Flashcards in MoD Session 4- Healing And Repair Deck (30)
What is regeneration/resolution?
The growth of cells and tissues to replace dead/damaged tissue.
What can't damage be in order for regeneration to occur?
What are stem cells?
Cells with a prolonged proliferative activity that show asymmetric replication.
What is asymmetric replication?
Where one daughter cell remains a stem cell, whilst the other differentiates into a mature, non-dividing cell.
Where a cell can give rise to only one type of adult cell.
Where a cell can give rise to multiple types of cell.
When a cell can give rise to any type of cell.
Give an example of a unipotent cell.
Give an example of a totipotent cell.
Embryonic stem cells
What are labile tissues? Give an example.
They are continuously dividing tissues that contain short lived cells that are continuously being replaced by rapid proliferation of stem cells.
What are permanent tissues?
Give an example.
They are non-dividing tissues that contain cells that have already left the cell cycle. There may be some stem cells present, but they can't generate an effective proliferative response.
Neurones, cardiac myocytes
What are stable tissues?
Give an example.
They are tissues that normally have a low level of replication, but the mature and stem cells present can be induced to more rapidly proliferate, if necessary.
Osteoblasts, fibroblasts, hepatocytes.
What is fibrous repair and when does it occur? (3)
It is replacement of functional tissue with fibrous tissue because normal regeneration can't occur.
It occurs when: the collagen framework is destroyed, there is chronic inflammation, there is necrosis of parenchymal cells.
What is the five step process of fibrous repair?
1. Phagocytosis-of necrotic debris
2. Angiogenesis-formation of small capillaries due to endothelial cell proliferation
3. Granulation tissue formation- fibro and myofibroblasts synthesis collagen
4. Fibrous scar formation- granulation tissue becomes less vascular.
5. Maturation- fibrils contract
Give examples of local and systemic factors that affect healing and repair.
Local- size, location and type of wound; blood and nerve supply; infection; necrotic tissue; mechanical stress
Systemic- age; hypoxia, hypovalaemia; obesity, diabetes; genetic disorders; malnutrition; drugs; vitamin deficiencies.
How do cells communicate to produce a fibroproliferative response? (3)
What are the three forms of communication?
-autocrine- when cells respond to a signal that they have produced.
-paracrine- when adjacent cells respond to a signal produced by a cell.
-endocrine- when hormones are secreted into the blood stream.
What are growth factors? What do they do?
Polypeptides coded for by proto oncogenes that act on specific cell surface receptors.
They stimulate cell proliferation or inhibition.
What can growth factors effect besides proliferation/ inhibition of cells? (6)
What is the idea of contact inhibition?
That normal cells, when isolated from others, replicate until they have other cells touching them.
Cells adhere to each other using the adhesion molecule cadherin; and to ECM by integrin.
A loss of cell contact therefore promotes proliferation.
When does healing by primary intention occur?
When the wound is incisional, closed, sutured and not infected.
I.e clean wounds with opposed edges.
Which method of healing heals with more scarring?
Describe the 6 stages of primary intention healing.
-haemostasis- severed arteries contract and the space fills with clotted blood, so a scab forms and the wound is sealed off from the environment.
-inflammation - neutrophils appear
-cell migration- macrophages appear, activate and secrete cytokines, which attract fibroblasts and endothelial cells. Deposits of basement membrane are laid by the epithelial cells.
-regeneration- macrophages replace neutrophils and granulation tissue forms. Epithelial cells proliferate, causing the scab to come off. Collagen has been produced and angiogenesis continues.
-scarring- collagen produced by fibroblasts forms a scar.
-scar maturation- blood vessels disappear and the scar becomes white.
When does healing by secondary intention occur?
In excisional, open, unopposed wounds, with tissue loss/infection.
How is secondary intention different to primary intention healing? (3)
There is more scarring
How does cardiac tissue heal?
Limited regeneration and scar tissue follows an MI, which can compromise function.
How does liver heal?
It regenerates. If part of liver is removed, the lobes will enlarge in order to restore the liver to its original mass.
How do peripheral nerves heal?
Axons of severed nerve degenerates, but their stumps sprout and elongate. They are guided back to the tissue they innervated by Schwann cells.
Why doesn't cartilage heal well? (3)
It lacks blood, lymph and nervous supply.