Cardiovascular System Lecture 2 PDF

Cardiovascular system (心血管系统/循環系統) NUR1019 – Lecture 2 Dr. Wilson Leung 1 Learning Outcomes 1. Anatomy of the Heart 2. Physiology of the Heart 3. Anatomy of the Blood Vessels 4. Physiology of Circulation 5. Circulatory Routes...

Cardiovascular system (心血管系统/循環系統) NUR1019 – Lecture 2 Dr. Wilson Leung 1 Learning Outcomes 1. Anatomy of the Heart 2. Physiology of the Heart 3. Anatomy of the Blood Vessels 4. Physiology of Circulation 5. Circulatory Routes 2  Pulmonary Circuit (肺循環) Cardiovascular System Systemic Circuit (體循環) 3 Anatomy of the heart 4 Introduction - Shape/Size, Location, and Orientation of the Heart Hollow, cone-shaped, muscular organ Size: make a fist and then clasp the fist with your opposite hand Located in mediastinum (central compartment of the thoracic cavity 胸腔); lies on its right side that rests on the diaphragm The base (the widest part) of the heart is superior to its apex (the pointed tip), which rests on the diaphragm The base (the widest part) of the heart is direct toward the right shoulder, and the apex (the pointed tip) points to the left hip The base is deep to the second rib, and the apex is at the level of the fifth intercostal space 5 Introduction - Functions of the Heart Keep oxygenated blood separate from partially deoxygenated blood Keep the blood flowing in one direction – blood flows away from and then back to the heart in each circuit Create blood pressure, which moves the blood through the circuits Regulate the blood supply based on the current needs of the body Serve as an endocrine gland, producing atrial natriuretic hormone (ANH) for regulation of blood pressure 6 The Wall and Coverings of the Heart 3 layers of the heart wall: endocardium, myocardium and epicardium 1. Endocardium - Inner layer of heart wall - Its smooth nature helps prevent blood from clotting unnecessarily. 2. Myocardium - Thickest/central part of heart wall - Made of cardiac muscle - Contraction makes the heart beat for pumping blood. 3. Epicardium - Outermost layer of the heart - Also called the visceral serous pericardium - Functions: protect the heart, confine it to its location, and prevent it from overfilling 7 The Coverings of the Heart After covering the heart, the epicardium (visceral serous pericardium) folds back over the heart and create another layer called parietal serous pericardium. The space between the two layers is the pericardial cavity containing pericardial fluid (for reducing friction during heartbeat). The parietal serous pericardium is then fused to the outermost fibrous pericardium, which is a thick layer of fibrous connective tissue and contains major blood vessels. 8 Chambers of the Heart 4 hollow chambers: 2 superior atria (singular: atrium 心房) and 2 inferior ventricles (心室) Each atrium has an anterior pocket-like flap called auricle - It will expand fully when the atrium fills with blood - Contain cells that produce atrial natriuretic hormone (ANH) The atria are separated by the interatrial septum and the ventricles are separated by the interventricular septum - The heart’s pulmonary circuit (the right side) is completely separated from its systemic circuit (the left side) by the septa 9 Chambers of the Heart – Right Atrium Receives O2-poor blood from 3 veins: - Superior vena cava - Inferior vena cava - Coronary sinus - collects blood from the heart muscle Venous blood leaves right atrium through the right atrioventricular (AV) valve (tricuspid) → right ventricle - Directs the flow of blood - Prevents backflow - Has three cusps or flaps 10 Chambers of the Heart – Right Ventricle Thick-walled pump The cusps of the tricuspid valve are connected to fibrous cords, called chordae tendineae - Connected to the papillary muscles, which are the conical extensions of the myocardium, in ventricle Blood passes through the pulmonary semilunar valve into the pulmonary trunk and then the right and left pulmonary arteries to go to the lungs for gas exchange 11 Chambers of the Heart – Left Atrium Receives O2-rich blood from the lungs Blood enters the left atrium through 4 pulmonary veins (i.e., 2 veins from each lung) Blood leaves left atrium through the left AV valve (bicuspid or mitral valve) → left ventricle 12 Chambers of the Heart – Left Ventricle Very thick-walled pump Forms the apex of the heart Blood leaves the left ventricle through the aortic semilunar valve and enters the aorta to deliver blood to the body Just beyond the aortic semilunar valve lie the first branches from the aorta – coronary arteries - Blood vessels that lie on and nourish the