Human Digestive System

Digestion is the process our body uses to break down the food we eat into smaller parts so we can use it for energy, growth, and repair. It starts in the mouth when we chew food and continues in the stomach and intestines, where special juices break the food down even more. The useful parts of the food are absorbed into our blood, and the waste is removed from the body.

The food we eat is broken down in our body to form substances that can mix with the blood. This process happens inside a long, flexible tube called the alimentary canal.

• The alimentary canal starts at the mouth and ends at the anus. Even though it’s one long tube, the shape and structure of the tube change in different parts.
• These different parts are called digestive organs, and each part has its own job to help with digestion.
• Some glands, which are located outside the alimentary canal, also help with digestion by producing juices that break down food.

Human beings are complex animals with complex digestive systems. The human digestive system is composed of an alimentary canal and some accessory glands. The alimentary canal is divided into several parts, like the oesophagus, stomach, small intestine, large intestine, rectum and anus. The salivary gland, liver and pancreas are the accessory glands that lie outside the alimentary canal.

1. Mouth: intake of the food.

2. Teeth: Chewing/grinding of food.

3. Tongue: Rolling of food, tasting of food, swallowing/pushing down the food.

4. Salivary glands secrete saliva and mucus (a sticky, gelatinous material that lines your lungs, throat, mouth, nose and sinuses). Starch is converted into glucose by saliva (Salivary amylase)

5. Oesophagus: It takes the food from the mouth to the stomach by peristaltic movements (contraction and expansion of muscles of the oesophagus)

6. Stomach: Gastric glands present in the stomach secrete gastric juice.

7. Small intestine: it is the site of the complete digestion of carbohydrates, proteins and fats

• The walls of the small intestine secrete an intestinal enzyme that converts carbohydrates into glucose, fats into fatty acids + glycerol, and proteins into amino acids.
• It has villi (finger projections), which help absorb food into the blood. It receives the secretions of the liver and pancreas.
• The food is acidic, which makes it alkaline for the pancreatic enzymes to act. The pancreas secretes pancreatic juice, which contains enzymes like trypsin, which digests proteins, and lipase, which breaks down emulsified fats.
• Fats are present in the intestine in the form of large globules, which makes it difficult for enzymes to act on them. Bile salts break them down into smaller globules, which increases the efficiency of enzyme action

8. Large intestine: It absorbs excess water, and the rest of the material is eliminated from the body via the anus.