Digestion and Absorption (2) (2) (2)

Digestion and Absorption

• Overview of Digestion

  • Focused on the process by which food is broken down and nutrients are absorbed by the body.

  • Involves multiple organs and glandular secretions.

Organs and Their Functions

• Salivary Glands:

  • Secrete a lubricating fluid that contains enzymes for carbohydrate breakdown.

• Oral Cavity, Teeth, Tongue:

  • Engage in mechanical processing, moistening, and mixing food with saliva.

• Pharynx:

  • Muscles propel food into the esophagus.

• Liver:

  • Secretes bile for lipid digestion, stores nutrients, and has several vital functions.

• Esophagus:

  • Transports food to the stomach.

• Stomach:

  • Performs chemical breakdown of food using acids and enzymes; mechanically processes through muscular contractions.

• Gallbladder:

  • Stores and concentrates bile.

• Pancreas:

  • Secretes buffers and digestive enzymes; produces hormones.

• Large Intestine:

  • Dehydrates and compacts waste for elimination.

• Small Intestine:

  • Responsible for enzymatic digestion and absorption of components like water, organic substrates, vitamins, and ions.

Challenges of Digestion

• Key Challenges:

  • Move food through the digestive tract.

  • Protect cells from digestive enzymes.

  • Suspend food in liquid to facilitate movement.

  • Remove excess liquid from digested food.

  • Excrete undigested material without continuous waste production.

  • Deliver nutrients to cellular processes.

Nutritional Stages

• Nutrition Definitions:

  • Ingestion: Taking food into the body.

  • Digestion: Breakdown of food into simpler substances.

  • Absorption: Transfer of digested nutrients into the bloodstream.

  • Transport: Movement of absorbed nutrients throughout the body.

  • Assimilation: Incorporation of nutrients into tissues and cells.

  • Excretion: Removal of waste and indigestible materials from the body.

Digestive Processes Explained

• Ingestion: Intake of food and drink.

• Digestion:

  • Mechanical digestion (physical breakdown) e.g., chewing.

  • Chemical digestion (enzymatic breakdown) converts complex molecules to simpler forms.

• Absorption: Moving nutrients from the gastrointestinal tract into the circulatory system.

• Transport: Distribution of nutrients via blood and lymph.

• Assimilation: Incorporation of nutrients into cellular structures.

• Excretion: Elimination of waste products.

Journey of Ingested Food

• The gastrointestinal (GI) tract is a muscular tube approximately 25-30 feet long.

  • Mouth: Initiates digestion with taste and mechanical processing.

  • Esophagus: Moves food into the stomach as a bolus.

  • Stomach: Converts food into acidic chyme.

  • Small Intestine: Engages in digestion and absorption of nutrients.

  • Large Intestine: Absorbs water and compacts waste.

  • Sphincters: Control movement of food between organs.

Digestion Initiation

• Begins in the mouth through both mechanical (chewing) and chemical (saliva) processes.

Salivary Glands Functions

• Produce about 1 quart of saliva daily, which helps lubricate food and begins the digestion process.

  • Contains enzymes, antibodies, and electrolytes.

The Role of the Tongue

• Contains taste buds and helps form chewed food into a bolus for swallowing.

Esophagus Functionality

• Transports food to the stomach via two sphincters:

  • Upper esophageal sphincter: Initiates swallowing.

  • Lower esophageal sphincter: Regulates entry into the stomach.

Stomach Mechanics

• Holds about 1 cup when empty, expands to about 1 gallon when full.

• Minimal absorption occurs (notably alcohol and some medications).

  • Food remains for over 2 hours depending on composition.

Gastric Juices and pH Level

• Contains water, enzymes (e.g., pepsin), HCl (pH 2), and mucus.

  • Acidity aids in digestion and prevents bacterial growth.

  • Mucus protects the stomach lining.

Feedback Loop in Digestion

• Chyme release triggers feedback mechanisms that regulate digestion and enzyme action in the small intestine.

Role of Enzymes in Digestion

• Enzymes act as catalysts to speed up digestion and carry out chemical reactions such as hydrolysis.

Types of Digestive Enzymes

• Carbohydrases: Digest carbohydrates.

• Lipases: Digest lipids.

• Proteases: Digest proteins.

Enzyme Function Requirements

• Proper enzyme stimulation by nutrients, temperature, and pH is essential for optimal digestive enzyme function.

Small Intestine Structure

• Comprising three segments (duodenum, jejunum, ileum) and around 10 feet long, with a large surface area for absorption.

Mechanisms of Nutrient Absorption

• Villous architecture and specific channels aid in absorption including:

  • Passive diffusion

  • Facilitated diffusion

  • Active transport

  • Endocytosis

Gastric Motility

• Involves rhythmic contractions (peristalsis) that move food through the GI tract, influenced by location and external factors.

Liver Functions

• Largest internal organ, critical for digestion, metabolism, detoxification, and bile production to emulsify fats.

Gallbladder Roles

• Stores and concentrates bile produced by the liver and releases it when needed in the small intestine.

Pancreatic Functions

• Secretory roles: Digestive enzymes (exocrine) into the small intestine, and hormones (endocrine) to regulate blood sugar levels.

Nutrient Transportation

• Carbohydrates and proteins enter the bloodstream directly; fat-soluble nutrients first enter the lymphatic system.

Large Intestine Function

• Absorbs water and electrolytes, reduces fluid material to fecal matter, and plays a role in fiber fermentation.

Defecation Process

• Controlled by sphincters allowing for voluntary elimination of waste through the anus.

Digestive Enzymes Overview

• Various enzymes facilitate the breakdown of carbohydrates, proteins, and lipids at different stages of digestion.

Secretions of GI Tract

• Various secretions aid in digestion, protect mucosal linings, and support nutrient absorption throughout the GI tract.