32. Ishemia

Ishemia is organ or tissue locus blood filling decreasing as a result of arterial blood inflow limiting or complete stoppage. Ishemia is also called as local anaemia.

Features:

1. organ part pale colour;

2. local hypothermia;

3. sensitivity disorders (dumning, paresthesias et al.);

4. pain syndrome;

5. blood stream velocity decreasing in organ;

6. organ volume reducing;

7. blood pressure decreasing in locus located below to obstacle;

8. oxygen tension decreasing in ishemia locus;

9. tissular liquid hypoproduction and tissular turgor decreasing;

10. organ or tissue dysfunction.

Compressive ishemia occurs as a result of arteria pressure outside with ligature, scar, tumor, side body.

Obturational – is a result of arteries particular constriction or complete occlusion with atherosclerotic plaque, thrombus or embolus.

Angiospastic – appears due to arterial spasm caused by emotional influencing (fear, worrying, anger), physical stimuli (coldness, trauma, mechanical irritation), chemical stimuli, biological factors (bacterial toxins) and others. Nervous reflectory mechanisms or stimuli direct action to vessels smooth muscles (vasopressine, angiotensine II, endotheline).

Factors influencing on metabolic, functional and structural disorders at ishemia:

1. hypoxy degree which, in turn, depends on developmental speed and ishemia type, its duration, location, collateral circulation character as well as organ or tissue functional state;

2. ishemia at complete vessel obturation (occlusion) causes harder changings than at angiospasm;

3. rapid ishemia and prolonged one has harder course comparatively to slow and short-termed one;

4. vital organs (brain, heart) ishemia has harder results than the one of kidney, lungs, spleen and the ishemia of the latest ones – harder comparatively to ishemia of skeletal muscular, osseal or cartillageous tissue;

5. brain and heart are characterized by energy metabolism high level but at the same time their collateral vessels can’t compensate functionally circulation disorders; on the contrary, skeletal muscles and connective tissue especially are more resilient under ishemic conditions due to energy metabolism lower level;

6. arterial blood inflow retardation at organ hyperactivity (overloading) is more dangerous than under rest conditions.

Pathogenesis consequent stages:

1. energy metabolism disorders –are expressed in Krebs’ cycle and tissular respiration activity reducing and as final result – creatinephosphate and ATP level decreasing in cells; energy formation disorder in ishemia locus is delt with oxygen and substrates (necessary for oxidation) insufficient consumption, enzymes activity and synthesis dcreasing, enzymes exit from injured cells as well as oxidation and phosphorylation dissociation;

2. energy-dependent processes disturbances in cells caused by energy production decreasing; such cells specific functions as contractive, secretory one as well as substances active transport mechanisms (particularly ionic pumps activity) are disturbed; non-collagenic proteins biosynthesis is decreased; final result – cell injury and necrobiotic changings which can be ended in infarction (in the most difficult cases);

3. connective tissue components biosynthesis enforcement such as collagen, glycosamines, glyoproteins – they are basement for ishemized locus sclerosis.