This thin-walled vessel drains most of the coronary veins that return systemic blood from the heart. The majority of the internal heart structures discussed in this and subsequent sections are illustrated in Figure 8. While the bulk of the internal surface of the right atrium is smooth, the depression of the fossa ovalis is medial, and the anterior surface demonstrates prominent ridges of muscle called the pectinate muscles. The right auricle also has pectinate muscles. The left atrium does not have pectinate muscles except in the auricle.
The atria receive venous blood on a nearly continuous basis, preventing venous flow from stopping while the ventricles are contracting. While most ventricular filling occurs while the atria are relaxed, they do demonstrate a contractile phase and actively pump blood into the ventricles just prior to ventricular contraction.
The opening between the atrium and ventricle is guarded by the tricuspid valve. The right ventricle receives blood from the right atrium through the tricuspid valve.
They are composed of approximately 80 percent collagenous fibers with the remainder consisting of elastic fibers and endothelium. They connect each of the flaps to a papillary muscle that extends from the inferior ventricular surface.
There are three papillary muscles in the right ventricle, called the anterior, posterior, and septal muscles, which correspond to the three sections of the valves. When the myocardium of the ventricle contracts, pressure within the ventricular chamber rises.
Blood, like any fluid, flows from higher pressure to lower pressure areas, in this case, toward the pulmonary trunk and the atrium. To prevent any potential backflow, the papillary muscles also contract, generating tension on the chordae tendineae. This prevents the flaps of the valves from being forced into the atria and regurgitation of the blood back into the atria during ventricular contraction.
The image below shows papillary muscles and chordae tendineae attached to the tricuspid valve. Figure In this frontal section, you can see papillary muscles attached to the tricuspid valve on the right as well as the mitral valve on the left via chordae tendineae.
The walls of the ventricle are lined with trabeculae carneae , ridges of cardiac muscle covered by endocardium. In addition to these muscular ridges, a band of cardiac muscle, also covered by endocardium, known as the moderator band reinforces the thin walls of the right ventricle and plays a crucial role in cardiac conduction.
It arises from the inferior portion of the interventricular septum and crosses the interior space of the right ventricle to connect with the inferior papillary muscle.
When the right ventricle contracts, it ejects blood into the pulmonary trunk, which branches into the left and right pulmonary arteries that carry it to each lung. The superior surface of the right ventricle begins to taper as it approaches the pulmonary trunk.
At the base of the pulmonary trunk is the pulmonary semilunar valve that prevents backflow from the pulmonary trunk. After exchange of gases in the pulmonary capillaries, blood returns to the left atrium high in oxygen via one of the four pulmonary veins.
While the left atrium does not contain pectinate muscles, it does have an auricle that includes these pectinate ridges. Blood flows nearly continuously from the pulmonary veins back into the atrium, which acts as the receiving chamber, and from here through an opening into the left ventricle. Most blood flows passively into the heart while both the atria and ventricles are relaxed, but toward the end of the ventricular relaxation period, the left atrium will contract, pumping blood into the ventricle.
This atrial contraction accounts for approximately 20 percent of ventricular filling. The opening between the left atrium and ventricle is guarded by the mitral valve. Recall that, although both sides of the heart will pump the same amount of blood, the muscular layer is much thicker in the left ventricle compared to the right.
Like the right ventricle, the left also has trabeculae carneae, but there is no moderator band. The mitral valve is connected to papillary muscles via chordae tendineae. There are two papillary muscles on the left—the anterior and posterior—as opposed to three on the right. The left ventricle is the major pumping chamber for the systemic circuit; it ejects blood into the aorta through the aortic semilunar valve.
With the atria and major vessels removed, all four valves are clearly visible, although it is difficult to distinguish the three separate cusps of the tricuspid valve. A transverse section through the heart slightly above the level of the atrioventricular septum reveals all four heart valves along the same plane Figure The valves ensure unidirectional blood flow through the heart.
Between the right atrium and the right ventricle is the right atrioventricular valve , or tricuspid valve. It typically consists of three flaps, or leaflets, made of endocardium reinforced with additional connective tissue. The flaps are connected by chordae tendineae to the papillary muscles, which control the opening and closing of the valves. Emerging from the right ventricle at the base of the pulmonary trunk is the pulmonary semilunar valve, or the pulmonary valve ; it is also known as the pulmonic valve or the right semilunar valve.
