Introduction
Ischemia is a loss of blood supply to tissue, causing a lack of the oxygen needed for cellular metabolism. It occurs when arterial flow is prevented by atherosclerosis, thrombi or other causes, and may be pathological or physiological. Ischemia is the most common cause of hypoxia.
Ischemia is diminished blood flow to the tissue, compromising the delivery of substrates for glycolysis. Little or no ATP is formed, so active transport by the sodium/potassium pumps fails, causing cellular swelling and eventually necrosis, along with an increase in ROS and resultant damage.
Degrees of ischemia
- Absolute ischemia: complete vessel obstruction, no blood reaches the tissue, leading to necrosis.
- Relative ischemia: chronic, usually affecting the lower limbs (e.g. femoral stenosis); an atherosclerotic plaque restricts blood flow. During exercise the tissue cannot get enough blood, which causes pain.
Types of ischemia
- Angiospastic (reflex)
- Obstructive
- Compressive
- Due to redistribution of blood
Morphological features
Primary response (acute ischemia gives oedema):
- swelling or edema with dilation of the endoplasmic reticulum;
- dissociation of polysomes into monosomes;
- swelling of mitochondria;
- increased concentration of water, sodium and chloride, and decreased potassium in the cytoplasm.
If the duration is short, structure and functions can be restored. If ischemia persists, irreversible injury occurs:
- severe vacuolization of mitochondria;
- extensive damage to cytoplasmic membranes;
- swelling of lysosomes.