Chapter 20 notes (Heart)

From Biol557

Contents 1 Chapter 20: The heart 1.1 An introduction to the cardiovascular system 1.2 The heart is a four-chambered organ, supplied by the coronary circulation, that pumps oxygen-poor blood to the lungs and oxygen-rich blood to the rest of the body 1.2.1 The pericardium 1.2.2 Superficial anatomy of the heart 1.2.3 The heart wall 1.2.3.1 Cardiac muscle tissue 1.2.4 Internal anatomy and organization 1.2.4.1 The right atrium 1.2.4.2 The right ventricle 1.2.4.3 The left atrium 1.2.4.4 The left ventricle 1.2.4.5 Structural differences between the left and right ventricles 1.2.4.6 The heart valves 1.2.4.6.1 The atrioventricular valves 1.2.4.6.2 The semilunar valves 1.3 STUFF MISSING! 1.3.1 The Blood Supply to the Heart 1.3.1.1 The coronary arteries

Chapter 20: The heart

An introduction to the cardiovascular system

• There is a pulmonary circuit and a systemic circuit.
• Efferent vessels = arteries = away from the heart.
• Afferent vessels = veins = toward the heart.
• Capillaries = exchange vessels.
• The heart pumps 100k times per day, moving 8k liters!
• The right atrium receives blood from the systemic circuit; the left atrium receives blood from the pulmonary circuit.
• The ventricles pump at the same time and move the same volume of fluid into each circuit.

The heart is a four-chambered organ, supplied by the coronary circulation, that pumps oxygen-poor blood to the lungs and oxygen-rich blood to the rest of the body

• The heart lies slightly to the left of center, behind the sternum.
• The inferior tip of the heart is called the apex.
• The mediastinum is the region between the two pleural cavities.
• The mediastinum holds the heart (in the pericardial sac) and the great vessels as well as the thymus, esophagus, and trachea.

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The pericardium

• The pericardial sac is like a balloon in which one's heart is depressed.
• The pericardial sac has two tissue layers:
  • The visceral pericardium (epicardium) covers and adheres to the surface of the heart.
  • The parietal pericardium lines the inner surface of the sac.
• Between the membranes, there is pericardial fluid which serves to reduce friction between the membranes and to protect the heart.
  • Pericarditis is the reduction of pericardial fluid and thus presents with a scratching noise that can be heard via stethoscope.
  • Cardiac tamponade occurs when fluid builds up in the pericardial sac (from infection or wounding, perhaps) and thus restructs the movements of the heart.
    • Tampon means plug in latin.

Superficial anatomy of the heart

• The atria have thin, muscular walls that are highly expandable.
• The atria have auricles that go limp and wrinkle after contracting blood out of the atria.
• The coronary sulcus is a deep grove that marks the boundary between the atrium and the ventricle.
• The anterior / posterior interventricular sulci are shallower depressions that mark the boundary between the left and right ventricles.
• The sulci also contain the coronary arteries / veins and substantial amounts of fat.

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The heart wall

• There are three layers to the wall of the heart:
  • The epicardium is the same as the visceral pericardium and has two sub layers: the exposed mesothelium and the areolar tissue which is connected to the myocardium.
    • Areolar: "Areolar tissue known as areis exhibits interlacing, loosely organized fibers, abundant blood vessels, and significant empty space. Its fiber run in random directions and are mostly collagenous, but elastic and reticular fibers are also present." [1]
  • The myocardium contains nerves, blood vessles, and muscle tissue that intricately wraps around the great vessels, the atria, and the ventricles with a figure-eight pattern. The myocardium has multiple layers of muscle fibers.
  • The endocardium is a simple squamous epithelium that covers the inside of the heart, including the valves, and is continuous with the endothelium of the vasculature.
    • Squamous: "In anatomy, squamous epithelium (from Latin squama, "scale") is an epithelium characterised by its most superficial layer consisting of flat, scale-like cells called squamous cell". [2]

Cardiac muscle tissue

• Cardiac muscle fibers are connected with intercalated discs where the membranes of adjacent muscle cells interlock and are held together by desmosomes and gap junctions.
• These junctions allow for the fast propagation of action potentials.
• Note that cardiac muscle fibers can be differentiated in histological slides by:
  • their smaller size,
  • their single, centrally located nucleus,
  • their branching interconnections, and
  • the presence of intercalated discs.

Internal anatomy and organization

• The muscular interatrial and interventricular septums separate the atriums and the ventricles.
• The atrioventricular valves keep blood from flowing from the ventricle to the atrium.

