Basic A & P II Dr. L. Bacha Chapter Outline (Martini & Nath 2010) An Introduction to the Cardiovascular System - read the paragraphs under this heading on page 580 The Heart is a Four Chambered Organ describe the location of the heart: - it is situated about 2/3 to the left of the midline of the body size: the heart is about the size of a closed fist the heart is a cone shaped organ (see Fig. 18-2a) - the base is the broad superior part; it sits at the level of what costal cartilage? - the large arteries and veins attach to the heart at its base - define the apex of the heart: - it sits at the level of what intercostal space? the heart is surrounded by a two-layered sac, called the pericardium or pericardial sac, that encloses and protects the heart; it occupies the mediastinum define mediastinum: - what other structures, besides the heart, does the mediastinum contain? The Pericardium examine Fig. 18-2 b & c as you study the following parts of the pericardium: the pericardium is a double layer of serous membranes around the heart: 1. visceral pericardium - what is it also called? - covers and closely adheres to what? 2. parietal pericardium - lines the outer part of the pericardial cavity; it is fused to the fibrous pericardium the fibrous pericardium the superficial layer; it is fused to the parietal layer of the serous pericardium composed of tough, inelastic dense irregular connective tissue what does it stabilize? Chapter 18 The Heart 1
pericardial cavity = the space between and lined by the visceral pericardium and parietal pericardium pericardial fluid = a serous (watery) fluid produced by the serous membranes (visceral and parietal pericardium) that line the pericardial cavity what is the function of pericardial fluid? Superficial Anatomy of the Heart (See Fig. 18-3 and locate the following structures:) the heart consists of 4 chambers: two atria: a right atrium (RA) and a left atrium (LA) - these are the smaller, more thin-walled, superior chambers - each atrium has an expandable extension visible externally called the auricle two ventricles: a right ventricle (RV) and a left ventricle (LV) - these are the larger, inferior chambers indicate between what parts of the heart the following grooves form a border: coronary sulcus: anterior and posterior interventricular sulcus: The Heart Wall (identify the three layers of the heart wall in Fig. 18-4) epicardium what is the epicardium? it is made of delicate CT and an epithelium myocardium - thick middle layer that is formed mainly of cardiac muscle tissue (what does myo mean?) endocardium - made of an endothelium (which, specifically, is the simple squamous epithelium that lines the heart and vessels) and CT - provides a smooth lining of the chambers and covers the valves In order to expose the heart during dissection, you would have to snip through and peel back the outer layer of the pericardium (the fibrous pericardium and the parietal pericardium). Then, when you touch the surface of the heart, you would touch the thin, shiny, transparent epicardium (visceral pericardium). Cardiac Muscle Tissue review the features of cardiac muscle tissue in Chapt. 9 and in Table 18-1 what is the function of intercalated discs? Chapter 18 The Heart 2
Internal Anatomy and Organization name the structure that separates the two atria internally: name the structure that separates the two ventricles internally: The Right Atrium receives blood from the systemic circuit through what two veins that drain blood from the upper and lower part of the body? also part of the systemic circuit, blood from the wall of the heart flows into the coronary sinus, which opens into the right atrium name the oval opening in the interatrial septum that connects the two atria of the fetal heart: - name the small, shallow depression that persists in the interatrial septum after the foramen ovale closes at birth: The Right Ventricle blood flowing from the right ventricle enters what artery (p. 587)? The Left Atrium receives blood from what veins? The Left Ventricle do the two ventricles hold an equal amount of blood? describe the size of the left ventricle in contrast to the right ventricle: - what do its thick, muscular walls enable the left ventricle to develop? blood that leaves the left ventricle passes into what large artery? - the ascending aorta continues as the aortic arch that curves to the left side of the body and continues as the descending aorta through the thoracic and abdominal cavities - the pulmonary trunk is attached to the aortic arch by a fibrous band called what? - the ligamentum arteriosum is a remnant of the ductus arteriosus, a vessel in the fetus that shunts blood from the pulmonary to the systemic circuit The Heart Valves The Atrioventricular Valves what do the AV valves prevent? Chapter 18 The Heart 3
