Alimentary Canal Functions and Mouth Anatomy

Alimentary Canal Activities

• Ingestion: Taking food into the mouth.
• Digestion: Breaking down food into smaller molecules that can be absorbed.
• Absorption: Taking in the digested nutrients into the bloodstream.
• Assimilation: Using the absorbed nutrients to build and maintain body tissues.
• Egestion: Eliminating undigested waste products.

The Mouth - Mechanical

• Teeth: Mechanically break down food into smaller pieces.
• Uvula: Prevents food from entering the nasal cavity.
• Tongue: Plays a crucial role in mastication and swallowing.

The Mouth - Chemical

• Salivary Amylase: Breaks down starch into maltose.
• Taste Buds: Allow us to appreciate food and detect potential hazards.

The Bolus

• Definition: A rounded mass of food formed in the mouth.
• Formation: Food is crushed and ground by teeth (mastication) and moistened with saliva.

Salivary Glands

• Submandibular: Produces 70% of saliva.
• Sublingual: Produces 5% of saliva.
• Parotid: Produces 25% of saliva.
• Saliva Composition: 99.5% water, 0.5% other substances like mucin and salivary amylase.

Swallowing

• Process: Involves coordinated activity of the tongue, soft palate, pharynx, and esophagus.
• Phases:
  • Voluntary Stage: Food is pushed into the pharynx by the tongue.
  • Reflex Stage: Swallowing becomes an automatic process.

The Esophagus

• Function: Transports food from the mouth to the stomach.
• Structure:
  • Mucous membrane lining for lubrication.
  • Smooth muscle wall contracts to propel food downwards.

Peristalsis

• Definition: Rhythmic contractions of smooth muscles that move food through the digestive tract.
• Mechanism:
  • Circular muscle contraction behind the bolus.
  • Longitudinal contraction in front of the bolus.
• Result: Bolus moves towards the stomach.

Digestive Tract Movements: Segmentation and Vomiting

• Segmentation: Mixing movement in the small intestine. Constriction of segments without forward or backward movement.
• Vomiting: Propulsion by abdominal muscle contraction.

The Stomach

• Location: J-shaped organ on the left side of the abdominal cavity.
• Regions: Fundus, body , pylorus.
• Sphincters:
  • Pyloric Sphincter: Separates stomach from small intestine.
  • Esophageal Sphincter: Separates stomach from esophagus.
• Environment: Highly acidic.

Structures of the Stomach

• Rugae: Folds in the stomach lining that allow for expansion when eating.
• Gastric Glands: Secrete gastric juice.
• Types of Gastric Gland Cells:
  • Parietal Cells: Produce hydrochloric acid (HCl).
  • Chief Cells: Produce pepsin (for protein digestion).
  • Mucus Cells: Produce mucus (protects against HCl).

Stomach Lining

• Epithelium: Forms deep pits containing glands.
• Secretions: Enzymes, hormones, and mucus.
• Gastric Juice:
  • Hormones: E.g., gastrin (increases acid secretion and stomach motility).
  • Enzymes: E.g., pepsin.
• Absorption: Some water, lipids, caffeine, and alcohol are absorbed in the stomach.

The Small Intestine

• Key Function: Primary site for digestion and absorption of nutrients.

Accessory Organs

• Liver:
  • Largest solid organ and gland in the body.
  • Produces bile.
  • Processes nutrients and detoxifies harmful substances.
• Gall Bladder:
  • Stores and concentrates bile.
  • Releases bile into the duodenum in response to cholecystokinin.
• Pancreas:
  • Endocrine and exocrine function.
  • Exocrine: Secretes digestive enzymes and bicarbonate into the duodenum.
  • Endocrine: Produces insulin and glucagon.

Bile

• Source: Produced by the liver.
• Function: Emulsifies fats for digestion.
• Composition: Bile salts, bile pigments (bilirubin), cholesterol, and phospholipids.
• Reabsorption: Most bile is reabsorbed and recycled by the liver.

Pancreatic Fluid

• Composition:
  • Sodium Bicarbonate: Neutralizes stomach acid.
  • Pancreatic Amylase: Digests carbohydrates.
  • Pancreatic Lipase: Digests lipids.
  • Trypsin and Chymotrypsin: Digest proteins.
  • Nucleases: Digest nucleic acids.

The Large Intestine (Colon)

• Function:
  • Absorbs water, electrolytes, and some vitamins.
  • Stores and eliminates waste.
• Characteristics:
  • Less muscular.
  • Contains goblet cells (secrete mucus for lubrication).
  • No villi.
• Key Processes:
  • Fermentation of undigested material by bacteria.
  • Formation of feces.

The Rectum

• Location: Last 13 cm of the large intestine.
• Function: Stores feces until elimination.
• Sphincters: Relax to allow for defecation.

Digestion

• Definition: The process of breaking down food into smaller molecules for absorption.
• Types:
  • Mechanical: Physical breakdown of food (chewing, churning)
  • Chemical: Breakdown of food molecules by enzymes.

Digestive Juices

• Source: Stomach, small intestine, salivary glands, gall bladder, and pancreas.
• Key Components: Digestive enzymes.

Digestive Enzymes

• Types:
  • Amylase: Digests starches.
  • Lipase: Digests lipids.
  • Protease: Digests proteins.

Digestion of Carbohydrates

• Step 1: Salivary amylase (mouth) and pancreatic amylase (small intestine) break down polysaccharides into disaccharides.
• Step 2: Intestinal enzymes (sucrase, maltase, lactase) break down disaccharides into monosaccharides.

Digestion of Proteins

• Step 1: Pepsin (stomach) and trypsin and chymotrypsin (pancreas) break down proteins into smaller peptide chains.
• Step 2: Aminopeptidase (small intestine) breaks down peptides into amino acids.

Explore the key activities of the alimentary canal, including ingestion, digestion, absorption, assimilation, and egestion. Delve into the mechanical and chemical processes that occur in the mouth, highlighting the role of teeth, saliva, and taste buds in digestion.