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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Peristalsis and Food Movement
Ever wondered how that sandwich you ate for lunch travels through your body? It doesn't just slide down a tube! Your digestive system is an amazing machine that squeezes, pushes and moves food along its journey through your body. The star of this process is called peristalsis - a wave-like muscle movement that propels food from your mouth all the way to... well, the other end!
Key Definitions:
Your digestive system is about 9 metres long! Food travels through this winding path:
Understanding peristalsis helps us:
Peristalsis is like a Mexican wave at a football match, but inside your digestive tract! It involves coordinated muscle contractions that create a wave-like motion, pushing food forward. Without peristalsis, food would just sit in your stomach - not very helpful for getting nutrients!
Your digestive tract has two layers of muscles: circular muscles (that wrap around the tube) and longitudinal muscles (that run along the length). These work together to create the peristaltic motion:
Circular muscles in front of the food relax and stretch, creating space for the food to move into.
Circular muscles behind the food contract, squeezing the tube and pushing the food forward.
This pattern of relaxation and contraction creates waves that move along the digestive tract, propelling food forward.
Peristalsis is so effective that you could digest food even while standing on your head! The muscle contractions are strong enough to push food upward against gravity. This is why astronauts can still digest food properly in the weightless environment of space.
Peristalsis works slightly differently in each part of your digestive system. Let's explore the journey!
The journey begins in your mouth, where food is chewed and mixed with saliva to form a bolus. But how does this bolus get to your stomach?
Once you swallow, the bolus enters your oesophagus - a muscular tube about 25cm long. Peristalsis in the oesophagus is particularly strong and coordinated. The wave of muscle contractions pushes the bolus downward at a speed of about 3-4 cm per second. This means it takes about 8-10 seconds for food to travel from your throat to your stomach!
At the bottom of the oesophagus is a ring of muscle called the lower oesophageal sphincter (LOS). This normally stays closed to prevent stomach acid from flowing back up, but relaxes to let food enter the stomach.
Once in the stomach, food undergoes a different type of movement. The stomach walls contain three layers of muscle that contract to churn and mix food with gastric juices. This creates a semi-liquid mixture called chyme.
The stomach's peristaltic waves are more like a washing machine than a simple push. They mix the food thoroughly while gradually moving it toward the pyloric sphincter, which controls the release of chyme into the small intestine.
After leaving the stomach, chyme enters the small intestine, where most nutrient absorption occurs. Peristalsis here is gentler and more complex.
The small intestine has two main types of movements:
By the time food reaches your large intestine, most nutrients have been absorbed. The large intestine has three types of movements:
Gastroesophageal reflux disease (GERD) occurs when the lower oesophageal sphincter weakens, allowing stomach acid to flow back up into the oesophagus. This causes the burning sensation known as heartburn. About 20% of people in the UK experience GERD regularly. Treatments include lifestyle changes (avoiding trigger foods, not eating before bedtime) and medications that reduce acid production. This condition highlights the importance of proper sphincter function in the digestive system.
Peristalsis isn't a random process - it's carefully controlled by your nervous system and hormones.
Your digestive tract has its own nervous system called the enteric nervous system - sometimes called your "second brain"! It contains about 100 million neurons and can operate independently of your central nervous system.
When food stretches the walls of your digestive tract, stretch receptors send signals to these neurons, triggering peristalsis. This is why you can digest food even if your spinal cord is damaged.
Various hormones affect peristalsis, including:
When peristalsis goes wrong, various digestive disorders can occur:
Affects up to 20% of the UK population. Features abnormal peristalsis - sometimes too fast (causing diarrhoea) or too slow (causing constipation).
A rare condition where the lower oesophageal sphincter fails to relax properly and peristalsis in the oesophagus is reduced, making it difficult to swallow.
Reduced stomach peristalsis, causing delayed emptying. Often occurs in people with diabetes due to nerve damage.
Peristalsis is a remarkable process that allows food to travel through your digestive system, ensuring nutrients are absorbed and waste is eliminated. Without these coordinated muscle movements, digestion would be impossible.
The next time you eat something, think about the incredible journey it's about to take - pushed along by waves of muscle contractions, mixed and churned, broken down and absorbed. Your digestive system truly is an amazing feat of biological engineering!
For your IGCSE Biology exam, remember to describe peristalsis as "wave-like contractions of circular and longitudinal muscles that push food along the digestive tract." Be able to explain how peristalsis works in different parts of the digestive system, particularly the oesophagus and small intestine.
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