Human Digestive System

Overview

• The digestive system consists of the following parts:
  • Mouth
  • Salivary glands
  • Esophagus
  • Stomach
  • Liver
  • Pancreas
  • Gallbladder
  • Small intestine
  • Large intestine
  • Anus
• Food enters through the mouth and follows a path:
  • Mouth → Esophagus → Stomach → Small Intestine → Large Intestine → Anus
• This forms the alimentary canal with accessory glands like salivary glands, liver, gallbladder, and pancreas.

Process of Digestion

Initial Preparation

• Food must be made soft and wet for easy travel through the alimentary canal.
  • Teeth break food into smaller pieces.
  • Saliva (produced by salivary glands) wets the food and contains salivary amylase (also known as tyalin) which begins carbohydrate digestion by breaking down starch into sugars.
  • Tongue mixes food with saliva to form a bolus.

Movement Through Alimentary Canal

• Peristaltic Movements: Rhythmic contractions and relaxations of the canal's muscles create wave-like movements that propel food along the canal.

Digestion and Absorption

Stomach

• Receives food from the esophagus.
• Gastric glands secrete:
  • HCl (Hydrochloric Acid): Kills bacteria and provides an acidic pH necessary for protein digestion.
  • Pepsin: Enzyme that digests proteins.
  • Mucus: Protects stomach walls from acid.
• Partially digested food (chyme) is gradually released into the small intestine.

Small Intestine

• Highly coiled tube to fit in a small space.
• Receives:
  • Bile Juice from liver: Breaks fat globules and makes the environment alkaline.
  • Pancreatic Juice from pancreas: Contains enzymes like trypsin, lipase, and pancreatic amylase.
  • Intestinal Juice: Contains enzymes like peptidases and nucleases.
• Enzyme Activities:
  • Bile: Breaks down fats and maintains alkaline pH.
  • Pancreatic Amylase, Sucrase, Maltase, Lactase: Convert carbohydrates to simple sugars (glucose, galactose, fructose).
  • Trypsin, Chymotrypsin, Peptidases: Convert proteins to amino acids.
  • Lipase: Converts fats to fatty acids and glycerol.

Absorption

• Villi: Finger-like projections in the small intestine, rich in blood and lymph vessels, absorb nutrients and distribute them to the body.

Large Intestine

• Absorbs water from undigested food.
• Converts remaining waste into feces, excreted through anus.

Conclusion

• This lecture covered the anatomy of the digestive system and the processes of digestion and absorption.
• Understand the role of each organ and related enzymes for effective digestion.

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