Gastrointestinal Tract Overview

GIT System Subdivisions

• Alimentary Canal: Pathway for food and waste; includes mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
• Accessory Organs: Connected to the alimentary canal; involved in digestion but not in the passage of food; includes teeth, tongue, salivary glands, liver, gallbladder, and pancreas.

Digestion and Absorption Sequence

• Mechanical Homogenization: Mixing of food with digestive fluids throughout the GIT.
• Enzyme Secretion: Over 30g of digestive enzymes produced daily to break down macromolecules into smaller units (oligomers, dimers, monomers).
• Electrolyte Secretion: Acids and bases secreted to maintain an optimal environment for enzymes.
• Bile Acids: Function as biological detergents to emulsify lipids for better digestion and absorption.
• Intestinal Final Digestion: Completed by intestinal surface enzymes breaking down nutrients further.
• Nutrient Transport: Nutrients absorbed from intestinal lumen into the bloodstream.

Specialized GIT Components

• Glands and Epithelia: Specialized glands (salivary glands, stomach, pancreas, liver, intestines) support digestion.
• Exocrine Cells: Produce enzymes for digestion within the GIT lumen.

Salivary Secretion Control

• Autonomic Regulation: Salivary secretion controlled primarily by the autonomic nervous system, not by GIT hormones.
• Parasympathetic Activation: Increased salivation initiated by the salivatory nuclei in the brainstem; stimulated by taste, smell, and chewing.
• Inhibitors: Atropine inhibits saliva; agents like pilocarpine increase secretion.
• Sympathetic Stimulation: Leads to a smaller increase in salivation, primarily through beta-adrenergic receptors.

Stomach Structure

• Regions: Divided into Cardia (cardiac glands), Fundus and Body (oxytonic or parietal glands), and Antrum (pyloric glands).
• Surface Mucous Cells: Produce neutral mucins and bicarbonate (HCO3-).
• Digestive Function: Partial lipid digestion occurs via gastric lipase.

HCl Production and Regulation

• Alkaline Tide: During active acid secretion, parietal cells release HCl and HCO3- into the bloodstream, causing an alkaline shift.
• HCl Secretion Regulation: Driven by gastrin, histamine, and acetylcholine; absence of any factor affects H+ secretion.

Gastric Mucosa Protection

• Gastric Mucosal Barrier: Mucus gel and alkaline secretions protect the mucosa from acidic contents.
• Mucus Layer: About 0.2mm thick; maintains near-neutral pH for epithelial cells despite acidic luminal environment.

Intestinal Secretions

• Brunner's Glands: Secrete alkaline mucus in response to irritation, vagal stimulation, and secretin.
• Crypts of Liberkuhn: Produce intestinal juice with a volume of 1800 ml/day, pH 7.5-8; involved in acid neutralization and nutrient breakdown.
• Enzymes Present: Include peptidase, sucrase, maltase, lactase, lipase, and enterokinase.

Bile Secretion

• Composition: Roughly 97% water and 3% solids; contains bile salts, mucin, bile pigments, lipids, and inorganic substances.
• Physiological Roles: Aids in lipid digestion, cholesterol elimination, fat-soluble vitamin absorption, and cholesterol solubility to prevent galls stones.

Biliary Secretion Regulation

• Choleretics: Substances that enhance bile secretion; includes bile salts, secretin, gastrin, CCK, and vagal stimulation.
• Gallbladder Function: Stores bile, absorbs water to concentrate bile up to 5-10 times, and regulates pH to prevent gallstone formation.

Explore the subdivisions of the gastrointestinal tract (GIT) system, including the alimentary canal and accessory organs. This quiz delves into the sequence of events for digestion and absorption, focusing on the organs involved in these processes.