Circulation Circulation = is a process used for the transport of oxygen, carbon! dioxide, nutrients and wastes through-out the body Heart = muscular organ about the size of your fist which pumps blood. It! is divided into 4 parts or chambers -lies at a slight angle, 2/3 to left of midline ( 7.5 cm left of midline ) -located in the mediastinum of the thoracic cavity -fist size (~ 6 in X 4 in wide) 14 cm X 9 cm - ~ 11 oz in weight - apex, pointed end above the diaphragm at the 5th intercostal area -beats ~ 100,000 times/day -pumps blood through ~ 60,000 miles of vessels Refer to fig. 15.2, 15.3, 15.4 p.582 & 583 Pericardium = covering enclosing the heart, made up of 2 layers! -Fibrous = tough outer part of connective tissue;!!! attaches to the diaphragm, sternum and vertebral column! -Serous = inner lining, produces serous fluid to!!! reduce friction to reduce friction!between the membranes the! moves within See figs 15.5, p. 584 & Plates 56 and 57
Heart is composed of 3 layers:! Epicardium: thin, outer protective layer! Myocardium: middle layer, bulk of heart composed of cardiac!! muscle!! Endocardium: thin, inner layer, lines the valves and contains!! specialized cells called Purkinje fibers 4 Heart Chambers:! 1. Right Atrium! 2. Left Atrium!! ( upper chambers ) ---> Atria!!!! - contain auricles = ear-like projections on!!!! anterior part of atria! 3. Right Ventricle! 4. Left Ventricle!! ( lower chambers ) ---> Ventricles A septum (partition) separates the Rt. & Lt. atria. On the back wall of the Rt. atrium is an oval depression ( Fossa ovalis ). It is the remains of an opening in the fetal heart for blood to by-pass the lungs -so it only moves between the two atria. In the fetus this opening is called the ( Foramen ovale ). Sometimes children are born with this still open and it requires open heart surgery to repair. The chambers are separated by valves which keep the blood flowing in one direction.
Flow of Blood through the Heart * Rt atrium receives deoxygenated blood ( w/o oxygen ) from veins and! pumps it into the Rt ventricle *Veins pump blood to the heart*! 3 main vessels (veins) empty blood into the Right Atrium:!!!! Superior Vena Cava- blood from upper body!! Inferior Vena Cava- blood from lower body!! Coronary Sinus- from the heart walls * Rt ventricle pumps it through the pulmonary artery which takes it to the! lungs to pick up oxygen * Blood returns to the heart, oxygenated ( w/ oxygen ) through the! pulmonary vein to the left atrium, then the blood is pumped into * The Lt ventricle, then the blood is pumped to the aorta, which is an artery,! which pumps blood to the rest of the body Arteries = pump away from the heart! Veins = pump to the heart The heart has 4 one-way valves (flaps) to keep blood moving in one direction and prevents back- flow of blood within the heart. These are called A-V valves, A = atrial; V = ventricular Murmur = leakage or back flow between heart valves
The 4 valves of the heart include:! Tricuspid Valve -- ( 3 flaps ) controls flow of blood between the Rt!!!! atrium & Rt ventricle! Bicuspid Valve -- (mitral valve, miter =turban-like hat )-- ( 2 flaps )!!! controls flow from Lt atrium to Lt ventricles! Pulmonary Valve -- controls flow from Rt ventricle into the pulmonary!!!! artery which is going to the lungs! Aortic Valve -- controls the flow of blood out to the body (between the!!! Lt ventricle & aorta)!! The pulmonary and aortic valves are also called semilunar valves! because they contain 3 half moon cusps in each Aorta = largest artery in the body Arteries = tough, flexible tubes ( so can expand and stretch ) which are!!! thick & muscular to handle high pressure!! - carry blood away from the heart Veins = carry blood to the heart!! *Superior vena cava and the Inferior vena cava are the large!! veins where blood returns to the heart from the body!! -not as elastic as arteries!! -larger inside diameter, but less muscular because they donʼt have!! to withstand the same amount of pressure as arteries Blood flows from the aorta to smaller branches of arterioles & capillaries
Arterioles = smallest arteries Capillaries = tiny tubes ~ 1 cell thick where O 2 / CO 2 diffuses Heart sounds are due to the contraction and relaxation of the chambers and the opening and closing of the valves! *lubb - dupp sound!! -lubb = when ventricles contract (A-V valves close)! -dupp = when ventricles relax ( Pulmonary & Aortic valves close ) Cardiac Cycle Involves blood flow through the heart with the contractions & relaxations of both atria and both ventricles. The contraction of both atria, then contraction of both ventricles constitute a single cardiac cycle---a single heart beat. Blood Pressure = the force of blood against he arterial walls, measured!!!!! w/ 2 numbers!! Systolic = each time heart beats ( increase pressure of arteries )!! Diastolic = when the heart relaxes between beats ( decrease!!!!! pressure ) Relaxation of the ventricles (ventricles diastole) and contraction of the atria (atrial systole) draws blood from the atria into the ventricles. Contraction of the ventricles (ventricular systole) forces blood through the semi-lunar (SL) valves into the major vessels and relaxation of the atria (atrial diastole) collects incoming blood. Atria are relaxed when the ventricles contract.
