Mn chapter 20

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Mn chapter 20

  1. 1. BSC2086C Chapter 20 Cardiovascular System Introduction 1) Divided into 2 circuits a. Pulmonary circuit b. Systemic circuit 2) Three types of blood vessels a. Arteries b. Veins c. Capillaries 3) Heart: the topic of this chapter Anatomy of the Heart (Much of this section is covered in lab and in homework, meaning the lecture on this section may be abbreviated or left for independent study depending upon time.) 1) Location a. Size of closed fist b. In mediastinum c. 2/3 of mass to left of midline d. Apex e. Base f. Surrounded by a pericardial sac 2) Cardiac muscle tissue (how are they different from skeletal muscle cells?) a. Cardiac muscle cells i. Branching cells connected by intercalated discs 1. Contain desmosomes and gap junctions a. Functional significance? ii. Small iii. Single nucleus 3) Chambers of the heart a. Two atria i. Auricle ii. Interatrial septum iii. Coronary sulcus iv. Foramen Ovale
  2. 2. 1. Fossa ovalis b. Two ventricles i. Anterior interventricular sulcus ii. Posterior interventricular sulcus iii. Interventricular septum 4) Structural differences between left and right ventricles (and atria!) a. Thin layer of myocardium in atria i. Why? b. Thicker myocardium in ventricles i. Why? ii. Left ventricle has more myocardium then the right ventricle 1. Why? 5) Heart Valves a. 2 atrioventricular valves i. Location & purpose: ii. Leaf-shaped cusps 1. Attached to ventricles through chordae tendineae and papillary muscles iii. Right atrioventricular valve iv. Left atrioventricular valve (mitral valve) b. 2 semilunar valves i. Location and purpose: ii. 3 moon-shaped cusps (little hammocks) iii. Aortic valve iv. Pulmonary valve c. How do these valves operate? i. Valves open and close in response to pressure changes as heart relaxes and contracts 1. Importance of valves? ii. Atrioventricular valves 1. Ventricles relaxed a. AV valves open b. Points of cusps point into ventricle c. Papillary muscles relaxed, slack chordae tendinae a. Movement of blood?
  3. 3. 2. Ventricles contract a. Pressure of blood presses cusps upward b. Cusps meet and close off opening c. Papillary muscles contract and tighten chordae tendinae b. Importance? iii. Semilunar valves 3. Ventricles contract a. Pressure of blood higher in ventricle then in arteries b. Valves open c. Movement of blood? 4. Ventricles relax a. Pressure of blood higher in arteries then in ventricles b. Blood flows down towards ventricles, due to pressure (gravity) c. Blood fills valve cusps so valves close tightly a. Importance? d. Heart valve disorders i. Stenosis ii. Mitral valve prolapse iii. Rheumatic fever 6) Flow of blood through the heart as if you are a drop of deoxygenated blood coming from the body a. Superior vena cava, inferior vena cava, coronary sinus b. Right atrium c. Right atrioventricular valve d. Right ventricle e. Pulmonary valve f. Pulmonary trunk g. R and L Pulmonary arteries h. Pulmonary capillaries in lungs i. 4 Pulmonary veins j. Left atrium k. Left atrioventricular valve l. Left ventricle m. Aortic valve n. Ascending aorta The Conducting System of the Heart and The Electrocardiogram 1) Cardiac Physiology a. Two types of cells involved in a normal heart beat i. Cells of conducting system ii. Contractile cells
  4. 4. b. Cardiac cycle i. Sinoatrial node produces an action potential that begins each heartbeat ii. Action potential stimulates contraction of contractile cells 2) The Conduction System a. Specialized cardiac muscle fibers called autorhythmic fibers i. Self-excitable, repeatedly generate action potentials that trigger heart contractions ii. Act as pacemaker iii. Form conduction system 1. Network of specialized cardiac muscle fibers that provide a path for each cycle of cardiac excitation to progress through the heart 2. Significance? b. Components i. Sinoatrial node 1. Possesses a prepotential (pacemaker potential) 2. 