Anatomy & Physiology Chapter 20 The Heart
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Heart
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the pump in the cardiovascular system that distributes blood for all functions and to all tissues in the body
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Cardiology
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the study of the heart and the diseases associated with it
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Heat Beats
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100,000 times per day, 35 million times a year
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Heart Volume
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5 liters/min or 5.3 quarts, 14,000 liters a day, or 3,600 gallons
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Heart Size
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Man's fist: 5 in long, 3.5 in wide, 2.5 in thick
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Heart Mass
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8 oz. or 250 grams (female), 10 oz. or 300 grams (male)
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Heart is located in
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the mediastinum
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Heart apex
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is formed by the left ventricle and rests on the diaphragm
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Heart Base
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formed by the atria (mostly the left) and is the posterior surface
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Pericardium
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the membrane that surrounds and protects the heart
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Fibrous Pericardium
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tough connective tissue; prevents overstretching, protects and anchors the heart
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Serous Pericardium
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thin delicate membrane that forms a double layer around the heart; parietal and visceral
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Parietal layer
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outer layer fused to the fibrous pericardium
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Visceral layer
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inner layer; adheres tightly to heart surface; also called the epicardium
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Pericardial cavity
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space between the parietal and visceral layers containing pericardial fluid
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Pericardial fluid
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serous fluid; lubricates the heart and prevents friction as the heart moves
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3 layers of the heart wall
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epicardium, myocardium, endocardium
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Epicardium
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the visceral layer; thin transparent outer layer of the heart wall
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Myocardium
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cardiac muscle tissue; 95% of heart mass and responsible for pump action
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Myocardium
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striated, involuntary muscle that swirls diagonally around the heart in bundles
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Endocardium
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inner (within); thin layer of endothelium overlying a thin layer of connective tissue
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Endocardium
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endothelium provides a smooth lining for chambers and valves of the heart
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Percarditits
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often linked to a viral infection
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Myocarditis
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caused by: viral infection, rheumatic fever, or exposure to chemicals or radiation
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Endocarditis
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typically affects the heart valves; usually bacterially caused: treated with antibiotics
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Atria
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the superior, receiving chambers of the heart
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Auricle
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pouch-like structure on the anterior surface of each atrium to increase atrial capacity
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Ventricles
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the inferior, pumping chambers of the heart`
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Sulci
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grooves on the heart surface that mark external boundaries between chambers
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Types of Sulci:
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coronary sulcus, anterior interventricular sulcus, posterior interventricular sulcus
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Coronary sulcus
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external boundary between superior atria and inferior ventricles
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Anterior interventricular sulcus
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anterior groove between right and left ventricles
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Posterior interventricular sulcus
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posterior groove between right and left ventricles
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Right Atrium
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forms the right border of the heart and receives blood from veins of the body and heart
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Blood enters the atrium through 3 mains veins:
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superior vena cava, inferior vena cava, & coronary sinus
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Pectinate muscles
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muscular ridges in the anterior portion of the right atrium that extend into the auricle
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Interatrial septum
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thin partition between right and left atrium
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Fossa Ovalis
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remnant of the foramen ovale of the fetal heart; an opening through the interatrial septum that closes after birth
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Tricuspid Valve
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"right antrioventricular valve"; 3 cusps; blood passes through this valve from the right atrium to the right ventricle
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Tricuspid structure
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dense connective tissue overlain with endocardium
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Right Ventricle
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forms much of the anterior surface of the heart; pumps the blood to the lungs from the heart through pulmonary arteries
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Trabeculae Carneae
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ridges formed by raised bundles of cardiac muscle fibers
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Papillary muscles
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cone-shaped trabeculae carneae which anchor the chordae tendinae (tendon-like cords) to the cusps of the tricuspid valve
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Interventricular Septum
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muscular partition between the right and left ventricle
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Blow flow from the right ventricle
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Right ventricle contracts and squeezes(pumps) blood out through the *pulmonary semilunar valve* into the *pulmonary trunk* which divides into *right and left pulmonary arteries* which take blood to the lungs
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Left Atrium
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receives blood from the lungs through the 4 pulmonary veins
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Pectinate muscles of the left atrium
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are only present in the auricle not the atrium itself
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Bicuspid valve
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left atrioventricular valve; blood passes from the left atrium into the left ventricle; also called the mitral valve
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Left Ventricle
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the thickest chamber of the heart averaging 10-15mm, & forms the apex of the heart
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Blood flow of the left ventricle
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Blood is pumped through the *aortic semilunar valve* into the *ascending aorta*; from there blood flows into the *coronary arteries to the heart wall* and the remainder passes into the *aortic arch* or *descending aorta*
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Ductus arteriosis
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opening during fetal life that shunts blood from the pulmonary trunk into the aorta, so only small amounts of blood flow to the non-functioning lungs
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Ductus arteriosis
