Digestion: From Gut to Absorption

Year 11 Biology Understanding the digestive system From mouth to absorption

What happens to your lunch?

Think about the sandwich you ate at lunch Where is it now? What processes has it undergone?

Learning Objectives

Describe the structure and function of the digestive system Explain how food moves through the gut Understand the role of the stomach and small intestine Analyze digestion, absorption, and transport processes Examine the function of the large intestine

The Digestive System Overview

A complex system of organs working together Primary function: break down food into nutrients Secondary function: absorb nutrients into bloodstream Eliminate waste products Involves mechanical and chemical processes

Mechanical vs Chemical Digestion

{"left":"Physical breakdown of food\nChewing with teeth\nChurning in stomach\nMuscle contractions","right":"Chemical breakdown using enzymes\nSaliva contains amylase\nStomach acid and pepsin\nPancreatic enzymes"}

The Mouth: Where Digestion Begins

Mechanical digestion through chewing Chemical digestion via salivary amylase Saliva moistens food for swallowing Formation of bolus Taste buds detect flavors

Quick Activity: Salivary Amylase

Chew a piece of bread for 2 minutes Notice any change in taste What does this tell us about digestion? Why might it taste sweeter?

The Esophagus: Food Transport

Muscular tube connecting mouth to stomach Peristalsis moves food downward Takes 5-10 seconds to reach stomach Gravity assists but isn't essential Lower esophageal sphincter prevents reflux

The Stomach: Chemical Powerhouse

J-shaped muscular sac Produces gastric juice (HCl + pepsin) pH around 1.5-2.0 Mechanical churning creates chyme Can hold 1-2 liters of food

Why doesn't stomach acid digest the stomach itself?

The stomach produces strong acid pH can be as low as 1.5 What protects the stomach lining? Think about the mechanisms involved

Stomach Protection Mechanisms

Thick mucus layer acts as barrier Bicarbonate ions neutralize acid Rapid cell replacement every 3-5 days Prostaglandins regulate acid production Helicobacter pylori can disrupt these defenses

Journey Through the Small Intestine