Acute Inflammation 3: Healing

Question 1

What is healing?

Answer 1

Healing is the process by which the body replaces damaged tissue with living tissue. It involves the restoration of tissue architecture and function after injury.

Question 2

When does healing begin?

Answer 2

At the start of acute inflammation

Question 3

What is resolution?

Answer 3

The complete restoration of structure and function of tissue.

Question 4

What are parenchymal cells?

Answer 4

The distinguishing or specific cells of a gland or organ (cells of the functional element)

Question 5

What are the three types of parenchymal cells?

Answer 5

1. Labile (continuously renewing)
2. Stable (conditionally renewing)
3. Permanent (non renewing)

Question 6

What is the preferred method healing?

Answer 6

Regeneration

Question 7

What determines the occurrence of effective regeneration?

Answer 7

1. Type of cell
2. organisation of cells with respect to each other
3. CELLULAR MATRIX MUST BE INTACT

Question 8

What are the two types of healing, and define them?

Answer 8

1. Regeneration:
   Proliferation of cells that survive the injury or differentiation of tissue stem cells. Damaged parenchymal cells are replaced by similar cells and function/structure is restored.
2. Repair (scar formation):
   The laying down of connective (fibrous) tissue- a variable amount of replacement of parenchymal cells by CT. The fibrous scar can provide enough structural stability that the injured tissue is able to function.

Question 9

What is fibrosis?

Answer 9

The extensive deposition of collagen that occurs in organs due to chronic inflammation or infarction.

Question 10

What is Organisation?

Answer 10

The development of fibrosis in a tissue space occupied by an inflammatory exudate.

Question 11

How is repair achieved?

Answer 11

By granulation (Except in specialised tissue such as bone and the CNS)

Question 12

What does granulation tissue consists of?

Answer 12

1. Inflammatory cells
   - Mostly macrophages that phagocyose cellular and protein debris
   - Play a critical role coordinating via the secretion of cytokines to switch on fibroblasts
2. Myofibroblasts
   - Activated contractile fibroblastic cell with long tails
   - Synthesise matrix proteins, proteoglycans and glycosaminoglycan’s (make collagen-normal fibroblast too)
3. Newly formed blood vessels
   - Exhibit increased permeability and form from the bottom up.

Question 13

Restoration of the epithelial layer to cover the wound and granulation tissue involves what?

Answer 13

Migration of adjacent uninjured epithelial cells, yielding a thin continues epithelial surface

Cellular proliferation to re-establish normal epithelial thickness

Question 14

How do scars form?

Answer 14

1. Angiogenesis- the migration and proliferation of endothelial cells
2. Formation of granulation tissue- Migration and proliferation of fibroblasts and deposition of connective tissue with vessels and interspersed leukocytes
3. Remodelling of connective tissue- Vascular regression, remodelling of the scar and scar contraction

Question 15

What is healing by primary intention?

Answer 15

Healing in an opposed, incised wound. There is limited inflammation, rapid restoration of epithelium by migration and proliferation, relatively little granulation tissue and minimal scarring

Question 16

What is healing by secondary intention?

Answer 16

Healing of substantial tissue loss. There is marked inflammation, ingrowth of granulation tissue, a variable degree of wound contraction, delayed re-epithelialisation and significant scaring.

Question 17

Provide insight into the mediators of healing

Answer 17

Sequentially released, locally acting cytokines (notably by platelets, macrophages and mast cells) is crucial in the healing process. These cytokines are often called ‘growth factors’ and exhibit AUTOCRINE and PARACRINE action. Most have multiple effects (pleiotropic) that may overlay with the effects of other cytokines (redundancy)

Question 18

What is autocrine signalling?

Answer 18

Signalling molecules secreted by the cell affect adjacent cells of the same type.

Question 19

What is paracrine signalling?

Answer 19

Signalling molecules secreted by the cell effect adjacent cells of a different type

Question 20

What is endocrine signalling?

Answer 20

A mediator is released into the bloodstream and acts on distant target cells (IL-1 and TNF-a)

Question 21

What are the factors effecting healing?

Answer 21

Local:

Vascularity
Infection
Mechanical trauma
Chemical injury
Foreign bodies
Irradiation
Neoplasia

Systemic Factors:

Age
Nutritional status
Coexisting systemic diseases
Hormonal status