Cellular Repair Flashcards
What are the three processes which occur during wound healing?
Haemostasis, inflammation and regeneration & repair
What is regeneration?
This is where there is growth of cells to replace structures lost during injury.
What two things are needed for regeneration?
Intact stem cells to give rise to the new cells and a connects tissue scaffold.
When is regeneration not possible?
When there has been extensive connective tissue damage, or when there are not sufficient intact stem cells.
What is the name given to the tissue type where cells proliferate throughout life to replace destroyed cells?
Labile
What is a stable tissue?
This is a tissue where there is normally a low level of cell proliferation but can respond to a stimuli to repair the tissue.
Give examples of a permanent tissues
Cardiac muscle, neurones,
What features do cells in a permanent tissue have?
They have left the cell cycle and are unable to proliferate to repair the tissue.
What can be said about most cells in the body and their ability to divide?
Most cells in the body are terminally differentiated and this means that they cannot divide.
What type of replication do stem cells display?
Asymmetrical replication in which one daughter cell is produced which remains a stem cell and the other becomes terminally differentiated.
Why in adults, are stem cells called multi potent?
They are lineage specific and so can only give rise to a small number of different cell types.
What type of cells are involved in proliferation in stable tissues?
Both mature and stem cells. In this type of tissue stem cells replicate slowly.
What is a complication which is associated with fibrous repair?
If the tissue is supposed to be able to stretch then it may rupture.
When does fibrous repair occur?
This occurs when the collagen network has been destroyed and so is replaced by fibrosis ulnar connective tissue.
What is the initial stage of fibrous repair?
Necrotic tissue debris are phagocytosed and then endothelial cells proliferate and small capillaries grow.
What cell types proliferate during fibrous repair?
Fibroblasts and myofibroblasts. These secrete granulation tissue which looses its vascularity and matures into a fibrous scar which shrinks as myofibroblast fibres contract.
What is scurvy? What is the link between this and poor healing?
This is vitamin C deficiency which means that pro collagen cannot be hydroxylated and so patients are unable to heal and bleeding occurs.
What are patients with ehlers-danlos syndrome predisposed to?
Predisposed to joint dislocation and large vessel rupture. It is a condition in which collagen lacks strength and so their healing is poor.
What is Alport syndrome?
This is a condition which affects type IV collagen and patients suffer from haematouria which lads to chronic renal failure.
How do cells communicate to produce a fibro-proliferative response?
Local mediators (growth factors), hormones and direct contact.
What is the action of growth factors on a cell?
They bind and stimulate specific transcription of genes which regulate entry into the cell cycle.
Over what distance do growth factors work?
They work over short distances locally.
What cell types does epidermal growth factor stimulate proliferation of?
Epithelial cells, hepatocytes and fibroblasts.
What is the function of vascular endothelial growth factor?
It induces vasculogenesis and angiogenesis in tumours, chronic inflammation and wound healing.
What growth factor leads to proliferation of smooth muscle cells and monocytes?
Platelet derived growth factor.
What is the function of tumour necrosis factor?
It induces fibroblast migration, proliferation and collagenase secretion.
What is a Cadherin?
This is an adhesion molecule which allows cells to adhere to one and other.
What is an integrin?
These allow cells to bind to Extracellular matrix.
What does contact inhibition mean?
This is where when a cell becomes isolated it will proliferate until it comes into contact with more cells and adheres to them.
What type of wounds heal by primary intention?
Incisional closed wounds (like from surgery). Healing occurs through all layers of skin at the same time.
What is a seroma?
This is a fluid filled pocket under the skin that forms with primary intention healing.
What happens first in primary intention healing?
Haemostasis, and contraction of the severed blood vessels.
Why does inflammation occur with sterile wounds?
Neutrophils migrate to the edges of the wounds to ward off bacteria, and this leads to automatic triggering of inflammation.
What function do macrophages have in primary intention healing?
They scavenge dead cells to phagocytose, and they secrete cytokines which leads to migration of other cells to the wound site such as fibroblasts.
What processes occur during regeneration in primary intention healing?
Angiogenesis continues. As the epithelial cells thicken the scab falls off. Fibroblasts synthesise collagen.
What is the difference between scar tissue and normal skin?
Skin appendages such as hair do not form.
What happens during scar maturation?
If the scar has few elastic fibres then there is little recoil. Capillaries disappear and so over time the scar becomes more white.
What type of wound will undergo secondary intention healing?
Wounds where the two sides are not aligned and the edges are separated.
What happens to an open wound at the beginning of healing?
It fills with granulation tissue and this grows from the wound margins. A large clot also forms.
Name two ways in which wound contraction occurs with secondary intention healing.
Myofibroblasts contract and pull the edges of the wound together and also the scab shrinks as it dries and this pulls the wound edges together also.
What systemic factors can affect wound healing?
Age, sex, ethnicity, obesity, malignancy, anaemia, hypoxia, hypovolaemia, genetic disorders, diabetes, vitamin deficiencies and malnutrition and drugs.
What local factors can affect wound healing?
Infection, mechanical stress, haematouria, blood supply, foreign bodies, necrotic tissues denervation, size and location of wound, protection (dressings) and surgical techniques
What is a keloid scar?
This is when there is over production of collagen and this leads to an enlarged scar.
What is the problem with loss of architecture in a tissue?
This leads to complex tissue relationships being disrupted.
Name some complications of fibrous repair:
Fibrous adhesion formation which compromises organ function or can block tubes. Extensive scar contraction which can also block tubes. Loss of function due to scar tissue.
Describe healing in cardiac muscle.
Cardiac muscle has a very limited regeneration ability and so scar formation occurs, this impairs the function of the heart.
What is notable about healing in the liver?
The liver has an amazing ability to regenerate and so if part is removed compensatory growth can replace it.
Can peripheral nerves regenerate?
Yes, but very slowly. Upon damage, a stump forms and the distal axon degenerates. Axons sprout and are guided by schwann cells.
Why can’t cartilage heal well?
It is avascular, does not have a nerve supply and lacks lymphatic drainage.
What happens in the CNS when there is tissue damage?
This neural tissue is permanent and so the space becomes filled with glial cells.
