The Heart: Anatomy, Physiology, and Function - PDF

Chapter 20: The Heart **An Introduction to the Heart** The cardiovascular system includes... - Heart - Blood - Blood vessels The heart... - Beats approximately 100,000 times each day. - Pumping about 8000 liters of blood per day. 20-1 The heart is a four-chambered organ that pumps...

Chapter 20: The Heart **An Introduction to the Heart** The cardiovascular system includes... - Heart - Blood - Blood vessels The heart... - Beats approximately 100,000 times each day. - Pumping about 8000 liters of blood per day. 20-1 The heart is a four-chambered organ that pumps blood through the systemic and pulmonary circuits. The heart pumps **oxygen-poor blood** to the **lungs** within the **pulmonary circuit** and **oxygen-rich blood** to the **rest of the body** within the **systemic circuit**. **Overview of Heart Functions: The Pulmonary and Systemic Circuits** **[Pulmonary circuit:]** carries blood to and from gas exchange surfaces of lungs. **[Systemic circuit:]** carries blood to and from the rest of the body. Each circuit begins and ends at the heart. - Blood travels through these circuits in sequence. **Types of Blood Vessels** **[Arteries:]** carry blood away from heart. **[Veins:]** return blood to heart. **[Capillaries (*exchange vessels*):]** interconnect smallest arteries and smallest veins. - Exchange dissolved gases, nutrients, and wastes between blood and surrounding tissues. **Four Chambers of the Heart** **[Right atrium:] receives** blood from **systemic** circuit. **[Right ventricle:]** **pumps** blood into **pulmonary** circuit. **[Left atrium:]** **receives** blood from **pulmonary** circuit. **[Left ventricle:]** **pumps** blood into **systemic** circuit. **Heart Location and Position** - Great vessels connect at **[base]** (superior). - Pointed tip is **[apex]** (inferior). - Sits between two pleural cavities in mediastinum. **[Pericardium:]** surrounds heart. - Outer **fibrous** pericardium - Inner **serous** pericardium - Outer **parietal** layer - Inner **visceral** layer - **[Pericardial cavity:]** between parietal and visceral layers. - Contains **[pericardial fluid]**. **[Pericarditis:]** caused by pathogens in pericardium. - Inflamed pericardial surfaces rub against each other. - Producing **distinctive scratching sound**. - **[Cardiac tamponade:]** restricted movement of the heart. - Due to excess fluid in pericardial cavity. **Heart Superficial Anatomy, Heart Wall, and Cardiac Skeleton** **[Atria:]** two thin-walled top right and left chambers of the heart. - Each with an expandable outer **[auricle]**. **[Sulci:]** grooves that contain fat and blood vessels. **[Coronary sulcus:]** marks border between atria and ventricles. **[Anterior interventricular sulcus and posterior interventricular sulcus:]** mark boundary between left and right ventricles. The heart wall consists of three distinct layers... **[Epicardium:]** covers outer surface of heart. - **[Visceral layer of serous pericardium:]** covers surface of heart. - **[Parietal layer of serous pericardium:]** covers the visceral layer. **[Myocardium:]** cardiac muscle tissue. **[Endocardium:]** covers inner surface of heart. **Connective Tissues of the Heart** - Physically support cardiac muscle fibers, blood vessels, and nerves of myocardium. - Distribute forces of contraction. - Add strength and prevent overexpansion of heart. - Provide elasticity that helps return heart to original size and shape after contraction. **[Cardiac skeleton:]** four dense bands of tough elastic tissue. - Encircle heart valves and bases of pulmonary trunk and aorta. - Stabilize positions of heart valves and ventricular muscle cells. - Electrically insulate ventricular cells from atrial cells. **Heart Chambers, Valves, and Great Vessels** The chambers of the heart are separated by muscular partitions called **[septa]**. **[Interatrial septum:]** separates atria. **[Interventricular septum:]** separates ventricles. - Much **thicker** than interatrial