Human Digestive System

Digestive System

• The digestive system is a complex process by which the body breaks down and absorbs nutrients from food.
• It consists of the following organs:
  • Mouth
  • Esophagus
  • Stomach
  • Small intestine
  • Liver
  • Pancreas
  • Gallbladder
  • Large intestine (colon, rectum, and anus)

Glands

• The digestive system has several glands that produce digestive enzymes and hormones:
  • Salivary glands (produce salivary amylase)
  • Gastric glands (produce pepsin and gastric amylase)
  • Pancreatic glands (produce pancreatic amylase, lipase, and trypsin)
  • Liver (produces bile)
  • Gallbladder (stores bile)

Process of Digestion

• Mechanical digestion: food is broken down into smaller pieces by chewing and grinding
• Chemical digestion: enzymes break down molecules into smaller nutrients
• The process of digestion occurs in the following order:
  1. Mouth: food is mixed with salivary amylase
  2. Esophagus: food is swallowed and passes through the esophagus
  3. Stomach: food is mixed with pepsin and gastric amylase
  4. Small intestine: most of chemical digestion and absorption occurs
  5. Large intestine: water and electrolytes are absorbed, and waste is prepared for elimination

Enzymes

• Enzymes are biological molecules that speed up chemical reactions
• Digestive enzymes break down macromolecules into smaller nutrients:
  • Carbohydrases (e.g. amylase): break down carbohydrates into simple sugars
  • Proteases (e.g. pepsin, trypsin): break down proteins into amino acids
  • Lipases (e.g. pancreatic lipase): break down fats into fatty acids and glycerol

Absorption

• Absorption is the process by which nutrients are taken into the bloodstream
• Occurs mainly in the small intestine, where the walls are lined with finger-like projections called villi
• Villi increase the surface area for absorption, allowing more nutrients to be absorbed
• Absorbed nutrients are transported to the liver for processing and distribution to the rest of the body

Digestive System

• Consists of multiple organs: mouth, esophagus, stomach, small intestine, liver, pancreas, gallbladder, large intestine (colon, rectum, and anus)
• Breaks down and absorbs nutrients from food

Glands and Enzymes

• Salivary glands produce salivary amylase
• Gastric glands produce pepsin and gastric amylase
• Pancreatic glands produce pancreatic amylase, lipase, and trypsin
• Liver produces bile
• Gallbladder stores bile
• Enzymes speed up chemical reactions, breaking down macromolecules into smaller nutrients
• Carbohydrases (e.g. amylase) break down carbohydrates into simple sugars
• Proteases (e.g. pepsin, trypsin) break down proteins into amino acids
• Lipases (e.g. pancreatic lipase) break down fats into fatty acids and glycerol

Process of Digestion

• Mechanical digestion: food is broken down into smaller pieces by chewing and grinding
• Chemical digestion: enzymes break down molecules into smaller nutrients
• Food is mixed with salivary amylase in the mouth
• Food is swallowed and passes through the esophagus
• Food is mixed with pepsin and gastric amylase in the stomach
• Most of chemical digestion and absorption occurs in the small intestine
• Water and electrolytes are absorbed, and waste is prepared for elimination in the large intestine

Absorption

• Occurs mainly in the small intestine, where the walls are lined with finger-like projections called villi
• Villi increase the surface area for absorption, allowing more nutrients to be absorbed
• Absorbed nutrients are transported to the liver for processing and distribution to the rest of the body

Digestive System

• Consists of the mouth, esophagus, stomach, small intestine, and large intestine
• Responsible for breaking down food into nutrients that can be absorbed and utilized by the body

Glands and Their Roles

• Salivary glands produce saliva with enzymes to break down carbohydrates
• Gastric glands produce stomach acid and enzymes to break down proteins
• Pancreatic glands produce digestive enzymes to break down carbohydrates, proteins, and fats
• Intestinal glands produce enzymes to break down carbohydrates and proteins

Process of Digestion

• Food is broken down into smaller pieces by teeth in the mouth
• Saliva with enzymes breaks down carbohydrates in the mouth
• Food is swallowed and passes through the esophagus into the stomach
• Stomach acid and enzymes break down proteins in the stomach
• Most of the nutrient absorption takes place in the small intestine
• Water and electrolytes are absorbed, and the remaining waste is prepared for elimination in the large intestine

Enzymes and Their Functions

• Amylase breaks down carbohydrates into simple sugars
• Protease breaks down proteins into amino acids
• Lipase breaks down fats into fatty acids and glycerol
• Peptidase breaks down peptides into amino acids
• Lactase breaks down lactose into glucose and galactose

Absorption of Nutrients

• Mechanisms of absorption include passive transport, active transport, and facilitated diffusion
• Most of the nutrient absorption takes place in the small intestine
• Surface area, blood flow, and enzyme activity influence absorption