heart itself The rest of the blood stays in the aorta, which continuous as the arch of the aorta and then the descending aorta 13 Operation of the Heart Valves AV (atrioventricular) valves – tricuspid and bicuspid (mitral) valves - Open when ventricles are filling with blood - Forced closed when ventricles begin to contract - Papillary muscles contract, preventing valves from reverting into an atrium Semilunar valves – pulmonary and aortic - Normally closed - Contraction of ventricles forces valves open - Closed again due to the blood falling backward toward the valve when the ventricles relax 14 Heart Sounds First sound, “lub” - Ventricles begin to contract - AV valves close - Lasts longer and has a lower pitch Second sound, “dup” - Ventricles relax - Semilunar valves close Heart murmurs (雜音) - Due to ineffective, leaky valves (incompetent valves) - Valves do not close properly - Allows blood to backflow into atria or ventricles after valves have closed 15 Coronary Circulation The left and right coronary arteries branch from the aorta (just superior to the aortic semilunar valve) - Coronary arteries branch - The heart is encircled by small blood vessels After blood passes through cardiac capillaries it enters the cardiac veins Cardiac veins enter the coronary sinus to the right atrium 16 Anterior View of Exterior Heart Anatomy 17 Physiology of the Heart 18 Conduction System of the Heart The conduction system of the heart is the route of specialized cardiac muscle fibers that initiates and stimulates contraction of the atria and ventricles. Intrinsic – does not need external nervous stimulation Coordinates contraction of atria and ventricles - The atria contract simultaneously, and the ventricles then contract simultaneously. 19 Conduction System of the Heart – Nodal Tissue The heartbeat is controlled by nodal tissue Has muscular and nervous characteristics SA (sinoatrial) node – upper posterior wall of the right atrium Initiates the heartbeat – pacemaker (起搏器) (intrinsic rate is the fastest in the system) Sends out an excitation impulse every 0.85 seconds (~70 beats/min) Signals spread out over the atria, causing them to contract AV (atrioventricular) node – base of the right atrium Impulse is delayed that allows the atria to finish their contraction before the ventricles begin their contraction Signals the ventricles to contract Atrioventricular bundle (AV bundle; bundle of His) and bundle branches Travels down the interventricular septum toward the apex Purkinje fibers Delivers impulse to the myocardium of the ventricles and papillary muscles Ectopic pacemaker Develops a rate of contraction that is faster than SA node May cause an extra beat Caffeine and nicotine can stimulate an ectopic pacemaker 20 Cardiac Cycle All events that occur during one heartbeat - On average, the heart beats at about 70 bpm (varying from 60-100 bpm) at rest - Systole – contraction of heart muscle - Diastole – relaxation of heart muscle 3 phases of a cardiac cycle: a. Phase 1: Atrial Systole; 0.15s - Both atria are in systole (contracted) - Both ventricles are in diastole (relaxed) - Both AV valves are open - Blood enters the ventricles - The semilunar valves are closed - Blood flowing backward causes the AV valves to close (“lub” sound) 21 Cardiac Cycle 3 phases of a cardiac cycle: b. Phase 2: Ventricular Systole; 0.30s - Both ventricles are in systole (contracted) - Both atria are in diastole (relaxed) - Semilunar valves are forced open as blood is pumped out of the ventricles - Both AV valves are closed - At the end of ventricular systole, the backflow of blood in the pulmonary artery and aorta forces the semilunar valves to slam shut (“dup” sound). c. Phase 3: Atrial and Ventricular Diastole; 0.40s - Both atria and both ventricles are in diastole (relaxed) - Blood returning to the heart - Both AV valves are open - The semilunar valves are closed 22 Stages in the Cardiac Cycle 23 Cardiac Cycle – Electrocardiogram (ECG or EKG) (心電圖) A graph that records the electrical activity of the myocardium (muscle action potential) during a cardiac cycle Helps a physician detect and diagnose the cause of an irregular heartbeat (arrhythmias 心 律不整) Components of an ECG - P wave – depolarization of the atria; impulse travels from the SA node to the AV node; leads to atrial systole (contraction) - QRS complex – (1) Depolarization of the ventricles that leads to ventricular systole; (2) Repolarization of the atria that leads to atrial diastole (relaxation) - The QRS complex shows greater voltage changes than the P wave because the ventricles have