Diagram of the human body showing the circulatory system. The heart is labeled on the diagram, and the veins are depicted throughout the body. Blood flow and oxygen saturation are shown by colors. Red indicates that the blood contains oxygen, which is being pumped to the parts of the body, and blue indicates that the blood is lacking oxygen, which is being pumped back to the lungs. A closeup of red blood cells is on the opposite side of the page. The text titled ‘Liquid tissue’ reads: Blood is a mixture of cells – red blood cells, white blood cells, and platelets – suspended in a water-based solution called plasma. Nutrients, vitamins, and minerals also travel in blood, dissolved in the plasma. The cells and other substances remain suspended in the blood because the heart’s pumping action keeps the blood moving. The text titled ‘Blood components’ reads: When left to sit, blood separates into its parts. About 55 percent makes up the liquid top layer and 45 percent makes up the cellular layer below. The clear amber liquid is labelled Plasma and the text with it reads: The liquid part of the blood is about 90 percent water. The other 10 percent includes many dissolved substances, such as proteins and glucose. The dark component at the bottom is labelled White blood cells and platelets and red blood cells. The text with White blood cells and platelets reads: White blood cells help the body fight disease. Platelets help the blood to clot when bleeding occurs. The text with Red blood cells reads: These cells contain the compound haemoglobin, which carries oxygen from the lungs to cells throughout the body. The text next to the human circulatory system reads: Blood flow: The body’s circulation system contains two circuits. In the first, blood is pumped by the heart to the lungs. As oxygenated blood returns to the heart, it is pumped to the remaining tissues in the body through the second circuit. Lungs: In the lungs, carbon dioxide is removed from the blood, oxygen is taken up by red blood cells. Heart: The heart pumps oxygenated blood, shown in red, from the lungs around the body. At the same time, the heart pumps deoxygenated blood, shown in blue, back to the lungs. Cells: Oxygen is delivered to each cell in the body, and carbon dioxide is removed. It is also important to maintain blood pH levels. For the body to function normally, blood pH must be kept within a narrow range. Buffer systems ensure pH levels are maintained within that range. A buffer is a chemical or a combination of chemicals that can absorb either hydrogen ions or hydroxide ions. Buffers maintain a relatively constant hydrogen ion concentration. Hydrogen ions produced by chemical reactions in the body are the main threat to your blood’s pH. A very important blood buffer system consists of hydrogen carbonate ions and carbonic acid as shown in this equation