Lecture 6 CVS Physiology 1 PDF

CVS The heart and blood vessels constitute a closed system, through which the blood circulates. Cardiovascular system Heart Blood vessels 1- Elastic vessels: arteries...

CVS The heart and blood vessels constitute a closed system, through which the blood circulates. Cardiovascular system Heart Blood vessels 1- Elastic vessels: arteries 2- Resistant vessels: arterioles 3- Exchange vessels: capillaires 4- Capacitance vessels: veins  Systemic circulation (general circulation): (from heart to body cells then heart again) The blood leaves the left ventricle via the aorta  arteries  arterioles  capillaries  venules  veins  SVC & IVC right atrium. Pulmonary circulation (lesser circulation) (from heart to lung then heart again) Blood leaves the right ventricle via the pulmonary artery  two pulmonary arteries (one supplying the right lung and the other to the left)  pulmonary arterioles  pulmonary capillaries  venules  which unit to form 4 pulmonary veins  left atrium.  The Heart It is a hollow muscular organ Site: The left side of the thoracic cavity partly behind the sternum Size Size of a man's fist Ventricles  Structure of the Heart A. 2 Atria (Rt and Lt) Functions of atria: 1. Blood reservoirs during ventricular systole. 2. Pumping 30% of venous return into the ventricles during their diastole. 3. Atria contain SAN and AVN which are important for initiation and propagation of heartbeat. B. 2 Ventricles (Rt and Lt) Functions of ventricles : Pump blood into the aorta and pulmonary artery  Cardiac valves: allow passage of blood only in one direction inside the heart; - from atria to ventricles - from ventricles to aorta and pulmonary artery Types of cardiac valves: 1. The atrioventricular valves (A-V valves): a) The tricuspid valve (separates right atrium from right ventricle) b) The mitral valve (separates the left atrium from the left ventricle) 2. The semilunar valves: a) Aortic valve: It communicates the left ventricle with the aorta. b) Pulmonary valve: It communicates the right ventricle with the pulmonary artery.  Properties of Cardiac Muscle I- Rhythmicity: It is the ability of heart to beat regularly. II- Excitability: It is the ability of the cardiac muscle to respond to stimuli. III. Conductivity: It is the ability to conduct excitation wave from one part of the heart to another. IV. Contractility: It is the ability of the cardiac muscle to contract N.B. Rhythmicity is myogenic (not neurogenic). The nerves control the rate but do not initiate the beat. Impulse (action potential) is originated from SAN "pace maker of the heart". Then propagated to the AVN Then through AV bundle To right and left bundle branch To purkinji fibers To the rest of the ventricular muscles.  Cardiac Cycle Def., Events that occur in the heart from the beginning of one heartbeat to the beginning of the next Cycle Heartbeat Next Heartbeat  Cardiac Cycle Duration: Normal heart rate is 75 b/min So, the duration of each beat or cycle = 60/75 = 0.8 sec 0.8 sec Start Start  Cardiac Cycle Phases : Each cardiac cycle consists of; 1) A period of contraction called systole (0.3 sec in duration). 2) A period of relaxation called diastole (0.5 sec in duration).  Heart Rate Normal count of heart rate at rest is approximately 60 - 90 beats/ minute. Bradycardia: heart rate less than 60 beat / minute. Tachycardia: heart rate more than 100 beat / minute. Methods of counting the HR: 1. Counting the radial pulse or apex beats/min. 2. Counting the cardiac cycles or heart sounds by stethoscope. 3. Recording the ECG.  Methods of counting the HR Counting the radial pulse /min 1- Counting heart sounds by 2- stethoscope ECG 3- Physiological variations of heart rate: 1. Age: In newly born infant, the heart rate is about 120 beats/min 2. Sex: The heart rate is higher in females than in males 3. Physical training: The basal heart rate is slower in well-trained athletes at rest (50-60 beats/min) than in non trained persons. 4. Sleep: quiet sleep diminishes the heart rate by 10-20 beats/min. 5. Emotional excitement or muscular exercise: accelerates the heart to above 100 beats/min. 6. Body temperature: A rise of body temperature 1oC increases the heart rate by 10 beats/min 7. Hypoxia (↓O2 supply ): increase heart rate (tachycardia)  Regulation of Heart Rate Nervous Physical Chemical Regulation Regulation Regulation  Parasympathetic  rise of temp 1°C→ ↑es  Adrenaline, atropine, → bradycardia the heart rate by 10 thyroxine → ↑es the HR  Sympathetic → beats/min  Acetylcholine and tachycardia  drop of temp 1°C→ morphine: → ↓es the HR ↓es the heart rate by 10 beats/min Def Cardiac output (COP) is the volume of blood pumped by each ventricle per minute. Value Normally, it is about 5 liters / min during rest. COP = Heart rate x Stroke volume 20  Cardiac Output End-diastolic volume Volume in ventricles at the end of diastole = 130 ml End-systolic volume Volume in ventricles at the end of systole = 60 ml Stroke volume (SV) It is the volume of blood pumped by each ventricle per beat = 70 ml SV= EDV- ESV 21 22  Venous Heart Myocardial ABP Return Rate Contractility ↑VR → ↑COP  Moderate  ↑ABP → ↓COP COP is directly changes in HR  ↓ ABP → ↑COP proportional to has no effect on contractility COP  Marked changes in HR →↓ COP