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closes after birth and forms the ligamentum arteriosum which connects the aortic arch to the pulmonary trunk
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Ventricle walls
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are thicker than atrial walls
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Right ventricle pumps
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an equal amount of blood as the left ventricle but over shorter distances and with less resistance to blood flow
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Left ventricle lumen shape
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circular
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Right ventricle lumen shape
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crescent sliver
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Fibrous skeleton of the heart:
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four dense connective tissue rings that surround the valves of the heart, fuse with one another, and join at the interventricular septum
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Fibrous skeleton functions
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forms foundation for the heart valves; prevents valves from overstrectching; point of insertion for cardiac fibers; and electrical insulators between atria and ventricles
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Valves
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respond to pressure changes by opening to allow flow or closing to prevent backflow
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Blood circulation is
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dependent on the pumps and valves
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Cardiac Cycle
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a complete heartbeat consisting of systole and diastole of both atria and both ventricles
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Atrioventricular valves
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tricuspid & bicuspid
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Atrium contracts whil
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ventricles, papillary muscles, and chordae tendonae are relaxed
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AV valves are held closed by
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contracted papillary muscles and tendonae chordae
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Semilunar valves
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aortic valve & pulmonary valve; contain 3 moon-shaped cusps
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Stenosis
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narrowing of the heart valve opening restricting blood flow
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Insufficiency
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or incompetence; the failure of a valve to close completely
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Mitral stenosis
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narrowing of the mitral valve; caused by scar formation or congenital effects
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Mitral insufficiency
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backflow of blood from the left ventricle back into the left atrium
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Mitral valve prolapse (MVP)
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one or both cusps of the mitral valve protrude into the right atrium during right ventricle contraction; most common valvular disorders; affects 30% of population and more frequent in women
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Aortic stenosis
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narrowing of the aortic valve
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Aortic insufficency
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backflow of blood from the aorta to the left ventricle
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Rheumatic fever
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acute systemic inflammatory disease; brought on by streptococcal infection of the throat
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Systemic Circulation
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route; *oxygenated blood* flows from left ventricle through the aorta to all the body and *deoxygenated blood* returns to the right atrium
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Pulmonary Circulation
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route; *deoxygenated blood* flows from right ventricle through the pulmonary trunk and arteries to the lungs and *oxygenated blood* returns to the left atrium
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Right side of heart
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pulmonary circulation
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Left side of heart
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systemic circulation
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Conary/Cardiac Circulation
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network of blood vessels supplying the myocardium of the heart through coronary arteries
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Coronary arteries
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branch off the ascending aorta and encircle the heart like a crown; supply blood to the heart myocardium
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2 coronary arteries
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the left and right
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Left coronary artery branches
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anterior interventricular branch & the cirumflex branch
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Anterior interventricular branch
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in anterior interventricular sulcus; supplies both ventricles
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Circumflex branch
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runs through coronary sulcus; supplies left side (left atrium and left ventricle)
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Right coronary artery branches
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atrial branches, posterior interventricular branch, marginal branch
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Atrial branches
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supply right atrium
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Posterior interventricular branch
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in posterior sulcus; supllies both ventricles
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Marginal branch
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in coronary sulcus; supplies the right ventricle
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Route for supplying the heart
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Arteries-> arterioles-> capillaries
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Coronary sinus
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where deoxygenated blood drains after supplying the heart and empties into the right atrium
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Veins that carry deoxygenated blood to the coronary sinus
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great cardiac vein, middle cardiac vein, small cardiac vein, & the anterior cardiac veins
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Great cardiac vein carries blood
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from areas supplied by the left coronary artery including the left atrium and both ventricles
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Middle cardiac vein carries blood
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from areas supplied by the posterior branch of the right coronary artery including both ventricles
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Small cardiac vein
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lies in the coronary sulcus; drains the right atrium and right ventricle
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Anterior cardiac vein
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drains right ventricle; opens directly into the right atrium
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Anastomoses
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connections between arteries that provide alternate routes for blood in case the main route becomes obstructed
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Collateral circuits
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the name for the alternate routes anastomoses provide to reach organs or tissues
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Myocardial ischemia
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condition of reduced blood flow to the myocardium due to partial obstruction of blood flow in the coronary arteries; silent myocardial ischemia is deadly
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Hypoxia
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reduced oxygen supply to tissues and cells which does not kill them; can be caused by ischemia
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Angina pectoris
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"strangled chest", pain that accompanies myocardial ischemia; may often manifest in the neck, chin, and left arm to elbow
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Reperfusion
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reestablishment of blood flow to tissue in hypoxia, with the result of possible further damage caused by free radicals in the reintroduced oxygen
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Myocardial Infarction
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a heart attack; complete obstruction of blood flow in a coronary artery
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Infarction
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death of an area of tissue because of interrupted blood supply= dead