more muscle mass than the atria. - Atrial diastole (repolarization) does not show up on an ECG as an independent event because the voltage changes are masked by the QRS complex. - T wave – repolarization of the ventricles that leads to ventricular diastole Heart arrhythmias (心律不正) - Bradycardia (心跳過慢) – 100 beats/min - Fibrillation (心房顫動) – rapid, uncoordinated contractions, potentially deadly 24 Electrocardiogram A portion of an electrocardiogram An enlarged normal cycle 25 Cardiac Output (心輸出量) Volume of blood pumped out of a ventricle in one minute Average cardiac output at rest is 5,250 ml/minute (= total volume of blood in the human body) Dependent on 2 factors: - Cardiac output (mL/min) = Heart rate (心率) [beats per min (bpm)] x Stroke volume (每搏輸出量) (mL/beat) 26 Cardiac Output (心輸出量) 1. Heart rate (bpm) - Can be altered by the autonomic nervous system (自主神經系統) – cardioregulatory center in the medulla oblongata - Parasympathetic (副交感神經) motor signals (conducted by the vagus nerve) cause the heart slow - Sympathetic (交感神經) motor signals cause the heart rate to increase - Receive sensory input from receptors within the cardiovascular system - e.g., Stretch receptors called baroreceptors in the aorta and carotid arteries – If blood pressure falls, as it sometimes does when we stand up quickly, the baroreceptor signal the cardioregulatory center to increase the heart rate - Cardioregulatory center is also under the influence of the cerebrum and the hypothalamus - e.g., Feeling anxious will increase the heart rate - The adrenal medulla releases the hormone norepinephrine and epinephrine to increase the heart rate. - Activities, like meditation (冥想) or yoga, lead to activation of the vagus nerve, which slows the heart rate. 27 Control of Heart Activity 28 Cardiac Output (心輸出量) 2. Stroke volume (每搏輸出量) in mL/beat - Amount of blood pumped by a ventricle each time it contracts - Depends on the strength of contraction - Influenced by blood electrolyte concentration, the activity of the autonomic nervous system (sympathetic and parasympathetic), and hormones from the adrenal medulla - The strength of contraction influenced by 2 factors: 1. Venous return (靜脈回流) 2. Differences in blood pressure between the ventricles and their attached arteries 29 Cardiac Output (心輸出量) 2. Stroke volume (每搏輸出量) in mL/beat 1. Venous return (靜脈回流) - Heart adjusts strength of its own contraction beat by beat based on the amount of blood entering the heart chambers - Frank Starling Law – the more blood entering the heart (stretches the walls), the stronger the contraction (higher stroke volume) - When more blood is returned to the heart, the ventricular walls are stretched more and they will contract more and more forcefully. - Exercise squeezes veins within skeletal muscles and returns blood faster. 30 Cardiac Output (心輸出量) 2. Stroke volume (每搏輸出量) in mL/beat 2. Differences in blood pressure between the ventricles and their attached arteries - Strength of ventricular contraction must be strong enough to oppose blood pressure in the aorta and pulmonary arteries to open SL valves - If a person has hypertension or atherosclerosis, the opposing arterial pressure may reduce the effectiveness of contraction and stroke volume 31 Anatomy of Blood Vessels 32  Types and Functions of Blood Vessels 3 types of vessels a. Arteries (動脈) b. Capillaries (微血管) c. Veins (靜脈) Vessels function to: a. Transport blood and its contents b. Carry out gas exchange c. Regulate blood pressure d. Direct blood flow 33 Arteries (動脈) and Arterioles Transport blood away from the heart Thick, strong walls composed of 3 layers: - Tunica intima (interna) – endothelium - Tunica media – middle layer of smooth muscle and elastic fibers - Tunica externa – outer connective tissue layer Arterial walls are thick that they are supplied with their own blood vessel The radius of an artery allows the blood to flow rapidly Elasticity allows an artery to expand and recoil - Blood continuous to flow in an artery even when the heart is diastole Arterioles are small arteries (just visible to naked eyes) - Constriction and dilation affect blood distribution and blood pressure - Autonomic nervous system regulates the number of arterioles that are contracted - Helps to determine blood pressure - ↑ Number of arterioles contract → ↑ Resistance to blood flow → ↑ Blood pressure 34 Capillaries (微血管) Arterioles branch into capillaries, which are extremely small, microscopic blood vessels Walls are composed of only one layer of endothelial cells connected by tight junctions - Thin walls easily allow