The pulmonary valve is comprised of three small flaps of endothelium reinforced with connective tissue. When the ventricle relaxes, the pressure differential causes blood to flow back into the ventricle from the pulmonary trunk. This flow of blood fills the pocket-like flaps of the pulmonary valve, causing the valve to close and producing an audible sound. Unlike the atrioventricular valves, there are no papillary muscles or chordae tendineae associated with the pulmonary valve.
Located at the opening between the left atrium and left ventricle is the mitral valve , also called the bicuspid valve or the left atrioventricular valve. Structurally, this valve consists of two cusps, known as the anterior medial cusp and the posterior medial cusp, compared to the three cusps of the tricuspid valve. In a clinical setting, the valve is referred to as the mitral valve, rather than the bicuspid valve.
The two cusps of the mitral valve are attached by chordae tendineae to two papillary muscles that project from the wall of the ventricle. At the base of the aorta is the aortic semilunar valve, or the aortic valve , which prevents backflow from the aorta. It normally is composed of three flaps. When the ventricle relaxes and blood attempts to flow back into the ventricle from the aorta, blood will fill the cusps of the valve, causing it to close and producing an audible sound.
In the image above, the two atrioventricular valves are open and the two semilunar valves are closed. This occurs when both atria and ventricles are relaxed and when the atria contract to pump blood into the ventricles.
The image below shows a frontal view. Although only the left side of the heart is illustrated, the process is virtually identical on the right.
The two atrioventricular valves are open; the two semilunar valves are closed. The atria and vessels have been removed. When the mitral valve is open, it allows blood to move from the left atrium to the left ventricle. The aortic semilunar valve is closed to prevent backflow of blood from the aorta to the left ventricle. Image a above shows the atrioventricular valves closed while the two semilunar valves are open.
This occurs when the ventricles contract to eject blood into the pulmonary trunk and aorta. Closure of the two atrioventricular valves prevents blood from being forced back into the atria. This stage can be seen from a frontal view in image b above. The two atrioventricular valves are closed, but the two semilunar valves are open. The aortic semilunar valve is open to allow blood to be ejected into the aorta.
When the ventricles begin to contract, pressure within the ventricles rises and blood flows toward the area of lowest pressure, which is initially in the atria. This backflow causes the cusps of the tricuspid and mitral bicuspid valves to close.
These valves are tied down to the papillary muscles by chordae tendineae. During the relaxation phase of the cardiac cycle, the papillary muscles are also relaxed and the tension on the chordae tendineae is slight image b above. However, as the myocardium of the ventricle contracts, so do the papillary muscles. This creates tension on the chordae tendineae image b above , helping to hold the cusps of the atrioventricular valves in place and preventing them from being blown back into the atria.
The aortic and pulmonary semilunar valves lack the chordae tendineae and papillary muscles associated with the atrioventricular valves. Instead, they consist of pocket-like folds of endocardium reinforced with additional connective tissue. When the ventricles relax and the change in pressure forces the blood toward the ventricles, the blood presses against these cusps and seals the openings.
Figure 14 shows an echocardiogram of actual heart valves opening and closing. When heart valves do not function properly, they are often described as incompetent and result in valvular heart disease, which can range from benign to lethal. Some of these conditions are congenital, that is, the individual was born with the defect, whereas others may be attributed to disease processes or trauma.
Some malfunctions are treated with medications, others require surgery, and still others may be mild enough that the condition is merely monitored since treatment might trigger more serious consequences. Valvular disorders are often caused by carditis, or inflammation of the heart. One common trigger for this inflammation is rheumatic fever, or scarlet fever, an autoimmune response to the presence of a bacterium, Streptococcus pyogenes , normally a disease of childhood.
While any of the heart valves may be involved in valve disorders, mitral regurgitation is the most common, detected in approximately 2 percent of the population, and the pulmonary semilunar valve is the least frequently involved. When a valve malfunctions, the flow of blood to a region will often be disrupted.
The resulting inadequate flow of blood to this region will be described in general terms as an insufficiency. The specific type of insufficiency is named for the valve involved: aortic insufficiency, mitral insufficiency, tricuspid insufficiency, or pulmonary insufficiency. If one of the cusps of the valve is forced backward by the force of the blood, the condition is referred to as a prolapsed valve.
Prolapse may occur if the chordae tendineae are damaged or broken, causing the closure mechanism to fail. The failure of the valve to close properly disrupts the normal one-way flow of blood and results in regurgitation, when the blood flows backward from its normal path. Using a stethoscope, the disruption to the normal flow of blood produces a heart murmur.