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Treatment for myocardial infarction
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clot-dissolving agents, coronary angioplasty, coronary artery bypass grafting
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Cardiac Muscle Tissue
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tissue of the heart wall composed of branched striated fibers; one or two centrally located nulcei; contain intercalated disc
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Intercalated discs
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found only in cardiac muscle; irregular transverse thickening of the plasma membrane that connect ends of neighboring muscle fibers
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Intercalated discs contain
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desmosomes and gap junctions
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Desmosomes
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"glue" that holds the muscle fibers together during rigorous contractions of the heart; spot-weld-like junctions between cardiac muscle cells
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Gap junctions
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gaps between calls that enable nerve impulses to spread instantly across the myocardium so that the atria or ventricles contract as a single coordinated unit
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Cardiac muscle control
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involuntary; not consciously controlly
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Function of cardiac muscle
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pump blood to all parts of the body
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Autorhythmic fibers
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a network of specialized cardiac muscle fibers that are self-excitable; generate action potentials that trigger heart contractions that will continue even after the heart has been removed from the body
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Autorhythmic fibers
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constitue about 1% of muscle fibers formed during development; act as a *pacemaker* setting the rhythm of electrical excitation that causes contraction of the heart
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Autorhythmic fibers
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form the conduction system; a network of specialized cardiac muscle fibers that provide a path for each cycle of cardiac excitation
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Step 1 of the Conduction system
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excitation begins at the *sinoatrial node* near the opening of the vena cava in the right atrium;
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Step 1 of the Conduction system
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the SA node repeatedly depolarizes and this depolarization is called the pacemaker potential; when pacemaker potential reaches threshold it triggers an action potential which propagates through gap junctions in both atria and the *atria contract*
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Step 2 of the Conduction system
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the same action potential from step 1 is conducted to the *atrioventricular node* in the interatrial septum
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Step 3 of Conduction system
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From the AV node, the action potential enters the *atrioventricular bundle "Bundle of His"*
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Bundle of His
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the only site where action potentials can conduct from the atria to the ventricles due to the insulation of the fibrous skeleton
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Step 4 of Conduction system
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action potential propagates along the AV bundle of his and enters the right and left branches down through the interventricular septum toward the apex
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Step 5 of Conduction system
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large diameter *Purkinje fibers* rapidly conduct the action potential throughout the *ventricular myocardium*; and the *ventricles contract* pushing blood toward the semilunar valves
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Timing of the pacemaker can only be modified by
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the autonomic nervous system & blood-born horones
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The fundamental rhythm is established by
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the sinoatrial (SA) node
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Artificial pacemakers
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used when the SA node becomes damaged or diseased to maintain normal heart rate
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Contractile fibers
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the working atrial and ventricular muscle fibers that are excited by the *sinoatrial node*
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Contraction steps in order
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rapid depolarization, plateau, and repolarization
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Step 1 of contraction
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rapid depolarization; contractile fibers are usually at resting potential- when contractile fibers are subjected to an electrochemical gradient, rapid depolarization is produced and the excitation spreads through the gap junctions and the contractile fibers *contract as a unit*
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Step 2 of contraction
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plateau; a period of maintained action potential in a contractile fiber; much longer than normal neuron periods being about 250 millisec; is the prolonging of contraction
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Step 3 of contraction
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repolarization; the recovery of the resting membrane potential, getting ready for the next contraction
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Refractory period
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period of time in muscle during which a second action potential cannot be triggered; is longer than the contraction
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Cardiac muscle produces ATP
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by aerobic cellular respiration
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Cardiac muscle produces ATP
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from creatine phosphate
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Creatine Kinase presence indicates
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injury of cardiac muscle usually caused by myocardial infarction (heart attack)
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Electrocardiogram
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a composite record of the action potentials produced by all the heart muscle fibers during each heartbeat; recording can be detected at the surface of the body
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During an electrocardogram 3 waves appear
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P-wave, QRS complex, and the T-wave
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P-wave
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small upward deflection on the EKG at *atrial depolarization* spreading from the *SA node*
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QRS complex
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*rapid ventricular depolarization* as action potentials spread through * ventricle contractile fibers*;
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QRS complex
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begins as a downward deflection, continues as a large upward triangular wave, and ends as a downward wave
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T-wave
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dome shaped upward deflection that indicated *ventricular repolarization*
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T-wave
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occurs just as the ventricles start to relax
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Larger P-wave indicates
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enlargement of atrium
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Enlargement of Q-wave indicates
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a myocardial infarction
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Enlarged R-wave indicates
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enlarged ventricles
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Flat T-wave indicates
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the heart muscle is receiving insufficient oxygen; sign of coronary artery (heart) disease
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Elevated T-wave indicates
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hyperkalemia (high potassium level in blood)
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Time span between waves are called
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intervals and segments
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P-Q interval
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time from beginning of P-wave to beginning of the QRS complex
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P-Q interval
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represents conduction time from beginning of atrial excitation to the beginning of ventricle excitation
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Lengthened P-Q interval could indicate
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coronary artery disease or rheumatic fever produced scar tissue that slowed the impulse
