9.3 – Physiology of the Heart
In order for the heart to do its job of pumping blood to the lungs and to the body, nutrients and oxygen must be supplied to the cells of the heart. The heart also needs to coordinate its contractions so that all parts are working together to pump blood effectively. To understand how all of this works together to give the heart its ability to pump blood, we will examine three interdependent aspects of heart function.
- Circulation through the heart: blood is pumped by the heart in order to provide oxygen and nutrients to every cell in the body.
- The heart as an organ (coronary blood supply): the heart is an organ, made of cells and tissues which require their own blood supply.
- The heart’s electrical conduction system: the heart is able to independently generate and transmit instructions to the myocardium, in order to make it contract and pump the blood.
1. Circulation Through the Heart: The Heart as a Pump
The heart pumps blood to two distinct but linked circulatory systems called the pulmonary and systemic circuits. The pulmonary circuit transports blood to and from the lungs, where it picks up oxygen and drops off carbon dioxide. The systemic circuit transports freshly oxygenated blood to virtually all of the tissues of the body and returns relatively deoxygenated blood and carbon dioxide to the heart to be sent back to the pulmonary circulation.
Did You Know?
- Blood that is carrying carbon dioxide and waste products from the body tissues is returned to the right atrium via the superior vena cava and the inferior vena cava.
- From the right atrium, the deoxygenated blood moves through the tricuspid valve into the right ventricle.
- The right ventricle pumps deoxygenated blood through the pulmonary valve into the pulmonary trunk, which splits into the right and left pulmonary arteries, leading toward the lungs. These arteries branch many times before reaching the pulmonary capillaries, where gas exchange occurs: carbon dioxide exits the blood and oxygen enters. The pulmonary arteries are the only arteries in the postnatal body that carry deoxygenated blood. Did you notice that they are often coloured blue on diagrams of the heart?
- Freshly oxygenated blood returns from the lungs to the left atrium via the pulmonary veins. These veins are the only postnatal veins in the body that carry highly oxygenated blood and are often coloured red on heart images.
- From the left atrium, the blood moves through the mitral valve into the left ventricle.
- The left ventricle pumps blood through the aortic valve, into the aorta, delivering blood to all parts of the body.
Concept Check 1
- On Figure 9.3 below, use your finger to trace the pathway of blood flowing through the right side of the heart, naming each each of the following structures as you encounter them: superior and inferior venae cavae, right atrium, tricuspid valve, right ventricle, pulmonary valve, right and left pulmonary arteries.
- Suggest what would happen i