PADI RTO First Aid Student Manual

What is the general purpose of the circulatory system? Most cells in the human body are not in direct contact with the external environment. The purpose of the circulatory system is to act as a transport service to provide these cells with the essentials of life. The circulatory system transports both blood and lymph. The heart, blood and blood vessels form the cardiovascular system, while lymph nodes, lymph and lymph vessels form the lymphatic system. How many litres of blood are there in an average-sized adult body? An average-sized adult body contains approximately six litres of blood liquid and blood solids. Liquids make up 55% and solids the remaining 45%, including red blood cells, white blood cells and platelets. Blood transports oxygen, nutrients, carbon dioxide and waste products. Blood also defends us against disease and helps regulate body temperature. How big is the heart, what is its general shape and where is it located? The heart is pear-shaped in size, it is a muscular organ hardly bigger than your fist. Your heart does approximately 70 beats/minute = 2.5 billion beats/lifetime. The heart is located in the chest cavity, behind the breast-bone and between the lungs. The right side pumps blood to the lungs and the left side pumps blood to other body parts. What is the name of the heart cells that trigger its beating action? Pacemaker cells initiate a chain reaction that causes the heart to contract in waves; they are located in the top right portion of the heart. The top cells contract first, followed by the lower portion of the heart. If pacemaker cells are deprived of oxygen, abnormal rhythm (ventricular fibrillation) may occur.

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What is the name of the blood vessels that take blood away from the heart? During each heart contraction, blood surges into the arteries – the vessels that carry blood away from the heart. Arteries are strong and elastic. What is a pulse and blood pressure? As blood enters an artery after the heart contracts, it stretches. This stretching can actually be felt when an artery is near the surface of the skin. This feeling of the stretching of arteries is called a pulse. Contraction of the heart propels the blood through the arteries with considerable force. This force is called blood pressure. When an artery is cut, blood spurts out under pressure in regular intervals. Typically, arterial blood is bright red because it is oxygen-rich.

What is the name of the one cell wide blood vessels located at the site of nutrient and waste exchange? As blood moves away from the heart through the arteries, the vessels get smaller and smaller. Eventually the arteries branch into a network of tiny vessels called capillaries. All the body’s cells are in close proximity to a capillary network. This close association between capillaries and cells allows for the exchange of materials. Since capillary walls are only one cell thick, gases and nutrients can easily diffuse into and out of the thin walls.   A small cut or abrasion anywhere on the skin is sure to damage a bed of capillaries. When capillaries are cut, the blood oozes slowly and typically stops quickly due to clotting.

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PADI RTO