Peristalsis A wave of muscular action that pushes food along the digestive system.
Peristalsis After chewing, food is swallowed and pushed down the oesophagus by a wave of muscular action called peristalsis. Food enters the stomach where further physical and chemical digestion occurs.
Activity Model-making
A wave-like muscular contraction called peristalsis pushes food through the digestive system. You can model this process using a tennis ball, liquid hand soap and a pair of knee-length nylon ‘pop socks’.
l l
l l
Cut the foot section off the nylon pop sock. Stretch the stocking and note that it can stretch in length and width. The same applies to the digestive system.
Soak the stocking and the tennis ball in water and spread some liquid soap over them. Insert the ball at the top of the stocking. Gently squeeze the stocking above the ball. Observe what happens. Continue to squeeze above the ball until it comes out at the foot.
This model demonstrates how the muscles in the digestive system squeeze to push the food along, while the muscles in front of the food relax to allow it to be pushed forward.
10.7 The stomach Structure of the stomach
Mucus A
slippery, sticky, thick liquid.
The stomach is a muscular bag. It is lined with a thick layer of mucus to prevent acid and digestive enzymes from damaging the stomach wall. It has two special muscles called sphincter muscles. One is at the entrance to the stomach and opens to allow food in, then closes to stop the contents of the stomach being pushed back up the oesophagus. There is also one at the bottom of the stomach. It closes to hold the food in the stomach long enough for digestion to occur, then opens to allow food to enter the small intestine.
108 Oesophagus
Stomach
Fig. 9 Food is pushed down through the oesophagus to the stomach.
