1. Gastrin: It is produced by the G-cells of the stomach and helps in the secretion of gastric juice. The hormone gastrin regulates HCl secretion.
2. Somatostatin: This hormone is released from G-cells and hypothalamus and inhibits gastrin secretion. It also reduces gastric secretion and pancreatic juice secretion.
3. Kallikrein: It is secreted from the salivary glands and dilates the blood vessels of the salivary glands. It increases blood circulation. As a result, the amount of salivary secretion also increases.
4. Secretin: Secretin hormone helps in the production of bicarbonate ions in pancreatic and liver cells. Pancreatic juice and bile are more alkaline due to bicarbonate ions. As a result, an alkaline environment is created in the digestive system.
5. Cholecystokinin: It helps in the secretion of bile in the duodenum. In 1928 scientists Ivy and Oldberg discovered the hormone cholecystokinin.
6. Villikinin: Villikinin hormone increases the absorption capacity by strengthening the villi of the small intestine.
7. Testosterone and Estrogen: Testosterone and estrogen regulate protein metabolism.
8. Pancreasin: This hormone helps in the secretion of pancreatic juice. In 1943, Harper and Rapper discovered the hormone pancreozynin.
9. Enterocrinein: This hormone helps in the secretion of intestinal juice. Intestinal juice participates in digestion.
10. Diocranin: It is produced by the wall of duodenum and helps in the secretion of intestinal juice.
11. Peptide YY: Peptide YY is secreted from the wall of the ileum. It makes the food flow slowly. It completes food digestion and absorption.
12. Gastric inhibitory peptide: Gastric inhibitory peptide is secreted from the wall of the duodenum. It controls the passage of food from the stomach into the intestine. It initiates insulin secretion.
13. Vasoactive intestinal peptide: This hormone is secreted from the epithelial wall of the small intestine. It dilates the blood vessels of the intestinal wall. Stops gastric acid secretion.
14. Hormones that regulate hunger and satiety: The hypothalamus of the brain has the hunger center. It regulates human appetite and food intake. Peptide YY, gastric inhibitory peptide (GIP), vasoactive intestinal peptide (VIP), glucagon like peptide-1 (GLP-1), pancreatic polypeptide (PP) and ghrelin act as neurotransmitters in the brain. Among them, peptide YY, pancreatic polypeptide and ghrelin regulate food intake. When the level of ghrelin hormone increases in the blood, hunger is stimulated. When the levels of pancreatic polypeptide and peptide YY hormones increase in the blood during food intake, food satisfaction comes.

Mechanical digestion of food
1. Segmentation of food occurs in the small intestine. Food mixes well with intestinal juices and mucus. Food moves equally everywhere from front to back.
2. Chyme moves slowly through the circulation by peristalsis.
3. Intestinal mucin mixes with food to lubricate it and move it from one place to another.
4. Mucus secreted by Brunner’s glands and goblet cells protects the small intestinal wall from enzyme action.
5. Bile reduces the action of bacteria and increases the speed of bile digestion.
6. The hormone cholecystokinin causes the gallbladder to contract. As a result, bile reaches the small intestine.
7. The brass emulsifies the lubricant into tiny particles like soap suds.
Chemical digestion of food
1. Protein digestion
(i) Amino peptidase enzyme breaks down polypeptides into amino acids.
(ii) Prolidase enzyme cleaves the peptide into proline.
(iii) Dipeptide and amino acids are produced from tripeptide under the action of tripeptidase enzyme.
(iv) Dipeptidase enzyme breaks down dipeptide into amino acids.
2. Carbohydrate digestion
(i) Amylase enzyme breaks down starch and dextin into maltose, maltotriose and minor dextin.
(ii) Maltose and glucose are produced from isomaltose under the action of isomaltase enzyme.
(iii) Maltotriase enzyme breaks down maltotriose into glucose.
(iv) Glucose is produced from maltose under the action of maltase enzyme.
(v) Sucrase enzyme breaks down sucrose into glucose and fructose.
(vi) Glucose and galactose are produced from lactose under the action of lactase enzyme.
3. Lipid digestion
(i) The enzyme lipase breaks down triglycerides and diglycerides into fatty acids, glycerol and monoglycerides.
(ii) Fatty acids and glycerol are produced from monoglycerides under the action of monoglyceridase enzyme.

