Digestive System Overview

Digestive System Overview

• The digestive system breaks down food into absorbable nutrients for energy, growth, repair.
• It includes the alimentary canal (food passage) and accessory organs.

Key Functions

• Ingestion: Taking in food and liquids.
• Digestion: Breaking down food into smaller units.
• Mechanical Digestion: Physical breakdown (chewing, churning).
• Chemical Digestion: Enzymatic breakdown to simpler molecules.
• Absorption: Nutrients enter bloodstream/lymph.
• Defecation: Removal of undigested material.

Alimentary Canal (GI Tract)

• A long, continuous tube from mouth to anus.
• Transports and processes food.

Mouth (Oral Cavity)

• Ingestion point, beginning of digestion.
• Mechanical Digestion: Chewing (mastication).
• Chemical Digestion: Salivary amylase (carbohydrate breakdown).
• Teeth: Mechanical breakdown.
• Tongue: Moves and mixes food with saliva.

Pharynx (Throat)

• Passageway from mouth to esophagus.
• Parts: Nasopharynx, oropharynx, laryngopharynx.
• Deglutition (swallowing): Muscular contractions.

Esophagus

• Muscular tube transporting food from pharynx to stomach.
• Peristalsis: Wave-like contractions move food.
• Esophageal Sphincters: Upper and lower control food movement and prevent reflux.

Stomach

• J-shaped organ mixing food with gastric juices.
• Mechanical Digestion: Churning and mixing.
• Chemical Digestion: Gastric juices (HCl, pepsin).
• Gastric Mucosa: Protects stomach lining.
• Pyloric Sphincter: Controls release of chyme (partially digested food) to small intestine.

Small Intestine

• Primary site of nutrient absorption and digestion.
• Parts: Duodenum, jejunum, ileum.
• Villi and Microvilli: Increase surface area for absorption.
• Enzymes from pancreas and bile aid digestion.

Large Intestine (Colon)

• Absorbs water and electrolytes from undigested material.
• Forms feces.
• Parts: Cecum, colon (ascending, transverse, descending, sigmoid), rectum, anus.
• Bacteria aid in digestion (e.g., fiber).

Accessory Organs

• Produce or store digestive substances.
• Salivary Glands: Produce saliva with amylase. (Parotid, submandibular, sublingual)
• Liver: Produces bile (fat emulsification). Detoxifies, stores glycogen.
• Gallbladder: Stores and concentrates bile.
• Pancreas: Produces pancreatic juices with enzymes (lipase, amylase, proteases). Neutralizes stomach acid.

Digestive Process

• Food is ingested, propelled and digested.
• Nutrients are absorbed.
• Waste is eliminated.

Peritoneum and Peritoneal Cavity

• Peritoneum: Thin membrane lining abdominal cavity and covering organs.

• Parietal peritoneum: lines abdominal wall.

• Visceral peritoneum: covers abdominal organs.

• Peritoneal Cavity: Space between parietal and visceral peritoneum; contains serous fluid for lubrication.

• Mesentery: Double-layered peritoneum holding intestines to abdominal wall.

• Omentum: Folds of peritoneum connecting stomach to other organs.

Histology of the Alimentary Canal

• The structure of the layers of the alimentary canal.

Mucosa (Innermost Layer)

• Secretes mucus, enzymes, hormones, absorbs nutrients.
• Epithelium: Specialized cells (stratified squamous for mouth/esophagus, v simple columnar for other sections),
• Lamina Propria: Connective tissue with blood/lymphatics.
• Muscularis Mucosae: Thin muscle, increases surface area.

Submucosa

• Supports mucosa, connects to next layer. Rich in blood vessels, lymphatic vessels, nerves.

Muscularis Externa

• Responsible for peristalsis and segmentation.
• Circular and longitudinal muscle layers.
• (Sometimes) oblique muscle layer for stomach mixing.

Serosa/Adventitia (Outermost Layer)

• Serosa: Smooth outer layer in peritoneal cavity.
• Adventitia: Fibrous connective tissue in areas outside peritoneal cavity.

Summary

• The digestive system efficiently breaks down, absorbs, and eliminates waste through coordinated actions.