Stem Cells and Tissue Repair Quiz

Repair

• Repair is the replacement of damaged tissue with new healthy tissue.

Learning Objectives

• Recognize the types of repair.
• List the factors that control repair.
• Describe the mechanisms that control repair.
• Learn about stem cells and their types.
• Understand examples of repair.
• Study healing by connective tissue.
• Investigate wound healing by primary and secondary intention.

Types of Repair

• Regeneration: Replacement of damaged cells by new cells of the same type.
• Healing by connective tissue: Replacement of damaged cells by connective tissue (fibrosis or gliosis).

Cell Types

• Permanent: These cells do not regenerate after injury. Examples include neurons, cardiac muscle.
• Stable: These cells can regenerate under specific conditions. Examples include liver, kidney, pancreas mesenchymal cells (like fibroblasts), endothelial cells, smooth muscle.
• Labile: These cells continuously divide and replace lost cells. Examples include hematopoietic cells of bone marrow, surface epithelia.

Stem Cells

• Stem cells are capable of:
  • Self-renewal capacity: Ability to divide and remain undifferentiated.
  • Asymmetric replication: Some daughter cells remain undifferentiated after division.
  • Multilineage potential or multipotent: Can differentiate into multiple cell types.
  • Long-term viability.

Types of Stem Cells

• Embryonic: Totipotent stem cells.
• Adult:
  • Marrow (Hemocytoblast): Hematopoietic stem cells.
  • Non-marrow (Reserve): Other stem cells.

Applications of Stem Cells in Medicine

• Treatment of diabetes, Alzheimer's.
• Replacing damaged tissues (brain, muscle, liver, bone, cartilage).
• Regrowing human teeth and hair.

Factors Affecting Repair

• Local factors: Infection, ischemia (reduced blood flow), foreign bodies, hematoma (blood collection), mechanical stress, and necrotic tissue.
• Systemic factors: Diabetes, ionizing radiation, age, malnutrition, vitamin deficiencies, drugs (steriods), and malignancy.

Mechanisms Controlling Repair

• Growth factors (EGF, FGF, PDGF, TGF alpha and beta).
• Removal of chemical factors inhibiting mitosis (chalones).
• Removal of contact inhibition.
• Cell matrix interaction.

Regeneration

• Skin:
  • Epidermis - regeneration of basal cells.
  • Dermis - granulation tissue → scar.

Repair of Liver after Damage

• Normal liver: Intact framework.
• Mild damage: Intact framework, regeneration.
• Massive damage: Destroyed framework, liver cirrhosis (scarring).

Liver Cirrhosis

• A condition where healthy liver tissue is replaced by scar tissue.

Repair of Bone

• Steps of bone fracture healing:
  • Hematoma formation.
  • Inflammation.
  • Granulation tissue formation (soft callus).
  • Provisional callus (woven bone).
  • Hard osseous callus (lamellar bone).
  • Remodeling.
  • Bone marrow regeneration.

Remodeling

• Performed by osteoblasts and osteoclasts. Directed by muscle and weight-bearing stresses.

Causes of Imperfect Bone Healing

• Local factors: Inadequate immobilization, pathological fracture, soft tissue interposition, ischemia, infection.
• General factors: Old age, nutritional deficiencies, glucocorticoids, diabetes mellitus.

Healing of Nervous System

• Central nervous system (CNS): Gliosis (scarring).
• Peripheral nervous system: Regenerate.

Healing by Connective Tissue (Scar)

• Replacement of damaged tissue by granulation tissue that matures into fibrous tissue (scar).

Steps of Repair by Scar

• Hemostasis.
• Inflammation.
• Proliferation.
• Remodeling.

Proliferation Stage

• Angiogenesis (New capillaries): Arising from capillaries at edges of damaged area and new endothelial buds.
• New capillaries have no basement membrane.
• They provide nutrition to proliferating fibroblasts.

Granulation Tissue

• Composed of capillaries and fibroblasts.
  • Moist, red, granular, velvety tissue.
  • Fragile, bleeds easily.
  • Not sensitive to infection.
• Microscopic features: Myriads of newly formed, thin-walled capillaries; active plump fibroblasts; scant collagen type I.

Maturation of Granulation Tissue (Scarring)

• Fibroblasts produce collagen fibers and ground substance.
• Fibroblasts contract (myofibroblasts), reducing the size of the lesion.
• Fibroblasts become fibrocytes.
• Remodeling into avascular, strong fibrous tissue.

Remodeling

• Rearranging collagen fibers parallelly to the surface to increase tissue strength.

Wound Healing

• Primary intention (union): For clean surgical incisions/non-gapping wounds.
  • Small blood clot, debris removal.
  • Epithelialization.
  • Granulation tissue formation (10-14 days).
  • Scarring (Months-years).
• Secondary intention (union): For infected, gapping crush wounds.
  • Large blood clot, necrotic debris, pus.
  • Granulation tissue formation.
  • Epithelialization.
  • Scarring (Months-years).

Complications of Wound Healing

• Excessive healing: Hypertrophic scars, keloids.
• Defective healing: Chronic ulcers, sinus, fistula, contracture, implantation cysts.