Walls of the Heart:
The heart is a four-chambered muscular organ located in the mediastin/um, the area of the chest between the lungs. Its primary purpose is to pump blood through the arteries, veins, and capillaries. The walls of the heart are composed of the
Review the structures of the heart and label its three layers in Figure Heart structures.
The endo/ cardi/ um, the inner membranous layer, lines the interior of the heart and the heart valves. The my/o /cardi /um, the middle muscular layer, is composed of a special type of muscle arranged in such a way that the contraction of muscle bundles results in squeezing or wringing of the heart chambers to eject blood from the chambers. The peri/ cardi /um, a fi- broussac, surrounds and encloses the entire heart.
When we talk about the muscular layer of the heart, we are referring to the my/ o/ cardi/ um. When we talk about the fibrous sac that encloses the entire heart, we are referring to the peri/ cardi/ um.
The prefix peri- means around. Peri/card/itisis an inflammation or infection of the pericardial sac with an accumulation of pericardial fluid. When the fluid presses on the heart and prevents it from beating, the condition is known as cardi/ ac tamponade. If necessary, peri/ cardi/ o/ centesis may be performed.
Cross-striations of cardi/ac muscle provide the mechanics of squeezing blood out of the heart chambers to maintain the flow of blood in one direction. Identify the muscul/ar layer of the heart responsible for this function.
The layer that lines the heart and the heart valves is known as the endo/cardi/um
The fibrous sac surrounding the entire heart and composed of two membranes separated by fluid is called the peri/cardi/um
The middle specialized muscular layer is called the my/o/cardi/um
Circulation and Heart Structures
The circulatory system is commonly divided into the cardiovascular system, which consists of the heart and blood vessels, and the lymphatic system, which consists of lymph vessels, lymph nodes, and lymphoid organs(spleen, thymus, and tonsils). Review Figure interrelationship of the cardiovascular system with the lymphatic system.
Some of the main vessels associated with circulation are illustrated in Figure Heart structures. Observe the locations and label the structures as you read the following material.
The (4) aorta, the largest blood vessel in the body, is the main trunk of systemic circulation. It starts and arches out at the left ventricle.
Deoxygenated blood enters the (5) right atrium via two large veins, the vena cavae(singular, vena cava).
The (6) superior vena cava conveys blood from the upper portion of the body (head and arms);
the (7) inferior venacava conveys blood from the lower portion of the body (legs).
Blood in the veins except for pulmonary veins has a low oxygen content (deoxygenated) and a relatively high concentration of carbon dioxide. In contrast to the bright red color of the oxygenated blood in the arteries, deoxygenated blood has a dark blue to purplish color.
The term in this frame that means low oxygen content is deoxygenated
Label Figure Heart structures as you continue to identify and learn about the structures and functions of the circulatory system. The (8) pulmonary trunk is the only artery that carries deoxygenated blood. As deoxygenated blood is pumped from the right ventricle, it enters the pulmonary trunk. The pulmonary trunk runs diagonally upward, then divides abruptly to form the branches of the right and left pulmonary arteries. Each branch conveys deoxygenated blood to the lungs.
The (9) right lung has three lobes; the (10) left lung has two lobes. Oxygen-rich blood returns to the heart via four pulmonary veins, which deposit the blood into the (11) left atrium. There are two (12) right pulmonary veins and two (13) left pulmonary veins.
Internally, the heart is composed of four chambers. The upper chambers are the (1) right atrium (RA) and (2) left atrium (LA). The lower chambers are the (3) right ventricle (RV) and (4) left ventricle (LV). Locate and label the chambers of the heart in Figure Internal structures of the heart. Red arrows designate oxygen-rich blood flow; blue arrows designate oxygen-poor blood flow.
The CF ventricul/o means ventricle (of heart or brain). A ventricle is a small cavity, such as the right and left ventricles of the heart or one of the cavities filled with cerebrospinal fluid in the brain. Incisions are sometimes performed into these cavities. An incision of a ventricle is known as a ventricul/o/tomy
The term atri/o/ventricul/ar (AV) refers to the atrium and the ventricle. It also pertains to a connecting conduction event between the atria and ventricles.
