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: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

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The mode of Fibrocytes

(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

③Wover bone and cartilage Calcification of cartilage and osteoid

④ Conversion to lamellar bone⑤ Remodelling