The Heart as a Pump – I PDF

The The Heart as a Pump – I Dr Panayiotis Avraamides MBBS Lond, BSc, FRCP Lond, FRCP Edin, FESC, FEACVI, FACC, FAHA, FSCAI, FHRS Clinical Professor of Cardiology Lecture at glance o The heart as a part of the circulatory system o Anatomy and Physiology of the Heart Introducti on Injecting a dy...

The The Heart as a Pump – I Dr Panayiotis Avraamides MBBS Lond, BSc, FRCP Lond, FRCP Edin, FESC, FEACVI, FACC, FAHA, FSCAI, FHRS Clinical Professor of Cardiology Lecture at glance o The heart as a part of the circulatory system o Anatomy and Physiology of the Heart Introducti on Injecting a dye that shows up in X-ray images is used to examine the blood vessels supplying the heart muscle. Shown here is a normal left coronary artery (blue) that supplies much of the heart. The body has specific needs O2 and nutrients (Picked up from the external environment) Waste products must continually be removed Excess heat generated by muscles must be transported to the skin (maintain the body temperature) Transfer of hormones (from the site of production to the site of action) Circulatory System The heart (the pump=imparts P to the blood and establish P gradient). Blood flows down a P gradient (from an area of higher P to an area of lower P). The blood vessels (passageways). The blood [transport medium, materials are being transported long distances in the body (O2, CO2, nutrients, wastes, electrolytes, hormones)].  The heart Hollow, muscular organ at the size of a clenched fist Lies in the middle of thoracic cavity (sternum and backbone) Broad base (upper) and apex (lower) The heart’s position between bony structures anteriorly and posteriorly, makes it possible to manually drive blood out of the heart when it is not pumping effectively external cardiac compression (part of CPR). Heart=single organ, two separate pumps (left and right halves) Two chambers per half (atria and ventricles) Veins=return blood from the body to atria Arteries=carry blood away from the ventricles to the tissues Septum=continuous muscular partition (avoids oxygen mixing) Blood travels continuously through the circulatory system to and from the heart through 2 separate vascular loops, both originating and terminating at the heart. The complete circuit of blood flow  The complete circuit of blood The left side of the heart receives O2- blood from the pulmonary circulation and pumps it into the systemic circulation. The systemic circulation, in contrast to pulmonary (all blood flows through the lungs), may be viewed as a series of parallel pathways. Blood flow through and pump action of the heart  Comparison of the right and left pump Both sides of the heart simultaneously pump equal amounts of blood. The pulmonary circulation is a low-P, low-R system, whereas the systemic circulation is a high-P, high-R system. P: the force exerted on the vessel walls by the blood pumped into them by the heart. R: the opposition of blood flow (caused by friction between the flowing blood and the vessel wall). the L side works harder because it pumps an equal volume of blood at a higher pressure into a higher-R and longer system The heart muscle on the L side is thicker (stronger pump) than the muscle on the R side The left side is a stronger pump Heart wall and coverings The endothelium (endocardium): a thin inner layer, (epithelial tissue) that lines the entire circulatory system. The myocardium: a middle layer (cardiac muscle) and constitutes the bulk of the heart wall. The epicardium: a thin external layer, that covers the heart  Heart wall and coverings The heart is enclosed in the double-walled, membranous pericardial sac. The sac consists of two layers: a tough, fibrous covering and a secretory lining. The outer fibrous layer attaches to the connective tissue partition that separates the lungs. This attachment anchors the heart so that it remains properly positioned within the chest. The sac’s secretory lining secretes a thin pericardial fluid, which provides lubrication to prevent friction between the pericardial layers (as they glide over each other with every day beat of the heart.) Pericardi tis Pericarditis: inflammation of the pericardial sac that results in painful friction between the two pericardial layers. Occurs occasionally because of viral or bacterial infection.  The spirally arranged cardiac muscle fiber The myocardium consists of interlacing bundles of cardiac muscle fibers arranged spirally around the circumference of the heart When the ventricular muscle contracts and shortens, the diameter of the ventricular chambers is reduced The apex is simultaneously pulled upward toward the base of the heart in a rotating manner Oxygen supply to the heart is performed by the coronary arteries and their branches. The coronary arteries originate at the root of the aorta, run along the heart surface and penetrate the muscle at a 90° angle. Myocardium compresses its blood vessels upon contraction. During systole, pressure inside the LV is slightly higher than in the aorta. Blood flow in the arteries that supply the subendocardial portion of the LV only occurs during diastole. At rest, the heart pumps about 65% of the oxygen contained in every unit of blood volume. Only if blood flow is enhanced, it is possible to increase oxygen intake. Heart Valves Blood flows through the heart in one fixed direction: Veins to Atria to Ventricles to Arteries The presence of 4 one-way heart valves ensures this unidirectional blood flow. The valves are positioned so that they open and close passively because of P differences, like a one-way door. A forward P gradient (=a greater P behind the valve) forces the valve open, whereas a backward P gradient (=a greater P in front of the valve) forces the valve closed. Mechanism of valve function Heart Valves The right AV Valve (tricuspid=3 cusps or leaflets) The left AV Valve (bicuspid or mitral) The edges of the AV valve leaflets are fastened by tough, thin cords of tendinous-type tissue, the chordae tendinae, which prevent the valve from everting (=from being forced by the high ventricular P to open in the opposite direction into the atria). These cords extend from the edges of each cusp and attach to small, nipple-shaped papillary muscles which protrude from the inner surface of the ventricular walls Heart Valves No valves between atria and veins Backflow of blood from the atria into the veins usually not a significant problem for two reasons: 1. Atrial Ps usually are not much higher than venous Ps. 2. The sites where the venae cavae enter the atria are partially compressed during atrial contraction Fibrous skeleton surrounding Four interconnecting rings of dense connective tissue known as the fibrous skeleton of the heart, surround and support the 4 heart valves. The fibrous skeleton also separates the atria from the ventricles and provides a rigid support of the cardiac muscle. Membrane junctions Desmosome: a type of adhering junction that mechanically holds cells together. It is particularly abundant in tissues such as the heart that are subject to considerable mechanical stress. Gap junction: the opposing membranes approach each other closely to form gap junctions, which are areas of low electrical R that allow APs to spread from one cardiac cell to adjacent cells. Heart as an endocrine system Heart muscle performs also an endocrine function. The atria and ventricles each secrete a hormone involved in the regulation of BP. These related hormones act on kidneys to promote elimination of H2O-retaining salt into the urine. The resultant H2O loss in the urine reduces blood volume and BP accordingly.