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.