gases, nutrients, and wastes to diffuse between the capillary and the surroundings cells Not all capillary beds (networks of many capillaries) are in use at the same time - Most capillary beds have a shunt (分流) that allows blood to move directly from an arteriole to a venule when the capillary bed is closed - Precapillary sphincters control the entrance of blood into capillaries - After a meal, the capillary beds of the digestive tract are usually open. - During muscular exercise, the capillary beds of the skeletal muscles are open. 35 Capillary Exchange Takes place across thin capillary walls Most cells of the body are near a capillary Oxygen and nutrients leave a capillary Cellular wastes and carbon dioxide enter a capillary Exchange is reversed in pulmonary capillaries - Oxygen enter blood and carbon dioxide leaves Substances leaving and entering a capillary pass through tissue fluid - The fluid that surround the cells of the body - A water-based solution that contains sodium chloride, other electrolytes, and scant (不足) protein - Substances that leave a capillary pass through tissue fluid before entering the body’s cells, and substances that leave body’s cells pass through tissue fluid before entering the capillaries - Tissue fluid stays relatively constant because of capillaries exchange - Any excess tissue fluid is collected by lymphatic capillaries, which are always found near blood capillaries 36 Capillary Exchange 3 processes influencing capillary exchange: a. Blood pressure (an outward force) – pushes blood through the capillary and against vessel walls b. Diffusion – movement of a substance from an area of higher concentration to an area of lower concentration c. Osmotic pressure (an inward force) – force caused by a difference in solute concentration on either side of a membrane 37 Capillary Exchange Arterial end of capillary - Blood pressure (30 mmHg) (i.e., outward force) is higher than osmotic pressure (21 mmHg) (i.e., inward force) - Water and other small molecules (e.g. glucose and amino acids) are pushed out. - Red blood cells and a large proportion of the plasma proteins generally remain in a capillary because they are too large to pass through its wall. Midsection of capillary - Diffusion takes place along the length of the capillary. - Oxygen, glucose, and amino acids that are needed by cells move out of the capillary. - Carbon dioxide and other wastes as a result of metabolism diffuse into a capillary. Venous end of capillary - Blood pressure is reduced (15 mmHg) and osmotic pressure is the same (21 mmHg), but now higher than blood pressure. - Water and other wastes tend to diffuse into a capillary. Only about 85% of the water that leaves a capillary at the arterial end returns at the venous end – reason for the lymphatic system 38 Veins (靜脈) and Venules Return blood to the heart Venules - Drain blood from the capillaries - Join together to form veins Vein walls are thinner than arterial walls – tunica media (less muscle and elastic fibers) is thinner Valves in veins prevent backward flow of blood At any given time, over half of the body’s blood is in veins - Can act as a blood reservoir by constriction to provide more blood to the rest of the body during hemorrhaging (出血) 39 Physiology of Circulation 40 Velocity of Blood Flow Circulation – the movement of blood through blood vessels from the heart to the body and back to the heart Flows the fastest in the arteries due to the contraction of the left ventricle Flows the slowest in capillaries - Cross-sectional area is at its maximum - Allows time for gas, nutrient, and waste exchange Blood flow increases as venules combine to form veins Velocity of blood returning to the heart is lower than that of blood leaving the heart - Contractions of the powerful left ventricle generate a greater velocity for arteriole blood 41 Blood Pressure The force of blood against blood vessel walls Highest in the aorta Decreases with distance from left ventricle and is lowest in the venae cavae (0mm Hg) The pressure difference can be explained by the action of the heart. During systole, the left ventricle is pumping blood out of the heart, and during diastole the left ventricle is resting. 