septum. **Atrioventricular (AV) Valves** **\*\*\* They separate the atria from the ventricles, hence the name. \*\*\*** There are two AV valves: tricuspid and mitral valves. - Folds of fibrous tissue that extend into openings between atria and ventricles. - Permit blood flow in one direction. - From right atrium to right ventricle. - From left atrium to left ventricle. **Semilunar Valves** There are two semilunar valves: aortic and pulmonary valves. - Prevent backflow of blood into ventricles. **The Vena Cavae, Right Atrium, and Tricuspid Valve** **Right Atrium** Right atrium receives blood from... - **[Superior vena cava:]** carries blood from head, neck, upper limbs, and chest. - **[Inferior vena cava:]** carries blood from trunk, viscera, and lower limbs. **[Foramen ovale:]** before birth, the opening through interatrial septum, which connects the two atria of fetal heart. - Closes at birth, eventually forming **[fossa ovalis]**. **[Pectinate muscles:]** prominent muscular ridges. - On anterior atrial wall and inner surface of auricle Blood flows from the **right atrium** to the **right ventricle** through the... **Tricuspid Valve (*Right Atrioventricular Valve*)** - Has three cusps (hence its name). - Prevents backflow of blood. - Free edges of valve attach to **[chordae tendineae]** from **[papillary muscles]** of ventricle. - Prevent valve from opening backward. **The Right Ventricle, Pulmonary Valve, and Pulmonary Trunk** **Right Ventricle** **[Trabeculae carneae:]** muscular ridges on internal surface. - Of both, right and left ventricles. **[Moderator band:]** muscular ridge that delivers stimulus for contraction to papillary muscles. **[Conus arteriosus:]** at superior end of right ventricle. - Ends at **[pulmonary valve]**. **Pulmonary Valve** - Three semilunar cusps. - Leads to pulmonary trunk. - Start of pulmonary circuit, - Divides into left and right pulmonary arteries. **The Pulmonary Veins, Left Atrium, and Mitral Valve** **Left Atrium** **[Left atrium]** receives blood from **[left and right pulmonary veins]**. Blood flows from the left atrium to the left ventricle passes to left ventricle through... **Mitral Valve (Left Atrioventricular Valve or Bicuspid Valve)** - Two cusps **The Left Ventricle, Aortic Valve, and Ascending Aorta** **Left Ventricle** Similar to right ventricle but, does **NOT** have moderator band. Blood leaves left ventricle through aortic valve into ascending aorta. **[Aortic sinuses:]** saclike expansions at base of ascending aorta. - **[Ascending aorta]** turns to become **[aortic arch]**, - Becomes **[descending aorta]**. Compared to left ventricle, the right ventricle... - Holds and pumps the **SAME** amount of blood. - Has thinner walls. - Develops less pressure. - Is more pouch-shaped than round. **Blood Flow through the Heart Valves** The heart valves prevent backflow of blood. **The AV Valves: Atria to Ventricles** **[Atrioventricular (AV) valves:]** between atria and ventricles. There are two AV valves: tricuspid and mitral valves. - When ventricles contract, - Blood pressure closes valves - Papillary muscles contract and tense chordae tendineae, - Prevents regurgitation of blood into atria. - **[Regurgitation:]** backflow of blood. **The Semilunar Valves: Ventricles to Great Vessels** **[Semilunar valves:]** prevent backflow of blood into ventricles. There are two semilunar valves: pulmonary and aortic valves. - No muscular braces - **[Valvular heart disease (VHD):]** deterioration of valve function. - May develop after **[carditis:]** inflammation of heart. - May result from **[rheumatic fever:]** inflammatory autoimmune response to streptococcal bacteria. **The Blood Supply to the Heart** **Coronary Circulation** **\*\*\* Coronary circulation will supply blood FIRST to muscle tissue of heart before the blood goes anywhere else. \*\*\*** **Coronary Arteries** **[Coronary arteries:]** originate at aortic sinuses. - Elevated blood pressure and elastic rebound of aorta maintain blood flow through