Lecture # 29 Tissue Repair, Regeneration, Healing & Fibrosis – 1 Dr. Iram Sohail Assistant Professor Pathology College of Medicine Majmaah University

OBJECTIVES Control of cell proliferation Cell cycle Proliferative capacity of tissues Stem cells

INTRODUDUCTION REPAIR Restoration of tissue architecture & function after an injury. 2 Types

1.Regeneration If the damaged tissue will return to a normal state.

2.Healing by scar formation If the damage is severe, the repair occurs by laying down the connective tissue and results in scar formation.

CONTROL OF CELL PROLIFERATION During tissue repair, following type of cells proliferate i.Remnants of injured cells – To restore normal structure

ii.Vascular endothelial cells – To create new blood vessels for providing nutrients to repairing tissue iii.Fibroblast – For scar formation Proliferation of these cells is possible by growth factors

CELL CYCLE Cell cycle consists of series of steps. G1 – Pre synthetic growth phase S – Synthesis phase G2 – Pre-mitotic phase M – Mitotic phase The cell cycle has multiple positive & negative controls.

PROLIFERATIVE CAPACITIES OF TISSUES The reparative ability of tissue is influenced by their proliferative capacity. Based on proliferation criteria, the tissues are divided into 3 types

1.Continuously dividing tissues (Labile tissue) – Continuously dividing cells – Lost & replaced by cells Examples – Hematopoietic cells in bone marrow – Surface epithelial cells – Skin, oral cavity, vagina, cervix

2.Stable tissues – Minimal replicative capacity – Capable of proliferating in response to injury or loss of tissue mass. Examples – Liver, kidney, pancreas – Wound healing

3.Permanent tissue – Non proliferative cells Examples – Cardiocytes (heart cells) – Neurons (brain cells) The heart & brain are non-proliferating cells and injury to them results in scar formation. Skeletal muscle cells are also non dividing cells but with some regenerative capacity.

STEM CELLS Definition Stem cells are undifferentiated cells, that can differentiate into specialized cells and can divide to produce more stem cells.

Stem cells have 2 important properties 1.Self-renewal capacity – Self-renewal means that they renew itself. 2.Asymmetric replication – Asymmetric replication means that after each cell division, some cells will be differentiated and other will remain undifferentiated.

Pluripotent stem cells Human embryonic stem cells with the capacity to generate multiple cell lineages.