Exploring the Heart: Chambers and Blood Vessels

HUMAN ANATOMY AND PHYSIOLOGY LECTURE CHAMBERS AND BLOOD VESSES CHAPTER 12 - HEART CHAMBERS HEART • • • • • • • Size - size of a fist and weighs less than 1 lb. Location - between lungs in thoracic cavity Orientation - apex (bottom) towards left side Regulates blood supply Generates blood pressure Routes blood Ensures 1-way blood flow HEART COVERINGS • • • • • • • • Pericardium - double-layered sac that anchors and protects heart Parietal pericardium - membrane around heart’s cavity Visceral pericardium - membrane on heart’s surface Pericardial cavity - space around heart 4 Chambers o left atrium (LA); right atrium (RA) o left ventricle (LV); right ventricle (RV) Coronary sulcus - separates atria from ventricles Atria o Upper portion; Small, thin walled o Holding chambers o Contract minimally to push blood into ventricles o Interatrial septum - separates right and left atria Ventricles o Lower portion; Thick, strong walled o Pumping chambers o Contract forcefully to propel blood out of heart o Interventricular septum - separates R&L ventricles HEART LAYERS VALVES • • • • • Epicardium - surface of heart (outside) Myocardium - thick middle layer made of cardiac muscle Endocardium - smooth, inner surface • • Cardiac Muscle o 1 centrally located nucleus o Branching cells o Rich in mitochondria o Striated (actin and myosin) o Ca2+ and ATP used for contractions o Intercalated disks connect cells • • structures that ensure 1 way blood flow Atrioventricular valves (AV) o between atria and ventricles o Tricuspid valve ▪ AV valve between RA and RV ▪ 3 cusps o Bicuspid valve (mitral) ▪ AV valve between LA and LV ▪ 2 cusps o Chordae tendineae - attached to AV valve flaps; support valves Semilunar valves (SV) o Pulmonary - base of pulmonary trunk o Aortic - base of aorta What happens when Bicuspid Valve is Open? o Blood flows from LA into LV. o Aortic semilunar valve is closed. o Tension on chordae tendineae is low. What happens when Bicuspid Valve is Closed? o Blood flows from LV into aorta. o Aortic semilunar valve is open. o Tension on chordae tendineae is high. RIGHT SIDE OF HEART • • Pulmonary circuit o carries blood from heart to lungs o blood is O2 poor, CO2 rich Right Atrium - receives blood from 3 places: superior and inferior vena cava and coronary sinus o Superior vena cava - drains blood above diaphragm (head, neck, thorax, upper limbs) o • Inferior vena cava - drains blood below diaphragm (abdominopelvic cavity and lower limbs) o coronary sinus - drains blood from myocardium Right Ventricle - opens into pulmonary trunk o Pulmonary trunk - splits into right and left pulmonary arteries o Pulmonary artery - carry blood away from heart to lungs • • • LEFT SIDE OF HEART • • • • Systemic circuit o carries blood from heart to body o blood is O2 rich, CO2 poor Left Atrium - 4 openings (pulmonary veins) that receive blood from lungs Left Ventricle o opens into aorta o thicker, contracts more forcefully, higher blood pressure than right ventricle has to get to body Aorta - carries blood from LV to body • • CONDUCTION SYSTEM OF THE HEART • • • • • BLOOD FLOW THROUGH HEART 1. 2. 3. 4. 5. 6. 7. Superior and Inferior Vena Cava RA Tricuspid valve RV Pulmonary semilunar valve Pulmonary trunk Pulmonary arteries 8. 9. 10. 11. 12. 13. 14. 15. Depolarization phase o Na+ channels open o Ca2+ channels open Plateau phase: o Na+ channels close o Some K+ channels open o Ca2+ channels remain open Repolarization phase: o K+ channels are open o Ca2+ channels close Plateau phase - prolongs action potential by keeping Ca2+ channels open. In skeletal muscle action potentials take 2 msec, in cardiac muscle they take 200-500 msec. Lungs Pulmonary veins LA Bicuspid valve LV Aortic semilunar valve Aorta Body contraction of atria and ventricles by cardiac muscle cells Sinoatrial node (SA node) o in RA where action potential originates o functions as pacemaker o large number of Ca2+ channels Right and left bundle branches - conduct action potentials from the atrioventricular bundle through Purkinje fibers to the ventricular muscle. Path of Action Potential through Heart 1. SA node 2. AV node (atrioventricular) 3. AV bundle 4. Right and Left Bundle branches 5. Purkinje fibers Process of Conduction System of the Heart 1. Action potentials originate in the sinoatrial (SA) node and travel across the wall of the atrium from the SA node to the atrioventricular (AV) node 2. Action potentials pass through the AV node and along the atrioventricular (AV) bundle, which extends from the AV node, through the fibrous skeleton, into the interventricular