Chapter 2 Tissues Repair Norman Bethune College of Medicine Jilin University Li Yulin

Regeneration necrotic parenchymal cells may be replaced by new parenchymal cells of the same type in a process known as regeneration. Section 1 Cell Regeneration Replacement of lost parenchymal cells by division of adjacent surviving parenchymal cells (regeneration) can restore injured tissue to normal.

The regeneration of cells involves cell division (mitosis) 1. regenerative capacity of involved cells 2.number of surviving viable cells, 3.presence of a connective tissue framework that will provide a base for restoration of normal tissue structure. Regeneration occurs depends on

Labile cells Normally divided actively to replace cells that are being continuous lost from the body. The chances of restoration by regeneration are excellent. Include basal epithelium stem cells, hematopoietic stem cell in bone marrow. The regenerative capacity types of cells-1

Stable cells a long life span and are characterized by a low rate of division, retain the capacity to enter the mitotic cell cycle if the need arises. Chances of regeneration remain. Including parenchymal cell of solid glandular organ (liver, pancreas) and mesenchymal cells. The regenerative capacity types of cells-2

Permanent cells no capacity for mitotic division in postnatal life. Neurons, striated and cardiac muscle cells, smooth muscle cells. But peripheral nerve has retained the capacity for regeneration with damage. The regenerative capacity types of cells-3

Regenerative process of tissues the regeneration process requires (1) the regenerative ability of the cells. (2) the intact of tissues framework.

Regeneration of Epithelial Tissues Covering epithelial cells may regenerate completely The cells at the cut margins start to regenerate by division and migrate out as a thin layer over the denuded surface Some cell and tissue Regeneration

Regeneration of Epithelial Tissues Glandular epithelial cell: enough viable tissue remaining to provide a source of parenchymal cells for regeneration and Regeneration is dependent upon the integrity of the adjacent connective tissue

Regeneration of Connective tissue (fiber tissue) Fibrocytes (Primitive cells) ↓ situated around capillaries and loose connective tissues Fibroblasts Secretion of ground substance including adhesive Glycoproteins: Fibronectins. Secretion of Tropocollagen (very fine fibrils detected by EM) ↓ condensation to form Reticulin fibres ↓ condensation to form Collagen fibres ↓ Bonding and weaving ↓ Fibrocytes Scar tissue

Angiogenesis Enzymatic dissolution of the basement membrane of existing capillaries,allowing formation of capillaries spout. Endothelial cells proliferate, migrate, and begin to form vascular channels. The channels join adjacent capillaries to form a series of vascular channels. At first, the newly formed vessels have gaps between the endothelial cells and a poorly formed basement membrane. Some vessels become arterioles. Others enlarge to form thin-walled venules.

Regeneration of Bone, cartilage and Tendon Regeneration of Skeletal, smooth and Cardiac Muscle In cartilage injury, Restitution is performed by the perichondriurn, chondroblasts proliferate and transform to chondrocytes. Fibroblasts from the cut tendon's sheath become active, and lay down collagen fibers, which can restore most of the original strength of the tendon. But in many conditions, the injured skeletal muscle is usually replaced by scar

Section 2 Repair by Scar formation when necrotic cells are permanent cells when the connective tissue framework of a tissue composed of stable cells has been destroyed when necrosis is so extensive that no cells are available for regeneration. Scar Repaired Formed

The area of injury is prepared for scar formation by removal of the inflammatory exudates. Liquefied material is removed by lymphatic; any particulate residue is removed by macrophage phagocytosis. several overlapping phases for Scar Formation Preparation

In Growth of Granulation tissue Definition of Granulation Tissue is highly vascularized connective tissue composed of newly formed capillaries, proliferating fibroblasts, and residual inflammatory cells

Function  anti-infection and protecting the surface of wound  filling wound or loss of tissue  organization or encapsulation: (granulation tissue replace necrotic tissue, blood clot, and foreign bodies)

Section 3 Skin Wound healing Types of skin injury A. Abrasion (Scrape) B. Incision (Cut) and Laceration (Tear) C. Wounds with Epidermal Defects (Laceration)

Clinical types of wound healing Healing by first intention Usually occurs in a clean wound where there is a small space between the margins, e.g., –Minor skin wounds –Most surgical wounds Complete repair of the wound almost without a scar Complete replacement of necrotic epithelium and connective tissue

Clinical Types of Wound Healing Healing by secondary intention Occurs if: –Wound is very large in lacerations characterized by in ability to achieve apposition of wound margins when foreign material is present when necrosis is extensive when infection occurs. Tissue does not have a normal structure after repair. Usually replaced by scar tissue Repair is slow due to systemic illness

Causes of Defective Wound Healing ① Local factors Foreign or necrotic tissue or blood Infection Abnormal blood supply Decreased viability of cells ② Failure of collagen synthesis ③ Excessive collagen production (keloids ) ④ Diabetes Mellitus ⑤ Excessive levels of adrenal corticosteroids

Section 4 Fracture Repair Traumatic Fracture: Mechanical force Pathologic or Spontaneous fracture: previously diseased bone Bone fracture

1.Hematoma (Hemorrhage and inflammation) 2.Provisional Callus (Organization and proliferation of periosteal cells) 3. Bony Callus (Formation of cartilage and immature bone) 4.Bony Remodeling (Conversion to lamellar bone ) Fracture Repair