1. Protein digestion
(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.
(R) Peptides are produced from collagen by the action of collagenase enzyme.
2. Carbohydrate digestion
(i) Enzyme amylase breaks down starch and glycogen into maltose, maltotriose and dextin.
(ii) Maltose is converted to glucose in the presence of maltase enzyme.
3. Lipid digestion
(i) The enzyme lipase breaks down lipids into fatty acids and glycerol.
(ii) Phospholipids are converted into fatty acids and monoglycerides in the presence of phospholipase enzymes.

1. The biliary system of bile emulsifies the substance and makes it suitable for the action of lipase.
2. Acts as an activator of bile lipase.
3. Bile creates an alkaline environment by neutralizing the acidity of the digestive tract.
4. Bile helps in the absorption of fat soluble vitamins.
5. Gallbladder increases the peristalsis of the colon and aids in the evacuation of stool.
6. Toxins, cholesterol, bile acids, zinc, copper, mercury etc. are released through bile.

1. Mechanical digestion of food
(i) Crushed red food passes through the cardiac orifice into the stomach. At this time cardiac and pyloric sphincter openings are closed.
(ii) Peristalsis waves are initiated in the stomach. The peristalsis wave begins at the fundus of the stomach and ends at the pylori.
(iii) Peristalsis occurs due to contraction of circular muscles and longitudinal muscles. At the top of the esophagus are the circular muscles and at the bottom are the longitudinal muscles.
(iv) Cardiac sphincter dilates when food reaches end of esophagus and food is expelled into stomach.
(v) Gastric juice and hydrochloric acid mix with food inside the stomach to form chyme.
(vi) HCl secreted from the stomach destroys food microbes. Creates an acidic environment for digestion.
2. Chemical digestion of food
(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.
(iii) Lipase enzyme breaks down lipids to produce fatty acids, glycerol and monoglycerides.

Mechanical digestion
1. Saliva moistens and softens food. Water moistens the mouth and tastes. Saliva helps in chewing and swallowing food.
2. The taste buds of the tongue receive sensations from wet food. Then it is possible to understand the taste of food.
3. Mucin converts food into lubricators.
4. Saliva helps in chewing and swallowing food. Helps to neutralize acid and alkali.
5. Chloride present in saliva activates amylase.
6. Salivary bicarbonate acts as a buffer. It reduces the strength of mouth acid and prevents erosion of tooth enamel.
7. Salivary immunoglobulin acts as antibacterial.
8. Saliva cleans food debris from the teeth and maintains the sensitivity of the soft parts of the mouth.
Chemical digestion
1. The enzyme tyalin breaks down starch and glycogen into maltose, maltotriose and isomaltose.
2. Maltose is converted into glucose under the action of maltase enzyme.

1. Digested in the mouth
There are no enzymes that digest lipids in the mouth. The mucin of the salivary glands makes the food slippery.
2. Digestion in the stomach
The enzyme lipase breaks down lipids to produce fatty acids, glycerol and monoglycerides.
3. Digestion in the pancreatic juice of the small intestine
(i) The enzyme lipase breaks down lipids into fatty acids and glycerol.
(ii) Phospholipids are converted into fatty acids and monoglycerides in the presence of phospholipase enzymes.
4. Digestion in the intestinal juice of the small intestine
(i) The enzyme lipase breaks down triglycerides and diglycerides into fatty acids, glycerol and monoglycerides.
(ii) Fatty acids and glycerol are produced from monoglycerides under the action of monoglyceridase enzyme.
Lipids are complex biochemical substances. It is complex, insoluble and non-absorbable for the organism. It is of no benefit to the organism. Lipids are digested into fatty acids and glycerol by the action of various enzymes. Fatty acids and glycerol are simple, soluble and absorbable by the body. Our body cells absorb fatty acids and glycerol. These fatty acids and glycerol provide energy to our body.

