🍽 The Digestive Journey
Food travels about 9 metres through your digestive system! It starts in your mouth and ends at your anus, taking roughly 24-72 hours to complete the entire journey. That's like food going on a three-day adventure inside you!
Nutrition - Humans » Digestive System Organs
What you'll learn this session
Study time: 30 minutes
- Identify the main organs of the human digestive system
- Understand the structure and function of each digestive organ
- Explain how food moves through the digestive tract
- Describe the role of enzymes and digestive juices
- Analyse adaptations of organs for efficient digestion
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Unlock This CourseIntroduction to the Human Digestive System
Your digestive system is like a brilliant food processing factory that works 24/7! It breaks down everything you eat into tiny particles that your body can absorb and use for energy, growth and repair. This amazing system includes several organs, each with a special job to do.
Key Definitions:
- Digestion: The breakdown of large food molecules into smaller, soluble molecules that can be absorbed.
- Mechanical digestion: Physical breakdown of food (like chewing).
- Chemical digestion: Breakdown of food using enzymes and acids.
- Absorption: Taking digested food molecules into the bloodstream.
- Peristalsis: Wave-like muscle contractions that push food through the digestive system.
The Mouth - Where It All Begins
Your mouth is the gateway to digestion. Here, both mechanical and chemical digestion start working together to prepare your food for its journey.
Teeth - Nature's Food Processors
Your teeth are perfectly designed cutting and grinding tools. You have different types for different jobs:
🦶 Incisors
Sharp, chisel-like teeth at the front for cutting and biting food into smaller pieces.
🦷 Canines
Pointed teeth for tearing and gripping food, especially useful for meat.
🦸 Molars
Large, flat teeth at the back for grinding and crushing food into a paste.
Amazing Saliva Facts
You produce about 1.5 litres of saliva every day - that's enough to fill a large bottle! Saliva contains an enzyme called amylase that starts breaking down starch into sugar. This is why bread tastes sweeter if you chew it for a long time.
The Oesophagus - The Food Highway
The oesophagus is a muscular tube about 25cm long that connects your mouth to your stomach. It's like a one-way motorway for food!
How Peristalsis Works
The oesophagus uses powerful wave-like muscle contractions called peristalsis to push food down to your stomach. These muscles work so well that you could actually swallow whilst standing on your head - though we don't recommend trying this!
The Stomach - The Acid Bath
Your stomach is a stretchy, J-shaped bag that can hold up to 1.5 litres of food and liquid. It's like having a personal blender and acid bath combined!
🧠 Stomach Structure
The stomach wall has three layers of muscle that contract in different directions. This creates a churning motion that mixes food with gastric juice, turning it into a soup-like mixture called chyme.
Gastric Juice - The Ultimate Food Dissolver
Your stomach produces up to 3 litres of gastric juice daily. This powerful mixture contains:
- Hydrochloric acid: So strong it could dissolve metal! It kills bacteria and activates pepsin.
- Pepsin: An enzyme that breaks down proteins into smaller pieces.
- Mucus: Protects the stomach lining from being digested by its own acid.
Case Study: Stomach Ulcers
For years, doctors thought stress and spicy food caused stomach ulcers. In 1982, Australian scientists Barry Marshall and Robin Warren discovered that most ulcers are actually caused by bacteria called Helicobacter pylori. Marshall even infected himself with the bacteria to prove his theory - and won a Nobel Prize for it!
The Small Intestine - The Absorption Superstar
Despite its name, the small intestine is actually the longest part of your digestive system at about 6 metres long! It's called 'small' because it's narrower than the large intestine.
Three Sections, Three Jobs
🍔 Duodenum
The first 25cm where most chemical digestion happens. Bile and pancreatic juice are added here.
🍝 Jejunum
The middle section where most nutrient absorption occurs. It's lined with millions of tiny finger-like projections called villi.
🍧 Ileum
The final section that absorbs vitamin B12, bile salts and any remaining nutrients.
Villi - The Absorption Champions
The small intestine is lined with millions of tiny projections called villi (singular: villus). Each villus is covered in even tinier projections called microvilli. This creates a massive surface area - about the size of a tennis court - packed into your abdomen!
Each villus contains:
- A network of blood capillaries to absorb sugars and amino acids
- A lymphatic vessel (lacteal) to absorb fats
- A thin wall (one cell thick) for efficient absorption
The Liver - The Body's Chemical Factory
Your liver is the largest internal organ and performs over 500 different functions! In digestion, it produces bile - a greenish liquid that helps break down fats.
🩸 Bile Production
The liver produces about 1 litre of bile each day. Bile contains bile salts that emulsify fats - breaking large fat droplets into smaller ones, like washing-up liquid breaking up grease on dishes.
The Gall Bladder - The Bile Storage Tank
This small, pear-shaped organ stores and concentrates bile from the liver. When you eat fatty foods, it contracts and squirts bile into the duodenum through the bile duct.
The Pancreas - The Enzyme Factory
The pancreas produces pancreatic juice containing three main enzymes that complete the digestion process:
🍞 Amylase
Breaks down starch into maltose (a type of sugar).
🥩 Protease
Breaks down proteins into amino acids.
🧀 Lipase
Breaks down fats into fatty acids and glycerol.
The Large Intestine - The Final Frontier
The large intestine is about 1.5 metres long and includes the colon, rectum and anus. Its main jobs are to absorb water and form faeces.
The Colon's Important Work
By the time food reaches your colon, most nutrients have been absorbed. The colon absorbs water and minerals, turning liquid waste into solid faeces. It's also home to billions of helpful bacteria that produce vitamins and protect against harmful microbes.
Gut Bacteria - Your Microscopic Helpers
Your large intestine contains more bacterial cells than there are human cells in your entire body! These 'good bacteria' help digest fibre, produce vitamins like vitamin K and support your immune system. They're so important that scientists now call them your 'second genome'.
How It All Works Together
The digestive system is a perfect example of teamwork. Each organ has evolved specific adaptations to do its job efficiently:
- Teeth have different shapes for cutting, tearing and grinding
- The stomach has thick muscular walls and produces strong acid
- The small intestine has villi to maximise absorption surface area
- The liver produces bile to help digest fats
- The pancreas produces enzymes to complete digestion
- The large intestine absorbs water to prevent dehydration
From the moment you take a bite to the moment waste leaves your body, this incredible system works continuously to keep you alive and healthy. It truly is one of nature's most impressive achievements!