1. Buccal Digestion: Buccal does not contain any protein digesting enzymes. Mucin present in saliva makes the food slippery.
2. Digestion in the stomach
(i) Inactive pepsinogen is converted to active pepsin under the influence of HCl. Pepsin breaks down proteins into proteases and peptones.
(ii) Gelatinase enzyme breaks down gelatin to produce peptones and polypeptides.
3. Digestion in the pancreatic juice of the small intestine
(i) Inactive trypsinogen is converted to active trypsin under the action of enterokinase enzyme. Trypsin converts peptone into dipeptides and polypeptides.
(ii) Inactive chymotrypsinogen is converted to active chymotrypsin with the help of trypsin enzyme. Chymotrypsin breaks down milk casein into paracasein.
(iii) Elastase enzyme breaks down elastin into peptides.
(iv) Peptides are produced from collagen by the action of collagenase enzyme.
4. Digestion in the intestinal juice of the small intestine
(i) Amino peptidase enzyme breaks down polypeptides into amino acids.
(ii) Prolidase enzyme cleaves the peptide into proline.
(iii) Dipeptides and amino acids are produced from tripeptides under the action of tripeptidase enzyme.
(iv) Dipeptidase enzyme breaks down dipeptide into amino acids.
Protein is a complex biochemical substance. It is complex, insoluble and non-absorbable for the organism. It is of no benefit to the organism. Proteins are digested and converted into amino acids by the action of various enzymes. Amino acids are simple, soluble and absorbable by the body. Our body cells absorb amino acids. Later amino acids combine to form proteins. These proteins make up our body.

Food digestion in the human body occurs in two processes. Mechanical and Chemical.
1. Mechanical Digestion: The process in which food moves inside the alimentary canal through circulatory action is called mechanical digestion. During this time food is broken down into tiny pieces, chewed, digested and transported.
2. Chemical Digestion: The process in which complex food is converted into simple and absorbable material with the help of acid, acid, alkali and enzymes through a series of reactions is called chemical digestion.

It takes 24-72 hours for a healthy person to digest food. Very high-calorie fatty foods are digested in 6 hours and sugary foods in 2 hours. Food mixes with saliva to form a lumpy bolus. In the stomach, food is converted into chyme. Peristalsis or food waves occur in the stomach every 15-20 seconds. Love breaks down food into tiny granules. This process is called emulsification.
Stages of digestion
6 steps of complex food digestion in human body.
1 . Ingestion of food and water
2 . Mechanical digestion of food
3 . Chemical digestion of food
4 . Movement of food
5 . Absorption of food and water
6 . Waste disposal

The signal by which the number, position and nature of adult human teeth is known is called dental signal. Humans are diphyodont (grow twice) in nature. Babies have a total of 20 milk teeth in both jaws. Between the ages of 18-24, baby teeth fall out and 32 permanent teeth emerge. An adult human has four types of teeth. Incisor, Canine, Pre-molar and Molar.
1. Incisor: There are 4 incisor teeth in the front of each jaw. The teeth are sharp and suitable for tearing food. The incisors can exert a force equivalent to 55 pounds.
2. Canine: Each jaw has one incisor after the incisor. Its number is 2. The teeth are conical in shape and suitable for tearing hard food.
3. Pre-molar: Each jaw has two incisors after the incisors. Its number is 4. It involves chewing (mastication) and grinding food.
4. Molar: Each jaw has three molars after the incisors. Its number is 6. It chews and grinds food. Grinding teeth can exert a force equivalent to 200 pounds. Babies don’t have molars.

A diet that contains the six elements in equal amounts and provides nutrients and energy to the body is called a balanced diet. The 6 components of a balanced diet are sugars, proteins, fats, vitamins, minerals and water.

All enzymes present in the plasma membrane of microvilli are called membrane enzymes. Some membrane enzymes are holo-aminopeptidase, maltase, sucrase, lactase, alkaline phosphatase, nucleotidase, nucleosidase etc.

(i) Intestinal juice contains mucus. Mucus protects the intestinal wall from the action of enzymes.
(ii) Enterokinase in intestinal juice converts inactive trypsinogen to trypsin.
(iii) Maltase in intestinal juice converts maltose, sucrase converts sucrose and lactase converts lactose to glucose.
(iv) Peptidase enzyme in this juice converts polypeptides into amino acids.

(i) Water: Water content of intestinal juice is 98.5%.
(ii) Organic components: Intestinal juice contains enterokinase, trypsinogen, peptidase, amylase, maltase, lactase, sucrase and lipase.
(iii) Inorganic components: Intestinal juice contains sodium, potassium, calcium and magnesium salts.

The juice secreted from the small intestine or intestinal glands is called intestinal juice. This is called saccus intericus. It is alkaline in nature. Its pH value is 6.5-7.5.

The single-celled glands located in the mucosa layer of the intestinal wall are called enteric glands or small intestinal glands. The glands of the small intestine are – Brush cells, goblet cells, Libercun’s glands, Paneth cells, Argentefint cells and Bræner’s glands.