Blocks blood

AFB Acid-fast bacillus aortofemoral bypass aspirated BBB Bundle-branch block, blood-brain barrier... 

In situations where inappropriate clot formation results in the blockage of a blood vessel, the tissue damage that ensues depends, to a point, upon how long the clot blocks blood flow. Rapid removal of the clot can often minimize the severity of tissue damage. Thus, several thrombolytic (clot-degrading) agents have found medical application (Table 12.5). The market for an effective thrombolytic agent is substantial. In the USA alone, it is estimated that 1.5 million people suffer acute myocardial infarction each year, and there are another 0.5 million suffer strokes. 

Materials for blocking blood flow temporarily to restrict chemotherapy drug to the intended site of action. 

The number of active LDL receptors is also affected by a condition called familial hypercholesterolemia, in which there is a defective gene coding for the receptor. In either case, the reduction of active receptors means that the LDL carrying cholesterol is unable to enter the cell interior instead, it is deposited in the arteries leading to the heart or brain. These deposits build up over time and may block blood supply to the heart muscle or brain, resulting in a heart attack or stroke. In contrast, HDL transports cholesterol from other parts of the body to the liver, where it is degraded to bile acids. 

The treatments nsed to improve the brain s oxygen supply include vasodilators, anticoagulants, and raising the oxygen content of the blood. Vasodilators work by dilating arteries. When the arteries supplying the brain are opened wide, the plaques of atherosclerosis are less likely to block blood flow. Vasodilators including papaverine, cyclandelate, isoxsuprine, vincamine, and cinnarizine have all been tried. 

Anticoagnlants, medications that block the formation of clots, have also been used. These work by preventing clots from forming around the atherosclerotic plaques that would further block blood flow. A variety of anticoagulants including warfarin (Coumadin), pentoxifylline (Trental), and aspirin have been used. 

Cyanide chloride Blocks blood s oxygen intake. 

Health consequences of chronic heroin abuse include scarred and collapsed veins, bacterial infections of the blood vessels and heart valves, boils, a variety of soft-tissue infections, kidney problems, and liver disease. Pneumonia, tuberculosis, and other lung diseases are also common among long-term users, which can be attributed to either poor nutrition and depressed respiratory function or both. Many of the additives heroin is cut with do not dissolve in the body and can block blood vessels, translating into higher risk of sudden death from stroke or heart attack. 

Trans fats come from hydrogenated oils like Crisco. Researchers have linked trans fats to heart disease, blocked blood vessels, higher levels of "bad" cholesterol, and lower levels of "good" cholesterol in the body. Trans fats seem to be so unhealthy that the Food and Drug Administration decided in 2003 that all food labels should show the amount of trans fats so that people could make better decisions about eating them. 

Ischemia The condition where there is reduced or blocked blood flow to a tissue, which will lead to ischemic tissue damage. 

Although most applications try to avoid agglomeration, the intentional formation of a blockage of magnetic nanoparticles to block blood supply to a tumor has been investigated [67, 70, 137]. Aggregation and selective uptake has been used to destroy cells via the application of pulsed magnetic fields and subsequent rupture of cells [205]. 

Citric acid is used in soft drinks, candies, wines, desserts, jellies, jams, as an antioxidant in frozen fruits and vegetables, and as an emulsifier in cheese. As the most versatile food acidulant, citric acid accounts for about 70 percent of the total food acidulant market. It provides effervescence by combining the citric acid with a biocarbonate/carbonate source to form carbon dioxide. Citric acid and its salts are also used in blood anticoagulants to chelate calcium, block blood clotting, and buffer the blood. Citric acid is contained in various cosmetic products such as hair shampoos, rinses, lotions, creams, and toothpastes. More recently, citric acid has been used for metal cleaning, substituted for phosphate in detergents, for secondary oil recovery, and as a buffer/absorber in stack gas desulfurization. The use of sodium citrate in heavy-duty liquid laundry detergent formulations has resulted in a rapid increase in the use of citric acid. 

Q1 A stroke involves significant reduction in blood flow to a part of the brain. It can be caused either (i) by an embolus or by intravascular clotting, which blocks blood flow to an area (approximately 85% of strokes), or (ii) by haemorrhage from a ruptured blood vessel, which compresses the brain tissue (approximately 15% of strokes). Patients with extensive atherosclerosis are at risk of intravascular coagulation and blockage of cerebral blood flow, but a vessel can be blocked by a thrombus originating in another part of the circulation. This cause of stroke is common in elderly patients >60 years of age. Aneurysms which rupture suddenly are a more common cause of stroke in younger patients. 

