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Cardiovascular System

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Cardiovascular System The heart & Cardiovascular system •‘The heart’s continuous pulse create a base for our understanding of rhythms in everyday life.’ •Bonnie Bainbridge Cohen The heart constantly beats throughout our lives never rests blunt, round, cone-shaped weighs between 1/2 and 3/4 pounds Dimensions approx: 5” in lgth, 3” width, 2” depth Location: •LENGTH: Top of the heart is located behind the sternum at the sternal angle (2nd and 3rd Ribs) at the junction between the manubrium and the body of the sternum. The apex of the heart is located at the Xiphoid process. •WIDTH: top right side is located between the 2nd intercostal space on the right lateral border of the sternum. The bottom right side is located at the 5th intercostal space (between the5th and 6th ribs) at the right lateral border of the sternum. The top left side is located at the 2nd intercostal space (between 2nd and 3rd rib) about 1” from the left lateral border of the sternum. The apex of the heart is tilted to the left and slightly forward in relationship to the central axis of the body. Covering of the heart •Smooth muscle •Is a hollow muscle divided into three layers which run in spirals through the heart. •Three layers are: endocardium, myocardium and epicardium. • The pericardium surrounds the heart and has two layers. •The inner layer is a double walled sac containing fluid which reduces friction created by the pumping of the heart. •The outer fibrous layer serves to enclose the heart and anchor it to the surrounding structures. •The fibrous ligaments of the pericardium are attached to the diaphragm, manubrium, ziphoid and spine. • • coronary circulation •The heart has its own blood transport system •within which are the coronary arteries and cardiac veins • It relies on aerobic respiration for energy production • It needs a constant supply of oxygenated blood. • Its metabolic requirements are exceeded only by the brain Four chambers of the heart •Right atria - deoxygenated blood comes to the heart via the vena cava vein •Right ventricle - takes this blood up to the lungs via the pulmonary artery •Left atria - the oxygenated blood enters from the lungs via the pulmonary vein •Left ventricle - oxygenated blood leaves the heart via the aorta to be pumped around the body - known as the pulmonary circuit AV valves •Tissue-paper thin but tough, the valves of the human heart open and close to pump 6 quarts of blood a day through 60,000 miles of vessels. •On the right the Tricuspid valve prevents back flow of (deoxygenated blood coming from the right atria into the right ventricle •On the left the mitral (bicuspid) valve prevents the back flow of (oxygenated blood coming from the left atria into the left ventricle •As the blood flows through from the atria into the ventricles, the valves are loose and fall into the ventricle chambers. When the pressure rises in the ventricles, the valves contract and flap open allowing the blood to flow •Semi-Lunar valves - there are two: •On the right is the pulmonary valve which is between the ventricle and the pulmonary artery •On the left - is the aortic valve which is between the left ventricle and the aorta •When the ventricles fill, the valves close to prevent back flow. •when the ventricles contract, the valves open to allow the blood to flow). Blood circulation •The circulatory system maintains the life of every other organ in the body by supplying oxygen, nutrients from the digestive system, hormones from the endocrine glands, substances for facilitating metabolism and removal of waste. • The systemic circuit • Deoxygenated blood is carried via the vena cava vein into the right aorta, • through the right ventricle into the pulmonary artery to the lungs. • Oxygenated blood goes back via the the pulmonary vein to the left atria then left ventricle and out the aorta to the body. • This oxygenated blood is taken to all of the tissues of the body - organs, muscles, connective tissue. The vessels gradually get smaller going from the strong, thick multiple layers of elastic tissue artery to the smaller arterioles to the capillaries (some are larger). The capillary beds are areas of transition between fluids passing out of the arterial capillaries into the interstitial fluid then into the capillary bed area also known as the ‘Zone of Isoring' • Cardiac contraction • initiated by a pacemaker, or conduction, • specialised myocardial cells which are grouped into nodes • Composition of blood In a newborn, it is composed of 75% water In an adult 56% water Blood cells are produced in the yoke sac. 45% cells - red and white blood platelets in cellular fluid 55% plasma - viscous, proteinous fluid - 90% water, 10% organic and inorganic substances and antibodies & extracellular fluid. Embryologic development Flat disc The three germ layers • Ectoderm - skin, nervous system, brain • Endoderm - digestive tract & related organs & glands • Mesoderm - heart, fascia, muscles, bone, blood, lymph, urogenital system, kidneys, connective tissue in general Formation of the heart • Around week four, the two lateral endocardial tubes fuse along the midline • These become the arteries and the veins and form around the same time as the heart • It is the first organ to be asymmetric as it this point it starts to loop and spiral due to the fluids flowing through it. • Day 22 - The heart is now bilaterally symmetrical. There is a heart beat. • Day 24 - the blood circulates throughout the embryo. • Weeks 5 - 8 The four chambers of the heart are there. Beginning and end of fourth week .
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