coronary arteries. **[Right coronary artery (RCA) ]** Supplies blood to... - Right atrium - Portions of both ventricles - Portions of electrical conducting system of heart Gives rise to... - Marginal arteries - Posterior interventricular artery **[Left coronary artery (LCA)]** Supplies blood to... - Left atrium - Left ventricle - Interventricular septum Gives rise to... - Circumflex artery - Anterior interventricular artery **[Arterial anastomoses:]** interconnect anterior and posterior interventricular arteries. - Maintain constant blood supply to cardiac muscle. **Cardiac Veins** **[Great Cardiac Vein ]** - Drains blood from region supplied by anterior interventricular artery. - Returns blood to coronary sinus, - Opens into right atrium. **[Posterior Vein of Left Ventricle, Middle Cardiac Vein, and Small Cardiac Vein]** - Empty into great cardiac vein or coronary sinus. **Anterior Cardiac Veins** - Empty into right atrium. **[Coronary artery disease (CAD):]** areas of partial or complete blockage of coronary circulation. - Cardiac muscle cells need a constant supply of oxygen and nutrients, - Reduction in blood flow to heart muscle reduces cardiac performance. **[Coronary ischemia:]** reduced circulatory supply from partial or complete blockage of coronary arteries. **Coronary Artery Disease** - Usual cause is formation of a fatty deposit, or atherosclerotic plaque, in wall of coronary vessel. - The plaque, or an associated thrombus (clot), narrows passageway and reduces blood flow. - Spasms in smooth muscles of vessel wall can further decrease or stop blood flow. **[Angina pectoris:]** chest pain. - Commonly one of the first symptoms of CAD. - A temporary ischemia develops when workload of heart increases - Individual may feel comfortable at rest - Exertion or emotional stress can produce sensations of pressure, chest constriction, and pain - Pain may radiate from sternal area to arms, back, and neck. **[Myocardial infarction (MI):]** part of coronary circulation becomes blocked, also called heart attack. - Cardiac muscle cells die from lack of oxygen. - Death of affected tissue creates a nonfunctional area known as an **[infarct]**. - Most commonly results from severe CAD. **[Coronary thrombosis:]** thrombus formation at a plaque. - Most common cause of an MI. Consequences depend on site and nature of circulatory blockage... - If near the start of one of the coronary arteries, - Damage will be widespread and heart may stop beating. - If blockage involves small arterial branch, - Individual may survive the immediate crisis. - But may have complications such as reduced contractility and cardiac arrhythmias. Myocardial infarctions... - Causes intense, persistent pain, even at rest, - BUT pain is not always felt. - May go undiagnosed and untreated. - **Often diagnosed with ECG and blood studies.** - Damaged myocardial cells release enzymes into circulation, - **[Cardiac troponin T]** - **[Cardiac troponin I]** - A form of **[creatinine phosphokinase, CK-MB]** **Risk Factor Modification** - Stop smoking - Treat high blood pressure - Adjust diet to lower cholesterol and promote weight loss - Reduce stress - Increase physical activity **Noninvasive Surgery** **[Atherectomy:]** long, slender catheter is inserted into coronary artery to remove plaque. **[Balloon angioplasty:]** tip of catheter contains inflatable balloon. - Inflated balloon presses plaque against vessel walls, - Plaques commonly redevelop. - A **[stent]** may be inserted to hold vessel open. **[Coronary artery bypass graft (CABG):]** small section of another vessel is removed. - Used to create detour around obstructed portion of coronary artery. - Up to four coronary arteries can be rerouted during a single operation, - Single, double, triple, or quadruple coronary bypasses. 