I have had fun playing Frankenstein with this game from BBC Science. You have to rotate the organs so that they are aligned and then put them into the body in the correct location. I only managed 58% – will you do better?
The small intestine looked pretty weird to me but it connected itself up in the end. I like the small intestine because it is a useful structure for teaching how organs are adapted for their function. The first section is known as the duodenum, the middle section is called the jejunum and the final piece is the ileum. I am going to treat it as a whole calling it the SI or the gut.
The job of the SI is the digestion and absorption of food. Digestion means turning insoluble molecules in the food you eat into soluble ones that can be absorbed into the blood supply. Digestion is carried out by special catalysts called enzymes that are pumped into the SI by the pancreas. There are three main types of food being digested; protein, fat (lipid) and carbohydrate.
- Protein is broken down into amino acids
- Fat is digested to fatty acids
- Carbohydrate is split into sugars.
These molecules are then absorbed through the SI lining and into the blood stream.
The SI is such a long tube so that there is enough time for the food to be digested. Animals with diets that are less digestible have longer intestines, carnivores tend to have rather shorter ones. Muscular walls massage the food along and this is one of the reasons why fibre is so important in your diet. It provides some bulk for the SI muscles to act against, keeping everything moving smoothly through your system.
The SI is lined with tiny finger-like projections called villi. These increase the surface area of the SI, greatly increasing the rate at which the products of digestion can be absorbed. And, since each villus has a network of capillaries within it, it provides easy access to the bloodstream too. The lacteal (part of the lymphatic system) transports digested fats away. The outer layer of the villus is only a single layer of epithelial cells thick so it is easy for the products of digestion to pass through to the capillaries within.
Food that passes through the small intestine undigested enters the large intestine where water is removed from the waste and it is prepared to be egested from the body.
Questions…
- What is the job of the small intestine?
- Suggest three ways in which the small intestine is specially adapted to its job.
- Name a digestive enzyme found in saliva. What reaction does it enable?
- Undigested food is egested from the body. Name a chemical that is excreted from the body. Which organ(s) is/are responsible for this excretion?
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