One of the key functions of blood is transport. Blood vessels are like networks of roads where deliveries and waste removal take place. Oxygen, nutrients and hormones are delivered around the body in the blood and carbon dioxide and other waste products are removed. Show The heart is constantly pumping blood so it is always moving around the body. OxygenTransporting oxygen is a vital role of the red blood cells. When we breathe in, the millions of air sacs in the lungs fill with fresh oxygenated air. The oxygen then moves into the blood by passing first through the very thin walls of the air sacs and then into the capillaries, which are tiny blood vessels in a network within the lungs.  Red blood cells are adapted for the transport of oxygen. They are small and flexible so they can fit through narrow vessels, have a bi-concave shape which maximises their surface area to absorb oxygen, have a thin membrane so gases easily diffuse through, and contain haemoglobin which binds to oxygen. (Picture: red blood cells) It is the millions of iron-containing haemoglobin proteins that make blood red. Molecules with more oxygen bound to them are brighter red. When the red blood cells reach tissues that need oxygen, the oxygen is released from the haemoglobin and diffuses into the cells where it is used to make energy. All the systems in our body rely on oxygen to make energy. If our blood didn’t move the oxygen we breathe into our organs and tissues, we wouldn’t be able to carry out normal functions such as moving our muscles, digesting food or thinking. Blood keeps us alive. At the same time, red blood cells will pick up waste carbon dioxide that has been released from the cells and entered the blood stream. Red blood cells carrying less oxygen are a duller red colour, which is why deoxygenated blood in our veins is a darker red than oxygenated. Red blood cells then travel within veins back to the right side of the heart. From the heart the blood is pumped back to the lungs where the carbon dioxide is released from the blood into the air sacs to be breathed out. Air is breathed in, oxygen is picked up by the blood and the journey begins again. All the systems in our body rely on oxygen to make energy. If our blood didn’t move the oxygen we breathe into our organs and tissues, we wouldn’t be able to carry out normal functions such as moving our muscles, digesting food or thinking. Blood keeps us alive. At the same time, red blood cells will pick up waste carbon dioxide that has been released from the cells and entered the blood stream. Red blood cells carrying less oxygen are a duller red colour, which is why deoxygenated blood in our veins is a darker red than oxygenated. (Picture: the circulatory system) NutrientsThe blood carries nutrients such as vitamins, minerals, sugars, fats and proteins around the body. Digested nutrients are absorbed into the blood through capillaries in the small intestine. They are then moved to the cells around the body where they are needed. The blood vessels near to the cells are small in diameter so the blood flows more slowly, allowing the cells to take up nutrients from the blood and to exchange waste products into the blood to be removed. Waste products are transported to the organs that remove them from the blood and then eliminate them from the body. For example, excess water is filtered out by the kidneys and toxins are removed from the blood by the liver. Red blood cells, or erythrocytes, are one of the components of blood. (The others are plasma, platelets and white blood cells.) They are continuously produced in our bone marrow. Just two or three drops of blood can contain about one billion red blood cells – in fact, that’s what gives our blood that distinctive red color. Blood is a vitally important fluid for the body. It is thicker than water, and feels a bit sticky. The temperature of blood in the body is 38°C (100.4°F), which is about one degree higher than body temperature. How much blood you have depends mostly on your size and weight. A man who weighs about 70 kg (about 154 pounds) has about 5 to 6 liters of blood in his body. Blood has three important functions: TransportationThe blood transports oxygen from the lungs to the cells of the body, where it is needed for metabolism. The carbon dioxide produced during metabolism is carried back to the lungs by the blood, where it is then exhaled (breathed out). Blood also provides the cells with nutrients, transports hormones and removes waste products, which organs such as the liver, the kidneys or the intestine then get rid of. RegulationThe blood helps to keep certain things in the body in balance. For instance, it makes sure that the right body temperature is maintained. This is done both through the liquid part of the blood (plasma), which can absorb or give off heat, as well as through the speed at which the blood is flowing: When the blood vessels expand, the blood flows more slowly and this causes heat to be lost. When the temperature outside the body is low, the blood vessels can contract to reduce the amount of heat lost. Even the pH value of the blood is kept at a level ideal for the body. The pH value tells us how acidic or alkaline a liquid is. A constant pH value is very important for things in the body to function