Circulatory System Lesson 2 - The Human Heart (PDF)

Circulatory System: Lesson #2 The Human Heart The Human Heart The human heart Right Left weighs between 200 to Side Side 425 grams and is a little larger than the size of your fist The heart is located between your lungs in the middle of your chest, behind...

Circulatory System: Lesson #2 The Human Heart The Human Heart The human heart Right Left weighs between 200 to Side Side 425 grams and is a little larger than the size of your fist The heart is located between your lungs in the middle of your chest, behind and slightly to the left of your sternum The apex of the heart is oriented to the left side of the body Rat Dissection Left Side Lungs Heart Liver Lungs Right Side Diaphragm Evolution of Vertebrate Heart Two distinctly different chambers: 1) atrium (pl. atria) thin walls and very elastic designed to collect blood from the body 2) ventricle thick walls and very muscular designed to pump blood to the body Pericardium A double-layered membrane sac called the pericardium surrounds the heart The outer parietal pericardium surrounds the roots of your heart's major blood vessels, is attached by ligaments to your spine, diaphragm, and other parts of your body and secretes a small quantity of lubricating liquid The inner visceral pericardium is attached to the heart muscle and also secretes fluid for lubrication. Pericardium This space between the visceral and parietal pericardium is the pericardial cavity Pericardial fluid separates the two layers of membrane, letting the heart move as it beats, yet still be attached to your body  Myocardium The major portion of the heart is composed of cardiac muscle cells, collectively called the myocardium Myocardium has a "stringy" look compared to skeletal muscle  Myocardium Cardiac muscle tissues are involuntary, branched, irregularly shaped, striated and uninucleated. They have numerous blood vessels (BV) between them Intercalated disks are specialized cell-to-cell adhesion/communicati ons and are found only in cardiac muscle. I. The Anatomy of the Heart Your heart has 4 chambers: 1) atrium (left and right) (pl. atria) thin walls and very elastic designed to collect blood from the body protruding appendages called auricles 2) ventricle(s) (left and right) thick walls and very muscular designed to pump blood to the body  Atrium Ventricle Ventricle  Heart Septum An internal wall of muscle called the septum separates the right and left side. The right side of the heart is a pump Left Ventricle for the pulmonary circulation and the Right left side of the Ventricle heart is a pump for systemic circulation Heart Valves The heart has two types of valves: (AV) atrioventricular valves and semilunar valves 1. Right AV = tricuspid (3 flaps/ cusps) Left AV = bicuspid or mitral valve (2 flaps/cusps) They have fibrous strands called chordae tendineae on their cusps that attach to papillary muscles located on the ventricular walls The papillary muscles contract during ventricular contraction and generate tension on the valve leaflets via the chordae tendineae to prevent the AV valves from inverting back into the atria  no back flow of blood Semilunar valves 2. There are 2 semilunar valves: The pulmonary semilunar valve (half moon shaped) located between the RV and pulmonary artery The aortic semilunar valve located between the LV and aorta NOTE: Semilunar valves do not have chordae tendineae  Blood Flow: Right side The right atrium receives deoxygenated blood from the body via the superior and inferior vena cava Deoxygenated blood flows from the right atrium, across the atrioventricular tricuspid valve, and into the right ventricle The right ventricle contracts and pumps deoxygenated blood to the lungs via the pulmonary artery The semilunar pulmonary valve prevents back flow of the blood into the right ventricle Blood Flow: L Side Heart Oxygenated blood returns to the heart from the lungs via four pulmonary veins that enter the left atrium Blood flows from the left atrium, across the atrioventricular mitral (or bicuspid) valve into the left ventricle The left ventricle has a very thick muscular wall so that it can generate high pressures during contraction Oxygenated blood from the left ventricle is pushed across the aortic semilunar valve and into the aorta for transport to the body Pig Pluck Dissection: Youtube https://youtu.be/mMh4F06YSzA STOP ! Next up: Heartbeat and the cardiac cycle Lub Dub, Lub Dub….. Cardiac Cycle: The heartbeat Diastole: Systole: The Resting Phase The Working Phase: Relaxation of the Contraction of the atria and ventricles atria at the same (all four chambers) time followed by the contraction of the ventricles. Heartbeat and Cardiac Cycle Fun Fact: When surgically removed from the body, the heart will continue to beat for several hours provided it is supplied with the appropriate nutrients and salts This is possible because the heart possesses its own specialized conduction system and can beat independently even after being separated from its nerve supply. The extrinsic (arising external to the heart) nerve supply coming from the nervous system (medulla oblongata) serves to modify and control the intrinsic (inherent to the heart itself) beating established by the heart (nodes)  Heart Conduction System Atrioventricular Bundle SA node Inter-nodal Fiber Bundle AV node Purkinje fibers Heartbeat and Cardiac Cycle There are five basic components to the heart's intrinsic conduction system (1) sinoatrial node (SA node) (2) inter-nodal fiber bundle (3) atrioventricular node (AV node) (4) atrioventricular bundle (5) Purkinje fibers SA Node The sinoatrial (SA) node is a small mass of specialized cardiac muscle situated in the upper dorsal surface of the right atrium Because the SA node is able to initiate each beat of the heart, it is often referred to as the pacemaker of the heart The excitation impulse occurs every 0.85 seconds  approximately 72 times per minute and causes the atria to contract SA Node Excitation of the SA node sends a nerve impulse to: (1) the muscles of the atria causing them to contract (atrial systole) while the ventricles relax (ventricular diastole), and (2) the AV node along the inter-nodal fiber bundle Atrial systole takes 0.15 seconds of the 0.85 second cardiac cycle AV Node From the SA node, inter- nodal fiber bundles conduct the nerve impulse to the atrioventricular (AV) node The AV node is located in the right atrium near the lower part of the interatrial septum There is a short delay in transmission of the impulse to the ventricles This is important because it permits the atria to complete their contraction and empty their blood into the ventricles before the ventricles contract Purkinje Fibers Once the nerve impulse leaves the AV node, it travels through the 2 branches of the atrioventricular bundle and enters specialized muscle fibers called Purkinje fibers Purkinje fibers permit a very rapid and simultaneous distribution of the nerve impulse throughout the muscular walls of both ventricles This results in a contraction of the ventricles that proceeds upward from the apex of the heart toward its base Ventricle contraction (systole) and atria relaxation (diastole) takes 0.30 seconds of the cardiac cycle Purkinje Fibers Once the ventricles have contacted, there is a period of atrial and ventricular relaxation This recovery period occupies the final 0.40 seconds of the cardiac cycle Time Atria Ventricles 0.15 sec Systole Diastole 0.30 sec Diastole Systole 0.40 sec Diastole Diastole Cardiac Cycle Atrial Ventricular Atrial & Systole Systole Ventricular Diastole 0.15 sec 0.30 sec 0.40 sec Review of Cardiac Cycle 1. The spontaneous generation of a nerve impulse within the SA node represents the start of the cardiac cycle. This electrical impulse spreads throughout the atrial muscle and leads to contraction of the two atria. 2. As the atria contract, the AV valves remain open and blood is forced into the ventricles. The aortic and pulmonary semilunar valves remain closed, keeping blood in the ventricles. 3. After the atria have contracted and the ventricles have filled, the AV valves close. 4. The nerve impulse reaches the AV node, travels through the Purkinje fibers and the ventricles begin their contraction. 5. Ventricular contraction forces blood through the semilunar valves into the aorta and pulmonary arteries. 6. As the ventricles begin to relax, the aortic and pulmonary valves close, the AV valves open, and blood flows into the ventricles to begin another cycle.