Learning About the Digestive System

Next up in our series about the human body, we investigated the digestive system. This didn't involve the most visually impressive set of activities and experiments but they were very effective at showing the girls the steps involved. We started out sitting down with a biscuit to eat. As the girls bit into and chewed their biscuit I asked them to think about how they ate it, what was happening to the biscuit and which parts of their mouth were involved. They were quick to identify that teeth crunched up food and their tongue pushed it around the mouth. We simulated this with a dry cracker in a ziploc bag to snap and crush as the teeth do. As the girls worked on 'chewing' the cracker, I asked a few questions to lead them to think about how the food changed from dry and crumbly to wet and mushy in their mouth and how that made it easier to swallow. This is their saliva glands working.

The tongue pushes the masticated food (the girls loved that word!) to the back of the mouth and the throat where it is swallowed. It travels down the oesophagus, down which rings of muscle contracting one after the other create a 'wave' of movement that pushes the bolus down to the stomach. We simulated this with a plastic Easter egg inside a pair of children's tights (idea from the science matters website). The girls made rings with their fingers and contracted them above the plastic egg, pushing it down the leg of the tights.

Once the food has arrived into the stomach, strong muscles in the stomach wall contract to churn and mash the food into a pulp that is slowly fed into the small intestine. Acidic juices are secreted onto the food to help break it down. To simulate this we added some soda water to the cracker in the bag and continued to churn the contents into mush.

We moved on in the journey of the food bolus into the small intestine. As the small intestine is so long, we measured out the approximate length of 6.7m with a piece of red wool and snaked it backwards and forwards on the table. The girls also tried stretching it to see if it was as long as our house! We talked about how the food is broken down even further with the assistance of the gall bladder, pancreas and liver into it's smallest components to allow the body to absorb it and use the nutrients, carbohydrates, fats and proteins from the food. The girls remembered how the capillaries run very close to pick up oxygen from the lungs from when we looked at the cardiovascular system, they linked it to the small intestine and asked if that was how the nutrients were picked up - I was pleased they were linking previous knowledge to this session. It takes around four hours from when food is eaten to it being absorbed and used by the body. The final part of the journey is the large intestine where the last of the nutrients and much of the water is reabsorbed.

To show how effective the use of acidic secretions is in breaking down food, the girls put a whole sweet into two jars and a crushed up sweet into another two jars. To one example of each they added water and to the other example of each they added vinegar as an acid. We left them for a few hours without agitating the jars at all then came back to see what had changed......

The jars containing acids had clearly had a lot greater effect on the sweet than the jars containing water. the crushed up sweet in the acid had completely gone, leaving a fluffy pinkish residue on the surface and sugar crystals on the bottom of the jar, whilst the water had only managed to liberate a few grains of sugar from the crushed up sweet. It was a simple but powerful way of demonstrating the need for acidic secretions in the digestive system.

Whilst waiting for the acid to break down the sweets, the girls coloured a picture of the digestive system and sellotaped their woollen small intestines onto the centre. We added them to the body outlines we have been making through our human body studies.