The Cardiac Cycle

OPTION H: Further human physiology

The Cardiac CycleThe cardiac cycleRepeating 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:

Atrial systole:

http://img2.tfd.com/mk/C/X2604-C-74A.pngVentricular systole:

http://img2.tfd.com/mk/C/X2604-C-74A.pngDiastole:

http://img2.tfd.com/mk/C/X2604-C-74A.png

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_COMPANION_(OXFORD)/original/Page-343.html(Pearson pg 620)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_COMPANION_(OXFORD)/original/Page-343.htmlThe 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_COMPANION_(OXFORD)/original/Page-343.htmlAfter 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_COMPANION_(OXFORD)/original/Page-343.htmlArtherosclerosis and heart attacks.-Coronary heart disease (CHD) refers to damage to the heart as a consequence of reduced blood supply.

http://2.bp.blogspot.com/_4smz8ewivFs/TElpOu-gEwI/AAAAAAAAAq4/Am8Hqj4qZZs/s1600/hearth+coroner+diseases.jpegAtherosclerosis 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:ANd9GcTeBYa6nJyQiMc6acnSgqJw9twYVQLY1w__4Y09cswGlhgh5DgyThe 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.

http://www.texasheartinstitute.org/HIC/Topics/Cond/CoronaryArteryDisease.cfmSymptoms of coronary thrombosis include:Pain in the chest area, often radiating out towards the left arm.Constricting sensation in or around the throat.Breathing difficultiesSevere dizziness, sometimes fainting.

http://us.123rf.com/400wm/400/400/kmiragaya/kmiragaya1201/kmiragaya120100076/11874750-grunge-image-of-a-man-having-a-chest-pain-or-heart-attack.jpgRisk factors affecting coronary heart disease:Old age leads to less flexible blood vesselsHeredity, having parents who have experienced heart attacks indicates a genetic preconditionRace, some ethnic groups have far higher rates of CHD than othersGender, 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/heart_disease_s6_lifestyle_risk.jpgRisk factors affecting coronary heart disease:Smoking raises blood pressure because nicotine causes vasoconstrictionHigh salt diet, excessive amounts of alcohol and stress are also correlated with CHDEating too much saturated fat and cholesterol promotes plaque formation Obesity strains the heartSedentary 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

SourcesAllot, 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.

Questions:Answer exercises 12, 13, and 14 from the Pearson IB Biology HL book pg 627.