Teeth and Digestive System
- They are produced in two sets – temporary and permanent.
- The teeth are four types : incisors, canines, premolars and molars.
- A tooth consists of 3 regions : crown, neck and root.
- The crown is exposed. It is covered by a shining material called enamel.
- Enamel is the hardest substance in the human body.
- There are 4 incisors, 2 canines, 4 premolars and 6 molars in the upper jaw and exactly the same arrangement in the lower jaw. The Full number, i.e. 32.
- The premolars and the molars are called grinding teeth. The last molars are called the wisdom teeth.
- Linked with pharynx.
The human alimentary canal
Stages in digestive system
- In the mouth, the food is called bolus.
- In the stomach, the food is called chyme.
- Digestion initiates right from mouth, where Salivary gland secretes the Saliva in the mouth in which two types of enzymes are found, ptyalin and maltase.
- Around 1.5 litres of saliva is secreted in human on an average day, it is acidic in nature (pH 6.8)
- Also contains lysosome which kills bacteria.
- Through a food pipe or Oesophagus (25cm long tube), food reaches into the stomach. Food is carried by peristaltic movement.
- Gastric juices produced in the stomach help in digestion of food. Also contains HCl which kills bacteria and provides an acidic medium.
- Pepsin and Renin are the enzymes in the gastric juice.
- Hydrochloric acid makes the food acidic by which the ptyalin reaction of the saliva ends.
- Pepsin breaks down the protein into peptones and Renin breaks down the Caseinogen into Casein.
- Small intestine (duodenum+jejunum+ileum) : here the food is mixed with bile (from liver) and pancreatic juice(from pancreas).
- Bile converts food from acidic nature to alkaline nature.
- Pancreatic juice from pancreas combines with food and it contains the following enzymes:
- Trypsin: It converts the protein and peptone into polypeptides and amino acids.
- Amylase: It converts the starch into soluble sugar.
- Lipase: It converts the emulsified fats into glycerol and fatty acids.
- In the small intestine, intestinal juices secrete and it is alkaline in nature and around 2 litres of intestinal juice secreted per day.
- Intestinal juice contains the following enzymes:
- Erepsin: It converts the remaining protein and peptone into amino acids.
- Maltase: It converts the maltose into glucose.
- Sucrase: It converts the sucrose into glucose and fructose.
- Lactase: It converts the lactose into glucose and galactose.
- Major part of digestion takes place in the small intestine.
- Length of small intestine is 6mt (20ft) and large intestine 1.5mt (5ft).
- Both jejunum and ileum have numerous finger-like projections called the villi. Villi absorbs the products of digestion.
- Large intestine (caecum, colon, rectum) : it receives undigested food from the small intestine and absorbs water.
- Cellulose digestion takes place in caecum. It is very large in herbivores.
- The remaining waste material is sent to rectum and discharged from anus.