Blood Flow Through the Heart

Deoxygenated blood is returned to the heart from the arms and head by a large vein called the superior vena cava. Deoxygenated blood is returned to the heart from the legs and trunk by a large vein called the inferior vena cava. The blood empties into a chamber called the right atrium. Upon contraction of the right atrium, blood flows over a valve called the tricuspid valve. This valve consists of three cusps or flaps. Attached to the inferior aspect of the tricuspid valve are fine tendon-like cords called chordae tendineae. The chordae tendineae attach to papillary muscles located in the right ventricle. The papillary muscles are made up of cardiac muscle fibers.

Upon contraction of the right ventricle, blood flows over a valve called the pulmonary semilunar valve. This valve is made up of three half-moon-shaped cusps. After passing through the pulmonary semilunar valve, the blood enters the pulmonary trunk. The pulmonary trunk divides into the right pulmonary artery and the left pulmonary artery. These two arteries take blood to the lungs to be oxygenated.

After oxygenation, the blood is returned to the heart by four veins called pulmonary veins that empty into the left atrium. Two of these veins enter each side of the left atrium. Upon contraction of the left atrium, blood flows over a valve called the mitral valve. This valve consists of two cusps or flaps. Attached to the inferior aspect of the mitral valve are chordae tendineae attached to papillary muscles.

Upon contraction of the left ventricle, blood flows over a valve called the aortic semilunar valve. This valve is made up of three half-moon-shaped cusps. After passing over the aortic semilunar valve, the blood enters the aorta. The aorta is the largest artery in the body and is responsible for blood distribution to the various body structures. The portion of the aorta just past the aortic semilunar valve is called the ascending aorta. It curves to the left forming the aortic arch. The aortic arch then descends and is called the descending aorta.

Originating from the aortic arch are three arteries. These three arteries distribute blood to the arms and the head. The one closest to the right side of the heart is called the innominate artery. The middle one is called the left common carotid artery. The one closest to the left side of the heart is called the left subclavian artery.

Connecting the aortic arch and the pulmonary trunk is a ligament called the ligamentum arteriosum. The lig-amentum arteriosum is the remains of a fetal structure called the ductus arteriosus (see chapter 29).

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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