
  • Multipotent: Capable of developing into multiple cell types, but not all cell types.
  • Unipotent: Capable of developing into only one cell type.

• Adult stem cells: Hemocytoblasts, osteoblasts, and fibroblasts

Section 3: Mechanisms and Factors Affecting Repair

• Growth factors in repair: EGF, FGF, and TGF-β.
• Factors inhibiting repair:
  • Contact inhibition
  • Chalones
  • Inflammation
  • Matrix interaction

Section 4: Wound Healing

• Primary intention healing: Healing in clean surgical wounds, where the edges are brought together.
• First step in bone fracture healing: Hematoma formation
• Granulation tissue components: Collagen, fibrocytes, capillaries, and fibroblasts
• Type of collagen in mature scar tissue: Type I

Section 5: Granulation Tissue

• Granulation tissue composition: Primarily collagen and fibroblasts, capillaries.

Section 6: Complications

• Excessive collagen formation leads to: Keloids, contractures (abnormal tightening of skin tissues).
• Blind-end tract opening: Fistula
• Epithelial surface defect:: Ulcer
• Types of healing: Primary and secondary intent. Secondary intention healing occurs in large wounds or infected wounds.

Section 7: Types of Healing

• Secondary intention healing: Healing in wounds with significant tissue loss or infection.
• Characteristics of granulation tissue: Moist, red, and granular.

Section 8: Bone Healing

• Callus types:
  • Soft callus: Forms first in healing.
  • Hard callus: Develops after soft callus.
  • Lamellar bone: Mature bone tissue.
• Bone remodeling agents: Osteoclasts and osteoblasts
• Factors hindering bone healing, including old age, ischemia (reduced blood flow), and nutritional deficiency.

Section 9: Complications of Wound Healing

• Excessive healing: Hypertrophic scars, sinuses, fistulas, and cyst formation
• Scar characteristics: Keloids have scar tissue that extends beyond the margins of the wound.
• Contractures: Occur with nervous system injuries or overgrowth of granulation tissue.
• Cysts: Filled with blood, pus, keratin, or collagen.
• Hypertrophic scar versus keloid: Hypertrophic scars are contained within wound boundaries and keloids extend beyond the wound.