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Biology 12
10.8 Circulatory System Disorders
Circulatory system disorders are also known as cardiovascular disease (CVD). CVD is the leading
cause of death in most Western countries
Examples of CVD include:
• Atherosclerosis
• Hypertension
• Heart Valve Disease
• Stroke, Heart Attack, and Aneurysm
Atherosclerosis
Atherosclerosis is the accumulation of soft masses of fatty materials (e.g., cholesterol) beneath
the inner linings of arteries.
• Deposits of these materials are called plaque
• Plaque narrows arteries by protruding into the blood vessel; this results in restricted
blood flow
• Plaque can also cause platelets to adhere to the arterial wall, forming a clot
o If the clot remains stationary, it is called a thrombus
o If the clot dislodges, it is called an embolus
o Thromboembolism is a clot that has been carried in the blood and has become
lodged in a blood vessel
Hypertension
Hypertension is high blood pressure.
• Under the age of 45 years, blood pressure above 130/90 mm Hg is considered
abnormally high
• Called “the silent killer” because it may not be detected until a stroke or heart attack
occurs
• Occurs secondary to a narrowing of arteries due to atherosclerosis
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o Narrowed arteries cause an increase in blood pressure, since more force is
needed to move blood through the blood vessels
Treatment involves vasodilators (which dilate blood vessels) and diuretics (which
decrease blood volume by increasing urine)
Heart Valve Disease
Heart valve disorders result in the backflow of blood, and range from mild to severe.
• Heart valves can be malformed at birth, or they can degenerate due to age or infections
• Result from narrowing (stenosis) of the aortic valve opening, or from mitral valve
prolapse (abnormally thickened leaflets of the mitral valve protrude into the left
ventricle)
• Treatment involves repair of faulty valves in open-heart surgery or replacement with
artificial valves or valves from an animal or deceased human
Stroke, Heart Attack, Aneurysm
Stroke
• Occurs when an arteriole in the brain bursts or is blocked by an embolus (a clot that has
been dislodged)
• Results in lack of oxygen (due to impaired blood flow) to the brain, causing a portion of
the brain to die
• Paralysis or death can result
• Symptoms of stroke include numbness in the hands or face, difficulty speaking, or
temporary blindness
Heart Attack
• When a coronary artery becomes partially blocked, angina pectoris occurs, resulting in a
squeezing or burning sensation in the chest
• When a coronary artery is completely blocked, a portion of the heart muscle dies due to
lack of oxygen, and a heart attack (myocardial infarction) occurs
• Treatment includes vasodilators (nitroglycerin) to dilate blood vessels
Aneurysm
• Occurs when there is a ballooning of a blood vessel, most often the abdominal aorta or
the arteries leading to the brain
• Atherosclerosis and hypertension can weaken the wall of the artery to the point that an
aneurysm develops
• If the aorta bursts, about 50% of victims die before reaching the hospital
• Treatment involves replacing the damaged or diseased portion of the vessel with
a synthetic graft
Biology 12
Treatment for Cardiovascular Disorders
Coronary Bypass Operations
• Involves grafting arteries to bypass an obstructed coronary artery
• A segment from another blood vessel in the body is stitched to one end of the aorta; the
other end is stitched to a coronary artery past the point of obstruction
Stem Cells
• Stem cells may be used to regenerate heart muscle that has been damaged by a heart
attack
• Stem cells injected directly into the damaged heart muscle of mice and rats
differentiated into new heart muscle cells and new blood vessels
• A “bioartificial” human heart has been grown by a research group by using cardiac
muscle cells from a cadaver as a “scaffold” for human stem cells
Clearing Clogged Arteries
• Angioplasty involves inserting a catheter into a
clogged artery.
o When the catheter reaches the site of the
clogged artery, a balloon is inflated to force
the vessel open
• A stent is a metal mesh tube that inflates, expands,
and locks the balloon into place.
o Some stents are coated with medications
that inhibit inflammation and scar formation
Dissolving Blood Clots
• Thromboembolisms can be treated with tissue plasminogen activator (tPA)
o Converts plasminogen to plasmin, an enzyme that dissolves blood clots
• Aspirin can be prescribed for individuals with symptoms of angina or stroke
o Reduces stickiness of platelets and lowers the probability of clot formation
Heart Transplants and Artificial Hearts
Heart transplants
• The need for hearts to transplant is greater than the supply
• A left ventricular assist device (LVAD) can be implanted in the
abdomen of patients waiting for an implant
o A tube passes blood from the left ventricle to the
LVAD, which pumps it into the aorta
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Artificial hearts
• A total artificial heart (e.g., AbioCor) contains:
o An internal battery
o A controller (regulates pumping speed)
o An external battery (powers the device by passing
electricity through the skin)
• A pump moves silicon hydraulic fluid between the left and
right sacs to force blood out of the heart and into the
pulmonary trunk and aorta