Digestion: From the mouth to the stomach

Learning Outcomes

Identify the parts of the gastrointestinal tract, including the mouth, oesophagus, and stomach
Recall the role of enzymes in digestion and name the enzymes amylase and pepsin
Describe the structure of, and digestive processes that occur in the mouth, oesophagus, and stomach

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Protein

A nutrient found in food that is made up of smaller parts called amino acids. It is a necessary part of the diet and keeps cells healthy and functioning normally. Also assists in building muscle tissue.

Enzyme

A kind of protein that speeds up or slows down chemical reactions in our digestive system.

Amylase

An enzyme found in saliva that breaks down carbohydrates found in food.

Carbohydrate

A substance, such as starch or sugar, that is rich in energy and is made up of carbon, hydrogen and oxygen and is an important part of human diets.

Mucus

A thick, slimy substance that protects things from drying out. Found in the nose, lungs and intestines.

Esophagus

A tube that transports the food down the throat, to the stomach.

Gastrointestinal tract

A system of organs, glands and vessels that assists with taking in food, breaking it down, absorbing energy and nutrients from the food, and getting rid of the remaining waste in the form of feces and urine.

Hydrochloric acid

A strong acid found in the stomach, which helps to break down food.

Pepsin

An enzyme produced in the stomach that breaks down proteins found in food.

A measure between 0 and 14 that indicates how acidic or basic a chemical is.

Hmmm- aaaah! -Hei! -Aah! -What ARE you doing? -I’m pooping. -What?? Pooping. All animals do it, from time to time. It’s one way for our bodies to deal with the bits of food we can’t use, waste products. -Exactly. We get the energy we need from the food we eat.

Food also gives us the building blocks needed for the cells, muscles, hair and all the other things that together form a body. If we simplify our body somewhat, it’s a bit like this toilet roll. The white paper is the skeleton, blood, nerves and everything else that sits around the tube in the centre. In your body, between the mouth and the anus runs a long pipe, or canal: the Gastro-Intestinal Tract. The intestines are folded back and forth – and if you were to straighten out the whole canal, it would be many times longer than you: more than seven metres!

When she eats, Maria takes in lots of nutrients, such as: carbohydrates from potatoes, protein from chickpeas, and fat from coconut oil. The first stage in the food’s journey through the body is: the mouth. Here the food is broken down - digested - in two ways: it’s done mechanically by the teeth AND chemically by the saliva. Saliva specifically contains a protein that cuts long-chain carbohydrates into smaller pieces. The kind of protein that speeds up or slows down chemical reactions is known as an enzyme.

And this enzyme is called amylase. And so the saliva moistens up the food and works as a lubricant to make the next stage of the journey easier. Step two - the Esophagus - an empty passageway. When the food is chewed the right amount, it is pushed to the back of the mouth by your tongue, and then your throat responds automatically. We call it the swallowing reflex.

The esophagus is surrounded by very strong muscles. They move in waves that carry the pieces of food from the mouth down to the stomach. The Esophageal Muscles are so strong that it’s possible to swallow water doing a handstand. Step three - the stomach - a lot happens here! The stomach has several different functions.

To begin with, it is a food storage place; an internal lunchbox! A full stomach can hold about a liter, but when empty it contracts to half that size. Around the stomach sit powerful muscles that process food mechanically. They knead and mix the food into a paste. But what happens chemically here?

Well, now we're at the most acidic place in our body, with a pH as low as two! It is the gastric juice that makes it so sour; it contains hydrochloric acid. The acidic environment protects us from infections, because many of the bacteria we ingest are killed by acid. In the gastric juice there is also an enzyme that breaks down proteins. It's called pepsin.

To protect the rest of the body from the stomach's acid, so that it doesn’t corrode the innards below, a mucous membrane lines the inside of the stomach. If this lining is damaged, we can get an ulcer. -Do you think you own the toilet, or what? -Maria, you've been in there forever! -It's probably best that we take a little break here. In the next film we'll find out whether Maria manages to sh.. do a number two before the family breaks down the door - and of course what happens in the digestive tract when food leaves the stomach.