Chapter 6

Introduction

• Textbook: Nutrition for Health and Health Care

• Authors: Linda Debruyne, Kathryn Pinna

• Edition: Seventh

• Focus: Digestion and Absorption (Chapter 2)

Learning Objectives

• Understand the path of food during digestion, including muscular actions.

• Learn about digestive secretions: their actions and origins.

• Examine the anatomical details of the GI tract; identify features of intestinal cells aiding nutrient absorption.

• Explain nutrient delivery from the GI tract to body cells via the vascular system, including types of lipoproteins.

• Investigate the influence of hormones, nerves, and bacteria on GI tract health.

• Understand causes and effects of foodborne illnesses and methods for ensuring food safety.

Anatomy of the Digestive Tract

• The digestive tract selectively absorbs materials of nutritive value while excreting non-nutritive materials.

• Gastrointestinal Tract: A flexible muscular tube from mouth to anus where nutrients enter the body.

Key Organs of the Gastrointestinal Tract

• Mouth: Chews and mixes food with saliva.

• Pharynx: Directs food to the esophagus.

• Epiglottis: Protects airways during swallowing.

• Esophagus: Passes food to the stomach.

• Stomach: Churns food, adding acids and enzymes.

• Small Intestine: Secretes enzymes, a primary site for nutrient absorption.

• Large Intestine: Absorbs water and minerals; excretes waste.

• Rectum and Anus: Store and eliminate waste, respectively.

The Digestive Process

Digestion Phases

1. Mouth: Saliva begins breakdown of food; enzymes have minimal effect on fats or proteins.

2. Stomach: Gastric juices (water, enzymes, hydrochloric acid) facilitate protein breakdown; mucus protects stomach lining.

3. Small Intestine: Pancreas and liver significantly contribute digestive juices. Bile emulsifies fats; enzymes break down carbohydrates, proteins, and fats.

4. Large Intestine: Final absorption; intestinal bacteria aid in fiber degradation and water recycling.

Absorptive System: The Small Intestine

• Main site of nutrient absorption, facilitated by villi and microvilli which increase surface area.

• Specific GI tract cells are adapted to absorb different nutrients efficiently.

Nutrient Absorption Mechanism

• Water-soluble nutrients enter the bloodstream directly, while fat-soluble nutrients require packaging as chylomicrons, eventually entering the lymphatic system before blood circulation.

• Importance of inter-nutrient synergy (e.g., Vitamin C enhances iron absorption).

Transport of Nutrients

Vascular System

• Arterial blood to the digestive system and then veins carry it away.

• Hepatic portal vein directs nutrients to the liver, acting as a major metabolic hub.

Lymphatic System

• Transports fat-soluble nutrients, muscles aid in fluid movement, eventually entering the bloodstream at the heart.

Lipoproteins

• Include VLDL (transports triglycerides), LDL (carries cholesterol), and HDL (transports excess cholesterol to the liver).

• Health implications: High LDL and low HDL link to increased heart disease risk.

GI Tract Regulation

• Hormonal and nervous systems maintain digestive homeostasis.

• Prebiotics promote beneficial bacterial growth, contributing to gut health.

Food Safety

Foodborne Illness

• Primary food safety concern; can cause severe symptoms and risks, especially in vulnerable populations.

• Types: Foodborne infection (e.g., norovirus), food intoxication (toxin-induced).

Prevention Practices

• Medical attention sought for severe symptoms (e.g., bloody diarrhea, prolonged vomiting).

• Safe handling practices help minimize foodborne pathogens in commercial settings.

Safe Food Handling

• Suggested consumer actions and safe storage practices outlined, emphasizing cleanliness and proper cooking temperatures.

• Specific recommended storage times for various food types.