Absorption and Assimilation
Absorption is the process by which digested food molecules pass through the intestinal walls into the bloodstream or lymph. Assimilation is the utilization of these absorbed nutrients by body cells for energy, growth, and repair.
How Nutrients are Absorbed
The absorption of nutrients occurs mainly in the small intestine, where digested food is absorbed into the blood or lymph. Different nutrients are absorbed in specific ways:
- Carbohydrates → Broken down into glucose → Absorbed into the blood via active transport and facilitated diffusion.
- Proteins → Broken down into amino acids → Absorbed into the blood through active transport.
- Fats → Broken down into fatty acids and glycerol → Absorbed into the lymphatic system via lacteals.
- Water and Minerals → Absorbed directly into the blood by diffusion and osmosis.
- Vitamins
- Water-soluble vitamins (B, C): Absorbed directly into the blood.
- Fat-soluble vitamins (A, D, E, K): Absorbed with fats into the lymph.
Role of Villi in Small Intestine
The villi are small finger-like projections lining the walls of the small intestine, increasing the surface area for absorption. Their functions include:
- Increased Surface Area – More absorption due to their numerous folds.
- Rich Blood Supply – Capillaries transport glucose and amino acids into the bloodstream.
- Lacteals – Absorb fatty acids and glycerol into the lymphatic system.
- Thin Walls – Help in the easy diffusion of nutrients.
Transportation of Nutrients
Once absorbed, nutrients are transported throughout the body:
- Bloodstream – Glucose, amino acids, water, and minerals are transported via blood to different organs.
- Lymphatic System – Fats are transported via lacteals and later enter the bloodstream.
- Liver (Hepatic Portal System) – Nutrients first pass through the liver for detoxification and storage before distribution.
- Cells and Tissues – Nutrients are delivered to cells, where they are used for energy, growth, and repair.