Digestion and Nutrient Absorption

Digestion, Absorption, and Transport

• Digestion is the breakdown of large, insoluble food molecules into smaller, water-soluble molecules that can be absorbed into the bloodstream. This process occurs in the alimentary canal.

• Mechanical digestion involves physical breakdown of food, increasing the surface area for chemical digestion. This includes chewing (mastication) and churning of food in the stomach.

• Chemical digestion involves the use of enzymes to break down large complex molecules into smaller simpler molecules for absorption. This includes the action of enzymes like amylase, protease, and lipase.

Nutrient Absorption

• Nutrient absorption is the process by which the products of digestion are taken up from the alimentary canal into the bloodstream or lymphatic system.

• This absorption primarily occurs in the small intestine.

• Different nutrients are absorbed by different mechanisms, influenced by their chemical structure.

Types of Nutrient Absorption

• Carbohydrates are absorbed as monosaccharides (e.g., glucose).
• Proteins are absorbed as amino acids.
• Lipids are absorbed as fatty acids and glycerol.

Chemical Digestion

• Chemical digestion involves breaking down complex food molecules into smaller, simpler molecules using enzymes.
• Different enzymes are used for different nutrients:
  • Amylase breaks down carbohydrates.
  • Proteases break down proteins.
  • Lipases break down lipids.
• Enzymes are highly specific in their action; each enzyme works on only a particular type of molecule.
• The enzymes' activity is affected by factors like pH and temperature.

Transport Mechanisms

• Once absorbed, nutrients need to be transported to different parts of the body for utilization.
• Different transport mechanisms exist depending on the nutrient's chemical nature and the site of absorption.
• Simple diffusion involves passively moving molecules across a concentration gradient.
• Facilitated diffusion uses carrier proteins for moving molecules across a membrane.
• Active transport requires energy to transport molecules against the concentration gradient.
• Lymphatic system plays a crucial role in transporting fat-soluble vitamins and lipids.
• Bloodstream carries water-soluble nutrients to various cells and tissues for utilization, storage, or further metabolism.

Summary of Digestion Processes

• Mouth: Mechanical digestion (chewing) begins, and salivary amylase initiates chemical digestion of starch.
• Stomach: Mechanical digestion (churning) continues, and protein digestion by pepsin begins.
• Small intestine: Major site of chemical digestion and absorption. Enzymes from the pancreas and the small intestine complete the breakdown of carbohydrates, proteins, and fats. The products of digestion are absorbed into the bloodstream.
• Large intestine: Absorbs water and electrolytes, forming feces.
• Rectum and anus: Feces are eliminated from the body.