ZIMSEC O Level Combined Science Notes: Alimentary Systems
- Unlike plants, animals are just consumers and cannot make their own food.
- They rely on plans as producers.
- Most of the food eaten is made up of large insoluble molecules which need to be changed into small, soluble molecules that can be easily absorbed by the body.
- Digestion is the process by which large food particles are converted into smaller ones.
- Alimentary canal-the whole passage along which food passes through the body from mouth to anus during digestion.
- The alimentary canal is the whole system of organs and structures that digests food.
- The alimentary canal in mammals is made up of different organs.
- Each organ has its own function but all the organs act together and complement each other during the digestive process.
- Food is taken into the mouth.
- Each mammal has its own way of eating food.
- Ingestion-is the process of taking in food.
- Digestion of food begins as soon as the food enters the mouth.
- Different food molecules are digested at different parts of the digestive system.
- Juices are produced in their respective organs e.g. pancreas, salivary glands and liver.
- These juices assist with the digestive process.
- By the time the food reaches the large intestines digestions would have been completed.
- In the small intestine the food which has been digested is taken from the alimentary system into the bloodstream.
- Absorption-is the process by which soluble food molecules pass from the small intestines into the bloodstream.
- The absorbed food molecules are used for growth and repairing damaged structures.
- Assimilation-is the process where absorbed food molecules are used for growth and repairing damaged body structures. Food molecules are re-arranged into new molecules for example to form bone, muscle, skin and other structures of the body.
- Water is absorbed in the large intestines.
- Not all the food eaten can be used and some cannot even be digested at all.
- These leftovers or waste from the alimentary system are passed out as waste through the anus.
- This process is referred to as ingestion.
- Different kinds of mammals have different alimentary systems.
- The digestive system of a wow is different from say that of a lion.
The table below shows different organs and their functions in the human digestive system.
|Tongue||Mixes food with saliva and takes part in the swallowing process.|
|Salivary glands||Produce saliva, which moistens food and contains|
|Teeth||Masticate (chew food into small pieces) and mix food with saliva|
|Oesophagus/Gullet||Transports food from the mouth to the stomach|
|Stomach||holds food for about an hour. Produces gastric juice which contains acid and enzyme to begin protein digestion.|
|Liver||Produces bile, stores vitamins and mineral and regulates blood sugar.|
|Gall bladder||Stores bile. Bile emulsifies fats and oils and neutralizes stomach acids.|
|Pancrease||Produces many enzymes for the digestion of proteins and starch and to begin the digestion of fats and oils.|
|Bile duct||Carries bile to the duodenum.|
|Duodenum||the first part of the small intestine immediately beyond the stomach.|
|Small intestines/ileum||Glands in the ileum wall produce enzymes which continue the digestion of proteins, starch, sugars, fats and oils. End products are absorbed into the blood stream through the villi.|
|Colon/Large intestines||Absorbs water and salts|
|Ceacum||In herbivores, the cecum stores food material where bacteria are able to break down the cellulose. Serves no useful purpose in humans.|
|Rectum||Holds undigested remains (faeces) before egestion.|
|Appendix||No useful function in humans.|
|Anus||Indigestible matter (faeces) are passed out of the body (egestion)|
To access more topics go to the Combined Science Notes page.
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