septum 3. The AV bundle divides into right and left bundle branches, and action potentials descend to the apex of each ventricle along the bundle branches 4. Action potentials are carried by the Purkinje fibers from the bundle branches to the ventricular walls BLOOD SUPPLY TO HEART • • • Coronary arteries o supply blood to heart wall o originate from base of aorta (above aortic SV) Left coronary artery o has 3 branches o supply blood to anterior heart wall and left ventricle Right coronary artery o originates on right side of aorta o supply blood to right ventricle ELECTRICAL ACTIVITY OF THE HEART ACTION POTENTIALS IN CARDIAC MUSCLE • Changes in membrane channels’ permeability are responsible for producing action potentials and is called pacemaker potential. ELECTROCARDIGRAM (ECG) • • Record of electrical events within the heart. Used to detect abnormal heart rates or rhythms, abnormal conduction pathways, hypertrophy or atrophy of the heart, and the approximate location of damaged cardiac muscle • • • • • P wave - atrial depolarization QRS complex - ventricular depolarization, contain Q, R, S, waves T wave - ventricular repolarization Atrial contraction - occurs during the PQ interval QT interval - ventricles contract and relax o • CARDIAC CYCLE • • • • • • • • • • • • Heart - 2 side by side pumps: right and left Atria - primers for pumps Ventricles - power pumps Cardiac Cycle - repetitive pumping action which includes contraction and relaxation Cardiac muscle contractions - produce pressure changes within heart chambers. Pressure changes - responsible for blood movement. Blood moves from areas of high to low pressure. Atrial systole - contraction of atria Ventricular systole - contraction of ventricles Atrial diastole - relaxation of atria Ventricular diastole - relaxation of ventricles Heart Sounds • Stethoscope - used to hear lung and heart sounds • First sound is lubb, second is dupp • Sounds result from opening and closing valves • Murmurs - due to faulty valves REGULATION OF HEART FUNCTION • • • Stroke Volume - volume of blood pumped per ventricle per contraction; 70 ml/beat Heart Rate - number of heart beats in 1 min.; 72 bpm Cardiac Output - volume of blood pumped by a ventricle in 1 min; 5 L/min.; CO = SV x HR INTRINSIC REGULATION OF HEART • • • • • • Mechanisms contained within heart Venous return - amt. of blood that returns to heart Preload - degree ventricular walls are stretched at end of diastole Venous return, preload, and stroke volume are related to each other Starlings Law of the Heart o relationship between preload and stroke volume o influences cardiac output o Ex. Exercise increases venous return, preload, stroke volume, and cardiac output After load - pressure against which ventricles must pump blood EXTRINSIC REGULATION OF HEART • • • • • Mechanisms external to heart Nervous or chemical regulation Sympathetic stimulation - increases stroke volume and heart rate Parasympathetic stimulation - decreases heart rate Nervous Regulation: Baroreceptor Reflex o mechanism of nervous system which regulates heart function o keeps heart rate & stroke volume in normal range Baroreceptors -monitor blood pressure in aorta and carotid arteries (carry blood to brain) o changes in blood pressure cause changes in frequency of action potentials o involves medulla oblongata Chemical Regulation: Chemoreceptor Reflex o Chemicals - affect heart rate and stroke volume o Epinephrine and norepinephrine - from adrenal medulla can increase heart rate and stroke volume o excitement, anxiety, anger an increase cardiac output o depression can decrease cardiac output o medulla oblongata has chemoreceptors for changes in pH and CO2 o K+, Ca2+, and Na+ affect cardiac function HEART DISEASES AND DISORDERS • • • • • • • • Heart Attack o Thrombus ▪ blood clot blocks coronary blood vessel causes heart attack ▪ daily aspirin can prevent by thinning blood o Infarct - area that dies from lack of O2 Heart Procedures o Angioplasty - procedure open blocked blood vessels o Stent - structures inserted to keep vessels open o Bypass - procedure reroutes blood away from blocked arteries Endocarditis - inflammation of the endocardium Pericarditis - inflammation of the pericardium Cardiomyopathy - disease of the myocardium; weakened cardiac muscle, causing chambers of the heart to enlarge Rheumatic heart disease - results from a streptococcal infection in young people; can cause rheumatic fever Coronary heart disease - reduces the amount of blood the coronary arteries can deliver to the myocardium Coronary thrombosis - formation of blood clot in a coronary artery