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The heart is an organ that supplies blood and oxygen to all parts of the body. ‘The heart muscle is usually called the cardiac muscle and like all muscles it contracts and relaxes to produce movement. As the heart contracts it squeezes blood out into the arteries which then carry the blood off to all parts of the body. The contractions of the heart are caused by electrical impulses generated by the heart muscle. These impulses begin in the sino atical node and cause the heart to contract; in turn they regulate the beating of the heart which is its rhythm. The Sino atrial node and the atrioventricular node is the heart natural pacemaker. The Sino atrial is located at the opening of the right atrium and is made up of specialized cells that produce action potential, it beats at about 140-160 speed. The atrioventricular node is located at the junction of the right atrium and beats at 100-120 speed. (class notes)The heart is the hardest working muscle in the body and is about 10 cm long and the size of the owner's fist. The heart has four chambers; the upper two are the right and left atria. The lower two are the right and left ventricles. Blood is pumped through the chambers, aided by four heart valves which are the tricuspid valve, mitral valve, aortic valve and pulmonary valve. The valves keep blood flowing in the right direction through the heart. The Heart is located in the thoracic cavity behind the breast bone, between the lungs and above the diaphragm. It is surrounded by a fluid filled sac called the Pericardium. The function of the Pericardium is to nourish and protect the heart. (Bailey 2009)
The Heart is composed of three layers of tissue the Pericardium, the Myocardium and the Endocardium.The Pericardium is a double-layered membrane that surrounds your heart like a sac. The outer layer of the pericardium surrounds the roots of your heart's major blood vessels and is attached by ligaments to your spinal column, diaphragm, and other parts of your body. The inner layer of the pericardium is attached to the heart muscle. A coating of fluid separates the two layers of membrane, letting the heart move as it beats, yet still be attached to your body. (Ross and Wilson)
The Myocardium is the muscular middle layer of the wall of the heart. It is composed of contracting cardiac muscle fibre that allows the heart to contract.
The Endocardium is the inner part of the heart it forms the lining of the myocardium and the heart valve. It consists of epithelial cells and is continuous with the inner lining of blood vessels. (Ross and Wilson)
The heart is the main power supply for the circulatory System. The cardiovascular system and the lymphatic system collectively make up the circulatory system. The lymphatic system consists of lymph vessels that are situated between the blood capillaries and tissue cells. The lymphatic system helps maintain fluid balance, absorb fat soluble nutrients and defend the body against disease .It gets rid of harmful diseases out of the tissues fluid before it's returned to the blood. Our bodies have two circulatory systems: The pulmonary circulation which is a short loop from the heart to the lungs and back again, and the systemiccirculation that sends blood from the heart to all the other parts of our bodies and back again. The main role of the circulatory system is to transport nutrients, gases such as oxygen and co2, hormones and waste through the body. The circulatory system is composed of the heart, blood and blood vessels. The blood vessels transports blood throughout the body ,there are three major types of blood vessels they are; the arteries which carry blood away from the heart, the veins which return blood to the heart and the capillaries which link the arteries and veins. (Bailey 2009)Substances are transported around the body by blood through a network of blood vessels. The amount of blood in an adult's body is about 5 to 6 litres. The blood is normally thicker than water and consists of plasma and cells. The plasma is mostly water that contains dissolved substances such as: oxygen, carbondixide, nutrients, wastes and hormones. The blood cells have three groups which are the erythrocytes, leukocytes and thrombocytes. The erythrocytes or the red blood cells carry oxygen in the blood to various cells in the body. The leukocytes or the white blood cell are responsible for fighting foreign organisms that enter the body. The thrombocytes or platelets are cells that play a key role in blood clotting. (Ross and wilson)
Diagram showing the heart and the different types of blood vessels in the body's circulatory systems.
The respiratory system is also involved in the journey of blood. It involves the taking in of oxygen and the giving off of carbon dioxide; this is done when we breathe by inhaling and exhaling. This is a form of gas exchange and it is the respirators' way of getting oxygen to the blood. Organs involved in respiration are the mouth, nose, trachea, larynx, bronchi, lungs and diaphragm. When oxygen enters the mouth and nose it then passes through the larynx and trachea then into the chest cavity. After passing the larynx oxygen moves into the bronchi that carries oxygen in and out of the lungs. The bronchial branch into small and smaller tubes called bronchioles .The Bronchioles results into grape like sac known as aveoli.The alveoli are surrounded by capillaries in the arterial blood. The waste blood from the veins release carbon dioxide into the alveoli. The diaphragm is a sheet of muscles that lie across the bottom of the chest cavity. The diaphragm job is to help with getting carbon dioxide out of the lungs, and oxygen in the lungs .The diaphragm relaxes to let carbon dioxide out and contracts to let oxygen in. (Franklin Institute 2009)
For the heart to function properly the four chambers must be working together in a coordinated way.The chambers that are filled with blood pumps it around to create a cardiac cycle .The process begins when blood from the body that is low in oxygen returns through the superior and inferior vena cava to fill the right atrium of the heart. The right atrium that's filled with blood contracts and pushes the blood through the tricuspid valve into the right ventricle. The tricuspid valve which is made up of three semi lunar cups prevents the blood from backing up in to the right atrium. The right ventricle which is now filled with blood contracts and pushes towards the lungs. The blood then leaves the right ventricle and enters the pulmonary artery then into the lungs where oxygen is taken in and carbon dioxide is let off. When the blood picks up oxygen it then enters the pulmonary veins that carry oxygenated blood to the left atrium. The left atrium contracts then pumps blood into the left ventricle. The left atrium is situated above the left ventricle and is separated by the bicuspid valve(mitral valve)-this valve also prevents the back flow of blood from the left ventricle to the left atrium. The left ventricle also contracts and pushes blood into the aorta. At the opening of the aorta there is a valve that acts as a barrier to prevent blood from going back to the left ventricle. Blood leaves the aorta and travels through the aortic arch which is one of the many arteries that carry oxygen rich blood to all parts of the body.
The journey of the blood to and from the heart is a repeated cycle with contractions of the atria and ventricles.(Ross and Wilson)