The cardiovascular system is the primary circulatory system of the human body. It’s main function is transport. It also provides protection against foreign substances. The arteries of this system generally carry blood from the chambers of the heart to the tissues of the body, while the veins carry blood from the tissues of the body to the chambers of the heart. The blood circulation is a two cycle system which involves both the pulmonary cycle and the systemic cycle. In the former, the pulmonary cycle, blood circulates from the heart to the lungs and back to the heart.
In simple organisms such as unicellular and one or two layer organisms, materials can be transferred among cells by simple processes of diffusion. However, in large organisms, a system is needed for the distribution and collection of materials. The circulatory system is used by the human body to carry substances. Some substances are collected from the body cells for elimination. The body also produces hormones which are the products of the endocrine glands.
Some of the liquids of the body are blood, lymph or cerebrospinal fluid. Some of the vessels of the body include the blood vessels and lymph vessels. Blood is composed of the following: plasma and formed elements. Plasma makes up about 55 percent of the total blood volume. Water is also a part of our body composition. It has an ample heat-carrying capacity. Along with dissolved salts, plasma proteins help to maintain the tonicity of the plasma. Fibrinogen is important to blood clotting. The percentage by volume of red blood cells in the blood is called haematocrit. Haemoglobin, a special protein, is found within red blood cell cytoplasm. The normal, mature red blood cell is a biconcave disc. White blood cells are another of the formed elements of the blood, they are also known as leucocytes. There are several types of white blood cells including neutrophils, monocytes, phagocytes and lymphocytes. Platelets are also another type of formed element in the blood.
The blood is the vehicle for the cardiovascular system; it is used to transport substances around the body. Oxygen in the air fills the alveolus of the lung and carbon dioxide is produced during metabolic oxidation within the individual cell.
The blood carries glucose and oxygen around the body. When the hormone epinephrine is secreted by the Adrenal Gland, it is delivered to all parts of the body by the cardiovascular system. In periods when much energy is required, the body can use its stores of fat as a source of energy.