The right atrium

• The right atrium receives blood from the superior and inferior vena cava and coronary sinus.
• The superior vena cava delivers blood from the head, neck, upper limbs, and chest.
• The inferior vena cava delivers blood from the rest of the trunk, the viscera, and the lower limbs.
• The coronary sinus delivers blood from the coronary veins.
• The foramen ovale allows blood to pass from the right atrium to the left atrium until birth when it closes.
• The formen ovale is generally permanently closed by three months of age leaving only the fossa ovalis.
• When the foramen ovale doesn't close, there are serious cardiovascular problems.
• The posterior side of the right atrium has a smooth surface while the anterior side and the auricle have muscular ridges called pectinate muscles.

The right ventricle

• Blood flows from the right atrium to the right ventricle via the right atrioventricular valve which is also called the tricuspid valve because there are three cusps made of fibrous tissue.
• There are chordae tendinae that are attached to the papillary muscles inside the ventricle that keep the cusps from being forced backward into the atrium when the ventricle contracts and blood pressure increases.
• There is a band called the moderator band that connects the internal conduction system to the papillary muscles so that the papillary muscles will be contracted before the rest of the heart flexes.
• The blood in the right ventricle is pumped through the pulmonary valve (also called the pulmonary semilunar valve) and into the pulmonary trunk and then into the left and right pulmonary arteries.

The left atrium

• The left atrium receives blood from the four pulmonary veins.
• Like the right atrium, the left atrium has an auricle.
• The right atrium has an atrioventricular valve, called the bicuspid valve or the mitral valve.
• Remember that you "tri (sic) to be right when remembering where the tricuspid valve is located."

The left ventricle

• The left ventricle is similar to the right ventricle:
  • It has chrodae tendinae that support the atrioventricular valve (the mitral valve) to prevent backflow.
  • There are large muscular ridges.
  • The two ventricles hold the same volume of blood.
• The left ventricle has much thicker walls than the right ventricle, however, so that it can generate the increased pressure needed to circulate blood throughout the entire body.
• Blood leaves the left ventricle via the aortic semilunar valve (also called the aortic valve) to enter the ascending aorta and then the aortic arch and the descending aorta.
• In the fetus, the pulmonary branch of the circulatory system is linked to the systemic branch through a blood vessel that later deteriorates into a fibrous ligament called the ligamentum arteriosum.

Structural differences between the left and right ventricles

• The function of the atria are almost identical and thus they look almost identical; the ventricles, however, are different because they have different duties.
• The right ventricle only has to push blood through the short pulmonary circuit which has relatively wide vessels and is therefore able to be effective which much lower pressures. Therefore, it has developed into a bellow-like compartment that compresses into the wall of the left ventricle.
  • Bellows: "A bellows (AKA Bagpipe) is a device for delivering pressurized air in a controlled quantity to a controlled location. Basically, a bellows is a deformable container which has an outlet nozzle. When the volume of the bellows is decreased, the air escapes through the outlet." ref
• The right ventricle has a circular cross section and concentric muscular form.
• When contracting, the right ventricle both narrows its diameter and shortens the chamber and can thus generate 4-6 times as much pressure as the right ventricle.
• The contraction of the left ventricle causes it to bulge into the chamber of the right ventricle and thus helps pump blood into the pulmonary system as well.
  • Sometimes, patients with damage to their right ventricle can survive because of this physiological effect.

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The heart valves

The atrioventricular valves

• Backflow of blood is also called regurgitation.

The semilunar valves

• The semilunar valves (those that lead from ventricles to either the systemic or pulmonary circuits) don't need supporting chordae because there is no pressure on the blood in the circuit trying to get back into the ventricle.
• When the semilunar valves close, the three flaps support each other like the three legs of a tripod.
• At the aortic valve, there are aortic sinuses (sacs) that keep the cusps of the valve from sticking to the walls of the aorta as blood is flowing outward.
• The coronary arteries originate at the aortic sinuses.

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• Valvar heart disease occurs when a patient's heart valves misfunction to the point that a steady flow of blood cannot be maintained.
  • Often VHD develops after carditis (an inflammation of the heart tissue) which can be caused by infections.
  • Rheumatic fever, an autoimmune inflammatory response to an infection is often the cause of carditis.

STUFF MISSING!

The Blood Supply to the Heart

• Blood flow to cardiac tissue can increase by 9 or 10 fold at times of greatest exertion.

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The coronary arteries