Gangrene: • It’s a necrosis with putrefaction,. • It has 3 types: • 1- Dry or senile gangrene. Gradual arterial occlusion usually affect the extremities • 2- Moist gangrene. Sudden arterial and venous occlusion, Bacterial invasion , skin is black, moist and of foul odour • 3- Gas gangrene. Due to infection with gas producing organism
1- Dry gangrene “Gross”: Dry gangrene: Gradual arterial occlusion, usually affect the extremities. The skin is dark brown or black and dry. There is a line of demarcation between the gangrenous area and the healthy tissues. e.g. senile gangrene of the lower limb
Healing: • Replacement of damaged tissue by new, healthy, living tissue. • Either by: 1- Regeneration mechanism : Replacement of damaged cells by new cells of the same kind 2- Scaring “fibrosis”: is the replacement of tissue by Granulation tissue which matures to fibrous tissue.
2- Granulation tissue: The damage area is invaded by granulation tissue that consist of: new capillaries form, spindle shaped fibroblasts, Homogenous pale pink ground substance showing few pink collagen fibers and and inflammatory cells .
4- Primary union of wounds: Blood clot formation at the site of wound. Phagocytic cells remove debris. Granulation tissues fibrous tissues scar. Epithelium regenerate and move toward the center
5- Secondary union of wounds : Large tissue defect More inflammation More granulation tissue
6- Myocardial scaring: Scar tissue appearing between cardiac muscles, it is appears homogenous, pink in color and new capillaries and fibroblast formed
7- Repair after myocardial infarction: -the infarct area shows loss of details of the muscle fibers, the necrotic muscle fibers appear granular and pink with blue nuclear fragments.