Flutter is an a/rrhythm/ia in which there is very rapid but regular rhythm (250–300 beats per minute) of the atria or ventricles. The heart chambers do not have time to completely fill with blood before the next contraction. Flutter can progress to fibrillation.When the flutter occurs in the atrium, it is called an atri/al flutter. When the flutter occurs in the ventricle, it is called a ventricul/ar flutter.
Flutter that progresses to fibrillation (a / rrhythm / ia in which there is a rapid, uncoordinated quivering of the my/ o /cardi / um) can affect the atria or the ventricles.
Internal structures of the heart. Red arrows designate oxygen-rich blood flow; blue arrows designate oxygen-poor blood flow
A wall or partition dividing a body space or cavity is known as a septum (plural, septa). Some septa are membranous; others are composed of bone or cartilage. Each is named according to its location in the body. In the heart, there are several septa, one of which is the interventricular septum(IVS), the partition that divides the LV from the RV. Label the (5) interventricular septum (IVS) in Figure Internal structures of the heart. Red arrows designate oxygen-rich blood flow; blue arrows designate oxygen-poor blood flow.
The ventricles are separated by a thick muscular IVS, whereas the atria are separated by a thinner muscular interatrial septum (IAS). The prefix brady- is used in words to mean slow. People with symptoms of brady/cardia commonly have difficulty pumping an adequate supply of blood to the tissues of the body.
Blood Flow Through the Heart
Although general circulatory information was discussed previously, this section covers in greater detail the specific structures involved in the flow of blood through the heart. The heart’s double pump serves two distinct circulations: pulmonary circulation, which is the short loop of blood vessels that runs from the heart to the lungs and back to the heart; systemic circulation routes blood through a long loop to all parts of the body before returning it to the heart.
Continue to label Figure Internal structures of the heart. Red arrows designate oxygen-rich blood flow; blue arrows designate oxygen-poor blood flow as you read the following information. The right atrium receives oxygen-poor blood from all tissues except those of the lungs. The blood from the head and arms is delivered to the RA through the (6) superior vena cava (SVC). The blood from the legs and torso is delivered to the RA through the (7) inferior vena cava (IVC).
Blood flows from the right atrium through the (8) tricuspid valve and into the right ventricle. The leaflets (cusps) are shaped so that they form a one-way passage, which keeps the blood flowing in only one direction. Label the tricuspid valve in Figure Internal structures of the heart. Red arrows designate oxygen-rich blood flow; blue arrows designate oxygen-poor blood flow.
The ventricles are the pumping chambers of the heart. As the right ventricle contracts to pump oxygen-deficient blood through the (9) pulmonary valve into the pulmonary artery, the tri/cuspid valve remains closed, preventing a backflow of blood into the right atrium. When the blood passes through the pulmonary trunk, also known as the main pulmonary artery, it branches into the (10) right pulmonary artery and the (11) left pulmonary artery. The pulmonary arteries carry the oxygen deficient blood to the lungs. Label the structures introduced in this frame in Figure Internal structures of the heart. Red arrows designate oxygen-rich blood flow; blue arrows designate oxygen-poor blood flow.
The right and left pulmonary arteries leading to the lungs branch and subdivide until ultimately they form capillaries around the alveoli. Carbon dioxide is passed from the blood into the alveoli and expelled out of the lungs. Oxygen inhaled by the lungs is passed from the alveoli into the blood.
Oxygenated blood leaves the lungs and returns to the heart via the (12) right pulmonary veins and (13) left pulmonary veins. The four pulmonary veins empty into the LA. The LA contracts to force blood through the (14) mitral valve into the LV. Label the structures in Figure Internal structures of the heart. Red arrows designate oxygen-rich blood flow; blue arrows designate oxygen-poor blood flow.
The aorta is the largest artery of the body and originates at the LV of the heart. The combining form aort/o refers to the aorta. Any disease of the aorta is called aort/o/pathy Aortic stenosis, a narrowing or stricture of the aortic valve, may be due to congenital malformation or fusion of the cusps. The stenosis obstructs the flow of blood from the LV into the aorta, causing decreased cardi/ac output and pulmon/aryvascul/ar congestion. Treatment usually requires surgical repair.
