HUMAN DIGESTION

Term 2 Unit Topic

LEARNING INTENTIONS

1. To know what the digestive system is.

LEARNING INTENTIONS

2. To know what jobs all the organs do.

LEARNING INTENTIONS

3. To understand the importance of a healthy diet.

WHAT IS THE DIGESTIVE SYSTEM ALL ABOUT?

The parts of the body that deal with food – from the first bite to getting rid of the waste – are known as the DIGESTIVE SYSTEM.

QUESTION!

How much food does a human adult need to eat in

a year?

500 kilograms!

HUMAN DIGESTIVE SYSTEMSwallowing is the start of a journey for your food that takes 24 hours or more and involves travelling up to 9 metres through a dark tube full of powerful chemicals.

HOW DIGESTION WORKS

The digestive tract is a long tube that starts at the mouth and ends at the anus.

HOW DIGESTION WORKS

1. Food is chewed in the mouth and swallowed down the throat.2. It is pushed through the Oesophagus into the stomach.

HOW DIGESTION WORKS

3. Then the food travels through the small and large intestines to the anus, where any waste is passed out.

WHAT MAKES US FEEL HUNGRY?The hypothalamus in our brains makes us feel hungry & thirsty.The brain stem controls the movements of the gut and the removal of food waste.

CHEWING & SWALLOWINGAfter you have taken bites of your food and chewed, it quickly becomes mushy due to saliva.Saliva is made in glands on the sides of your face which release up to 1.5 litres a day into your mouth!

SALIVA GLANDSThere are 3 glands on each side of your face.1. Parotid – in front of your ear.2. Submandibular – back of your lower jaw.3. Sublingual – under your tongue.

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QUESTION!

How many times a day does the average person

bite and chew?

Over 1100 times!

BREAKING DOWN THE FOODIn the digestive tract, the food is digested (broken down) and absorbed into the body.

IN THE STOMACHFood takes a few seconds to travel down the oesophagus. It is pushed into the bag-like stomach, which attacks the food with powerful acids, enzymes and other chemicals.

IN THE STOMACHThe stomach walls have many layers – 3 of these are made of muscle fibres. The muscles tighten and contract the stomach to squash, mix and mash the food.

IN THE STOMACHThe stomach also attacks the food with powerful chemicals. Its lining produces a strong acid called hydrochloric acid. The lining also makes enzymes and these both break down different parts of your meal.

GUTS GALOREAfter a few hours in the stomach, your meal has become a thick, dark, mushy soup. The mixture then heads down to the small intestine.

SMALL INTESTINEThe small intestine contains many more enzymes that attack food and continue to break it into smaller pieces. These enzymes come from another digestive organ called the pancreas, which is on the left of your body under the stomach.

SMALL INTESTINEThere are many folds in its lining, made of millions of tiny fingers called villi.

Every single one has a system of tiny vessels for blood and nutrients.

QUESTION!

How long is your small intestine?

About 6 metres!

ON THE WAY OUTThe last part of the digestive tract is the large intestine.Its job is to take a few more nutrients from the food and remove as much water as the body needs.

QUESTION!

Why is faeces (poo) brown?

Because of a substance called bilirubin that comes from the

breakdown of old red blood cells in the liver.

LIVERThe liver is part of the digestive system but isn’t in the digestive tract.It has many jobs. One is to make bile, a green fluid that passes to a small storage bag called the gallbladder.

BILE

When food enters the small intestine, bile flows in and helps to break up fat in the food.

PANCREASThe pancreas makes digestive juices that flow through a duct into the small intestine. These juices help neutralize the stomach acid so it doesn’t burn the gut.

THE URINARY SYSTEMLiquid waste (urine) comes from the kidneys, which filter unwanted substances from the blood.

THE URINARY SYSTEM

The two tubes (ureters) carry urine down to the bladder – a stretchy bag that holds the urine until it is passed out into the toilet.

KIDNEYSALL of the body’s blood is filtered by the kidneys every 10 minutes. This means that your blood is filtered about 150 times a day!

NEED TO GO TO THE LOO?

Your bladder can hold about 0.5 litres of urine, although it is stretchy enough to hold twice that amount.However, when there is about 0.2 litres in your bladder you will feel like going to the loo!

QUESTION!

What is the heaviest organ inside the human body?

The liver! It weighs about 1.5-2 kg in a healthy adult.