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About John Locke
Expertise
I will answer all biology-related questions through the undergraduate level. I will explain unclear concepts and suggest approaches to solving problems, but would prefer not to completely solve homework problems for you. If you are completely stumped on homework, tell me what you already know and I will help you as much as possible. Please do not ask me for ideas on school research projects; part of research is determining a suitable area of investigation, and that's not a task that should be completed by someone else.
Experience
I have a BS in Bioengineering with a concentration in Chemical Engineering (which included a heavy focus on biology), and have taught biology, biochemistry, and related subjects for some time now.
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BS Bioengineering, Penn State University
MCAT/DAT/OAT Instructor
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You are here: Experts > Science > Biology > Biology > Circulation
Expert: John Locke - 10/31/2009
Question
Hi, First let me say I am grateful to have found this website and appreciate your expertise and willingness to help those of us who need it! Here's my question -
If the aorta directs blood into the coronary arteries to feed the heart during systole, how does the heart get fed in diastole (how does blood get into the coronary arteries without getting pumped into the aorta)?
Thank you so much
Answer
Thanks for using AllExperts. Your question is a fundamental one about the anatomy and physiology of the heart, and it's important to understand if you're seeking to know how the heart works.
There are two coronary arteries--right and left--that branch multiple times to supply the entire musculature of the heart. Coronary arteries may be divided into epicardial vessles, which run along the surface of the myocardium; and subendocardial vessles, which enter the muscle itself. The pattern of branching moves from epicardial to subendocardial, with perfusion taking place at the level of subendocardial capillaries. These arteries represent the only blood supply to the heart, and there is very little redundancy of circulation. Blockage of these arteries therefore produces severe clinical manifestations, including death.
The coronary arteries originate from the aorta immediately superior to the aortic valve, before the aortic arch forms or any branching of the carotid vessels takes place (review the anatomy here: http://www.cvphysiology.com/Blood%20Flow/BF001.htm or http://my.clevelandclinic.org/PublishingImages/heart/aortaLG.jpg). The myocardium receives the first blood to leave the aorta as a result. During systole, blood is ejected through the aortic valve under high pressure with some of it entering the epicardial coronary vessels. These vessels remain patent all the time and are mostly unaffected by the contraction of the myocardium. However, the subendocardial vessels do compress during systole and prevent any blood from entering the muscle itself. As a result, blood that has been forced into the epicardial vessels remains there until diastole, when the myocardium relaxes and blood can drain into the low-pressure areas of the subendocardial vessels.
An interesting side note: one of the beneficial effects of aerobic exercise is to increase cardiac pumping efficiency, which usually correlates with a lower heart rate. Decreased heart rate produces a longer amount of time available for cardiac perfusion; more efficient and extensive perfusion can take place as a result. The converse of this is ventricular tachycardia, when the period for diastole becomes so short that little perfusion takes place. Ventricular tachycardia that lasts for more than a few minutes puts someone at great risk for cardiac ischemia or infarction (heart attack).
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