80-100 per min ii. Atrioventricular node 1. Possesses a prepotential (pacemaker potential) 2. 40-60 per min iii. Conducting cells 1. Internodal pathway 2. Atrioventricular bundle 3. Bundle branches 4. Purkinje fibers c. Action potential propagation i. Sinoatrial (SA) node…atria contract…atrioventricular (AV) node…AV bundle…bundle branches in interventricular septum…Purkinje fibers…ventricles contract ii. Ventricles contract from apex to base so blood is pushed toward semilunar valves d. Heart beat is intrinsic to the heart i. **Heart rate can be modified but heart beat- fundamental rhythm- is caused by the cardiac muscle itself e. Problems associated with pacemaker function i. Tachycardia
  5. 5. ii. Bradycardia iii. Ectopic pace maker 3) The Electrocardiogram a. ECG, EKG b. Record of action potentials produced by all the heart muscle fibers during each heartbeat i. Uses c. Electrocardiograph d. 3 Major components of ECG i. P wave 1. Atrial depolarization ii. QRS complex 1. Rapid ventricular depolarization iii. T wave 1. Ventricular repolarization 4) Contractile cells a. Action potential begins at SA node and excites contractile fibers b. Similarities to skeletal muscle contraction (Ch 10) i. AP increases Ca2+ around myofibrils ii. Ca2+ -troponin binding permits contraction to occur c. Action potential in cardiac muscle cells i. Rapid depolarization 1. Resting membrane potential is –90mV in ventricular cardiac muscle fibers (skeletal muscle fibers is –85mV, neuron is -70mV)) 2. At threshold (-75mV), voltage-gated fast Na+ channels open 3. Rapid inflow of Na+ causes rapid depolarization= +30mV 4. Channels close and inflow decreases ii. Plateau 1. Period of maintained depolarization: 0mV, lasts 0.175 sec (neuron or skeletal muscle= 1 msec) a. Active contraction continues until plateau ends 2. Due to opening of voltage-gated slow Ca2+ channels 3. Ca2+ influx balances Na+ active transport outward (and some K+ outflow: small # of voltage-gated K+ channels open) a. Significance? 4. Ca2+ influx causes more Ca2+ to be released from sarcoplasmic reticulum a. Significance?
  6. 6. iii. Repolarization 1. Voltage-gated Ca2+ channels close 2. Voltage-gated K+ channels open and K+ outflow restores –90mV 5) Energy for cardiac contractions a. Almost exclusively aerobic respiration i. Where does the oxygen come from? b. Primary energy sources: fatty acids and glucose Events of the Cardiac Cycle (The information below has been pulled from the reading on pages 682-693 BUT the specific items may not follow the order presented in the text.) 1) Cardiac cycle= all events associated with one heartbeat a. Alternate contraction and relaxation of chambers force blood from areas of high pressure to areas of low pressure i. Occurs on both sides of heart at the same time ii. Contraction causes high pressure b. Systole: contraction of a chamber c. Diastole: relaxation of a chamber 2) Phases of the cardiac cycle a. Atrial and ventricular diastole (Ventricular diastole- Late) i. AV valves open ii. SL valves closed iii. Ventricles fill passively (70%, ~105ml)) b. Atrial systole (ventricles in diastole) i. Atria contract ii. Forces last bit of blood into ventricles (~25ml) iii. At the end of atrial systole/ventricular diastole, ventricles contain the end-diastolic volume (EDV) c. Ventricular systole i. Ventricles are contracting due to depolarization while atria are relaxing and filling with blood ii. First phase 1. Increase in blood pressure in ventricle closes AV valves 2. Semilunar valves still closed 3. Isovolumetric contraction occurs iii. Second phase 1. Ventricular ejection occurs 2. Pressure in ventricle rises above blood vessels and SL valves open 3. Stroke volume
