In this challenge, you will explore the remarkable pump that propels the blood into the vessels. There is no single better word to describe the function of the heart other than “pump,” since its contraction develops the pressure that ejects blood into the major vessels: the aorta and pulmonary trunk. From these vessels, the blood is distributed to the remainder of the body.
Although the connotation of the term “pump” suggests a mechanical device made of steel and plastic, the anatomical structure is a living, sophisticated muscle.
Although the term “heart” is an English word, cardiac (heart-related) terminology can be traced back to the Latin term, “kardia.” Cardiology is the study of the heart, and cardiologists are the physicians (medical doctors) who deal primarily with the heart.
The vital importance of the heart is obvious. If one assumes an average rate of contraction of 75 contractions per minute, a human heart would contract approximately 108,000 times in one day, more than 39 million times in one year, and nearly 3 billion times during a 75-year lifespan. Each of the major pumping chambers of the heart ejects approximately 70 mL of blood per contraction in a resting adult. This would be equal to 5.25 liters of fluid per minute and approximately 14,000 liters per day. Over one year, that would equal 10,000,000 liters or 2.6 million gallons of blood sent through roughly 60,000 miles of blood vessels. In order to understand how that happens, it is necessary to understand the anatomy and physiology of the heart.
2. Location of the Heart
The human heart is located within the thoracic cavity, the internal space formed by the sternum, ribs, and vertebrae. More specifically, the heart is found medial to the lungs, a space known as the mediastinum. Within the mediastinum, the heart is separated from the other mediastinal structures by a tough serous membrane known as the pericardium, or pericardial sac, and sits in its own space called the pericardial cavity. The posterior surface of the heart lies near the bodies of the vertebrae, and its anterior surface sits deep to the sternum and costal cartilages. The great veins and great arteries are attached to the superior surface of the heart, called the base. The base of the heart is located at the level of the third costal cartilage. The inferior tip of the heart, the apex, lies just to the left of the sternum between the junction of the fourth and fifth ribs near their articulation with the costal cartilages. The right side of the heart is deflected anteriorly, and the left side is deflected posteriorly. It is important to remember the position and orientation of the heart when placing a stethoscope on the chest of a patient and listening for heart sounds, and also when looking at images taken from a midsagittal perspective.
Position of the Heart in the Thorax - The heart is located within the thoracic cavity, medially between the lungs in the mediastinum. It is about the size of a fist, is broad at the top (called the base), and tapers toward the apex.
IN CONTEXT
Everyday Connection CPR
The position of the heart in the torso between the vertebrae and sternum allows individuals to apply an emergency technique known as cardiopulmonary resuscitation (CPR) if the heart of a patient should stop. By applying pressure with the flat portion of one hand on the sternum in the area between the line at T4 and T9 as shown below, it is possible to manually compress the blood within the heart enough to push some of the blood within it out into the attached blood vessels. This is particularly critical for the brain, as irreversible damage and death of neurons occur within minutes of loss of blood flow. Current standards call for compression of the chest at least 5 cm deep and at a rate of 100 compressions per minute, a rate equal to the beat in “Staying Alive,” recorded in 1977 by the Bee Gees. At this stage, the emphasis is on performing high-quality chest compressions, rather than providing artificial respiration. CPR is generally performed until the patient regains spontaneous contraction or is declared dead by an experienced healthcare professional.
When performing CPR, chest compressions can result in broken ribs or a broken sternum. It is also possible, if the hands are placed too low on the sternum, to manually drive the xiphoid process into the liver, a consequence that may prove fatal for the patient. Proper training is essential. This proven life-sustaining technique is so valuable that virtually all medical personnel as well as concerned members of the public should be certified and routinely recertified in its application. CPR courses are offered at a variety of locations, including colleges, hospitals, the American Red Cross, and some commercial companies. They normally include the practice of the compression technique on a mannequin. CPR Technique - If the heart should stop, CPR can maintain the flow of blood until the heart resumes beating. By applying pressure to the sternum, the blood within the heart will be squeezed out of the heart and into circulation. Proper positioning of the hands on the sternum to perform CPR would be between the lines at T4 and T9.
Term Pronunciation Table
Term
Pronunciation
Audio File
Mediastinum
me·di·a·sti·num
Pericardium
per·i·car·di·um
Pericardial
per·i·car·di·al
terms to know
Mediastinum
The region of the thoracic cavity located medial to the lungs.
Pericardium
The serous membrane that surrounds the heart.
Pericardial Cavity
The space around the heart formed by the pericardium and filled with serous fluid.
Base (of the heart)
The superior surface of the heart.
Apex (of the heart)
The inferior tip of the heart.