describe the components of the AV valves when the ventricles are relaxed: describe what happens to the components of the AV valves when the ventricles contract: The Semilunar Valves what do the semilunar valves prevent? as the ventricles contract, the semilunar valves open when pressure in the ventricles exceeds the pressure in the arteries, permitting ejection of blood from the ventricles as the ventricles relax, blood in the arteries starts to flow back into the ventricles; the blood fills the cusps of the valves, which causes the semilunar valves to close tightly My summary of the anatomy of HEART VALVES (see Fig. 18-6 and Fig. 18-8) - the valves open and close in response to pressure changes as the heart contracts & relaxes 1. ATRIOVENTRICULAR VALVES (AV VALVES) a. Tricuspid valve (right AV valve) b. Bicuspid valve (mitral valve; left AV valve) Structure of AV valves: cusps - tongue-like flaps chordae tendineae - are tendon-like fibrous cords which connect the cusps to papillary muscles - function: anchor the cusps to papillary muscles to prevent them from flipping up into the atria when the ventricles contract papillary muscles projections of cardiac muscle of ventricles to which chordae tendineae attach 2. SEMILUNAR VALVES a. Pulmonary semilunar valve b. Aortic semilunar valve Structure of semilunar valves: each semilunar valve is formed by three half-moon shaped, pocket-like cusps situated between a ventricle and the large artery that emerges from the ventricle; - each cusp attaches to the arterial wall along its outer margin - the free borders project into the lumen of the artery Chapter 18 The Heart 4
Systemic and Pulmonary Circulations ( NOTE: this is my summary; it is covered a bit on page 580,Fig. 18-1, and in Chapter 19!) the heart pumps blood into two circuits: Pulmonary circuit and Systemic circuit = vessel or chamber with deoxygenated blood (low O2; high CO2) = vessel or chamber with oxygenated blood (higho2; low CO2) Pulmonary circuit: RIGHT VENTRICLE PULMONARY TRUNK PULMONARY ARTERIES PULMONARY CAPILLARIES in the lungs (gas exchange takes place here between the blood in pulmonary capillaries & air in the lungs) PULMONARY VEINS LEFT ATRIUM Systemic circuit: LEFT VENTRICLE AORTA and OTHER SYSTEMIC ARTERIES throughout the body SYSTEMIC CAPILLARIES (gas exchange takes place here between the blood in systemic capillaries and cells of tissues throughout the body)) SYSTEMIC VEINS (from throughout the body) RIGHT ATRIUM Draw a long solid arrow from the words RIGHT ATRIUM to RIGHT VENTRICLE. Draw a long open arrow from the words LEFT ATRIUM to LEFT VENTRICLE. This should help you realize that these two circuits are continuous with each other! If we traced the pathway of a single red blood its path would alternate between the two circuits! Follow the diagram above and make a list of the chambers of the heart and the main blood vessels that contain oxygenated blood and deoxygenated blood: oxygenated blood deoxygenated blood Which side of the heart contains blood that is deoxygenated? Which side of the heart contains blood that is oxygenated? Do all arteries contain oxygenated blood?! Do all veins contain deoxygenated blood?! Chapter 18 The Heart 5
The Blood Supply to the Heart (page 590 and see Fig. 18-9) The wall of the heart requires oxygenated blood, like other organs. It is supplied by blood vessels of the systemic circuit that form the coronary circulation. (In other works, the coronary circulation is the part of the systemic circuit that supplies the cells of the wall of the heart itself with oxygen, etc.) = deoxygenated blood = oxygenated blood right and left coronary arteries that arise at the base of the aorta branch into capillaries in the myocardium (where exchange of gases, nutrients, and waste products takes place) coronary veins coronary sinus right atrium Cardiac Physiology read the summary of cardiac physiology beginning on p. 593 list the two types of cardiac muscle cells involved in a normal heartbeat and indicate the function of each: The Conducting System cardiac muscle tissue has automaticity (autorhythmicity), which means that it contracts on its own, in the absence of hormonal or neural stimulation (although hormones and the nervous system influence heart rate) Chapter 18 The Heart 6
the cardiac conduction system is a network of specialized cardiac muscle cells and includes: the sinoatrial node (SA node) the sinoatrial node is in the wall of what chamber of the heart? sinoatrial node consists of special cardiac muscle cells that are self-excitable; they initiate impulses that spread through the atria (by direct intercellular communication) to the AV node the SA node is the pacemaker for the heart its cells fire at about 60-100 x per min. ( fire means to initiate impulses!) the atrioventricular node (AV node ) the AV node is in the floor of what chamber? impulses from the AV node spread down the interventricular septum to Purkinje fibers, which distribute the impulses into the myocardium of the ventricles, leading to contraction of the ventricles The Electrocardiogram how is electrocardiogram abbreviated? an electrocardiogram is a recording of the electrical events that occur through the heart we will go over the features of a standard electrocardiogram in class: P wave: WHY THE K in EKG? Kardio is Greek for heart QRS complex: T wave: Events during a complete heartbeat constitute a cardiac cycle (page 601) define a single cardiac cycle: what is another term for systole? what is another term for diastole? Chapter 18 The Heart 7
