S4) Healing and Repair Flashcards
What are the three processes involved in wound healing?
- Haemostasis – as vessels are open
- Inflammation – as there has been tissue injury
- Regeneration (aka resolution) and/or repair – as structures have been injured or destroyed
What is regeneration?
Regeneration is the growth of cells and tissues to replace lost structures e.g. epithelia of skin and GI tract can regenerate after injury
Which cells replicate in regeneration?
New differentiated cells are mainly derived from stem cells as many terminally differentiated cells can’t divide
What are stem cells?
Stem cells are cells with prolonged proliferative activity which show asymmetric replication
What is asymmetric replication?
In asymmetric replication one of the daughter cells remains as a stem cell while the other differentiates into a mature, non-dividing cell
Whereabouts in the tissues are the stem cells?
Varies between tissues:
- Epidermis – basal layer adjacent to the basement membrane
- Intestinal mucosa – bottom of crypts
- Liver – between hepatocytes and bile ducts
Identify and describe the three different kinds of stem cells in terms of their regenerative capacity
- Unipotent – most adult stem cells, as they only produce one type of differentiated cell e.g. epithelia
- Multipotent – produce several types of differentiated cells e.g. haematopoietic stem cells
- Totipotent – can produce any type of cell and therefore any tissue of the body e.g. embryonic stem cells
Tissues of the body are divided into three groups on the basis of their proliferative activity.
What are these groups?
- Labile
- Stable
- Permanent
What are labile tissues?
Labile tissues are continuously dividing tissues which proliferate throughout life replacing cells that are destroyed
E.g. surface epithelia lining mucosa, columnar epithelia of GI tract and uterus, urothelium, cells of bone marrow and haematopoietic tissues
What are stable tissues?
Stable tissues are quiescent tissues which normally have a low level of replication can undergo rapid division in response to stimuli (induced to enter the cell cycle)
E.g. parenchymal cells of the liver, kidneys and pancreas, fibroblasts, bone osteoclasts and smooth muscle cells, vascular endothelial cells
What are permanent tissues?
Permanent tissues are non-dividing tissues which contain cells that have left the cell cycle and can’t undergo mitotic division in postnatal life
E.g. neurones, skeletal and cardiac muscle cells
Explain the role of stem cells in the three different groups of cells based on their proliferative activity
- Labile tissues contain cells that are short-lived and are continually being replaced by cells derived from stem cells
- In stable tissues the mature cells as well as stem cells are involved in proliferation in response to stimuli
- Permanent tissues contain terminally differentiated cells which cannot replicate
In what circumstances can regeneration occur?
- If the damage occurs in a labile/stable tissue
- If the tissue damage is not extensive (intact connective tissue scaffold)
What is fibrous repair?
- Fibrous repair is healing with formation of fibrous connective tissue (scar)
- Specialised tissue is lost and healing by secondary intention occurs
When does fibrous repair occur?
- If there is significant tissue loss
- If permanent or complex tissue is injured
- If there is ongoing chronic inflammation
How can we determine whether fibrous tissue or regeneration will occur?
In 6 steps, explain how a scar forms
⇒ Seconds - minutes: haemostasis
⇒ Minutes - hours: acute inflammation
⇒ 1 - 2 days: chronic inflammation
⇒ 3 days: granulation tissue forms
⇒ 7 - 10 days: early scar
⇒ Weeks - 2 years: scar maturation
Granulation tissue has a granular appearance and texture.
What does it consist of?
- Developing capillaries
- Fibroblasts and myofibroblasts
- Chronic inflammatory cells
What does granulation tissue do?
- Fills the gap
- Capillaries supply oxygen, nutrients and cells
- Contracts and closes the hole
Describe the six steps involved in fibrous repair