20-2 The cells of the conducting system distribute electrical impulses through the heart, causing cardiac contractile cells to contract. **Cardiac Physiology: Electrical Impulses Leading to the Contractions Making Up a Heartbeat** **[Heartbeat:]** a single cardiac contraction. All heart chambers contract in series... - First the atria, - Then the ventricles. **Two Types of Cardiac Muscle Cells** **[Autorhythmic cells:]** control and coordinate heartbeat. **[Contractile cells:]** produce contractions that propel blood. **The Conducting System: Pacemaker and Conducting Cells** **[Conducting system:]** consists of specialized cardiac muscle cells. - Initiate and distribute electrical impulses that stimulate contraction. **[Autorhythmicity:]** cardiac muscle tissue contracts without neural or hormonal stimulation. **Components of the Conducting System** Pacemaker cells are found in the... - **[Sinoatrial (SA) node:]** in wall of right atrium. - **[Atrioventricular (AV) node:]** at junction between atria and ventricles. Conducting cells are found in the... - **[Internodal pathways of atria]** - **[Atrioventricular (AV) bundle]** - **[Bundle branches]** - **[Purkinje fibers]** of ventricles **[Pacemaker potential:]** gradual depolarization of pacemaker cells. - Do NOT have a stable resting membrane potential. **Rate of Spontaneous Depolarization** - SA node is 60--100 action potentials per minute. - AV node is 40--60 action potentials per minute. SA node depolarizes first, which establishes **[sinus rhythm]**. **Impulse Conduction through the Heart** 1. SA node activity and atrial activation begin. 2. Stimulus spreads across atria and reaches AV node. 3. Impulse is delayed for 100 msec at AV node, - Atrial contraction begins. 4. Impulse travels in AV bundle to left and right bundle branches in interventricular septum. - To Purkinje fibers, - And to papillary muscles via moderator band. 5. Purkinje fibers distribute impulse to ventricular myocardium. - Atrial contraction is completed. - Ventricular contraction begins. **Cardiac Arrythmias** **[Arrythmias:]** disturbances in heart rhythm. **[Bradycardia:]** abnormally slow heart rate. **[Tachycardia:]** abnormally fast heart rate. **[Ectopic pacemaker:]** abnormal cells generate high rate of action potentials. - Bypasses conducting system. - Disrupts timing of ventricular contractions. **The Electrocardiogram (ECG)** **[Electrocardiogram (ECG or EKG):]** a recording of electrical events in the heart. - Obtained by placing electrodes at specific locations on body surface. - Abnormal patterns are used to diagnose damage. **Features of an ECG** **ECG Waves** **[P wave:]** depolarization of atria. **[QRS complex:]** depolarization of ventricles. - Ventricles begin contracting shortly after R wave. **[T wave:]** repolarization of ventricles. **ECG Intervals** The time intervals are between ECG waves. **[P--R interval:]** from start of atrial depolarization to start of QRS complex. **[Q--T interval:]** time required for ventricles to undergo a single cycle of depolarization and repolarization. **[Cardiac contractile cells:]** form bulk of atrial and ventricular walls. - Receive stimulus from Purkinje fibers. **Resting Membrane Potential** - Of ventricular cell is about --90 mV. - Of atrial cell is about --80 mV. **[Intercalated discs:]** interconnect cardiac contractile cells. - Membranes of adjacent cells are, - Held together by desmosomes. - Linked by gap junctions. - Transfer force of contraction from cell to cell, - Propagate action potentials. **Characteristics of Cardiac Contractile Cells** - Small size - Single, central nucleus - **[Intercalated discs:]** branch interconnections between cells. **Action Potential in Cardiac Contractile Cells** **[Rapid depolarization:]** massive influx of Na+ through **fast sodium channels**. **[Plateau:]** extracellular Ca2+ enters cytosol through **slow calcium channels**. **[Repolarization:]** K+ rushes out of cell through **slow potassium channels**. **Refractory Period** **[Absolute refractory period (200 msec):]** cardiac contractile cells cannot respond. **[Relative refractory period (50 msec):]** cells respond only to strong stimuli. **Action Potential in a Ventricular