Arteries are large vessels that convey blood away from the heart; they branch into smaller vessels called arteri/oles. The arteri/oles deliver blood to adjoining minute vessels called capillaries. (See Figure Interrelationship of the cardiovascular system with the lymphatic system. Blood flows from the heart to blood capillaries and back to the heart. Lymph capillaries collect tissue fluid, which is returned to the blood. The arrows indicate direction of flow of the blood and lymph.)
As a person ages, the arteries lose elasticity, thicken, become weakened, and deteriorate. Deterioration of arterial walls is also due to constant high pressure needed to transport blood throughout the body. The medical term for an abnormal condition of artery hardening is known as: arteri/o/scler/osis
High blood pressure and high-fat diets contribute greatly to early arteri/o/scler/osis. A healthy diet can decrease the risk for hardening of the arteries, also called arteri/o/scler/osis Capillaries carry blood from arteri/oles to ven/ules. Ven/ules form a collecting system to return oxygen-deficient blood to the heart through two large veins, the SVC and the IVC.
Normal veins have competent (healthy) valves whose ven/ous walls are strong enough to withstand the later/al pressure of blood that is exerted upon them. Blood flows through competent valves in one direction, which is toward the heart. In varic/ose veins, also known asaricosities,dilatation (dilation) of veins from long periods of pressure prevents complete closure of the valves. When damaged (incompetent) valves do not close completely, there is a backflow of blood in the veins. In turn, incompetent valves create varicosities which contribute to enlarged and twisted superficial veins. (See Figure Healthy and unhealthy veins and valves. (A) Valve function in competent and incompetent valves. (B) Varicose veins.)
Where as competent valves prevent a backflow of blood into the veins, incompetent valves result in blood collecting in the veins. The accumulated blood causes dilation and distention of the veins, a condition known as varic/ose veins. (See Figure Healthy and unhealthy veins and valves. (A) Valve function in competent and incompetent valves. (B) Varicose veins)
To classify a heart abnormality, it is important to identify the part of the organ in which the disorder occurs. A mitral valve murmur is caused by an incompetent, or faulty, valve. This type of murmur occurs in the valvular structure of the heart known as the mitral valve
Healthy and unhealthy veins and valves. (A) Valve function in competent and incompetent valves. (B) Varicose veins
Replacement surgery can be performed to replace a damaged heart valve. When the tri/cuspid valve is damaged, it is replaced at the level of the tri/cuspid valve.
Heart structures depicting valves and cusps. (A) Heart valves.(B) Valve cusps
Conduction Pathway of the Heart
Primary responsibility for initiating the heartbeat rests with the (1) sinoatrial (SA) node, also known as the pacemaker of the heart. The SA node is a small region of specialized cardiac muscle tissue located on the posterior wall of the (2) right atrium (RA). Label the two structures in Figure Conduction pathway of the heart. Anterior view of the interior of the heart. The electrocardiogram tracing is one normal heartbeat
The electric/al current generated by the heart’s pacemaker causes the atrial walls to contract and forces the flow of blood into the ventricles. The wave of electricity moves to another region of the myo/ cardi/um called the (3) atrioventricular (AV) node. Label the structure in Figure Conduction pathway of the heart. Anterior view of the interior of the heart. The electrocardiogram tracing is one normal heartbeat to learn about the conduction pathway of the heart.
The AV node instantaneously transmits impulses to the (4) bundle of His, a bundle of specialized fibers that transmits those impulses to the right and left (5) bundle branches. Label the structures in Figure Conduction pathway of the heart. Anterior view of the interior of the heart. The electrocardiogram tracing is one normal heartbeat.
From the right and left bundle branches, impulses travel through the (6) Purkinje fibers to the rest of the ventricul/ar my/o/cardi/um and bring about ventricul/ar contraction. Label the Purkinje (pŭr-KĬN-jē) fibers in Figure Conduction pathway of the heart. Anterior view of the interior of the heart. The electrocardiogram tracing is one normal heartbeat.
Conduction pathway of the heart. Anterior view of the interior of the heart. The electrocardiogram tracing is one normal heartbeat
Cardiac Cycle and Heart Sounds
The cardi/ac cycle refers to the events of one complete heartbeat. Each contraction, or systole, of the heart is followed by a period of relaxation, or diastole. This cycle occurs 60 to 100 times per minute in the normal functioning heart. The normal period of heart contraction is called systole; the normal period of heart relaxation is called diastole
When the heart is in the phase of relaxation, it is in diastole.
