02.05.2025_Nutrition and Physiology II.pptx

Introduction to Nutrition and Physiology II

• Instructor: Margaret Slavin, PhD, RDN

• Institution: University of Maryland, College Park

Agenda

• Overview of food processing in the body

• Roles of major organs in digestion

• Enzymes and secretions aiding in nutrient breakdown

• Absorption and transport mechanisms for nutrients

Key Definitions

Digestion

• Process of breaking down food into absorbable nutrients (both mechanical and chemical)

Absorption

• Uptake of nutrients by cells in the small intestine into the bloodstream or lymphatic system

Metabolism

• The process by which the body utilizes absorbed nutrients

More Key Definitions

Gastrointestinal (GI) Tract

• Digestive tract, including stomach and intestines

Digestive System

• All organs and glands involved in digestion and ingestion

Anatomy of the Digestive System

• Overview of the physical structure and components involved in digestion.

The Mouth

• Mastication: Chewing reduces food to smaller pieces and mixes it with saliva

• Contributes to taste and smell

• Role of the tongue in swallowing

Swallowing Process

• Food moves into the pharynx and passes the epiglottis, which prevents airway obstruction

• Bolus describes food that has been chewed and swallowed

• Path: Pharynx → Upper esophageal sphincter → Esophagus → Lower esophageal sphincter → Stomach

The Stomach

• Retains food and adds digestive juices

• Converts bolus into semi-liquid chyme

• Gradually releases chyme through the pyloric sphincter into the small intestine

The Small Intestine

• Approximately 10 feet long

• Receives secretions from gallbladder/liver and the pancreas via bile and pancreatic ducts

The Large Intestine

• Referred to as the colon

• Chyme enters via the ileocecal valve

The Exit Strategy

• Rectum: Stores solid waste until elimination

• Anus: Contains sphincters that control waste exit

Peristalsis

• Digestive movement caused by alternating contractions of circular and longitudinal muscles, propelling food forward

Sphincter Contraction

• Ring-shaped muscles regulate movement at junctions, preventing backward or uncontrolled flow of food

Digestive Enzymes

• Enzymes are biological molecules that accelerate chemical reactions

• Examples include:

  • Protease: Breaks down proteins

  • Lipase: Breaks down fats

  • Carbohydrase: Breaks down carbohydrates

Digestive Secretions in the Mouth

• Saliva: Moistens food; contains enzymes such as salivary amylase and lipase for initial digestion

Digestive Secretions in the Stomach

• Gastric Juice: Comprises water, enzymes, and hydrochloric acid

• Mucus: Protects stomach lining from acidic damage

• Inactivation of salivary amylase; pepsin (enzyme) aids in protein breakdown

Stomach Action

• Thick muscular walls allow for thorough mixing and churning of food into chyme

Intestinal Digestive Secretions

• Pancreatic Juice: Contains enzymes that act on macronutrients

• Bile: Emulsifies fats and is produced in the liver

• Bicarbonate: Neutralizes stomach acid

• Intestinal enzymes finalize nutrient breakdown

Nutrient Absorption

• Mainly occurs in the small intestine, facilitated by its structural adaptations

• Nutrients absorbed via simple diffusion or active transport

Absorption Mechanism

• Nutrients enter the bloodstream or lymphatic system to be transported throughout the body

Colon Functions

• Water and mineral reabsorption

• Fiber fermentation by gut bacteria, producing beneficial byproducts

Excretory Products

Feces

• Comprises undigested food, intestinal cells, microflora, and bile

Urine

• Contains urea, electrolytes, and waste compounds

Nutrient Transport

• Water-soluble nutrients: Enter bloodstream directly

• Large fats/vitamins: Packaged into chylomicrons and transported via the lymphatic system, bypassing the liver initially

The Lymphatic System

• Transports large fats and fat-soluble vitamins to the bloodstream

Summary

• The digestive system is complex, requiring a balanced diet for optimal health and function.