SPLATS about digestion and excretion
For an explanation, see
the main splats page
Digestion and excretion
Teeth are used to slice and crush food, increasing its surface area that can be exposed to enzymes that help food break down to molecules that can be absorbed.
Fluoride in water toughens tooth enamel by causing chemical changes in the enamel to a chemical form that is more resistant to the acids of dental plaque.
Animals have similar internal anatomy of the abdomen, with a few simple variations that relate to the diets of herbivores, carnivores and omnivores.
Parts of the alimentary canal nearest to openings may be investigated using an endoscope, a tube with light and camera, inserted through the mouth or anus.
The upper alimentary canal is made up of the stomach, duodenum and ileum, the lower alimentary canal is made up of the small intestine, caecum and anus.
Food is moved along the alimentary canal by waves of peristalsis, where a series of contractions around the tube push partly-digested food on its way.
In1825, William Beaumont began his study of the digestion of Alexis St Martin, who had a gunshot wound which left him with a permanent opening to the stomach.
In 1836, Theodor Schwann isolated the first animal enzyme when he discovered pepsin, a digestive enzyme, from extracts taken from the stomach lining.
Absorption transfers dissolved food from the alimentary canal to the circulatory system: it is carried passively until it reaches a place where it is needed.
Certain points along the alimentary canal are controlled by sphincter muscles, rings of muscle that surround the canal and block unwanted returns.
Elimination of faeces gets rid of the left-overs, the bacteria, the fibres and the undigested food, after most of the water has been reabsorbed.
The kidney takes dissolved wastes from the blood and disposes of them in urine, which is normally sterile, unless there is a kidney infection.
Urine is highly sterile, but makes a good culture medium for many bacteria, which make chemical changes in the urine, producing ammonia and later, nitrates.
Urine production in humans is controlled by the action of antidiuretic hormone (ADH) which controls the amount of urine sent to the bladder for storage.
Because bacteria turn the urea in urine to ammonia and then into nitrates, urine has been a common industrial chemical with many uses, since ancient times.
Some animals in dry environments rely mainly on metabolic water for their water supplies, water that is produced by respiration of carbohydrates and lipids.
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