Pathology
Wound Healing
Which of the following is an example of a permanent cell:
Answer:
Permanent tissues consist of cells that have left the cell cycle and so are incapable of division and cannot be regenerated e.g. brain cells, myocardial cells, skeletal muscle cells.Tissue Regeneration and Repair
Pathology / Wound Healing
Last Updated: 18th September 2024
Healing is the process of replacing dead and damaging tissue with healthy tissue; this may occur through regeneration or repair.
Regeneration vs Repair
Regeneration refers to total healing of a wound with restitution of the original tissues in their usual amounts, arrangements and with normal function. This can only occur if the connective tissue framework of the tissue is not disrupted and if the tissue is capable of regeneration.
Repair refers to the process where the original tissue is not totally regenerated and the defect is made good to a variable extent by scar tissue. This begins with the formation of granulation tissue which is then converted into a collagen-rich scar. Although the structural integrity is maintained, there is loss of function of the tissue that is scarred.
Types of Cells
The regenerative capacity of cells can be categorised in three main ways:
- Labile cells are constantly dividing and have a good capacity for regeneration; this allows the replacement of ageing tissue such as the surface epithelia of the skin, gastrointestinal tract and uterus; blood cells are derived from labile cells of the bone marrow.
- Stable cells are in a state of quiescence, meaning that the cells slowly replicate to maintain tissue size; such tissue may rapidly regenerate if stimulated e.g. liver, renal tubular epithelium, endocrine glands
- Permanent tissues consist of cells that have left the cell cycle and so are incapable of division and cannot be regenerated e.g. brain cells, myocardial cells, skeletal muscle cells.
The ultimate consequence of tissue injury, therefore, depends on many factors. Although labile and stable cells may be capable of division, complex tissue architecture might not be replaced.
Healing at Special Sites
Brain:
- The brain undergoes liquefactive degeneration after major injury, such as a stroke. Survivors have cystic spaces within their brains. In cases of acute damage, the initial functional loss often exceeds the loss of actual nerve tissue because of the reactive changes in the surrounding tissue. As these changes diminish, some function may be restored. No significant regeneration of neurons occurs (as these are permanent cells), but 'rewiring' of neuronal pathways is possible to a limited extent. Minor injuries related to infective organisms may heal by 'gliosis', the nervous system equivalent of scarring, by proliferation of astrocytes and the production of fibrillary glial acidic protein.
Peripheral Nerves:
- Axonal damage must be repaired by regeneration from the nerve cell body, a slow process which proceeds at about 1 mm per day. Schwann cells can regenerate myelin to form the nerves' insulation. Regeneration takes the form of sprouting of the cut ends of the axons. The results depend on the apposition of the distal remnant with the sprouting axons. The best results are seen in crush injuries where the sheaths remain in continuity. The muscle may have atrophied beyond repair by the time regeneration is complete and so must be kept stimulated. When axonal fibres are completely severed it is usually impossible for them to follow their original route back to their target muscle. Proliferation at the site of injury may cause a painful tumour-like nodule of nerve fibres and myelin - a traumatic neuroma.
Muscle:
- Smooth cells (stable cells) have the greatest capacity to regenerate of all the muscle cell types. The smooth muscle cells themselves retain the ability to divide, and can increase in number this way. As well as this, new cells can be produced by the division of cells called pericytes that lie along some small blood vessels.
- Skeletal muscle contains numerous 'satellite cells' underneath the basal lamina; these are mononucleated quiescent cells. When the muscle is damaged, these cells are stimulated to divide. After dividing, the cells fuse with existing muscle fibres, to regenerate and repair the damaged fibres. The skeletal muscle fibres themselves cannot divide. However, muscle fibres can lay down new protein and enlarge (hypertrophy).
- Cardiac muscle cells (permanent cells) cannot regenerate and scarring is normal after damage such as a myocardial infarction.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
