anastomosis (ah-nas"to-mo'sis) Connection between two blood vessels, sometimes produced surgically. angiospasm (an'je-o-spazm") Muscular spasm in the wall of a blood vessel.
arteriography (ar"te-re-og'rah-fe) Injection of radiopaque solution into the vascular system for an X-ray examination of arteries. asystole (a-sis'to-le) Condition in which the myocardium fails to contract.
congestive heart failure (kon-jes'tiv hart fal'yer) Inability of the left ventricle to pump adequate blood to cells. cor pulmonale (kor pul-mo-na'le) Heart-lung disorder of pulmonary hypertension and hypertrophy of the right ventricle.
embolectomy (em"bo-lek'to-me) Removal of an embolus through an incision in a blood vessel. endarterectomy (en"dar-ter-ek'to-me) Removal of the inner wall of an artery to reduce an arterial occlusion. palpitation (pal"pi-ta'shun) Awareness of a heartbeat that is unusually rapid, strong, or irregular. pericardiectomy (per"i-kar"de-ek'to-me) Excision of the pericardium.
phlebitis (fle-bi'tis) Inflammation of a vein, usually in the lower limbs.
phlebotomy (fle-bot'o-me) Incision or puncture of a vein to withdraw blood. sinus rhythm (si'nus rithm) The normal cardiac rhythm regulated by the S-A node. thrombophlebitis (throm"bo-fle-bi'tis) Formation of a blood clot in a vein in response to inflammation of the venous wall.
valvotomy (val-vot'o-me) Incision of a valve. venography (ve-nog'rah-fe) Injection of radiopaque solution into the vascular system for X-ray examination of veins.
Molecular Causes of Cardiovascular Disease
A variety of inherited and environmental factors contribute to causing cardiovascular disease. Many cases are probably due to a fatty diet and sedentary lifestyle, against a backdrop of genetic predisposition. Disorders of the heart and blood vessels caused by single genes are very rare, but understanding how they arise can provide insights that are useful in developing treatments for more prevalent forms of disease. For example, widely-used cholesterol lowering drugs called statins were developed based on analyzing the molecular malfunction behind the one-in-a-million inherited condition familial hypercholesterolemia.
a connective Tissue defect
In January 1986, volleyball champion Flo Hyman left the court during a game in Japan, collapsed, and suddenly died. Her aorta had burst, and death was instant. Hyman had Marfan syndrome, an inherited condition that also caused the characteristics that led her to excel in her sport—her great height and long fingers (fig. 15J).
In Marfan syndrome, an abnormal form of a connective tissue protein called fibrillin weakens the aorta wall. After Flo Hyman died, her siblings were examined, and her brother Michael was found to have a weakened aorta. By surgically repairing his aorta and giving him drugs to control his blood pressure and heart rate, physicians enabled him to avoid the sudden death that claimed his famous sister. Testing for the causative gene can alert physicians to affected individuals before the dangerous swelling in the aorta begins.
Each year, one or two seemingly healthy young people die suddenly during a sports event, usually basketball. The culprit is often familial hyper-trophic cardiomyopathy, an inherited overgrowth of the heart muscle. The defect in this disorder is different than that behind Marfan syndrome. It is an abnormality in one of the myosin chains that comprise cardiac muscle. Again, detecting the responsible gene can alert affected individuals to their increased risk of sudden death. They can adjust the type of exercise they do to avoid stressing the cardiovascular system.
Sometimes inherited heart disease strikes very early in life. Jim D. died at four days of age, two days after suffering cardiac arrest. Two years later, his parents had another son. Like Jim, Kerry seemed normal at birth, but at thirty-six hours of age his heart rate plummeted, he had a seizure, and he stopped breathing. He was resuscitated. A blood test revealed excess long-chain fatty acids, indicating a metabolic disorder, an inability to utilize fatty acids. Lack of food triggered the symptoms because the boys could not use fatty acids for energy, as healthy people do. Kerry was able to survive for three years by following a diet low in fatty acids and eating frequently. Once he became comatose because he missed a meal. Eventually, he died of respiratory failure.
Kerry and Jim had inherited a deficiency of a mitochondrial enzyme that processes long-chain fatty acids. Because this is a primary energy source for cardiac muscle, their tiny hearts failed.
Low-density lipoprotein (LDL) receptors on liver cells admit cholesterol into the cells, keeping the lipid from building up in the bloodstream and occluding arteries. When LDL receptors bind cholesterol, they activate a negative feedback system that temporarily halts the cell's production of cholesterol. In the severe form of familial hypercholesterolemia, a person inherits two defective copies of the gene encoding the LDL receptors. Yellowish lumps of cholesterol can be seen behind the knees and elbows, and heart failure usually causes death in childhood. People who inherit one defective gene have a milder form of the illness. They tend to develop coronary artery disease in young adulthood, but can delay symptoms by following a heart-healthy diet and regularly exercising. These people have half the normal number of LDL receptors.
In Niemann-Pick type C disease, a defective protein disturbs the fate of cholesterol inside cells. Normally, the protein escorts cholesterol out of a cell's lysosomes (a type of organelle), which triggers the negative feedback mechanism that shuts off cholesterol synthesis. When the
Shier-Butler-Lewis: IV. Transport 15. Cardiovascular System © The McGraw-Hill
Human Anatomy and Companies, 2001
Physiology, Ninth Edition protein is absent or malfunctions, the cell keeps producing cholesterol and LDL receptors. Coronary artery disease develops, which is typically fatal in childhood.
Homocysteine is an amino acid that forms when a different amino acid, methionine, loses a methyl (CH3) group. Normally, enzymes tack the methyl back onto homocysteine, regenerating methionine, or metabolize homocysteine to yield yet a third type of amino acid, cysteine. If an enzyme deficiency called homocystinuria causes homocysteine to build up in the blood, changes in arterial linings develop that encourage cholesterol plaque deposition, and the risk of heart attack and stroke rises dramatically. The complex biochemical pathways that recycle homocysteine to methionine, or break it down to cys-teine, depend upon three vitamins — folic acid, B6, and B12. The details of these pathways were deciphered in the 1960s, based on study of a handful of children with the rare homo-cystinuria. Their artery linings were like those of a much older person with severe atherosclerosis.
In the 1970s, a pathologist, Kilmer McCully, hypothesized that if extremely high levels of homocysteine in the blood of these children caused their severe heart disease, then perhaps more moderately elevated levels in others are responsible for more common forms of cardiovascular disease. However, much of the work on homocysteine was ignored, because at the time, the cholesterol-heart disease link dominated both pharmaceutical research and media interest. Since then, clinical trials on more than 70,000 individuals confirm the results of many preliminary investigations that correlated elevated blood homocysteine with increased risk of cardiovascular disease. The interesting piece of information that the research and clinical communities await is to see whether lowering ho-mocysteine level leads to improved heart and blood vessel health as was shown for cholesterol. If this is the case, the treatment for homocysteine-related cardiovascular disease is straightforward—being certain to obtaining sufficient folic acid, B6, and B12. Someday soon, homocysteine testing may be as commonplace as cholesterol testing. ■
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