3.01 Digestive System

Introduction

The digestive system, also known as the alimentary canal, digestive tract, or gastrointestinal (GI) tract, is a complex series of organs and glands that processes food. It spans approximately 30 feet from the mouth to the anus and is responsible for breaking down food into nutrients, which the body uses for energy, growth, and cell repair.

Key Sections

• Digestive System Overview

  • The digestive system is lined with the peritoneum, a double-layered serous membrane.

  • Functions include the physical breakdown of food, chemical digestion, nutrient absorption, and waste elimination.

• Structures and Functions

  • Mouth (Buccal Cavity)

    • Entry point for food; includes tongue, teeth, salivary glands, palate, and uvula.

  • Teeth

    • Different types (incisors, cuspids, bicuspids, molars) have specific functions in food processing.

  • Salivary Glands

    • Three pairs (parotid, submandibular, sublingual) secrete saliva to aid in digestion.

  • Pharynx

    • Passageway for air and food; divided into nasopharynx, oropharynx, and hypopharynx.

  • Esophagus

    • Muscular tube that transports food from the pharynx to the stomach.

  • Stomach

    • Divided into fundus, body, and pylorus; involved in food breakdown and nutrient extraction.

  • Small Intestine

    • Comprises duodenum, jejunum, and ileum; primary site for digestion and nutrient absorption.

  • Large Intestine (Colon)

    • Includes cecum, ascending, transverse, descending colon, sigmoid colon, rectum, and anus; involved in water absorption and feces formation.

  • Pancreas

    • Secretes digestive enzymes; has both exocrine and endocrine functions.

  • Liver

    • Largest organ; produces bile, stores glucose as glycogen, detoxifies substances.

  • Gallbladder

    • Stores and concentrates bile for fat digestion.

• Process of Digestion

  • Physical Digestion

    • Mechanical breakdown of food in the mouth and stomach.

  • Chemical Digestion

    • Enzymatic breakdown of food into absorbable units.

  • Absorption

    • Nutrients absorbed mainly in the small intestine; water reabsorbed in the large intestine.

  • Elimination

    • Removal of indigestible substances as feces.

• Disorders of the Digestive System

  • Anorexia Nervosa

    • Psychiatric disorder characterized by refusal to eat and significant weight loss.

  • Caries (Tooth Decay)

    • Decay caused by bacterial production on tooth surfaces.

  • Cholecystitis

    • Inflammation of the gallbladder often due to gallstones.

  • Cirrhosis

    • Liver disease resulting in scar tissue formation; often due to hepatitis C or alcohol abuse.

  • Cleft Palate

    • Birth defect affecting feeding and speech; treated surgically.

  • Constipation

    • Difficulty in bowel movements; often due to low fiber intake or inactivity.

  • Diarrhea

    • Loose, watery stools often caused by viral infections.

  • Gastroenteritis

    • Intestinal infection causing diarrhea and cramps.

  • GERD (Gastroesophageal Reflux Disease)

    • Stomach contents leak into the esophagus causing irritation.

  • Hepatitis

    • Liver infection caused by different viruses (Hepatitis A, B).

  • Irritable Bowel Syndrome (IBS)

    • Disorder affecting the large intestine with symptoms like cramping and diarrhea.

  • Peptic Ulcer

    • Sores on the lining of the stomach or intestines; associated with smoking and alcohol.

• Relevance of Nutrition to the Digestive System

  • Proper nutrition is crucial for maintaining digestive health and overall homeostasis. Essential nutrients include vitamins (A, D, E, K, C, B) and electrolytes (calcium, chloride, magnesium, phosphorus, potassium, sodium).