Blood is mainly comprised of Red Blood Cells, White Blood Cells, Platelets, and Plasma.
Red Blood Cells:
The most numerous blood cells, 4-5 billion Red Blood Cells are produced every hour! Red Blood Cells live for 120 days in the blood stream, but only 42 days outside of the body. When they die, they are removed from circulation by an organ called the spleen. Red Blood Cells transport oxygen through the bloodstream to the tissues and organs. After they deliver oxygen, red blood cells pick up a waste product called carbon dioxide (CO2). Then the red blood cells return through the veins back to the lungs, where the carbon dioxide can finally be released. Every time you breathe out, you are expelling carbon dioxide and waste. On average, it takes only 30-45 seconds for red blood cells to make one complete circuit.
The blood cells in your body are mixed together in a golden liquid known as plasma. Plasma is mostly made up of water, but also contains proteins, sugar and salt. In addition to carrying blood cells throughout your body, plasma also carries hormones, nutrients and chemicals. Plasma has the important function of maintaining the pH of the blood.
Platelets help prevent bleeding and make your blood clot when you get a cut. Platelets are normally round and smooth, but after they are used to produce clots, they turn spiky and jagged around the edges. After an injury occurs, platelets throw themselves over the cut. The platelets also attract a protein found in plasma (fibrin), and use it to form a dense netting that traps red blood cells and quickly becomes a clot.
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“Think of your blood as the transportation system in your body that's always on the move, making deliveries and pick-ups day and night. Pumped by your heart, your blood is circulated non-stop, carrying oxygen and nutrients to wherever they're needed, and collecting waste products called carbon dioxide."
-Rory, from My Blood, Your Blood