Carbohydrates are complex biochemical substances. It is complex, insoluble and non-absorbable for the organism. It is of no benefit to the organism. Sugars are digested into glucose, fructose and galactose by the action of various enzymes. Glucose, fructose and galactose are simple, soluble and absorbable by the body. Our body cells absorb glucose and fructose. Glucose and fructose are then used to build the body and produce the energy it needs. The requirements for carbohydrate digestion are discussed below.
1. Source of energy: Carbohydrates are the main source of energy in the body. Carbohydrates are oxidized to produce energy. Lack of this leads to lack of energy in the body and gradually weakens the body.
2. As stored food: Carbohydrates are digested to produce glucose and fructose. Glucose and fructose are stored in the body as stored food.
3. As a patient’s diet: Glucose is simple and soluble and acts as a patient’s diet. Therefore, for sick and weak people, carbohydrates need to be digested quickly.
4. Physical Growth: Glucose and fructose in quantity are essential for normal growth of the body.
5. Vitamin production: Carbohydrates are digested and converted into glucose. Glucose makes vitamin C in the body.
6. Structural material: Cellulose and hemicellulose act as the structural material of plants.
7. Blood volume regulation: Liver glycogen is converted to glucose. This glucose controls the amount of blood in the body.
Carbohydrates are the main source of energy in the body. Carbohydrates provide all the energy the body needs. Adequate intake of glucose is required for normal growth and keeping the body healthy. However, there is a possibility of diabetes if there is excess glucose in the blood.

1. Digested in the mouth
(i) Tyalin enzyme breaks down starch and glycogen into maltose, maltotriose and isomaltose.
(ii) Maltose is converted into glucose under the action of maltase enzyme.
2. Digestion in the stomach
(i) Lysozyme destroys bacteria ingested with food.
3. Digestion in the pancreatic juice of the small intestine
(i) The enzyme amylase breaks down starch and glycogen into maltose, maltotriose and dextin.
(ii) Maltose is converted to glucose in the presence of maltase enzyme.
4. Digestion in the intestinal juice of the small intestine
(i) Amylase enzyme breaks down starch and dextin into maltose, maltotriose and minor dextin.
(ii) Maltose and glucose are produced from isomaltose under the action of isomaltase enzyme.
(iii) Maltotriase enzyme breaks down maltotriose into glucose.
(iv) Glucose is produced from maltose under the action of maltase enzyme.
(v) Sucrase enzyme breaks down sucrose into glucose and fructose.
(vi) Glucose and galactose are produced from lactose under the action of lactase enzyme.
Carbohydrates are complex biochemical substances. It is complex, insoluble and non-absorbable for the organism. It is of no benefit to the organism. Sugars are digested into glucose and fructose by the action of various enzymes. Glucose and fructose are simple, soluble and absorbable by the body. Our body cells absorb glucose and fructose. It is this glucose and fructose that gives energy to our body.

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. This protein is essential for the body. Protein digestion requirements are discussed below.
1. Body Structure: Protein acts as the structural component of the human body. Fibrous proteins make connections between different tissues of the body. Collagen protein forms the body’s skin, tendons, bones, cartilage, etc. It protects the joints between muscles. Carotene protein forms hair and nails. Protein completes the necessary functions of the body through digestion.
2. As stored food: Protein is stored in the body as stored food after digestion.
3. Transmission of Hereditary Traits: Genetic information stored in DNA-molecules is released through protein synthesis. Histone proteins maintain the stability of chromosomes, bind nucleic acids and play special roles in gene expression. It transfers hereditary traits from generation to generation.
4. Physical Growth: Protein is essential for normal growth of the body. Humans are dwarfed due to lack of protein. It promotes the healthy development of the intelligence of the organism.
5. Immunity: Proteins produce antibodies in the body. As a result, the immune system of the body increases. Currently, various types of viruses have been identified as the cause of cancer. A special protein called interferon is used to treat blood cancer. If there is a deficiency of protein, the body gets sick easily. So protein needs to be digested in the body.
6. Energy production: Protein produces the energy required by the body. Lack of this leads to lack of energy in the body and gradually weakens the body. Therefore, protein digestion is very important in the body.
7. Organ Deformation: Proteins determine the shape of various body organs. Prevents nervous weakness. Smoothens the skin. Stops hair loss.
8. Transport function: A protein called hemoglobin transports oxygen and carbon dioxide in the body. It also transports some ions.
9. Structure of cell membrane: Protein forms the plasma membrane, nuclear membrane, membrane of various cellular organelles etc.
10. Hormone production: Protein plays a role in the production of various types of hormones.
11. Regulation of reactions: Proteins regulate different types of reactions in the body.
Protein is the main component of the body. Organisms cannot be formed without protein. In its absence, various organs of the body become damaged. The body is affected by various diseases. To keep the body healthy, strong and disease-free, it is necessary to consume enough protein. If the amount of protein in the body is normal, the structure of the body is smooth and the skin is smooth. But if there is a deficiency of protein in the body, the body will become weak and the organism will fall into the lap of death due to lack of it.