Stenosis is a condition in which the heart valves become rigid and may calcify over time. The loss of flexibility of the valve interferes with normal function and may cause the heart to work harder to propel blood through the valve, which eventually weakens the heart. Aortic stenosis affects approximately 2 percent of the population over 65 years of age, and the percentage increases to approximately 4 percent in individuals over 85 years.
Occasionally, one or more of the chordae tendineae will tear or the papillary muscle itself may die as a component of a myocardial infarction heart attack. Valve and septal disorders will trigger abnormal heart sounds.
Echocardiograms are sonograms of the heart and can help in the diagnosis of valve disorders as well as a wide variety of heart pathologies. Cardiologists are medical doctors that specialize in the diagnosis and treatment of diseases of the heart. After completing 4 years of medical school, cardiologists complete a three-year residency in internal medicine followed by an additional three or more years in cardiology. Following this year period of medical training and clinical experience, they qualify for a rigorous two-day examination administered by the Board of Internal Medicine that tests their academic training and clinical abilities, including diagnostics and treatment.
After successful completion of this examination, a physician becomes a board-certified cardiologist. This professional recognition is awarded to outstanding physicians based upon merit, including outstanding credentials, achievements, and community contributions to cardiovascular medicine.
Visit this site to learn more about cardiologists. Bureau of Labor Statistics. Growth within the field is fast, projected at 29 percent from to There is a considerable overlap and complementary skills between cardiac technicians and vascular technicians, and so the term cardiovascular technician is often used. Special certifications within the field require documenting appropriate experience and completing additional and often expensive certification examinations.
You will recall that the heart is a remarkable pump composed largely of cardiac muscle cells that are incredibly active throughout life. The fibrous skeleton is composed of dense connective tissue rings that surround the four heart orifices. The skeleton contains fibrocartilage in which nodules of bones ossa cordis may develop in some species. Although these bones occur most commonly in cattle, they are not restricted to this species. The skeleton performs several functions:. The heart contains four chambers.
The two upper chambers are the atria and the two lower chambers are the ventricles. On the cranial surface of each atrium is a pouch-like appendage called an auricle which is thought to increase the capacity of the atrium slightly. The thickness of the myocardium of the four chambers varies according to function. The atria are thin-walled because they deliver blood into the adjacent ventricles and the ventricles are equipped with thick muscular walls because they pump blood over greater distances.
Even though the right and left ventricles act as two separate pumps that simultaneously eject equal volumes of blood, the right side has a much smaller workload. This is because the right ventricle only pumps blood into the lungs, which are close by and present little resistance to blood flow. On the other hand, the left ventricle pumps blood to the rest of the body, where the resistance to blood flow is considerably higher.
Consequently, the left ventricle works harder than the right ventricle to maintain the same blood flow rate. This difference in workload affects the anatomy of the ventricular walls; the muscular wall of the left ventricle being significantly thicker than that of the right. The right atrium forms the dorsocranial section of the base of the heart and receives blood from the cranial vena cava, caudal vena cava and coronary sinus.
The interatrial septum is a thin partition dividing the right and left atria and possesses a characteristic oval depression called the fossa ovalis which is a remnant of the foetal foramen ovalis. The right atrium also houses the sinoatrial node. Blood flows from the right atrium to the right ventricle through the tricuspid valve also know as the right atrioventricular valve. In rabbits the right atrioventricular valve is bicuspid not tricuspid.
The right ventricle forms most of the anterior surface of the heart and is crescent-shaped in cross-section. The cusps of the tricuspid valve are connected to tendon-like cords, the chordae tendinae, which, in turn, are connected to cone-shaped papillary muscles within the ventricular wall.
The right ventricle is separated from the left by a partition called the interventricular septum. The trabecula septomarginalis is a muscular band that traverses the lumen of the right ventricle. Deoxygenated blood passes from the right ventricle through the pulmonary semi-lunar valve to the pulmonary trunk, which conveys the blood to the lungs.
The inferior border runs from the 6th costal cartilage on the right, through the xiphisternal joint, to the 5th intercostal space on the left. It runs as far as the midclavicular line. Because this inferior border lies along the surface of the diaphragm, it is often referred to as the "diaphragmatic" surface.
Diastole occurs when blood flows from the atria to fill the ventricles. Download Heart Lab Manual. See more from our free eBook library.
The Body Online. A description of the heart from the edition of Gray's Anatomy of the Human Body. Functions of the Blood. Blood Vessels: The Circulatory Network. Pulmonary and Systemic Circulation. Circulatory System Pathologies. When you select "Subscribe" you will start receiving our email newsletter. Use the links at the bottom of any email to manage the type of emails you receive or to unsubscribe.
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