Enzymes, Digestion, and Nutrient Absorption: A Detailed Look
Enzymes and Catalysis
Enzymes are biological catalysts produced by living organisms. A catalyst accelerates a reaction without being consumed. Enzyme activity is influenced by temperature and pH, which affect their shape.
Diffusion
Diffusion is the net movement of particles from a high concentration area to a low concentration area, occurring in liquids and gases due to random particle motion.
Macronutrients
Carbohydrates
Carbohydrates are composed of simple sugars, containing carbon, hydrogen, and oxygen (e.g., maltose, starch). Sources like pasta, rice, and sugar provide energy.
Proteins
Proteins are long chains of amino acids, containing carbon, nitrogen, hydrogen, and oxygen. Found in meat and fish, they are essential for tissue growth and repair.
Lipids
Lipids are made of fatty acids and glycerol, containing carbon, hydrogen, and oxygen. They provide insulation.
Testing for Sugars and Starches
- Glucose: Detected using Benedict’s solution.
- Starch: Detected using iodine solution.
Mineral Ions
- Calcium: Found in milk and cheese, crucial for bones and teeth.
- Iron: Found in red meat, essential for hemoglobin and healthy blood.
Digestive Enzymes
Digestive enzymes break down large molecules into smaller, soluble ones. Large molecules like starch, proteins, and fats are insoluble and cannot pass through the digestive system walls. Smaller molecules like sugars, amino acids, glycerol, and fatty acids are soluble and easily absorbed.
Enzyme Actions
- Amylase: Converts starch into maltose.
- Maltase: Converts maltose into glucose.
- Proteases: Convert proteins into amino acids.
- Lipases: Convert lipids into glycerol and fatty acids.
Bile
Bile neutralizes stomach acid and emulsifies fats.
The Alimentary Canal
The alimentary canal is the digestive tract through the body.
Organs of the Digestive System
- Mouth: Salivary glands produce amylase; teeth break down food mechanically.
- Oesophagus: Muscular tube connecting the mouth and stomach.
- Liver: Produces bile.
- Gall Bladder: Stores bile.
- Large Intestine: Absorbs excess water.
- Anus: Eliminates feces.
- Small Intestine: Produces protease, amylase, and lipase; absorbs nutrients.
- Pancreas: Produces and releases protease, amylase, and lipase into the small intestine.
- Stomach: Pummels food; produces pepsin (a protease) and hydrochloric acid.
Stomach Acid
Hydrochloric acid in the stomach kills bacteria and provides the correct pH (pH 2) for pepsin to function.
Peristalsis
Food is moved through the gut by peristalsis, which are waves of muscular contractions that squeeze food boluses through the digestive tract.
The Digestive Process
Ingestion
Putting food or drink into the mouth.
Digestion
The breakdown of large, insoluble molecules into small, soluble ones. This involves mechanical (teeth, stomach muscles) and chemical (enzymes, bile) processes.
Absorption
Movement of molecules through the intestinal walls into the blood.
Assimilation
Movement of digested molecules into body cells, where they become part of the cells.
Egestion
Elimination of undigested material (feces) through the anus.
Villi and Absorption
Villi in the small intestine enhance absorption. The small intestine is long, allowing time for digestion and absorption. Its large surface area, due to villi and microvilli, facilitates efficient nutrient uptake. Villi have a single permeable layer of surface cells and a good blood supply for quick absorption.