The cardiorespiratory system consists of the cardiovascular system (the heart and blood vessels) and the respiratory system (lungs and air passages). Together, both systems work to transport oxygen from the atmosphere to the cells of the working muscles and organs and to remove cabon dioxide and other waste products.
BLOOD is the fluid that flows through the circulatory system. Approximately 45% of blood volume is composed of red and white blood cells and blood platelets. The remainder is plasma which carries food, minerals, hormones and chemical substances needed for life. Red blood cells are able to transport and give up oxygen and carbon dioxide through iron-protein molecules called haemoglobin.
The circulatory system consists of vessels called arteries, veins and capillaries, which carry blood from the heart, around the body and return it to the heart.
ARTERIES have elastic walls to compensate for the surge in pressure each time the heart beats. With the exception of the pulmonary arteries, they transport oxygen-rich blood away from the heart.
CAPILLARIES are microscopic vessels that allow the exchange of oxygen, carbon dioxide, nutrients, hormones and waste products to pass between the blood and the tissues they are servicing. Once the blood has passed through the capillaries it returns to the heart via venuoles that enlarge into veins.
VEINS contain valves that ensure that the blood continue to flow in the right direction - towards the heart. The contraction and relaxation of skeletal muscle further assist the return of the blood to the heart. When there is no contraction or relaxation of the muscles, such as when standing in one position for a long period of time, there is a risk of experiencing blood pooling or the accumulation of blood in the large veins in the legs.
BLOOD PRESSURE is a measure of the force the heart needs to pump blood through the body. It shows the resistance of the blood vessels to the flow of blood around the circulatory system. Two recordings of the blood pressure are taken: systolic and diastolic blood pressure.
SYSTOLIC PRESSURE is the pressure on the artery walls when the heart contracts and pumps blood through the body.
DIASTOLIC PRESSURE is the pressure in the artery walls between pumps or heart beats, when the heart is relaxing.
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