Each cardiac cycle is stimulated by special conducting cells in the heart. The heart receives impulses from the autonomic nervous system. Heart cells can beat on their own until they run out of energy. The heart contains pace-setting cells which stimulate other adjacent cells to contract and are specialized to conduct electrical signals. These cells are located in the wall of the Rt. atrium at an area called the sinoatrial (SA) node, also known as the pacemaker. The SA node generates an electrical impulse that spreads to both atria. The SA node then stimulates the atrioventricular node (AV), which relays the signal to the ventricles by a bundle of fibers called the AV bundle or bundle of His. At the apex of the heart, the AV bundle forms branches of fibers called Purkinjie fibers which reach the cells of the ventricles, causing the ventricles to contract stimultaneously (ventricular systole). A recording of the electrical events in the cardiac cycle is called an electrocardiogram (ECG or EKG). Metal electrodes are placed at specific areas on the skin. A single cardiac cycle produces deflections called waves that represent changes in electrical activity. These deflections are recorded with a pen on a moving strip of paper. The up and down movements of the pen correspond to the electrical changes of the heart and the distances between the deflections indicate the time between the cardiac cycle phases. See figs. 15.16, 15.21, 22, 23, & Clinical Application 15.2. An EKG involves 3 waves: -P wave = first, small, upward deflection, atria are contracting (systole) -QRS complex Q, R, S waves = slightly downward at the beginning then!!!!! large upward spike, triangular shape,!!!!! then downward deflection. Impulse!!!!! spreads through the ventricles (systole) -T wave = ventricles repolarize, dome-shaped
! * Larger P wave indicates an enlarged atrium!! * An longer P-R interval (start of P to start of R) indicates scarring!!! or inflammation of atria or AV node!! * Larger Q wave may indicate heart attack!! * Larger R wave may indicate enlarged ventricles Arrhythmias Tachycardia = rapid heartbeat Bradycardia = slow heartbeat Fibrillations = uncoordinated contraction of the myocardium When small vessels in the heart thicken and lose elasticity they donʼt expand well and the blood pressure increases, so the heart works harder to pump blood through the narrow arteries. This restricted blood flow can cause kidney damage or blindness. Coronary arteries = arteries that support the heart muscle -lesions or hardening of arteries is called atherosclerosis, this forms blockages in the arteries, blood flow to the heart is reduced and / or blocked off and the heart muscle is starved for oxygen; this results in a heart attack. *See below We need to control the amount of fat in our diet. Eat less fatty foods ( meats, dairy products, deep fried foods ). Need to eat more veggies, fruits, lean meats and complex carbohydrates. In addition need to avoid smoking and need to exercise more. Ischemia = weakened cells due to reduced oxygen supply Angina pectoris = chest pain due to ischemia of the myocardium!!!! -causes: stress, heavy exercise after heavy meal, heart!!!! attack; nitroglycerin pills help dilate vessels Myocardial Infarction = A Coronary --- Heart Attack- more serious, death of tissue due to interrupted blood flow caused by a thrombus or embolus in a coronary artery