When the heart is in the contraction phase, it is in systole
The pumping action of the heart consists of contraction and relaxation of the myocardial layer of the heart wall. During relaxation, diastole, blood fills the ventricles. The contraction that follows, systole, propels the blood out of the ventricles and into the circulation.
Electr/o/cardi/o/graphy is the process of recording electric/al activity generated by the heart.
An electr/o/cardi/o/gram is a record of electric/al activity generated by the heart.
ECG and EKG are abbreviations for electr/o/cardi/o/gram. To evaluate an abnormal cardi/ac rhythm, such as tachy/cardia, an EKG may be helpful.
A normal heart rhythm, or sinus rhythm, shows five waves on the ECG strip, which represent electrical changes as they spread through the heart. The waves are known as P wave, QRS waves, and T wave.
The P wave represents atrial depolarization, conduction of an electrical impulse through the atria. These electrical changes cause atrial contraction. The QRS waves, commonly referred to as the QRS complex, represent ventricular depolarization, conduction of electrical impulses through the ventricle by way of the bundle of His and the Purkinje fibers. These electrical changes cause ventricular contraction. The T wave represents the electrical recovery and relaxation of the ventricles (during diastole).
Although the heart itself generates the heartbeat, factors such as hormones, drugs, and nervous system stimulation also can influence the heart rate. To evaluate a patient’s heart rate, a physician may order an EKG, which is an abbreviation for electr / o / cardi / o / gram
Micro/cardia, an abnormal smallness of the heart, is a condition that is not usually compatible with a normal life. A person diagnosed with an underdeveloped heart suffers from the condition called micro/cardia
Megal/o/cardia is an enlargement of the heart. Cardi/o/megaly also means enlargement of the heart
In patients with high blood pressure, the heart must work extremely hard. As a result, it enlarges, similar to any other muscle in response to excessive activity or exercise. A patient who develops an enlarged heart has a condition called cardi/o/megaly, or megal/o/cardia
Coronary artery disease (CAD) affects the arteries and may cause various pathological conditions, including a reduced flow of oxygen and nutrients to the myocardium. (See Figure Coronary artery disease. (A) Partial occlusion. (B) Total occlusion.) The most common type of CAD is coronary ather/o/scler/osis. It is now the leading cause of death in the Western world.
Arteri/o/scler/osis is a thickening, hardening, and loss of elasticity of arteri/al walls, which results in decreased blood supply. Thus, arteri/o/scler/osis is commonly referred to as hardening of the arteries. When the physician diagnoses a hardening of the arteries, the condition is recorded in the medical chart as arteri/o/scler/osis
Ather/o/scler/osis, a type of arteri/o/scler/osis, is characterized by an accumulation of plaque within the arterial wall. (See Figure Coronary artery disease. (A) Partial occlusion. (B) Total occlusion.) Both conditions develop over a long period and usually occur together.
Coronary artery disease. (A) Partial occlusion. (B) Total occlusion
Necr/osis of the my/o/cardi/um occurs when there is insufficient blood supply to the heart. Eventually, such a condition may result incardi/ac failure and death of the my/o/cardi/um.
A my/o/cardi/al infarction (MI), or infarct, is caused by occlusion of one or more coronary arteries. MI is a medical emergency requiring immediate attention.
Thromb/osisis a condition in which a stationary blood clot obstructs a blood vessel at the site of its formation. The surgical excision of a blood clot is called thromb/ectomy Anti/coagulants are agents that prevent or delay blood coagulation; they are used in the prevention and treatment of a thrombus.
An aneurysm is an abnormal dilation of the vessel wall due to a weakness that causes the vessel to balloon and potentially rupture. (See Figure Aneurysms.) A ballooning out of the wall of the aorta is called an aort/icaneurysm
If a cerebr/al aneurysm ruptures, the hem/o/rrhage occurs in the cerebrum or brain. If an aort/ic aneurysm ruptures, the hem/o/rrhage occurs in the aorta
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