Structure and Functions of the Gastrointestinal Tract

Introduction

• Human beings obtain energy from plants and animals by ingesting them.
• Ingested food materials pass through the digestive system (gastrointestinal tract).
• The gastrointestinal tract forms a tubular cavity, open at both ends, known as the elementary canal.
• Digestive and accessory organs help in digestion by secreting enzymes and digestive juices.
• Digested food is absorbed and transported to different body parts for metabolism.

Objectives of the Module

• Understand the structure of the elementary canal and its associated organs.
• Describe the functions of different parts of the alimentary canal in the digestion process.

Organization of the Digestive System

• The human digestive system consists of:
  • Gastrointestinal Tract
  • Accessory Organs

Mouth (Oral/Buccal Cavity)

• Includes the vestibule and oral cavity proper.
  • Vestibule: Area between teeth, lips, and cheeks.
  • Oral Cavity Proper: Contains salivary glands and tongue.
• Tongue: Muscular organ with taste buds; aids in grip and movement of food, and speech.
• Teeth: Chop and grind food; categorized into incisors, canines, premolars, and molars.
• Salivary Glands: Produce saliva to moisten and lubricate food.
  • Types of Saliva:
    • Parotid Glands: Watery saliva with enzymes.
    • Submandibular Glands: Both mucus and enzymes.
    • Sublingual Glands: Mucus only.
• Main Functions:
  • Ingestion, chewing, mixing food with saliva, and swallowing.

Pharynx (Throat)

• Muscular tube connecting mouth to esophagus.
• Serves as a common pathway for food and air.

Esophagus

• Long, collapsible tube extending from pharynx to stomach.
• Uses peristaltic waves to push food to the stomach.
• Contains upper and lower esophageal sphincters to regulate passage of food.

Stomach

• Elongated pouch between esophagus and small intestine.
• Regions:
  • Fundus: Largest region.
  • Body: Central part.
  • Pylorus: Lower portion ending at pyloric sphincter.
• Structure:
  • Four tissue layers: mucosa, submucosa, muscularis, and serosa.
  • Gastric glands secrete gastric juice containing hydrochloric acid and digestive enzymes.
• Functions:
  • Store, dissolve, and partially digest food; regulate emptying into the small intestine.

Small Intestine

• Long coiled loop in the abdominal cavity.
• Regions:
  • Duodenum: 20-25 cm long.
  • Jejunum: 2.5 m long.
  • Ileum: 3 m long.
• Villi and microvilli: Increase surface area for absorption.
• Functions:
  • Digestion and absorption of nutrients.
  • Receives digestive secretions from pancreas and liver.

Large Intestine

• Last part of the alimentary canal (5-7 feet long).
• Composed of:
  • Cecum: Receives chyme from ileum.
  • Colon (ascending, transverse, descending, sigmoid).
  • Rectum: Reservoir for feces.
• Functions:
  • Concentrate undigested materials, absorb water and salts.
  • Defecation: Expelling feces through the anus.

Accessory Digestive Organs

Liver

• Largest gland in the body, located in the upper right abdomen.
• Functions:
  • Detoxification, metabolism of proteins, carbohydrates, fats.
  • Stores vitamins and produces important plasma proteins.

Gallbladder

• Stores bile produced by the liver.
• Ducts (common bile duct) connect to the duodenum.

Pancreas

• Elongated gland behind the stomach with both endocrine and exocrine functions.
• Secretes digestive enzymes into the duodenum through the pancreatic duct.

Conclusion

• Structure and functioning of the gastrointestinal tract are interrelated.
• Digestive efficiency is tied to the anatomy of the digestive system, ensuring proper digestion and absorption of nutrients.