IGCSE Biology - Chapter 7 - Animal Nutrition II

There are some key ideas of alimentary canal in the IGCSE biology curriculum:

• Sphincter muscles can keep the food in one part of the alimentary canal. 
• The tongue mixes food with saliva, and forms it into a bolus. The bolus is then swallowed. 
• Saliva is a mixture of water, mucus and the enzymes amylase. 
• There are two tubes leading down from the back of the mouth. The one in the front is the trachea (windpipe), which takes air down to the lungs. Behind the trachea is the oesophagus, which takes food down to the stomach. 
• The entrance to the stomach from the oesophagus is guarded by a ring of muscle called a sphincter. 
• The mixture in the stomach is called chyme. 
• The stomach wall contains goblet cells which secrete mucus. 
• The main protease enzyme in the stomach is pepsin. Pepsin works best in acidic conditions. 
• Rennin is only produced in the stomach of young mammals. It causes milk that they get from their mothers to clot. The milk proteins are then broken down by pepsin. 

• The small intestine is about 5m long and is quite narrow. 
• Enzymes are made in the pancreas. 
• Pancreatic juice, which is a fluid made by the pancreas, flows along the pancreatic duct. 
• This fluid contains many enzymes, such as amylasem protease and lipase. These enzymes do not work well in acid environments. 

• Bile is a yellowish green, alkaline, watery liquid which flows through the duodenum. It helps netralise the acidic mixture from the stomach. 
• Bile helps digest fats. 

• Villi are tiny projections which line the inner wall of all parts of the small intestine. 
• Water, mineral salts and vitamins are absorbed in the small intestine. 
• The villi contain lacteals, which are part of the lymphatic system. Fats are absorbed into lacteals.
• Villi have walls only one cell thick. This means the digested nutrients can easily cross the wall to reach the blood capillaries and lacteals.

• The colon and rectum are sometimes called the large intestine, because they are wider tubes than the duodenum and ileum. 

• Diarrhea is the loss of watery faeces. It happens when not enough water is absorbed from the faeces. 
• Chlorea, a bacterium, lives and breeds in the small intestine. It releases a toxin. 

• After they have been absorbed into the blood, the nutrients are taken to the live, in the hepatic portal vein.
• If there is more glucose than necessary in the blood, the liver will convert some of it to the polysaccharide glycogen, and store it. 
• In IGCSE biology curriculum, by definition, assimilation= the movement of digested food molecules into the cells of the body where the are used, becoming part of the cells. 

End of this topic!

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