Q13 Arterial emboli, which can block blood vessels and cause ischaemia or infarction in the tissues they affect, tend to originate in the left heart and are associated with valvular disease and dysrhythmias. Mitral stenosis is associated with abnormal atrial rhythm, particularly atrial fibrillation. Fibrillation and other rhythm abnormalities in the atria favour blood coagulation, resulting in production of thromboemboli which can move to distant parts of the circulation, such as the cerebral circulation. Thrombi could also form on surfaces of valves distorted by calcification and other abnormalities. In view of the risks of thromboembolism, it is usual to provide anticoagulant therapy to patients with mitral valve problems and atrial fibrillation. 

Q6 A thrombus is a blood clot which is fixed to the blood vessel wall. When it detaches and is carried in the blood, it is known as an embolus. Both thrombi and emboli can block blood vessels and deprive tissues of oxygen. In arteries blood clots usually form because the inner surface has been altered by deposition of atheroma. In contrast venous thrombosis results from slow or stagnant blood flow in veins, or defects in mechanisms which normally oppose inappropriate coagulation. Three major risk factors for pulmonary embolism are (i) venous stasis, (ii) hypercoagulability ofblood and (iii) injury to vascular endothelium following trauma or plaque rupture. 

Figure Ic. With catheter in place balloon is inflated to block blood flow and catheter tip freezes damaged tissue.

A EXPERIMENTAL FIGURE 18-21 Atherosclerosis narrows and blocks blood flow through coronary arteries. X-ray multislice computed tomographic image of a human heart reveals a major occlusion (black arrow) of the left anterior descending artery (LAD, arrow) and a narrowing of a nearby vessel (white arrow) as a block in the stream of blood (seen in the arteries as a white tube). [From K. Nieman et al., 2001, Lancet 357 599.]... 

Sickle cell disease is caused by a gene that codes for an abnormal kind of haemoglobin. In low oxygen tension, this type of haemoglobin crystallizes and becomes rigid. As a result, the erythrocytes become distorted and easily ruptured. Sickle cells block blood vessels, cause pain and impair circulation. In young children, this produces hand-foot syndrome, in which there is swelling and pain in wrists and feet. 

Pruritus vomiting headache confusion depigmentation of hair skin eruptions corneal opacity weight loss partial alopecia extraocular muscle palsies exacerbation of psoriasis, eczema, and other exfoliative dermatoses myalgias photophobia irreversible retinal injury (especially when total dosage exceeds 100 grams) discoloration of nails and mucus membranes nerve-type deafness peripheral neuropathy and myopathy heart block blood dyscrasias hematemesis Crotamiton... 

As infusion of TPA lysed the clot blocking blood flow to Cora Nari s heart, oxygenated blood was reintroduced into the ischemic heart. Although oxygen may rapidly restore the capacity to generate ATP, it often increases cell death, a phenomenon called ischemia-reperfusion injury. 

Sickle cell anemia is a genetic disease that most often strikes people of West African descent. It causes the red blood cells to be misshapen ("sickleshaped"), which in turn causes them to stick together and block blood flow. NO is thought to bind to a special site on the hemoglobin molecule (the molecule that carries O2 from the lungs to the tissues). It is released when blood flow is impaired, causing dilation (expansion) of the blood vessels, thus helping to improve blood flow. 

Many animal cells take up cholesterol through receptor-mediated endocytosis and In this way acquire most of the cholesterol they require to make new membrane. If the uptake Is blocked, cholesterol accumulates In the blood and can contribute to the formation In blood vessel walls of atherosclerotic plaques - the deposits of lipid and fibrous tissue that cause strokes and heart attacks by blocking blood flow. In fact, It was through a study of humans with a strong genetic predisposition for atherosclerosis that the mechanism of receptor-mediated endocytosis was first clearly revealed. 

Poised Between Bleeding and Blocking Blood Flow... 

Formation of a blood clot involves a complex cascade of enzymatically controlled reactions the penultimate step of which is the formation of thrombin. Thrombin then cleaves peptides from fibrinogen to form fibrin monomers that associate to form the fibrin clot. Fibrin clot formation is a carefully poised process whereby a relatively minor injury will not allow excessive bleeding and result in death and whereby excessive clot formation will not block blood flow and result in death. As will be seen by examination of the relevant molecular structures, regardless of the balance struck, the key process of clot formation is the hydrophobic association of fibrin monomers. In demonstrating this perspective, the same T,-based mean residue hydrophobicity plot will be used as was used above in Figure 7.9 for understanding the hydrophobic association of hemoglobin subunits. 

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