Chapter two Repair Su Min （苏敏）

Definition: Repair is the process by which lost or destroyed cells are replaced by vital cells (regeneration).

Section 1 Regeneration

Definition: The surviving healthy cells nearby damage proliferate and move for repair.

1. Type: (1) Complete regeneration: The new tissue is the same with the loss in structure and faction. Commonly in physiological regeneration.

Conditions: ① the ability of regeneration of parenchymal tissue is strong. ② damage area is small and the stromal framework of the injured tissue is preservative well.

(2) Incomplete regeneration: granulation tissue (stromal or filler elements) proliferate to fill defect, replacement by scar. Commonly in pathological regeneration.Conditions: ① the ability of regeneration of parenchymal tissue is weak. ② damage area is extensive and the stromal framework of the injured tissue is not preservative well.

2. The regenerative capacity types of cells (1) Labile cells: normally a continuous process of active replacement is occurring.The chances of restoration by regeneration are excellent. Examples: the covering epithelium, the bone marrow cells and the lymphoid cells.

(2) Stable cells: Although normally the replacement requirements are minimal, they have not lost the capacity to proliferate in response to stimulation. Chances of regeneration remain. Examples: adenocytes of parenchymal viscera (including endocrine); all stromal elements.

(3) Permanent cells: Normally are unable to multiply after the growth early in life. Examples: nerve cells, striated and cardiac muscle cells, smooth muscle cells. But peripheral nerve has retained the capacity for regeneration with damage.

3. Regenerative process of tissues (1) Epithelial tissue ① Covering epithelia: Marginal proliferation may result in a perfect restoration.

② Glandular epithelia: Although in many instance the adenocytes of the organ can divide, the end-result is often dependent upon local factors, in particular the integrity of the basement membranes and reticulin scaffold that are necessary for the regenerating cells to be so grouped as to reform normal functional and anatomical glandular tissue.

(2) Fibrous 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 (fine fibrils stained by silver) ↓ condensation to form Collagen fibres ↓ Bonding and weaving ↓ Fibrocytes Scar tissue

(3) Blood vessel ① Capillaries: regeneration by sprout form. The initial step in the ingrowths of capillaries involves the enzymatic dissolution of the basement membrane of existing capillaries.

This is followed by proliferation of endothelial cells and migration of a solid sprout or bud of endothelial cells which differentiate, undergo canalization and by anastomosis with their neighbours form a series of vascular arcades.

At first the newly formed vessels show gaps between the endothelial cells, a poorly formed basement membrane, and long pseudopodia of the endothelial cells which reach out into the connective tissue spaces. Soon further differentiation may occur to adapt to needs of function. Some vessels acquire a muscular coat and become arterioles, whilst others enlarge to form thin- walled venules.

② Big blood vessels: Endothelial cells could be perfect restoration by complete regeneration; but cutting smooth muscle are connected by scar.

(4) Fractured long bone ① Haemorrhage and inflammation ② Organization and proliferation of periosteal cells ③ Wover bone and cartilage Calcification of cartilage and osteoid ④ Conversion to lamellar bone ⑤ Remodelling

Section 2 Repair by connective tissue

Proliferation of fibroblasts and capillary buds and the subsequent laying down of collagen to produce a scar is the usual consequence of most tissue damage.

1. Definition: This is young connective tissue, which is rich in young fibroblasts and capillaries 2. Morphology (1) gross feature: pink, soft, moist, and granular appearance.

(2) LM: fibroblasts: ① fibroblasts: new capillaries: ② new capillaries: capillary sprout and migrate toward the wound. The new capillary endothelial cells are swollen and capillary tubes are narrow. These new vessels have leaky interendotheial junctions. Allow the passage of proteins and red cells into the extravascular space, thus, new granulation tissue is often edematous. inflammatory cells ③ inflammatory cells

Granulation tissue

3. Consequences Granulation tissue fibroblasts New capillariesInflammatory cells collagen fibres vascularity diminishing gradually fibrocytes Bonding and weaving disappear Scar tissue

4. Function (1) anti-infection and protecting the surface of wound. (2) organization: granulation tissue replace necrotic tissue, blood clot, and foreign bodies. (3) encapsulation (4) filling wound or loss of tissue.

Section 3 Wound healing

1. Definition: Refers to the body ’ s replacement of destroyed tissue by living tissue 2. Stages in healing of wound (1) Escape of blood and exudates (2) Acute inflammation

(3) Contraction of the wound. The causes of contraction are not known but possible mechanisms are: ① Shrinkage of scab in superficial wounds ② Contraction properties of granulation tissue attributable to contraction of myofibroblasts or tissue re-modeling. ② Contraction properties of granulation tissue attributable to contraction of myofibroblasts or tissue re-modeling.

(4) Proliferation and migration of fibroblasts and endothelial cells. (5) Progressive increase in mature collagen fibres during the second week forming a scar. (6) Loss vascularity and shrinkage of the scar.

3. Type of wound healing (1) Healing by fist intention A clean wound with a minimum of space between the margins.

(2) Healing by second intention Healing by second intention differs from healing by first intention in: ① Greater tissue loss ② More inflammatory exudates and necrotic material to remove ③ More granulation tissue therefore a bigger scar

The orderly phases of wound healing

④ Wound contraction necessary ⑤ Slower process ⑥ Increased liability to infection (3) Healing under scab

Keloid ( 瘢痕疙瘩）

4. Factors influencing wound healing (1) Local factors adversely affecting healing ① Type of wounding agent; blunt, crushing, tearing etc. ② Infection ③ Foreign bodies in wound ④ Poor blood supply

⑤ Excessive movement ⑥ Poor apposition of margins, e. g. large haematoma formation ⑦ Poor wound contraction due to tissue tethering ⑧ Infiltration by tumor. ⑨ Previous irradiation.

(2) General factors adversely affecting healing ① Age ② Poor nutrition Deficiency of protein Lack of Vitamin C results in abnormal granulation tissue and deficient collagen production Zinc deficiency

③ Excessive glucocorticosteroid production or administration ④ Fall in temperature ⑤ Jaundice

(3) Factors accelerating wound healing ① Ultraviolet light. ② Administration of anabolic steroids, deoxycorticosterone acetate, cell growth factors. ③ Rise in temperature.