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S-T segment
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time of depolarization of the ventricular fibers; plateau phase
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S-T segment elevated above basline
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myocardial infarction
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S-T segment depressed below baseline
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insufficient oxygen
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Q-T interval
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time from beginning of ventricular depolarization to the end of ventricular repolarization
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Lengthened Q-T interval indicates
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myocardial infarction damage, ischemia, or conduction problems
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Stress testing
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looking for changes from the rest stage of the heart to times of exercise
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Continuous ambulatory electrocardiograph
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24 hour portable battery operated ECG which a patients wears
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Systole
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phase of contraction
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Diastole
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phase of relaxation
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ECG can predict
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systole and diastole timing
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Cardiac cycle
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all the events associated with one heartbeat
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Cardiac cycle includes
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systole and diastole of both atria and both ventricles
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A heart rate of 75 beats/min
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will produce a cardiac cycle of 0.8 seconds
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Step 1 Cardiac cycle
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Atrial systole; duration 0.1 seconds
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End-diastolic volume
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volume of blood in the ventricle at the end of its diastolic period
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During atrial systole
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atrium contracts forcing 25 ml of blood through the AV valves into the relaxed ventricle
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Step 2 cardiac cycle
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ventricular systole; duration 0.3 seconds
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During ventricular systole
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ventricles force blood out the semilunar valves
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Each ventricle ejects
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70ml of blood into the receiving artery, leaving 60ml in each ventricle
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Ventricular ejection
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period when SL valves and blood is ejected from the ventricles
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End-systolic volume
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blood left in ventricle after contraction
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Stroke volume
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volume of blood ejected per heartbeat from each ventricle
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Heart beating at rest formula
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SV=130ml-60ml=70ml
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Step 3 cardiac cycle
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relaxation period where both atria and both ventricles are relaxed; duration 0.4 seconds
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The relaxation period shortens
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as the heart rate increases; atrial and ventricular systole only slightly shorten
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Ventricular repolarization causes
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ventricular diastole, where the ventricles are relaxed
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During ventricular repoarization
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pressure drops in the ventricles; SL valves close because their cusps are filled from the backflow of the aorta and pulmonary arteries
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Dicrotic wave
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the rebound of blood off the closed cusps of the aortic valve
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Step 4 cardiac cycle
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ventricular filling
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Ventricular filling
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as ventricles relax, pressure drops in the ventricles below atria chamber pressure & the AV valves open and fill the ventricles; beings new cycle
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Auscultation
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the act of listening to sounds within the body
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Auscultation instrument
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stethascope
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Heartbeat sounds come from
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turbulance of blood caused by heart valves closing
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Each heartbeat produces how many sounds
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four sounds; but only two are normally heard
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Heart sound numbers
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S1, S2, S3, S4
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Which heartbeat sounds are normally heard
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S1, & S2
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Heart sound S1
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"lubb" sound caused by blood turbulence at the closure of the AV valves just after ventricular systole begins; louder and longer than S2
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Heart sound S2
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"dupp" sound caused by blood turbulence at the closure of the SL valves at the start of ventricular diastole
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Heart sound S3
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not normally heard; blood turbulence during *rapid ventricular filling*
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Heart sound S4
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not normally heard; blood turbulence during *atrial systole*
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Heart murmur
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an abnormal sound consisting of clicking, rushing, or gurgling noise heard during or between beats; common in children
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Heart murmur example in adults
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mitral incompetence (valve not fully closed); occurs during ventricular systole between S1 and S2
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Cardiac Output
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the volume of blood per *minute* ejected from the left or right ventricle into the aorta or pulmonary trunk
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Cardiac Reserve
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the difference between a person's maximum cardiac output & cardiac output at rest
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Two things that can affect cardiac output
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stroke volume & heart rate
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3 factors that regulate stroke volume
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preload, contractility, and afterload
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Hypertension
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elevated blood pressure
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Atherosclerosis
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narrowing of the arteries
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Increased afterload causes
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stroke volume to deecrease
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Decreased afterload caused
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stroke volume to increase
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2 factors that regulate heart rate
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ANS & hormones
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The cardiovascular center is located in
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the medulla oblongata
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Cardiac Accelerator Nerves are
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sympathetic nerves that extend out to the SA node, VA node, & myocardium
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Sympathetic path of cardiac accelerator nerves releases
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norepinephrine
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Parasympathetic path of cardiac accelerator nerves releases
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acetylcholine
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Hormones that regulate the heart rate are released by
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the adrenal medullae
