Physiology of the Heart

Functional Heart Anatomy: How does the heart work in general? The heart lies in the center of the thoracic cavity , also called the mediastinum. It has four chambers , two atria (singular: atrium ) and two ventricles . Blood flows through the heart. Humans possess a venous circulation and an arterial circulation. This ensures that oxygenated blood coming from the lungs and deoxygenated blood from the body pass through the heart without mixing. However, which one runs through which side?

Via the venous circulation (veins are blood vessels transporting blood to the heart), the deoxygenated blood (venous blood) flows back from the body organs and muscles into the right atrium via the superior and inferior venae cavae. Passing the tricuspid valve, it runs into the right ventricle, and from there it is pumped through the pulmonary valve into the pulmonary artery and into the lungs. Here, the carbon dioxide is released from and the oxygen is absorbed by the hemoglobin.

The oxygenated pulmonary venous blood returns to the left atrium through the pulmonary veins via the mitral valve into the left ventricle.

Via the arterial circulation (arteries are blood vessels taking blood from the heart) the body and the muscles are provided with oxygenated blood. From the heart, arterial blood is pumped through the aortic valve into the aorta.

Blood flows only over the lungs from the right side of the heart to the left side. The atrio-ventricular septum separates the two sides of the heart. However, the chambers themselves work together. The two atria contract simultaneously and the two ventricles contract simultaneously (see below).

What do we mean with systolic and diastolic pressure ? The systolic blood pressure is created in the arteries by the contraction of the left ventricle. After full-contraction, the left ventricle begins to relax and refills with blood from the left atria. The pressure in the arteries decreases while the ventricle refills. This is called diastolic blood pressure.

What is called a cardiac cycle? A sequence of events during one heartbeat is called a cardiac cycle. We have a simultaneous contraction of the two atria and followed – a second later – by the simultaneous contraction of the two ventricles.

An other term for contraction is systole and for relaxation is systole and diastole, respectively. The atrial systole is followed by the ventricular systole. Blood flows constantly from the veins into both atria.

What happens during one heartbeat? There is a constant blood flow from the veins into both atria. Then, blood accumulates and through this increased pressure the right and left atrioventricular (AV) valves opens. Two thirds of the atrial blood flow passively into the ventricles, the rest will be pumped into the ventricles by contraction of the atria. The atria then relaxe and the ventricles begin to contract. The increased blood pressure within the ventricles leads to closure of the AV valves and opening of both the aortic and the pulmonary semilunar valves. As a result of ventricle contraction and valve activity the heart pumps blood into the arteries. Consecutively the ventricles relax again and allow venous blood to flow into the atria and the cycle will begin again.

. . . and the heart sounds? Every heartbeat produces two sounds. The first one (the loudest and longest) is formed by closing the AV valves, caused by the ventricular systole.

The second sound is formed by closing the aortic and pulmonary semilunar valves.

What causes the chambers to contract? The electrical activity of the myocardium regulates the cardiac cycle. Cardiac muscle cells require no nerve impulses for contraction, they contract spontaneously (myogenic contraction).

The sinoatrial (SA) nodes comprise specialized cardiac muscle cells and also serve as the pacemaker of the heart. They are located in the wall of the right atrium. The SA nodes show the most rapid rate of contraction within the myocardium.

The impulses propagate from the SA node to the atrioventricular node. The AV node is located in the lower interatrial septum. This transmission (SA node – AV node) brings about the atrial systole. The ventricular systole is generated through the bundle of His (AV bundle) because it receives impulses from the AV node and transmits them on to the bundle branches . These impulses then go along to the Purkinje fibers within the ventricular systole.

One word on a normal human heart rate A healthy adult has a pulse of 60 to 80 bpm (beats per minute), a child’s normal heart rate is about 100 bpm, an infant’s normal heart rate is about 120 bpm and a near-term fetus has about 140 bpm.

BIBLIOGRAPHY 1. http://dict.leo.org. 2. Katz AM: Physiology of the Heart, 5th Edition, Wolters Kluwer, Lippincott Williams & Wilkins 2011. 3. www.dict.cc. 4. www.webster-dictionary.org.

EXERCISE: 1. Blood from the right ventricle is on its way to the _______________. Remember: The right ventricle pumps blood for the pulmonary circulation. a. Liver b. Lungs c. Windpipe

2. Which chamber receives the deoxygenated blood from the systemic system first? a. Right atrium b. Right Ventricle c. Left Atrium d. Left Ventricle

3. When the heart contracts for the heartbeat, one contraction is the atrial contraction while the other is the ventricular contraction. During ventricular contraction, which two valves of the heart open? a. Aortic and tricuspid valves b. Pulmonary and aortic valves c. Pulmonary and tricuspid valves d. Pulmonary and mitral valves

You’ll find the answer on: http://tinyurl.com/weiterbildung-englisch

CARMEN LOBITZ Carmen Lobitz ist freie Trainerin, Lehrerin und MTA. Sie gründete 1998 in Berlin lobitz seminare, die unter anderem Englischseminare für Health Professionals anbieten. Kontakt: mail@lobitz-seminare.de www.lobitz-seminare.de

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Lösung für Exercise: Answer: 1. b Answer: 2. a Answer: 3. b

Physiology of the Heart

Functional Heart Anatomy: How does the heart work in general?

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Physiology of the Heart

Functional Heart Anatomy: How does the heart work in general?

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