1. Main Purpose of Digestion in the Body

The main purpose of digestion is to break down food into smaller, absorbable components so that the body can extract and use nutrients like carbohydrates, proteins, fats, vitamins, and minerals. These nutrients are necessary for energy, growth, tissue repair, and maintaining overall bodily functions. Digestion also ensures that waste products are prepared for elimination.

2. Difference Between Mechanical Digestion and Chemical Digestion

Mechanical Digestion: This involves the physical breakdown of food into smaller pieces without changing its chemical structure. It includes processes like chewing (in the mouth), churning (in the stomach), and peristalsis (the wave-like muscle contractions that move food through the digestive tract). The goal is to increase the surface area of the food for more efficient chemical digestion.

Chemical Digestion: This is the breakdown of food into smaller, absorbable molecules through enzymatic reactions. Enzymes and digestive fluids (such as saliva, bile, and gastric juices) chemically break down complex molecules like carbohydrates, proteins, and fats into simpler molecules (like glucose, amino acids, and fatty acids), which can then be absorbed by the body.

3. Enzymes and Substances Involved in Breaking Down Proteins, Fats, and Carbohydrates

Proteins:

Pepsin: Secreted in the stomach, it starts breaking down proteins into smaller peptides.

Trypsin and Chymotrypsin: These enzymes, produced by the pancreas and released into the small intestine, further break down peptides into smaller amino acids.

Peptidases: Enzymes in the small intestine that break down smaller peptides into individual amino acids.

Fats:

Lipase: Secreted by the pancreas, it breaks down fats into fatty acids and glycerol in the small intestine.

Bile: Produced by the liver and stored in the gallbladder, bile emulsifies fats, breaking them into smaller droplets, which increases the surface area for lipase to act upon.

Carbohydrates:

Amylase: Found in saliva and pancreatic juices, amylase breaks down starches into simpler sugars like maltose.

Sucrase, Lactase, and Maltase: These enzymes, located in the small intestine, break down disaccharides (sucrose, lactose, and maltose) into monosaccharides (glucose, fructose, and galactose), which can be absorbed by the body.

4. Where Does Most Nutrient Absorption Occur in the Digestive System?

Most nutrient absorption occurs in the small intestine, specifically in the duodenum, jejunum, and ileum. The inner lining of the small intestine contains numerous folds, villi, and microvilli that greatly increase the surface area for absorption. This allows nutrients from digested food to pass through the walls of the intestine into the bloodstream or lymphatic system, where they are transported to various parts of the body.

5. Role of Villi and Microvilli in the Process of Absorption in the Small Intestine

Villi: These are tiny, finger-like projections on the inner lining of the small intestine. Each villus is covered with even smaller projections called microvilli. The villi increase the surface area for absorption and contain capillaries that allow nutrients to enter the bloodstream. They also contain lymphatic vessels (lacteals) for the absorption of fats.

Microvilli: These are even smaller hair-like structures found on the epithelial cells of the villi. They further increase the surface area for nutrient absorption. Microvilli contain enzymes that help break down nutrients into their simplest forms, and they transport these nutrients into the cells of the small intestine, where they are then absorbed into the blood or lymphatic system.