Contractile Cell** - 250--300 msec. - 30 times longer than that in skeletal muscle fiber. - Prevents summation and tetany. **Role of Calcium Ions in Cardiac Contractions** - Extracellular Ca2+ crosses plasma membrane during plateau phase, - Provides roughly 20% of Ca2+ required for contraction. - Entry of extracellular Ca2+ triggers release of additional Ca2+ from sarcoplasmic reticulum (SR). **Cardiac Muscle Tissue** - Very sensitive to extracellular Ca2+ concentrations. - As slow calcium channels close, - Intracellular Ca2+ is pumped back into SR or out of cell. **Energy for Cardiac Contractions** **[Aerobic energy:]** from mitochondrial breakdown of fatty acids and glucose. - Oxygen is delivered by circulation. - Cardiac contractile cells store oxygen in myoglobin. 20-3 The contraction-relaxation events that occur during a complete heartbeat make up a cardiac cycle. **Cardiac Cycle** **[Cardiac cycle:]** from start of one heartbeat to beginning of next heartbeat. - Includes alternating periods of contraction and relaxation There are two phases of the cardiac cycle within each chamber. - **[Systole:]** contraction. - **[Diastole:]** relaxation. The blood pressure in each chamber... - **Rises** during **systole**. - **Falls** during **diastole**. Blood flows from an area of higher pressure to one of lower pressure... - Controlled by timing of contractions. - Directed by one-way valves. **Cardiac Cycle and Heart Rate** - At 75 beats per minute (bpm), - Cardiac cycle lasts about 800 msec. When heart rate increases... - All phases of cardiac cycle shorten, particularly diastole. There are four phases of cardiac cycle... - Atrial systole - Atrial diastole - Ventricular systole - Ventricular diastole **Atrial Systole** 1. Atrial contraction begins. - Right and left AV valves are open. 2. Atria eject blood into ventricles. **Ventricular Systole and Atrial Diastole** 3. Atrial systole ends - Atrial diastole begins. - Ventricles contain maximum blood volume, - Known as, **[end-diastolic volume (EDV)]**. 4. Ventricles contract and build pressure - Closing AV valves - Producing **[isovolumetric contraction]**. **Ventricular Systole** 5. ​Ventricular ejection - Ventricular pressure exceeds arterial pressure - Opens semilunar valves, allowing blood to exit. - Amount of blood ejected = **[stroke volume (SV)]**. 6. Semilunar valves close - As ventricular pressure falls, - Ventricles contain **[end-systolic volume (ESV)]**. - About 40 percent of end-diastolic volume. **Ventricular Diastole** 7. **[Isovolumetric relaxation]** - All heart valves are closed. - Ventricular pressure is higher than atrial pressure, - Blood cannot flow into ventricles. 8. AV valves open; ventricles fill passively. - Atrial pressure is higher than ventricular pressure. Individuals can survive severe atrial damage, BUT ventricular damage can lead to **[heart failure]**. **Heart Sounds** - Detected with a stethoscope **[S1:]** loud sound as AV valves close. \*\*\* LUBB \*\*\* **[S2:]** loud sound as semilunar valves close. \*\*\* DUPP \*\*\* **[S3, S4:]** soft sounds as blood is flowing into ventricles and atrial contraction. **[Heart murmur:]** sounds produced by regurgitation through valves. 20-4 Cardiac output is determined by heart rate and stroke volume. **Cardiac Output** **[Cardiac output (CO):]** the amount of blood pumped by left ventricle in one minute. **CO = HR × SV** - CO = cardiac output (mL/min) - HR = heart rate (beats/min) - SV = stroke volume (mL/beat) **Stroke Volume** **[Stroke volume (SV):]** the amount of blood pumped out of a ventricle during each contraction. **SV = EDV -- ESV** **[End-diastolic volume (EDV):]** amount of blood in each ventricle at end of ventricular diastole. **[End-systolic volume (ESV):]** amount of blood remaining in each ventricle at end of ventricular systole. **[Ejection fraction (EF):]** percentage of EDV ejected during contraction. Factors affecting heart rate... - Autonomic activity - Circulating hormones **Autonomic Innervation** - Cardiac