  7. 7. a. Ejection fraction 4. End-systolic volume (40%, ~50ml) d. Ventricular diastole (Relaxation Period) i. Ventricles and atria both are in diastole ii. Early 1. Pressure in ventricles drops below that in the blood vessels 2. Blood flows towards ventricles and closes SL valves 3. AV valves still closed (ventricle pressure still greater then atrial pressure) a. Causes isovolumetric relaxation 4. Blood still flows into atria iii. Late 1. Ventricular pressure drops below atrial pressure 2. AV valves open 3. Ventricular filling begins 3) Heart Sounds a. Auscultation b. 4 heart sounds occur but 1 and 2 are the only one loud enough to be heard by a stethoscope i. S1: lubb: AV valves closing ii. S2: dupp: SL valves closing iii. S3: blood movement iv. S4: blood movement c. Abnormal sounds i. Heart murmurs Cardiodynamics: Factors That Affect Cardiac Output 1) Cardiac output= the amount of blood ejected from the left ventricle into the aorta each minute a. Affected by stroke volume and heart rate i. CO= SV x HR ii. Close to total blood volume iii. If SV or HR increase, cardiac input will increase 2) Factor affecting heart rate a. Autonomic innervation i. Nervous control from cardiovascular center in medulla oblongata 1. Input from: a. Proprioceptors b. Chemoreceptors c. Baroreceptors 2. Sympathetic innervation: cardioaccelatory center
  8. 8. a. Effect: 3. Parasympathetic innervation: cardioinhibitory center a. Effect: ii. Autonomic tone 1. Resting: parasympathetic effects dominate a. Acetylcholine b. Effect: c. Slows heart rate 2. During exercise: sympathetic effects dominate a. Norepinephrine b. Effect: c. Increases heart rate iii. Atrial Reflex 1. Increase in venous return= increase R atrial stretch= increase sympathetic activity= increase heart rate iv. Venous Return (in addition to atrial reflex) 1. SA nodes stretching = more rapid depolarization b. Chemical regulation of heart rate i. Hormones 1. Epinephrine, Norepinephrine, thyroid hormone increase heart rate and contractility a. Tachycardia ii. Cations 1. Potassium 2. Calcium 3. Sodium c. Other factors in heart rate regulation i. Age ii. Gender iii. Physical fitness 1. Bradycardia iv. Body temperature 1. Hypothermia 3) Factors affecting stroke volume
  9. 9. a. A healthy heart will pump out the blood that entered its chambers during the previous diastoleIf more blood returns during diastole, more is ejected during the next systole b. Factor 1: Preload (degree of stretch on a ventricle) i. Proportional to end-diastolic volume ii. Frank-Starling law of the heart 1. “The more in, the more out” 2. What does this mean??? iii. Factors that determine EDV 1. Duration of ventricular diastole 2. Venous return iv. Frank-Starling Law equalizes output of the R & L ventricles and keeps the same volume of blood flowing in systemic and pulmonary circulations c. Factor 2: Contractility i. Strength of contraction at any given preload ii. Positive inotropic agents iii. Negative inotropic agents d. Factor 3: Afterload i. Amount of tension the contracting ventricle must produce to force open the semilunar vales and eject blood (20mmHg in pulmonary trunk, 80mmHg in aorta) ii. An increase in afterload, decreases stroke volume
  10. 10. a. A healthy heart will pump out the blood that entered its chambers during the previous diastoleIf more blood returns during diastole, more is ejected during the next systole b. Factor 1: Preload (degree of stretch on a ventricle) i. Proportional to end-diastolic volume ii. Frank-Starling law of the heart 1. “The more in, the more out” 2. What does this mean??? iii. Factors that determine EDV 1. Duration of ventricular diastole 2. Venous return iv. Frank-Starling Law equalizes output of the R & L ventricles and keeps the same volume of blood flowing in systemic and pulmonary circulations c. Factor 2: Contractility i. Strength of contraction at any given preload ii. Positive inotropic agents iii. Negative inotropic agents d. Factor 3: Afterload i. Amount of tension the contracting ventricle must produce to force open the semilunar vales and eject blood (20mmHg in pulmonary trunk, 80mmHg in aorta) ii. An increase in afterload, decreases stroke volume

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