3. Shape and Size of the Heart
did you know
The shape of the heart is similar to a pine cone, rather broad at the base and tapering to the apex. A typical heart is approximately the size of your fist: 12 cm (5 in) in length, 8 cm (3.5 in) wide, and 6 cm (2.5 in) in thickness. Given the size difference between most members of the sexes, the weight of a female heart is approximately 250–300 grams (9 to 11 ounces), and the weight of a male heart is approximately 300–350 grams (11 to 12 ounces).
The heart of a well-trained athlete, especially one specializing in aerobic sports, can be considerably larger than this. Cardiac muscle responds to exercise in a manner similar to that of skeletal muscle. That is, exercise results in the addition of protein myofilaments that increase the size of the individual cells without increasing their numbers—a concept called hypertrophy. The hearts of athletes can pump blood more effectively at lower rates than those of non-athletes. Enlarged hearts are not always a result of exercise; they can result from pathologies, such as hypertrophic cardiomyopathy. The cause of an abnormally enlarged heart muscle is unknown, but the condition is often undiagnosed and can cause sudden death in apparently otherwise healthy young people.
Term Pronunciation Table
Term
Pronunciation
Audio File
Hypertrophic
hy·per·tro·phic
Cardiomyopathy
car·di·o·my·o·pa·thy
terms to know
Hypertrophic Cardiomyopathy
A pathological enlargement of the heart.
4. Chambers and Circulation Through the Heart
The human heart consists of four chambers: The left and right sides of the heart have one atrium and one ventricle each. The upper chambers, the right atrium (plural, atria) and the left atrium, act as receiving chambers and contract to push blood into the lower chambers, the right ventricle and the left ventricle. The ventricles serve as the primary pumping chambers of the heart, propelling blood to the lungs or to the rest of the body.
The right ventricle pumps deoxygenated blood into the pulmonary trunk, which leads toward the lungs and bifurcates into the left and right pulmonary arteries. These vessels in turn branch many times before gas exchange occurs - carbon dioxide exits the blood and oxygen enters. The pulmonary trunk arteries and their branches are the only arteries in the postnatal body that carry relatively deoxygenated blood. Highly oxygenated blood returning from the lungs through the pulmonary veins—the only postnatal veins in the body that carry highly oxygenated blood—enters the left atrium. The left atrium pumps blood into the left ventricle, which, in turn, pumps oxygenated blood into the aorta and on to the rest of the body. Eventually, these vessels will exchange nutrients and waste with the tissue fluid and cells of the body. In this case, oxygen and nutrients exit the blood to be used by the cells in their metabolic processes, and carbon dioxide and waste products will enter the blood.
The blood returning to the heart from the body is lower in oxygen concentration than when it left through the aorta. The many blood vessels from all over the body combine to form ever-larger veins, eventually flowing into the two major systemic veins, the superior vena cava and the inferior vena cava (plural, venae cavae) which return blood to the right atrium. The blood in the superior and inferior venae cavae flows into the right atrium, which pumps blood into the right ventricle. This process of blood circulation continues as long as the individual remains alive.
Dual System of the Human Blood Circulation - Blood flows from the right atrium to the right ventricle, where it is pumped to the lungs. The blood from the right ventricle is low in oxygen but relatively high in carbon dioxide. Gas exchange occurs in the lungs (oxygen into the blood, carbon dioxide out), and blood high in oxygen and low in carbon dioxide is returned to the left atrium. From here, blood enters the left ventricle, which pumps it to the rest of the body. Following exchange throughout the body (oxygen and nutrients out of the blood and carbon dioxide and wastes in), blood returns to the right atrium and the cycle is repeated.
Term Pronunciation Table
Term
Pronunciation
Audio File
Atrium
a·tri·um
Ventricle
ven·tri·cle
Pulmonary
pul·mo·na·ry
Aorta
a·or·ta
Vena Cava
ve·na ca·va
terms to know
Atrium
An upper chamber of the heart.
Ventricle
A lower chamber of the heart.
Pulmonary Trunk
A major artery receiving blood from the right ventricle.
Pulmonary Artery
Left and right branches of the pulmonary trunk that transport blood to the left and right lungs.
Pulmonary Vein
A major vein returning blood from the lungs to the left atrium.
Aorta
Major artery receiving blood from the left ventricle.
Superior Vena Cava
Major vein returning blood from the upper body to the right atrium.
Inferior Vena Cava
Major vein returning blood from the lower body to the right atrium.
summary
In this lesson, you learned about the basics of the heart. First, you learned about the location of the heart in the chest and its relevance to CPR. Then, you learned the approximate shape and size of the heart. Lastly, you learned about the chambers and great vessels of the heart and how they serve in blood circulation through the heart.