plexus innervates heart. - Vagus nerves (CN X) carry parasympathetic fibers to small ganglia in cardiac plexus. - Cardiac centers of medulla oblongata. - **[Cardioacceleratory center:]** controls sympathetic neurons that increase heart rate. - **[Cardioinhibitory center:]** controls parasympathetic neurons that slow heart rate. **Cardiac Reflexes** - Cardiac centers - **[Baroreceptors:]** monitor blood pressure. - **[Chemoreceptors:]** monitor arterial oxygen and carbon dioxide levels. - Adjust cardiac activity. **Autonomic Tone** - Maintained by dual innervation and release of ACh and NE. - Fine adjustments meet needs of other systems. **Effects on Pacemaker Cells of SA Node** - Membrane potentials of pacemaker cells, - Are closer to threshold than those of cardiac contractile cells. - Any factor that changes the rate of spontaneous depolarization or the duration of repolarization, - Will alter heart rate by changing time required to reach threshold. - **ACh** released by **parasympathetic neurons**, - **Decreases** heart rate. - **NE** released by **sympathetic neurons**, - **Increases** heart rate. **[Bainbridge reflex (*atrial reflex*):]** adjustments in heart rate in response to increase in venous return. - **[Venous return:]** amount of blood returning to heart through veins. Stretch receptors in right atrium trigger increase in heart rate by stimulating sympathetic activity. **Hormonal Effects on Heart Rate** Heart rate is increased by... - Epinephrine (E) - Norepinephrine (NE) - Thyroid hormone (T3) **Factors affecting Stroke Volume** - Changes in EDV or ESV affect stroke volume, - And thus cardiac output. There are two factors that affect EDV... - **[Filling time:]** duration of ventricular diastole. - Venous return **[Preload:]** degree of ventricular stretching during ventricular diastole. - Directly proportional to EDV - Affects ability of muscle cells to produce tension **EDV and Stroke Volume** - At rest, - EDV is low. - Myocardium is stretched very little. - Stroke volume is relatively low. - With exercise, - Venous return increases. - EDV increases. - Myocardium stretches more. - Stroke volume increases. **[Frank--Starling Principle:]** as EDV increases, stroke volume increases. **Physical Limits** Ventricular expansion is limited by... - Myocardial connective tissues - Cardiac skeleton - Pericardium **Three Factors affect ESV** **[Preload:]** ventricular stretching during diastole. **[Contractility:]** force produced during contraction at a given preload. - Affected by autonomic activity and hormones. **[Afterload:]** tension that must be produced by ventricle to open semilunar valve and eject blood. **Effects of Autonomic Activity on Contractility** **Sympathetic Stimulation** - NE released by cardiac nerves, - E and NE released by adrenal medullae, - Causes ventricles to contract with more force. - Increases ejection fraction, decreases ESV. **Parasympathetic Stimulation** - ACh released by vagus nerves, - Reduces force of cardiac contractions. **Hormones** Many hormones affect heart contractility. - Pharmaceutical drugs mimic hormone actions, - Stimulate or block alpha or beta receptors. - Block calcium channels. **[Afterload:]** increased by any factor that restricts blood flow. - As afterload increases, stroke volume decreases. **[Summary: The Control of Cardiac Output]** **Control Factors of Heart Rate** **Autonomic Nervous System** - Sympathetic and parasympathetic **Circulating Hormones** - Venous return and stretch receptors **Stroke Volume Control Factors** - EDV---filling time and rate of venous return - ESV---preload, contractility, and afterload **[Cardiac reserve:]** difference between resting and maximal cardiac outputs. **Heart and Vessels of Cardiovascular System** **Cardiovascular Regulation** - Ensures adequate circulation to body tissues. **Cardiac Centers** - Control heart rate and peripheral blood vessels. **Cardiovascular System Responds to...** - Changing activity patterns. - Circulatory emergencies.