Phases of the Cardiac Cycle During a cardiac cycle, not only is there contraction and relaxation of the myocardium of the heart chambers, but there is also opening and closing of the valves and changes in blood pressure within the chambers and the major arteries. Summary of the 2 step pumping action of the heart: 1. Atrial Systole - The RA and LA contract almost simultaneously 2. Ventricular Systole - 0.1 to 0.2 s later the RV and LV contract while the atria relax 3. Relaxation Period -all chambers are relaxed for a moment Remember, this is a cycle, and even though we study it as three steps, step 3 continues to step 1, to step 2, to step 3, to step 1, etc., as long as the heart continues to beat! 1. Atrial Systole - the walls of the atria contract - the sudden increase in blood pressure within the atria forces the final 30% of the blood into the ventricles - the atrioventricular valves are open and the semilunar valves are closed - in an adult at rest, the typical volume of blood in each ventricle at the end of systole is ~ 130ml 3 2 1 2. Ventricular Systole - the walls of the ventricles contract while the atria relax - as the ventricles begin to contract and the blood pressure in them rises, the cusps of the AV valves are pushed closed - once blood pressure in the ventricles exceeds that in the aorta and pulmonary trunk, the semilunar valves open - the result is that about 60% of the volume of blood in the ventricles is forced (ejected) into the aorta and pulmonary trunk. - define stroke volume (SV): 3. Relaxation Period: Atrial and Ventricular Diastole - both atria and both ventricles relax - the semilunar valves close - the AV valves open - venous return (blood returning to the heart) fills the atria and, because the AV valves are open, it fills the ventricles to about 70% of their final volume of blood Heart Sounds (p. 605) auscultation is the act of listening to sounds within the body name the instrument used for auscultation: S 1 (the first heart sound) is produced as what valves close? S 2 (the second heart sound) is produced as what valves close? a heart murmur is an abnormal heart sound Chapter 18 The Heart 8
Cardiodynamics examines the factors that affect cardiac output each time the heart beats, do the two ventricles eject equal amounts of blood? define cardiac output (C0): write the equation using the abbreviations CO, SV and HR to show the relationship of cardiac output, stroke volume and heart rate: now, using the above equation, calculate the normal resting CO in an adult, given an average HR of 75 bpm and SV of 70 ml/beat: define cardiac reserve ( see page 612): the average person: cardiac reserve is 4 to 5 times resting CO (18 to 30 L/min) in top athletes: cardiac reserve can be up to 7 to 8 times resting CO (to 40 L/min) Overview: Factors Affecting Cardiac Output (back to page 605) cardiac output can be adjusted by changes in what? Regulation of Heart Rate adjustments in heart rate are important in the short-term control of CO and blood pressure factors that regulate heart rate also regulate CO; CO varies directly with HR although the SA node initiates cardiac action potentials, the nervous system and chemicals influence HR and contractility: A. Autonomic Nervous System with sympathetic nerve impulses rate of firing of the sinoatrial node heart rate with parasympathetic nerve impulses rate of firing of the sinoatrial node HR B. Chemical Regulation of HR 1. Hormones epinephrine - released by the adrenal medulla - same effects as the sympathetic n.s; increases contractility and heart rate thyroid hormone - increases heart rate 2. Ions hypercalcemia (excess calcium ions in the blood) increases heart rate hyperkalemia (excess potassium ions in the blood) blocks contraction of the heart hypernatremia (excess sodium ions in the blood) blocks contraction of the heart Chapter 18 The Heart 9
Regulation of Stroke Volume The three main factors that affect SV (and therefore CO) are preload, contractility, and afterload. A. Preload: Degree of Stretch of Heart Muscle the more the cardiac muscle cells are stretched as the ventricles fill during diastole(preload), the greater the force of contraction of the ventricles during systole, and, therefore the greater the volume of blood the ventricles eject per beat (stroke volume) - this is known as the Frank-Starling principle the most important factor relating to stretching of cardiac muscle cells is venous return, which is the volume of blood returning to the heart anything that increases the volume or rate of venous return increases the volume of blood in each ventricle before it contracts, and increases therefore SV and CO e.g., slow heart rate allows more time for the ventricles to fill with blood e.g., exercise increases venous return due to an increase in HR and the squeezing action of the skeletal muscles on the veins returning blood to the heart B. Regulation of Contractility by the Nervous System contractility is the strength of contraction of the ventricles with an in sympathetic nerve impulses contractility of the ventricles stroke volume chemicals that increase contractility (positive inotropic agents): epinephrine, norepinephrine, Ca +2, glucagon, thyroxine, digitalis chemicals that decrease contractility (negative inotropic agents): excess H + (acidosis), high levels of K +, and drugs called calcium channel blockers C. Afterload: Back Pressure Exerted by Arterial Blood afterload = the pressure that the ventricles must overcome to eject blood into the pulmonary trunk and aorta to eject blood, the pressure that is generated by contraction of the ventricles must be greater than the back pressure exerted by the blood in the aorta and pulmonary trunk on the aortic and pulmonary semilunar valves hypertension (high blood pressure) reduces the ability of the ventricles to eject blood more blood remains in the heart after systole Clinical terms related to heart rate; define these from page 596: bradycardia: tachycardia: The End! Chapter 18 The Heart 10 The End!