lecture recording on 11 March 2025 at 20.39.58 PM

Digestive Physiology Overview

• Introduction to the digestive system as the first body system covered in the course.

• The digestive system breaks down food into nutrient molecules for absorption into the bloodstream.

• Indigestible material is eliminated as feces.

Structure of the Digestive System

• Digestive Organs: Divided into two groups:

  • Gastrointestinal (GI) tract: A muscular tube (~30 feet) from mouth to anus, responsible for digesting food and absorbing nutrients.

  • Accessory digestive organs: Assist GI tract in digestion (e.g., teeth, tongue, salivary glands, gallbladder, liver, pancreas).

GI Tract Components

• Key organs: Oral cavity, pharynx, esophagus, stomach, small intestine, large intestine.

• The purpose of the GI tract includes:

  • Digestion of food into smaller fragments for nutrient absorption into the blood.

Digestive Processes

• Several digestive system processes occur:

  Motility

  • Ingestion: Taking food into the oral cavity.

  • Deglutition: Swallowing food using tongue and pharynx.

  • Peristalsis: Waves of contraction and relaxation in the GI tract walls, pushing food along.

  Digestion

  • Mechanical digestion: Physical breakdown of food:

    • Mastication: Chewing food and forming it into a bolus.

    • Churning: Mixing food in the stomach, creating chyme.

    • Segmentation: Mixing contents in the small intestine for further breakdown.

  • Chemical digestion: Breakdown using enzymes that cleave chemical bonds, primarily occurring in the small intestine.

Secretion

• Release of exocrine (e.g., pancreatic juice, bile) and endocrine (hormones, e.g., gastrin) products into the GI tract to facilitate digestion.

Absorption

• Movement of digested end products (monomers like monosaccharides, amino acids, and fatty acids) from the GI tract into the blood or lymph, mainly occurring in the small intestine.

Storage and Elimination

• Temporary storage of food and indigestible remains in stomach and large intestine, leading to elimination or defecation of waste.

Enzymes in Digestion

• Enzymes (mostly proteins) function as biological catalysts, speeding up chemical reactions necessary for digestion.

  • Activation Energy: Enzymes lower the energy needed for a reaction to occur.

  • Specificity: Each enzyme is specific to its substrate, facilitating the breakdown of macromolecules into monomers.

Influencing Factors

• Factors affecting enzyme activity include:

  • Temperature: Optimal around 37°C; extreme heat denatures enzymes.

  • pH: Each enzyme has a specific pH for optimal activity.

  • Substrate Concentration: More substrate increases reaction rate until saturation reaches a plateau.

Summary of Digestive Functions

• Mechanical digestion breaks down food into smaller pieces, while chemical digestion relies on enzymes for breaking chemical bonds.

• Most digestion occurs in the small intestine, with water and electrolytes absorbed mainly in the large intestine.

• Understanding enzyme function is vital for grasping the digestive process, emphasizing the roles of chemical digestion and enzymatic action.