42 Blood Pressure Mean arterial blood pressure (MABP) - Pressure in the arterial system averaged over time - A better indicator of perfusion to vital organs than systolic blood pressure - Equals cardiac output x peripheral resistance a. Increasing cardiac output increases MABP - The greater the amount of blood leaving the left ventricle, the greater the pressure of blood against the wall of an artery b. Peripheral resistance: the resistance to the free flowing of blood in the body’s blood vessels – Depends on arterial diameter and length - The smaller the blood vessel or the longer the blood vessel the greater the resistance - The greater the resistance the higher the MABP - An obese person is apt to have high blood pressure because about 200 miles of additional blood vessels develop for each extra pound of adipose (fat) tissue 43 Blood Pressure and Cardiac Output The faster the heart rate the greater the cardiac output; as cardiac output increases, blood pressure increases The larger the stroke volume, the larger the cardiac output, the greater the blood pressure Stroke volume and heart rate increase blood pressure only if the venous return is adequate Venous return depends on: 1. A blood pressure difference – the blood pressure is higher in systemic veins than in the right atrium, which enables venous blood to empty into the heart 2. The skeletal muscle pump and the respiratory pump - Contraction of skeletal muscles compress the walls of veins causing blood to move past a valve - Valves prevent backward flow (skeletal muscle pump) - During inhalation, thoracic pressure falls and abdominal pressure rises and blood will flow from an area of higher pressure (abdominal cavity) to an area of lower pressure (thoracic cavity) (respiratory pump) 3. Total blood volume - If blood volume decreases (e.g. due to a hemorrhage), venous return blood ↓ → blood pressure falls - If blood volume increases (e.g. due to water retention), venous return blood ↑ → blood pressure rises 44 Blood Pressure and Peripheral Resistance Neural regulation - Baroreceptors in blood vessels near the heart detect changes in blood pressure and signal the cardioregulatory center - If blood pressure drops, the cardioregulatory center will activate vasomotor center in the medulla oblongata, then stimulates sympathetic nerve fibers to increase heart rate and constrict arterioles - Increase heart rate increases cardiac output - Constricting the arterioles increases peripheral ↑ Blood pressure resistance 45 Blood Pressure and Peripheral Resistance Hormonal regulation a. Epinephrine and norepinephrine increase heart rate and constrict arterioles in the skin, abdominal viscera, and kidneys - Arteriolar vasoconstriction increases blood pressure by increasing peripheral resistance in these large vascular beds b. Renin-angiotensin-aldosterone system - When the blood volume and blood sodium level are low, the kidneys secrete enzyme renin - Renin converts angiotensinogen to angiotensin I - Angiotensin-converting enzyme in lungs converts angiotensin I to angiotensin II - Angiotensin II stimulates the adrenal cortex to release aldosterone - Angiotensin II constricts the arterioles ↑ Blood pressure - Aldosterone causes the reabsorption of sodium and water in the kidneys 46 Blood Pressure and Peripheral Resistance c. Antidiuretic hormone (ADH) causes the reabsorption of water and vasoconstriction of smooth muscle in arteries and veins throughout the body - Secreted by posterior pituitary - ↑ Blood volume + ↑ peripheral resistance → ↑ Blood pressure d. Atrial natriuretic hormone (ANH) inhibits renin and aldosterone secretion; sodium and water are excreted - Release when the atria of the heart are stretched due to increased blood volume - Blood volume decrease and then blood pressure decrease 47 Hormonal Control of Blood Volume 48 Evaluating Circulation 1. Pulse (脈搏) - Alternating expansion and recoil of arterial walls - Can be felt in superficial arteries (pulse points) - Most common points a. Radial artery b. Common carotid artery - Pulse rate normally indicates the rate of the heartbeat - The arterial walls pulse whenever the left ventricle contracts. 49  Evaluating Circulation 2. Blood pressure - Usually measured in brachial artery - Sphygmomanometer is an instrument that records pressure changes - The blood pressure cuff is inflated until no blood flows through the artery - Thus no sounds can be heard through the stethoscope (聽診 器) - Korotkoff sounds - Systolic pressure produced when the pressure in the cuff is released and blood begins to hit the arterial walls; tapping sound - Diastolic pressure is when sounds end - Normal blood pressure is 120/80 - Higher number is systolic pressure (收縮壓) (i.e., SBP) – pressure recorded when the left ventricle contracts - Lower number is diastolic pressure (舒張壓) (i.e., DBP) – pressure recorded when the left ventricle relaxes - Hypertension – high blood pressure (>140/90) - Hypotension – low blood pressure (