OPTION H: Further human physiology The Cardiac Cycle
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The cardiac cycle Repeating sequence of actions in the heart
which result in the pumping of blood to the lungs and all other
parts of the body. Cardiologists refer to contraction of the hearts
chambers as systole and relaxation as diastole. There are three
sequences of contraction:
Ventricular systole: the ventricles contract and blood is
forced out into the arteries. The bicuspid and tricuspid
(atrioventricular) valves prevent blood from flowing back into the
atria. the atria relax and start to fill with blood again.
http://img2.tfd.com/mk/C/X2604-C-74A.png
Slide 6
Diastole: both atria and ventricles are relaxing and the heart
fills up with blood from the veins. Semilunar valves are closed and
prevent blood from passing back into the ventricles from the
arteries. http://img2.tfd.com/mk/C/X2604-C-74A.png
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The cardiac cycle includes all the events from the beginning of
one heartbeat to the beginning of the next.
http://aura.edu.in/read/IB/BIOLOGY_COURSE_COMPAN
ION_(OXFORD)/original/Page-343.html (Pearson pg 620)
Slide 10
To start the cycle, the sinoatrial node fires an electrical
signal throughout the walls of the atria. This causes the atria to
undergo systole. http://aura.edu.in/read/IB/BIOLOGY_COURSE_COMPAN
ION_(OXFORD)/original/Page-343.html
Slide 11
The signal then reaches the atrioventricular node, from which
the signal spreads throughout the heart via specialized heart
muscle tissue called Purkinje fibers. This causes the ventricles to
undergo systole. http://aura.edu.in/read/IB/BIOLOGY_COURSE_COMPAN
ION_(OXFORD)/original/Page-343.html
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After the ventricles are emptied, the semilunar valves close.
The ventricles begin diastole, the atrioventricular valves open and
ventricles start filling with blood. When the atria are filled and
the ventricles are 70 per cent filled, the cycle has ended
http://aura.edu.in/read/IB/BIOLOGY_COURSE_COMPAN
ION_(OXFORD)/original/Page-343.html
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Artherosclerosis and heart attacks.- Coronary heart disease
(CHD) refers to damage to the heart as a consequence of reduced
blood supply.
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Atherosclerosis is hardening of the arteries caused by the
formation of plaques, or atheromas, on the inner lining of
arteries. Plaques are areas that are swollen and accumulate a
diversity of debris composed of lipids, cholesterol, cell debris
and calcium. http://t3.gstatic.com/images?q=tbn:ANd9GcTeBYa6nJyQ
iMc6acnSgqJw9twYVQLY1w__4Y09cswGlhgh5Dgy
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The plaques can reduce the speed at which blood moves through
vessels. This can trigger a clot, or thrombosis, which can block
the blood flow through the artery and deny the tissue access to
oxygen.
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http://www.texasheartinstitute.org/HIC/Topics/Cond/CoronaryArteryDisease.cfm
There are three major coronary arteries which supply the heart
muscle with oxygen rich blood. These arteries carry blood that has
recently been to the lungs Cardiac muscle is highly oxygen
demanding. If one off the three major coronary arteries or their
branches is blocked, some portion of the heart muscle is likely to
be deprived of its oxygen. Coronary thrombosis occurs when a
coronary artery or one of its main branches become blocked. This is
also known as a heart attack.
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Symptoms of coronary thrombosis include: Pain in the chest
area, often radiating out towards the left arm. Constricting
sensation in or around the throat. Breathing difficulties Severe
dizziness, sometimes fainting.
http://us.123rf.com/400wm/400/400/kmiragaya/kmiragaya1201/kmiragay
a120100076/11874750-grunge-image-of-a-man-having-a-chest-pain-or-heart-
attack.jpg
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Risk factors affecting coronary heart disease: Old age leads to
less flexible blood vessels Heredity, having parents who have
experienced heart attacks indicates a genetic precondition Race,
some ethnic groups have far higher rates of CHD than others Gender,
risk in females increases post- menopause correlated with a fall in
estrogen levels; males are at greater risk compared with females
correlated with lower levels of estrogen. Hypertension/high blood
pressure causes the heart to work harder.
http://images.medicinenet.com/images/SlideShow/hea
rt_disease_s6_lifestyle_risk.jpg
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Risk factors affecting coronary heart disease: Smoking raises
blood pressure because nicotine causes vasoconstriction High salt
diet, excessive amounts of alcohol and stress are also correlated
with CHD Eating too much saturated fat and cholesterol promotes
plaque formation Obesity strains the heart Sedentary lifestyle,
lack of exercise is correlated with obesity. Diabetes when it is
not well managed. http://www.surgical-blog.com/wp-
content/uploads/2011/05/post-28-risk-factors-of-heart-
disease.jpg
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Sources Allot, A., & Mindorff, D. (2010). IB Biology Course
Companion. New York: Oxford University Press. Damon, A., McGonegal,
R., Tosto, P., & Ward, W. (2007). Biology Higher Level. London:
Pearson Baccalaureate.
Slide 22
Questions: Answer exercises 12, 13, and 14 from the Pearson IB
Biology HL book pg 627.