DEMO

ALIMENTARY SYSTEMS

Objectives: By the end of this subtopic learners should be able to:
  • a) Identify parts of the mammalian alimentary canal and their respective associated organs.
  • b) Describe the functions of the parts of the mammalian alimentary canal.
  • c) Compare ruminant and non-ruminant alimentary canals.

The Human Alimentary Canal

  • The alimentary canal is the whole passage along which food is processed from mouth to anus.
  • The alimentary system of a mammal is made up of many different organs which help with the processing of food.
  • Each organ in the alimentary system has got its own specific functions in helping processing the food.
  • The main parts involved in the digestion of food are mouth, stomach and the small intestine.
 

Functions of parts of the alimentary canal

a. Mouth

  • This is the part where food is taken into the alimentary system. The process of taking in food is called ingestion.
  • In the mouth are the teeth and the tongue.
  • The tongue is important in tasting food, mixing it with saliva and swallowing.
  • The teeth help to chew or masticate large pieces of food into smaller pieces. They also help to mix food with saliva.

b. Salivary glands

  • They produce saliva which moisten the food and contain the enzyme amylase which helps to digest starch.
  • They also contain mucus which glues the small food pieces together forming a ball called a bolus. The mucus also make the bolus slippery making it easy to swallow.

c. Stomach

  • The stomach is a muscular sac which holds food for about an hour.
  • The stomach walls produce gastric juices which contain an acid (hydrochloric acid) and enzyme to begin protein digestion.
  • It also helps to continue the mechanical breakdown of food.

d. Oesophagus (gullet)

  •  This is the passage or pipe that takes food from the mouth into the stomach.

e. Liver

  • It produces bile, store vitamins and mineral salts.
  • It also regulates blood sugar levels and removes toxins from the blood, for example alcohol.

f. Gall bladder

  • It stores bile produced in the liver. Bile emulsifies fats and oils making them easy to digest.
  • Bile also helps to neutralise acids from the stomach.
  • The bile duct carries bile from gall bladder to duodenum.

g. Pancreas

  • It produces pancreatic juices which contain enzymes that help to further digest proteins, carbohydrates and fats.

h. Duodenum

  • This is the first part of the small intestine.

i. Caecum

  • It accepts and stores processed material from the small intestine and moves it towards the colon.
  • It also absorbs water and salts.

j. Large intestines (Colon)

  • It absorbs water and salts.

k. Rectum

  • It holds the undigested matter called faeces before being passed out through the anus.

l. Anus

  •  This is where indigested food is passed out of the body as faeces. This is called egestion.

m. Small intestine (Ileum)

  •  They produce enzymes which continue the digestion of proteins, carbohydrates, fats and oils.
  • This is where most of the digestion and absorption of food into the blood stream take place.
  • Absorption into the blood stream happens through villi.
  •  The soluble food particles are carried to all body parts for use in growth, reproduction, tissue repairs and many more.
  • This use of food in the body is called assimilation.

Ruminant and Non-ruminant animals

  • Ruminants are animals which have a stomach with four sections which are rumen, reticulum, omasum and abomasum.
  • The stomach contains bacteria which helps to digest cellulose.
  • Examples of ruminant animals are cattle, goats and sheep.


Functions of parts of a ruminant

  •  When a cow ingests grass, the grass is passed into the first two chambers which are the rumen (1st stomach) and the reticulum (2nd stomach).
  • The grass is mixed with saliva and separate into layers of solid and liquid material. Inside the rumen and reticulum there are millions of bacteria which digest the cellulose by a process called bacterial fermentation.
  • Solids clump together to form cud or bolus.
  • The cud is then regurgitated back into the mouth and chewed to completely mix it with saliva and to break down the particle size.
  • The food is swallowed for the second time directly into the omasum where water and mineral salts are absorbed into the blood stream.
  • Food material from the omasum is then moved to the abomasum which is the true stomach.
  • The food material is finally moved to the small intestine where digestion and absorption of nutrients occurs.

Non-ruminants: are animals which have a single stomach. 

  • They do not regurgitate and re-chew food. Food is digested in one stomach.
  • Examples of non-ruminant animals are rabbit, pig and chicken.
  • The caecum contains millions of bacteria that help to digest cellulose by the process of bacterial fermentation.
  • A rabbit has a long caecum containing bacteria which help in the digestion of cellulose.
  • The caecum is where the small intestine joins the large intestine.  
  • Most of the animals that feed on plant matter rely on bacterial fermentation to help in their digestion process.


SUMMARY

  • Parts of the mammalian alimentary canal and its associated organs include oesophagus, stomach, small and large intestines, caecum, anus, salivary glands, liver, gall bladder and pancreas.
  • A ruminant animal chews the cud and has four stomach chambers – rumen, reticulum, omasum and abomasum.
  • A non-ruminant animal does not chew the cud.