Function of the digestion system
Ingestion - is the taking in of food into the body through the mouth.
Digestion - is the breakdown of large,insoluble food molecules into simple,soluble molecules by means of enzyme.
Mechanical Digestion - the cutting and/or crushing action of the teeth followed by the rhythmical contractions of the gut.
Chemical digestion - involves ezymes secreted by glands outside the gut (Salivary gland,Pancreas) and glands located within the gut wall itself
Absorption - is the passage of digested food through the gut wall into the blood.
Egestion - is the elimination from the body of food that can not be digested e.g. Cellulose cell walls of plants.
Human Digestion System
The main regions of the human gut are :
- Oesophagus (Gullet)
- Small Intestine (Duodenum,ileum)
- Large Intestine
Food is needed as a source of energy for :
- Synthesis of body tissues
- Keeping warm
- Active transport
Food is propelled along the gut by peristalsis and is processed as it passes through the regions of the gut.
Structure Of The Mammalian Gut
The gut wall from the mouth to the anus consist of 4 tissue layers surrounding the lumen of the gut :
- Serosa (Outer Layer)
- Muscle Layer
- Mucosa (Innermost Layer )
The muscle layer consists of 2 layers of muscle running in different directions:
- The inner circular muscle
- The outer longitudinal layer
The circular muscles contract behind the ball of food to squeeze the food along,while the longitudinal muscles relax.
The Human Digestion System Diagram
Large Glands Found Outside The Gut
- Salivary Glands which saliva into the mouth.
- Liver which secretes bile into the duodenum.
- Pancreas which secretes pancreatic juice into the duodenum.
Glands In The Gut
The glands of the gut are of 3 types :
- Large glands found outside the gut with secretion passing through the tubes or duct into the gut.
- Glands in the form of cells in the sub-mucosa.
- Glands in the form of cells in the mucosa.