In medicine, ischemia (Greek ισχαιμία, isch- is restriction, hema or haema is blood) is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia. Medicine is the branch of health science and the sector of public life concerned with maintaining human health or restoring it through the treatment of disease and injury. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... The arterial system The blood vessels are part of the circulatory system and function to transport blood throughout the body. ...

Mechanism

Rather than in hypoxia, a more general term denoting a shortage of oxygen, ischemia is an absolute or relative shortage of the blood supply to an organ. Relative shortage means the mismatch of blood supply (oxygen delivery) and blood request for adequate oxygenation of tissue. Hypoxia is a pathological condition in which the body as a whole (generalized hypoxia) or region of the body (tissue hypoxia) is deprived of adequate oxygen supply. ...

Ischemia can also be described as an inadequate flow of blood to a part of the body, caused by constriction or blockage of the blood vessels supplying it. Ischemia of heart muscle produces angina pectoris.

This can be due to:

• Tachycardia (abnormally rapid beating of the heart)
• Atherosclerosis (lipid-laden placques obstructing the lumen of arteries)
• Hypotension (low blood pressure, e.g. in septic shock, heart failure)
• Thromboembolism (blood clots)
• Outside compression of a blood vessel, e.g. by a tumor
• Foreign bodies in the circulation (e.g. amniotic fluid in amniotic fluid embolism)
• Sickle cell disease (abnormally shaped hemoglobin)

Tachycardia is an abnormally rapid beating of the heart, defined as a resting heart rate of over 100 beats per minute. ... The heart and lungs (from an older edition of Grays Anatomy) The heart (Latin cor) is a hollow, muscular organ in vertebrates that pumps blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in annelids, mollusks, and arthropods. ... Section of an artery An arterial road is a class of highway. ... In physiology and medicine, hypotension refers to an abnormally low blood pressure. ... Septic shock is a serious medical condition causing such effects as multiple organ failure and death in response to infection and sepsis. ... Thrombosis is the formation of a clot or thrombus inside a blood vessel, obstructing the flow of blood through the circulatory system. ... Tumor (American English) or tumour (British English) originally means swelling, and is sometimes still used with that meaning. ... The amniotic sac is a tough but thin transparent pair of membranes which holds a developing embryo (and later fetus) until shortly before birth. ... In medicine, an embolism occurs when an object (the embolus, plural emboli) migrates from one part of the body (through the circulation) and cause(s) a blockage (occlusion) of a blood vessel in another part of the body. ... ...

Consequences

Since oxygen is mainly bound to hemoglobin in red blood cells, insufficient blood supply causes tissue to become hypoxic, or, if no oxygen is supplied at all, anoxic. This can cause necrosis and cell death. 3-dimensional structure of hemoglobin. ... Human red blood cells Red blood cells are the most common type of blood cell and are the vertebrate bodys principal means of delivering oxygen from the lungs or gills to body tissues via the blood. ... Necrosis (in Greek Νεκρός = Dead) is the name given to unprogrammed death of cells/living tissue (compare with apoptosis - programmed cell death). ...

Ischemia is a feature of heart diseases, transient ischemic attacks, cerebrovascular accidents, ruptured arteriovenous malformations, and peripheral artery occlusive disease. There are different forms of heart disease: Coronary heart disease Ischaemic heart disease Cardiovascular disease Pulmonary heart disease The study of the heart (and diseases of the heart) is Cardiology. ... Transient ischemic attacks (TIA) are caused by temporary disturbance of blood supply to a restricted area of brain and cause recurrent and brief (less than 24 hours) neurologic dysfunctions. ... A stroke or cerebrovascular accident (CVA) occurs when the blood supply to a part of the brain is suddenly interrupted by occlusion (an ischemic stroke- approximately 90% of strokes), by hemorrhage (a hemorrhagic stroke - less than 10% of strokes) or other causes. ... Arteriovenous malformation or AVM is a congenital disorder of the veins and arteries that make up the vascular system . ... In medicine (vascular surgery), Peripheral artery occlusive disease (PAOD) (also known as Peripheral vascular disease or PVD) is a collator for all disease caused by the obstruction of large peripheral arteries, which can result from atherosclerosis, inflammatory processes leading to stenosis, an embolism or thrombus formation. ...

Tissues especially sensitive to inadequate blood supply are the heart, the kidneys, and the brain. Ischemia in brain tissue, for example due to stroke or head injury, causes a process called the ischemic cascade to be unleashed, in which proteolytic enzymes, reactive oxygen species, and other harmful chemicals damage and may ultimately kill brain tissue. The heart and lungs (from an older edition of Grays Anatomy) The heart (Latin cor) is a hollow, muscular organ in vertebrates that pumps blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in annelids, mollusks, and arthropods. ... Human kidneys viewed from behind with spine removed The kidneys are bean-shaped excretory organs in vertebrates. ... Comparative brain sizes In animals, the brain, or encephalon (Greek for in the head), is the control center of the central nervous system. ... A stroke or cerebrovascular accident (CVA) occurs when the blood supply to a part of the brain is suddenly interrupted by occlusion (an ischemic stroke- approximately 90% of strokes), by hemorrhage (a hemorrhagic stroke - less than 10% of strokes) or other causes. ... Traumatic brain injury (TBI), traumatic injuries to the brain, also called acquired brain injury, intracranial injury, or simply head injury, occurs when a sudden trauma causes damage to the brain. ... The ischemic cascade is a series of biochemical reactions that take place in the brain after seconds to minutes of ischemia (inadequate blood supply) (Arnold, 2003). ... Proteolysis is the directed degradation (digestion) of proteins by cellular enzymes called proteases or by intramolecular digestion. ... Neuraminidase ribbon diagram An enzyme (in Greek en = in and zyme = blend) is a protein, or protein complex, that catalyzes a chemical reaction and also controls the 3D orientation of the catalyzed substrates. ... Reactive oxygen species (ROS) include oxygen ions, free radicals and peroxides both inorganic and organic. ...

References

1. Oxford Reference: Concise Medical Dictionary (1990, 3rd ed.). Oxford University Press: Market House Books.

See also

• Cerebral ischemia
• Infarction
• Ischemic cascade