L7: Tissue Repair

Question 1

What is the definition of tissue repair?

Answer 1

replacement of damaged tissue by a healthy one.

Question 2

What are the types of tissue repair?

Answer 2

1- Repair by regeneration
2- repair by fibrosis
3- repair by organization

Question 3

What is the definition of healing by regeneration?

Answer 3

replacement of the damaged tissue by a healthy tissue of the same kind.

Question 4

What are the cells of the body classified according to?

Answer 4

• Cells of the body are divided according to the power of regeneration into three groups:
  (1) Labile cells: cells proliferate continuously throughout life e.g:

a- Cells of all epithelial surfaces: epidermis of the skin, gastrointestinal tract respiratory tract, and genitourinary tract.

b- Cells of bone marrow and lymphoid tissue.

(2) Stable cells: Do not proliferate under normal conditions, but proliferate in need.
E.g
a- Parenchymal cells of all glands.
b- Mesenchymal cells: fibroblast, chondroblast, and osteoblast.

(3)Permanent cells: cannot proliferate at all and include nerve cells.

Question 5

What are examples of regeneration?

Answer 5

I- Regeneration of skin: The epidermal cells are labile cells, which regenerate easily
II- Regeneration of liver cells.
III- Repair of bone fracture:

Question 6

Repair of bone fracture:

Answer 6

1- site of fracture is the seat of hemorrhage and necrotic bone cells. These products irritate the area leading to mild acute inflammation.

2- Macrophages and osteoclasts clean the area.

3- Provisional callus formation: woven bone produced by osteoblasts (External, intermediate, and internal callus).

4- Permanent bone The external and internal callus is removed by osteoclasts.
- Woven bone of intermediate callus is replaced by lamellar bone

Question 7

What is the definition of healing by fibrosis?

Answer 7

Replacement of damaged tissue by granulation tissue which matures to fibrous tissue.

Question 8

What is the granulation tissue?

Answer 8

It is a transitory tissue formed during the repair.

Question 9

What is the the N/E of granulation tissue?

Answer 9

“RBG VMR”

red granular, velvety, moist, bleeds easily, and resistant to infection.

Question 10

What is the M/E of granulation tissue?

Answer 10

capillaries and fibroblasts infiltrated by inflammatory cells.

Question 11

What is the mechanism of the formation of fibrosis (granulation tissue)?

Answer 11

1- The new capillaries arise as solid endothelial buds from the capillaries at the edges of the damaged area and form capillary loops.

2- Newly formed capillaries are highly permeable

3- Fibroblasts proliferate

4- Fibroblasts produce collagen fibers.

5- The collagen compresses and obliterates the capillaries.

6- Fibroblasts contract

7- Fibroblasts change to fibrocytes.

8- Fibrocytes and collagen fibers are remodeled to give a full tensile strength

9- Finally avascular strong fibrous tissue ( scar) is produced.

Question 12

What are the types of healing of wounds?

Answer 12

1- Primary union of wound (Healing by first intention)

2- Secondary union

Question 13

Where does Primary union of wound (Healing by first intention) take pale?

Answer 13

Occurs in:
1- clean incised wound
2- minimal tissue destruction
3- Approximated edges

e.g: Surgical wounds.

Question 14

What are the steps of the Primary union of wounds?

Answer 14

1- Blood is clotted between the wound edges and on the surface.

2- The incision causes mild acute inflammation in the edges of the wound. Then products of inflammation are rapidly removed by macrophages.

3- The basal cell layer of the epidermis on both edges of the wound proliferates across the clot to meet in the center.

4 -The gap of the wound under the new epithelium gets filled by granulation tissue

Question 15

What are the characters of the primary union?

Answer 15

1- occurs in clean incised wounds
e.g. surgical wounds.
2- minimal tissue destruction and gaping 
3- less inflammatory reaction
4- a small amount of granulation tissue
5- rapid healing 
6- small scar (thin and linear)
7- complications rare

Question 16

What are the characters of the secondary union?

Answer 16

1- occurs in septic wounds.
2- tissue destruction and gaping are present
3- more inflammatory reaction
4- a large amount of granulation tissue
5- slow healing
6- large scar (irregular)
7- complications as ulcer and keloid are more common

Question 17

What is the definition of repair by organization?

Answer 17

replacement of solid nonliving material as dead tissue, blood clots, or fibrin by fibrous tissue.

Question 18

What are the examples of repair by organization?

Answer 18

E.g; Serofibrinous inflammation, thrombus, hematoma, and infract heal by organization.

Question 19

What are the complications of repair?

Answer 19

A- Too less cellular proliferation resulting in:
1- Ulcer
2- Sinus
3- Fistula
4- Stretching of a weak scar and formation of incisional hernia.

B- Too much cellular proliferation and scar formation
1- Excessive granulation tissue (Proud flesh)
2- Excessive scaring forming keloid
4- Scar may be painful as in stump neuroma.
5-Squamous cell carcinoma rarely develops in a scar.

Question 20

What are the factors that impair repair?

Answer 20

Local and general

Question 21

What are the local factors that impair the repair process?

Answer 21

1- Infection
2- foreign body
3- ischemia
4- Severe damage

Question 22

What are the general factors that Impair repair process?

Answer 22

1- Age: repair is more rapid and adequate at a young age.

2- Nutrition
a- protein deficiency delays repair.
b- vitamin deficiency: Vit C deficiency causes the defective formation of collagen and osteoid tissue.
c- metals:
i- zinc deficiency: zinc is necessary for collagen synthesis.
ii- Calcium deficiency: Calcium is required for the maintenance of connective tissue and bone as well as other processes.

3- Hormones: e.g. cortisol depresses the repair.

4- Systemic disease: e.g. diabetes mellitus increases susceptibility to infection, so delay the repair.

5- Physical agents: e.g. ionizing radiation delays repair.

6- Chemicals and drugs e.g. cytotoxic drugs delay repair.