SCIENCE NOTES-DIGESTIVE SYSTEM-DIGESTION PROCESS
- Parts of body concerned with digestion, absorption and assimilation of food followed by elimination of undigestible remains is called digestive system.
- Digestion involves splitting of food molecules by hydrolyses into smaller molecules that can be absorbed through the epithelium of the gastro intestinal tract.
- Study of teeth is called odontology
- Enamel is the outer covering of teeth. It is the hardest part of human body.
- Maximum number of teeth are present in horse and pig.
- Elephant tusk is upper second incisor. It is the largest teeth.
Dental formula of some common mammals
Mammals – Dental formula – Total number of teeth
Child – 2120/2120 – 20
Man – 2123/2123 – 32
Dog – 3142/3143 – 42
Rabbit – 2033/1033 – 28
Horse – 3143/3143 – 44
Types of teeth
1. Incisors (8) = for cutting, Single rooted
2. Canines (4) = for tearing, Single rooted
3. Pemolars (8) = for breaking, two/three rooted.
4. Molars (12) = for grinding, four rooted
Note: Third molar teeth is also called wisdom teeth. It is vestigeal, grow after 17 years age.
Digestion in different parts of body
1. Digestion in Baccal cavity – Baccal cavity have salivary glands.
- The function of salivary glands is to produce saliva, which softens, moistens and dissolves food.
- Daily output of saliva is 1.5 litres and a pH-6.8 (6.2 to 7.4).
- The major enryme present in saliva is ptyalin (amylase)
- 20% starch digestion occurs here. (Structure of digestive system)
2. Digestion in stomach
- The food passes down through the esophagus into stomach.
- Now food is mixed with gastric juice.
- Stomach serves as a reservoir for food before release into small intestine.
- It secretes gastric juice, which contains HCI, Pepsin, intrinsic factor and gastric lipase.
- In stomach mainly protein digestion occur.
- The digestive action of the stomach reduce food particles to a solution known as chyme,
3.Digestion in small intestine
- Region of the small intestine includes the duodenum, jejunum and ileum.
- Chyme move to duodenum.
- Small intestine receive bile from the liver and pancreatic juice from the pancreas. The enzyme in pancreatic juice and enzymes produced by the intestinal wall complete the process of food digestion.
- No dgestive enzyme found in bile but it help in emulsification of fat.
- Bile have two pigment < Bilirubin, Biliverdin
- It daily output is 1/2 litre
- Bile is secreted from liver and stored in gall bladder.
- Formation of stones in gall bladder is due to the deposition of calcium oxalate.
- Chronic alcoholism and hepatitis ‘C’ (and B) are the most common cause of liver cirrhosis.
- Typsin is secreted from pancreas
- . It is the fastest protein digestive enzyme.
- About 70% starch is digested by the action of poncreatic anylas.
ABSORPTION AND ASSIMILATION OF DIGESTED FOOD
Ileum’s internal surface has finger like folds called villi. There is a dense network of blood capillaries and lymph capillaries in each villi. It helps in absorption of food. Absorption occurs by two type of processes passive and active absorption.