Digestive System and Lactose Intolerance

Introduction

Lactose is a milk sugar digestible only with the enzyme lactase.
Lactase Persistence: A genetic mutation allowing lactase production in adults, emerged ~7500 years ago in Europe.
- High lactase persistence in Northern Europe (> 90% in Britons and Scandinavians).
- Low persistence in Mediterranean (< 40%), Africa, and Asia (< 10%).
Impact: Inability to digest lactose leads to bacteria in the large intestine metabolizing it, causing gas, bloating, and diarrhea.

Stomach: Breaks down food physically, with limited chemical digestion.
Small Intestine: Main site for chemical digestion and nutrient absorption.
- Over 6-7 meters long, folded with villi and microvilli for increased surface area.
- Divided into duodenum, jejunum, and ileum.

Duodenum: Receives chyme and gastric juices, begins chemical digestion.
- Receives bile from the liver and gallbladder, enzymes from the pancreas.
- Home to brush border enzymes like lactase.
Jejunum: Main site for absorption.
Ileum: Absorbs vitamins A, B12, E, D, and K.

Liver: Produces bile for emulsifying fats; can regenerate itself.
Gallbladder: Stores and concentrates bile, releases it into the duodenum.
Pancreas: Produces enzyme cocktail for digestion.
- Enzymes include trypsin, peptidase, lipases, amylase, and nuclease.

Structure: Comprises the colon, rectum, and anus.
Function: Absorbs remaining water and hosts gut bacteria.
- Gut bacteria digest remaining chyme, produce vitamins B and K and gases.

Nachos as an Example: Illustrates digestive failures in lactose-intolerant individuals.
- Nachos can cause discomfort when bacteria in the large intestine try to digest lactose.

Summary: Small intestine handles chemical digestion and nutrient absorption with help from accessory organs.
Large Intestine's Role: Extracts last nutrients and deals with waste.

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