The Digestive System

The Digestive System

7th Grade

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Learning Objectives

• Describe the main functions of the digestive system: digestion, absorption, and elimination.

• Trace the path food takes through the main organs of the digestive system.

• Explain the roles of the liver, gallbladder, and pancreas in digestion.

• Explain the difference between mechanical and chemical digestion.

Key Vocabulary

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Digestion

The process of breaking down food so it can be used by the body for energy.

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Epiglottis

A small lid that covers the windpipe to prevent food from entering the lungs while swallowing.

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Peristalsis

The wave-like muscle contractions that move food through the digestive tract, starting from the esophagus.

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Mechanical Digestion

The physical breakdown of food into smaller pieces, primarily done by chewing with the teeth.

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Chemical Digestion

The breakdown of food into simpler nutrients by the action of enzymes, saliva, and acids.

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The Digestive System: An Overview

Mechanical Digestion

• ​Mechanical digestion is the physical process of breaking down food into much smaller pieces.

• ​​This is accomplished by using force, like when your teeth chew and crush food.

• ​The stomach also uses force by churning and mixing food with digestive juices.

Chemical Digestion

• ​Chemical digestion uses substances like enzymes and acids to break down food particles.

• ​​This process starts in the mouth, where enzymes in your saliva begin digestion.

• ​Digestion continues in the stomach, where powerful acids help to dissolve the food.

Multiple Choice

What is the key difference between mechanical and chemical digestion?

• Both processes are identical and occur only in the stomach.

• Mechanical digestion physically breaks down food using force, while chemical digestion uses chemicals like enzymes.

• Mechanical digestion absorbs nutrients, while chemical digestion eliminates waste.

• Mechanical digestion uses chemicals and force, while chemical digestion only uses force.

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The Journey Begins: Mouth & Esophagus

• Digestion starts in the mouth where teeth mechanically break down food.

• Saliva begins chemical digestion by breaking down carbohydrates with enzymes.

• The epiglottis is a flap that stops food from entering the windpipe.

• The esophagus uses muscle contractions called peristalsis to move food down.

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Multiple Choice

Based on the information provided, what are the initial steps of digestion in the mouth?

• Peristalsis moves the food into the mouth, where it is stored.

• Food is broken down by stomach acid, and the epiglottis pushes it down.

• Only mechanical digestion occurs, as teeth crush the food before it is swallowed.

• Teeth mechanically chew the food, while enzymes in saliva begin to chemically break down carbohydrates.

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The Powerhouses: Stomach & Small Intestine

Stomach

• ​Acts as a powerful mixer and grinder for the food you eat.

• ​​Secretes hydrochloric acid and chemicals to continue breaking down food.

• ​It turns food into a liquid paste called chyme.

Small Intestine

• ​This is where most of the digestion and nutrient absorption happens.

• ​​It is the longest part of your digestive tract, about 22 feet long.

• ​Nutrients from food are taken and distributed into the bloodstream.

Multiple Choice

What is the primary role of the small intestine?

• To use peristalsis to move food from the mouth to the stomach.

• To secrete hydrochloric acid to turn food into a liquid paste.

• To absorb most of the nutrients from digested food into the bloodstream.

• To produce bile and store it for later use.

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Final Stages: Large Intestine & Elimination

Large Intestine

• ​The large intestine, also known as the colon, is a muscular tube about 5 feet long.

• ​​Its main function is to absorb water from indigestible food matter coming from the small intestine.

• ​This process compacts the remaining material into solid waste, getting it ready for elimination.

Rectum

• ​The rectum is the final, straight section of the large intestine that connects to the anus.

• ​​It serves as a temporary holding chamber for solid waste before it is eliminated from the body.

• ​When this chamber becomes full, it signals the brain that it is time for elimination.

Multiple Choice

What is the main function of the large intestine?

• To absorb nutrients into the bloodstream.

• To produce enzymes for chemical digestion.

• To absorb water from remaining food and transmit waste to the rectum.

• To break down food with hydrochloric acid.

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The Helpers: Accessory Organs

• Accessory organs help digestion, but food does not pass through them.

• The liver is a large organ that produces a digestive chemical called bile.

• The gallbladder stores, concentrates, and releases bile into the small intestine.

• The pancreas produces pancreatic juice to break down carbohydrates, proteins, and fats.

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Multiple Choice

Which of the following correctly describes the roles of the accessory organs?

• Food passes through the pancreas, where it is mixed with pancreatic juice.

• The gallbladder produces pancreatic juice, and the liver stores it.

• The liver produces bile, the gallbladder stores it, and the pancreas produces digestive enzymes.

• The liver stores bile, and the gallbladder produces it.

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Common Misconceptions About Digestion

Misconception	Correction
The large intestine is longer than the small intestine.	The small intestine is longer, but the large intestine is wider.
Food passes through the liver, gallbladder, and pancreas.	These are accessory organs; food doesn't pass directly through them.
Digestion only starts when you begin to eat.	The sight and smell of food can trigger saliva production to start digestion.

Multiple Choice

Based on their functions, what is the correct path food takes through the digestive tract?

• Mouth → Esophagus → Stomach → Large Intestine → Small Intestine → Rectum

• Mouth → Esophagus → Liver → Stomach → Small Intestine → Large Intestine

• Mouth → Stomach → Esophagus → Small Intestine → Large Intestine → Rectum

• Mouth → Esophagus → Stomach → Small Intestine → Large Intestine → Rectum

Multiple Choice

How do the processes in the mouth and stomach differ in breaking down food?

• The mouth begins carbohydrate digestion with saliva, while the stomach uses acid to turn food into a liquid paste.

• The mouth uses acid while the stomach uses enzymes in saliva.

• Both use the exact same enzymes and acids to digest all types of food.

• The mouth only performs mechanical digestion, and the stomach only performs chemical digestion.

Multiple Choice

A patient's gallbladder is not releasing bile into the small intestine. What digestive process would be most affected?

• The absorption of water in the large intestine.

• The mechanical breakdown of food by chewing in the mouth.

• The chemical digestion of food that relies on bile in the small intestine.

• The movement of food down the esophagus via peristalsis.

Multiple Choice

Analyze the relationship between the small intestine and the pancreas. How does the pancreas support the small intestine's main function?

• The pancreas produces pancreatic juice with enzymes, which is released into the small intestine to help break down food for absorption.

• The pancreas absorbs water, allowing the small intestine to focus on absorbing nutrients.

• The pancreas stores waste from the small intestine before elimination.

• The pancreas produces hydrochloric acid for the small intestine.

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Summary

• The digestive system digests food, absorbs nutrients, and eliminates waste.

• Digestion includes mechanical processes like chewing and chemical processes involving enzymes.

• Food travels from the mouth to the esophagus, stomach, and intestines.

• The mouth starts digestion, the stomach creates a paste, and the small intestine absorbs nutrients.

• The large intestine's main function is to reabsorb water from undigested food.

• Accessory organs like the liver, gallbladder, and pancreas aid in chemical digestion.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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