Cell death is called necrosis. Special cells called Dendritic, that sense when cells are injured and dying initiate repair. Dead cells are fragmented, digested by other cells, and their remains removed. We may distinguish between reversible and irreversible damage.
Tissue restoration following reversible damage is complete. When transitional cells are hit, they are soon replenished with new cells generated by remaining stem cell (DS), and repair is perfect. Also when a small number of tissue units, with their stem cells are destroyed, complete repair is possible. Neighboring stem cells divide symmetrically, creating buds that replace the damaged units.. In contrast to the growing child, stem cell budding in the adult is sluggish, and if stem cell (or proliferon) damage is extensive, an inflammation ensues.
Inflammation is a process that is triggered by necrosis, whose purpose is to clear dead cell remnants, and repair the damage. Damage is generally irreversible, tissue units cannot be restored, and are replaced with a scar. The evolution of inflammation depends on the extent of necrosis.
Acute inflammation - White
cells, e.g., granulocytes and lymphocytes that circulate in the blood
enter the damaged site. Granulocytes digest cell remnants. If necrosis
is cleared, inflammation subsides. If not, it evolves further and becomes
Chronic inflammation - Occasionally bacteria invade the damaged area and increase the amount of necrosis. Now , larger white cells, called monocytes, enter. They are accompanied by in-growing blood vessels and connective tissue cells called fibroblasts, that attempt to wall off the damage with fibers that they produce. As more fibroblasts and blood vessels enter the area it thickens and is called granulation tissue. It is an ongoing attempt to wall off necrosis, and invading bacteria. If necrosis has been curbed, granulation tissue turns into a scar that replaces the damaged tissue. If these measures do not suffice, granulation tissue encloses necrosis with a wall, separating it from other tissues, and it becomes an abscess.
Myocardial infarct.- Is initiated
when a coronary artery that supplies blood to the heart muscle is obstructedd.
Oxygen supply to the muscle ceases, and heart muscle cells die. Inflammation
replaces damaged tissue with a scar.
Liver cirrhosis – Alcohol damages liver cells. As long as damage is reversible, repair is complete. With excessive alcohol intake, liver units are damaged, and replaced with a scar. As more and more liver units are replaced with scars, liver function deteriorates.
Inflammation is a life saving process.
When it fails bacteria enter the body and cause a dangerous infection, called
sepsis. Occasionally inflammation itself may be . damaging, like in
a brain abscess, that starts as an attempt to remove necrosis. When it fails,
inflammation encloses dead tissue into an abscess. As brain damage
continues, abscess grows, raising intra-cranial pressure. It has to
be drained, otherwise patient dies. We may thus distinguish between
two phases of inflammation.
Primary - which is generally life saving,
Secondary - that may cause damage.
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