Digestive System.2024

Page 1: Overview of the Digestive System

Course Outline

• Important Structures and Functions

  • Digestive System:

    • Accessory Organs:

      • Teeth, Salivary Glands, Pancreas, Liver, Gallbladder, Appendix

• Gastrointestinal Layers

• Peritoneum Types

• Enteric Nervous System

• Peristalsis and Gastrocolic Reflex

• Food and Fluid Regulation

• Nutrition & Metabolism

• Elimination Mechanisms

Learner Objectives

• Identify key structures and their functions in the digestive system.

• Explain the digestive system's functions in:

  • Digestion

  • Absorption

  • Nutrition and Metabolism

  • Elimination

General Function of the Digestive System

• Processes ingested food and fluids efficiently by:

  • Breaking down food into molecules

  • Absorbing nutrients into the bloodstream or lymphatic system

  • Eliminating waste from the body.

Structure of the Digestive System

• Known as the gastrointestinal system, comprises a 30 ft long coiled tube with:

  1. Upper Tract: Mouth, Esophagus, Stomach

  2. Lower Tract: Intestines.

Layers of the Gastrointestinal Tract Wall

• Mucosa:

  • composed of Epithelial Cells(Lamina Propria), Muscularis Mucosa

  • Involved in absorption and secretion.

• Submucosa:

  • contains Loose connective tissue, Meissner’s plexus, blood vessels, nerves and lymphatic tissue that support the mucosa and play a crucial role in regulating digestive functions.

• Muscular Layer (Muscularis Externa):

  • Contains thick circular and longitudinal fibers for peristalsis.

  • Manages the enteric nervous system (ENS); including Auerbach’s plexuses.

• Serosa:

  • Outermost layer with mesothelium for lubrication.

Nerve Plexuses and Peritoneum

• Intrinsic Nerve Plexuses:

  • Submucosal (Meissner’s) and Myenteric (Auerbach’s) regulate the mobility and secretory activity of the GIT organs.

  • The submucosal region regulates the configuration of the luminal surface, and controls grandular secretions, alters electrolyte and water transport, and regulates local blood flow.

  • Myenteric is responsible for the peristaltic movement of the bowels.

• Peritoneum: thin, double layer of serous membrane in the abdominal cavity.

  • Visceral peritoneum forms the inner lining, which covers the external surface of most organs

  • Parietal peritoneum forms the outer layer which lines the walls of the abdominal cavity; contains serous fluid for organ lubrication.

  • Intraperitoneal organs are organs that are lined by peritoneum and held in place by the mesentery: Organs like Spleen, Gallbladder, etc

  • Retroperitoneal organs with no peritoneum and are not held in place by the mesentery: Organs like Pancreas, Kidneys.

Page 2: Accessory Digestive Organs and Processes

Accessory Digestive Organs

1. Teeth:

   • Function in mastication (cutting, tearing, grinding).

   • Enamel covered crown is the visible portion of the tooth, and the root, embedded in the jawbone hold the tooth in place.

   • Incisors provide strong cutting action whilst Molars provide strong grinding action.

2. Salivary Glands:

   • Include Parotid, Submandibular, Sublingual;

   • Produce saliva aiding in food breakdown.

   • Parotid produces saliva that enters the mouth via Stensen’s Duct

   • Submandibular enters the mouth via Wharton’s Duct

   • Sublingual have many ducts.

   • Produces 1000 to 1500 ML of saliva daily.

3. Pancreas:

   • Exocrine function provides digestive enzymes; regulates digestion.

   • Vagus Nerve Stimulation, secretin and CCK trigger pancreatic action on digestion.

4. Liver:

   • Largest gland; responsible for metabolic processes, detoxification, bile production.

5. Gallbladder:

   • Stores and concentrates bile for fat digestion.

6. Vermiform Appendix:

   • Has uncertain function; contains lymphoid tissue for immunity.

Propulsion and Movement in the GI Tract

• Peristalsis: Wavelike movements for gut content transport.

• Types of Movements:

  • Haustral Movement: Churning movement for water absorption.

  • Peristalsis: the involuntary muscle contractions that propel food through the digestive tract.

  • Mass Peristalsis: Stronger colonic contractions for defecation preparation.

Page 3: Digestion Mechanisms

Digestion Phases

• Two Types:

  • Mechanical Digestion: Chewing and churning.

  • Chemical Digestion: Enzymatic breakdown.

• Oral Cavity: Mechanical and chemical digestion begins; starch is converted.

• Swallowing Mechanism:

  • Voluntary control via oral phase; involuntary phase involves cranial nerves.

Stomach Functions

• Structure: Cardiac region, Fundus, Body, Antrum.

• Secretes pepsinogen and gastrin; minimal absorption happens here.

• Chyme formation and exit through pyloric sphincter.

Small Intestine Functions

• Length: 20-22 ft; where most digestion and absorption occur.

• Sections include:

  • Duodenum: Handles gastric secretions; secretes hormones like secretin.

  • Jejunum: Absorbs carbohydrates and proteins.

  • Ileum: Absorbs water, fats, and bile salts.

Page 4: Absorption and Metabolism

Absorption Process

• Nutrients absorbed through villi and microvilli using various transport mechanisms.

• Most nutrient absorption occurs in the jejunum; bile salts absorption relates to the ileum.

Metabolism Overview

• Involves processes transforming nutrients for energy and cellular function.

• Products include glucose, amino acids, and fatty acids contributing to energy needs.

Elimination Processes

• Movement through ileocecal valve to colon; large intestine involved in fecal formation.

Page 5: Nutrition and Metabolism

Overview of Nutrition

• Encompasses dietary interactions with food; major categories include macronutrients and micronutrients.

Macronutrients & Metabolism

• Energy Values: Measured in kilocalories; fats store the most energy.

  • Sources include carbohydrates (grains, fruits), proteins (meat, legumes), and fats (oils, dairy).

Vitamins and Minerals

• Water-Soluble: Must be ingested daily; Fat-Soluble: Can be stored.

• Minerals essential for various body functions; water facilitates digestion and nutrient transport.

Page 6: Digestion and Metabolism Processes

Processes of Digestion & Metabolism

• Processes:

  1. Digestion: Breakdown of food; key enzymes act on macronutrients.

  2. Krebs Cycle: Central role in transforming fuel into energy (ATP).

• Summary of Nutrient Sources:

  • Include carbohydrates, proteins, and fats; glandular secretions in the mouth, stomach, and small intestine facilitate breakdown.