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Organ Systems (Digestive system (Different things happen to food as it…
Organ Systems
Digestive system
The food we eat has to be broken down into other substances that our bodies can use. This is called digestion. Without digestion, we could not absorb food into our bodies and use it.
Digestion happens in the digestive system, which begins at the mouth and ends at the anus.
After we swallow, our food passes through these organs in turn
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Liver and pancreas
The liver and the pancreas play an important part in digestion. The liver produces bile, which helps the digestion of lipids (fats and oil). The pancreas produces biological catalysts called digestive enzymes which speed up the digestive reactions.
Digestion is the process by which food is broken down to be absorbed into the bloodstream and distributed around the body
Enzymes
Our teeth break food down into small pieces when we chew. This is only a start to the process of digestion, as chewed pieces of food are still too large to be absorbed by the body. Food has to be broken down chemically into really small particles before it can be absorbed. Enzymes are the biological catalysts needed to make this happen quickly enough to be useful.
Enzymes are not living things. They are just special proteins that can break large molecules into small molecules. Different types of enzymes can break down different nutrients
Carbohydrates
Carbohydrates are digested in the mouth, stomach and small intestine. Carbohydrase enzymes break down starch into sugars.
The saliva in your mouth contains amylase, which is another starch digesting enzyme. If you chew a piece of bread for long enough, the starch it contains is digested to sugar, and it begins to taste sweet.
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Proteins
Proteins are digested in the stomach and small intestine. Protease enzymes break down proteins into amino acids. Digestion of proteins in the stomach is helped by stomach acid, which is strong hydrochloric acid. This also kills harmful microorganisms that may be in the food.
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Absorption
Digested food molecules are absorbed in the small intestine. This means that they pass through the wall of the small intestine and into our bloodstream. Once there, the digested food molecules are carried around the body to where they are needed.
Only small, soluble substances can pass across the wall of the small intestine. Large insoluble substances cannot pass through. The slideshow shows how this happens:
The villi (one of them is called a villus) stick out and give a big surface area. They also contain blood capillaries to carry away the absorbed food molecules.
Egestion
Excess water is absorbed back into the body in the large intestine. What is left then is undigested food. This is stored in the rectum, the lower part of the large intestine, until we are ready to go to the toilet. It then comes out of the rectum through the anus as faeces. This process is called egestion. Take care not to confuse egestion with excretion.
Reproductive system
Testes
The two testes (one is called a testis) are contained in a bag of skin called the scrotum. They have two functions:
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Sperm duct and glands
The sperm pass through the sperm ducts, and mix with fluids produced by glands (seminal vesicles). The fluids provide the sperm cells with nutrients. This mixture is called semen.
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The urethra is the tube inside the penis that can carry urine or semen. A ring of muscle ensures that urine and semen do not get mixed up.
Respiration system
The human respiratory system contains the organs that allow us to get the oxygen we need and to remove the waste carbon dioxide we don't need. It contains these parts
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Ventilation
Movements of the ribs, rib muscles and diaphragm allow air into and out of the lungs. Take care - this is called breathing or ventilation, not respiration. When we breathe in, we inhale. When we breathe out, we exhale.
Air passes between the lungs and the outside of the body through the windpipe, called the trachea. The trachea divides into two bronchi, with one bronchus for each lung.
Each bronchus divides further in the lungs into smaller tubes called bronchioles. At the end of each bronchiole, there is a group of tiny air sacs. These air sacs have bulges called alveoli to increase their surface area.
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Circulatory system
The diagram outlines the circulatory system. To make things clear, oxygenated blood is shown in red, and deoxygenated blood in blue.
Blood carries oxygen and nutrients to the body’s cells, and waste products away from them. The circulatory system consists of
the heart, which is the muscular pump that keeps the blood moving
the arteries, which carry blood away from the heart
the veins, which return blood to the heart
the capillaries, which are tiny blood vessels that are close to the body’s cells.