properly. ProtectionThis involves solid parts of the blood such as blood platelets and various substances that are dissolved in the blood plasma. If a blood vessel is damaged, these parts of the blood stick together (clot) very quickly and make sure that a scrape, for instance, stops bleeding. This prevents large amounts of blood loss. White blood cells and certain chemical messengers also play an important role in the immune system. The individual parts of bloodBlood is made up of about 55% blood plasma and about 45% different types of blood cells. Blood plasma is a light yellow, slightly cloudy liquid. Over 90% of blood plasma is water, while less than 10% consists of dissolved substances, mostly proteins. Blood plasma also contains electrolytes, vitamins and nutrients such as glucose and amino acids. Over 99% of the solid particles in blood are cells known as red blood cells (erythrocytes) due to their red color. The rest are pale or colorless white blood cells (leukocytes) and platelets (thrombocytes). Blood is made up of plasma and blood cells Red blood cells look like discs that are thinner in the middle. They can easily change shape to “squeeze through” narrow blood vessels. Unlike many other cells, red blood cells have no nucleus ("information center"). All red blood cells contain a red pigment known as hemoglobin. Oxygen binds to hemoglobin, and is transported around the body in that way. In tiny blood vessels in the lung, the red blood cells pick up oxygen from inhaled (breathed in) air and carry it through the bloodstream to all parts of the body. When they reach their goal, they release it again. The cells need oxygen for metabolism, which creates carbon dioxide as a waste product. The carbon dioxide is absorbed from the cells by the blood plasma (some of it binds to hemoglobin too) and is transported back to the lungs in the bloodstream. There it leaves the body when we breathe out. Red blood cells can also pick up or release hydrogen and nitrogen. By picking up or releasing hydrogen they help to keep the pH of the blood stable; when they release nitrogen the blood vessels expand, and blood pressure falls. Red blood cells live for about 120 days. When they're too old or damaged, they're broken down in the bone marrow, spleen or liver. White blood cells (leukocytes) have a cell nucleus and don't contain hemoglobin. There are different types of white blood cells. They are classified according to how their nucleus is shaped and what the inside of the cell looks like under a microscope. Granulocytes have small granules inside them. Monocytes and lymphocytes also contain granules, but their granules are extremely small and can't be seen under a microscope. There are many more red blood cells than white blood cells in the blood. But white blood cells can leave the bloodstream and move into tissues in the body. White blood cells play an important role in the immune system. Here the different blood cells have different functions: Some fight intruders such as bacteria, viruses, parasites or fungi themselves and render them harmless. Others make antibodies, which specifically target foreign objects or germs like viruses. Leukocytes also play a part in allergic reactions: For instance, they are the reason why people with a dust mite allergy get a runny nose when they come into contact with dust. Certain lymphocytes can also kill cancerous cells that have developed elsewhere in the body. Most white blood cells have a lifespan of only a few hours to several days. Some lymphocytes can stay in the body for many years, though. Blood platelets (thrombocytes) also look like little discs, as do red blood cells, and they also have no cell nucleus. But they are much smaller than red blood cells. They play an important role in blood clotting: If a blood vessel is damaged – for instance, if you accidentally cut yourself with a knife – the healing process begins with blood platelets gathering and clumping together on the inside of the damaged wall of the blood vessel. This quickly causes a plug to form and close the wound temporarily. At the same time, strong protein threads are made and they hold the clump in place, attached to the wound. Thrombocytes usually live only 5 to 9 days. Old thrombocytes are mainly broken down in the spleen. Production of blood cellsAll solid parts of the blood come from common parent cells known as stem cells. In adults, blood cells are mainly produced in the bone marrow. The various blood cells develop in several stages from stem cells to blood cells or blood platelets. White blood cells such as lymphocytes don't only mature in the bone marrow, but also in the lymph nodes. When the cells are ready, they are released into the bloodstream. In addition to these mature cells, the blood still contains a small number of precursor cells. Certain chemical messengers regulate the production of blood cells. For instance, the hormone erythropoietin, which is produced in the kidneys, promotes the production of red blood cells. And cytokines stimulate the production of white blood cells. Sources
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The function of red blood cells is to carry oxygen to the cells and then carry away carbon dioxide
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