Digestion and Absorption

Digestion Overview

  • Digestion involves breaking down food into usable parts.

  • Starts in the mouth and involves several organs including the stomach and intestines.

Key Definitions

  • Digestion: The process of breaking down food into parts usable by the body, which entails:

    • Ingestion: Chewing and mixing food with saliva.

    • Absorption: Transfer of digested nutrients into the body requiring a functioning small intestine and large intestine.

  • Upper GI Health: Involves stomach acid and digestive enzymes necessary for proper digestion.

Anatomy of Digestion

Mouth and Pharynx

  • Mouth: Where food is ingested, chewed, and mixed with saliva.

  • Salivary Glands: Secrete saliva containing starch-digesting enzymes.

  • Pharynx: Directs food from the mouth to the esophagus.

  • Epiglottis: Protects airways during swallowing.

Esophagus and Stomach

  • Esophagus: Passes food from mouth to stomach while preventing backflow.

  • Stomach: Mixes food with gastric juices, adding acid, enzymes, and fluids to create chyme.

    • Pyloric Sphincter: Regulates passage from stomach to small intestine.

Small Intestine

  • Responsible for digesting energy-yielding nutrients into absorbable forms.

  • Enables nutrient absorption into blood and lymph.

  • Ileocecal Valve: Prevents backflow from large intestine.

Digestive Organs and Their Functions

  1. Salivary Glands: Produce saliva that helps liquefy food and protects oral cavity.

  2. Stomach: Produces gastric acid to break down proteins and kill bacteria.

  3. Pancreas: Secretes enzymes into the small intestine to digest all macronutrients; neutralizes stomach acid.

  4. Liver: Produces bile for fat emulsification; helps in fat digestion.

  5. Gallbladder: Stores bile and releases it during fat digestion.

Digestion Mechanics

Muscular Involvement

  • Epiglottis: Controls airflow while swallowing.

  • Peristalsis: A wave-like muscle contraction for moving food through the gastrointestinal tract.

  • Segmentation: Rhythmic contractions that further break down food in the intestines.

Enzymatic Function

  • For digestive enzymes to function effectively, food particles must be small enough to allow for enzymatic action.

Absorption Processes

Small Intestinal Structures

  • Villi and Microvilli: Increase surface area for absorption of nutrients.

  • Types of Absorption Mechanisms:

    • Simple Diffusion: Movement across membranes without energy.

    • Facilitated Diffusion: Requires specific transport proteins.

    • Active Transport: Requires energy to move substances against a concentration gradient.

Nutrient Transportation

Circulatory System Roles

  • Vascular System: Transports water-soluble nutrients directly to the liver via the bloodstream.

  • Lymphatic System: Transports larger fats and fat-soluble vitamins, which bypass the liver initially and enter the bloodstream near the heart.

Gut Microbiome Function

  • Consists of bacteria that depend on diet and gut conditions.

    • Prebiotics: Feed beneficial gut bacteria; they are dietary fibers.

    • Probiotics: Contain live organisms beneficial for gut health.

    • Synbiotics: Combine prebiotics and probiotics.

Hormonal and Nerve Pathways

  • The digestive process is regulated by over 50 hormones and neural responses to changes in internal conditions.

    • Mechanisms include:

      • Release of gastrin in response to food, stimulating HCL production.

      • Secretin production in response to acidic chyme, prompting bicarbonate release from the pancreas.

      • Cholecystokinin (CCK) stimulating gallbladder contraction in response to fats.