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  1. Define ingestion as the taking of substances, e.g. food and drink, into the body through the mouth

Learn the definition, guys!

Ingestion is the taking of substances, e.g. food and drink, into the body through the mouth

 

  1. Define digestion as the breakdown of large, insoluble food molecules into small, water-soluble molecules using mechanical and chemical processes

Seriously, just memorise these definitions for the exam – it’s an easy way to rack up those marks.

 

  1. Define mechanical digestion as the breakdown of food into smaller pieces without chemical change to the food molecules

Look, yet another definition to learn!

 

  1. Define chemical digestion as the breakdown of large, insoluble molecules into small, soluble molecules

You guys should know the drill by now.

 

  1. Define absorption as movement of digested food molecules through the wall of the intestine into the blood

Learn the definition, my dudes.

 

  1. Define assimilation as the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells

Guess what you need to do!

That’s right – memorise the definition

 

  1. Define egestion as passing out of food that has not been digested, as faeces, through the anus

I’m not even going to say anything at this point

 

 

  1. Identify the main regions of the alimentary canal and associated organs, including mouth, salivary glands, oesophagus, stomach, small intestine, pancreas, liver, gall bladder, large intestine and anus

This diagram should explain it all:

Food passes through the alimentary canal using the following route:

  1. Mouth
  2. Oesophagus
  3. Stomach
  4. Small intestine (here, most of your nutrients and water are absorbed into your body)
  5. Large intestine (here, some nutrients and water are absorbed into your body)
  6. Anus

The organs listed above make up your alimentary canal.

Note: the alimentary canal is called a ‘canal’ because it is essentially one long canal that starts at your mouth and ends at your anus.

Note: your small intestine is made up of three parts. The ‘C’ shaped curve immediately after the stomach is the first part of your small intestine. It’s called the duodenum. After the duodenum is the jejunum, followed by the ileum. The jejunum and ileum don’t look significantly different. You don’t strictly need to know this, it’s just useful to know.

Food enters your body via the mouth, and leaves the body via the anus.

Now, for the associated organs:

Your salivary glands empty into your mouth using ducts.

The liver produces bile, a substance that is important for digestion. The bile is emptied into the gall bladder, where it is stored.

The pancreas and gall bladder both empty into the duodenum.

 

  1. Describe the functions of the regions of the alimentary canal listed above, in relation to ingestion, digestion, absorption, assimilation and egestion of food

Mouth:

The mouth contains saliva, which is secreted from the salivary glands. Saliva contains salivary amylase – an enzyme that breaks down carbohydrates (chemical digestion). The mouth also contains teeth, that cut, chew and grind food (mechanical digestion). Food is formed into a bolus, which is then swallowed.

The mouth is used for ingestion, as well as both mechanical and chemical digestion.

Since the salivary glands use nutrients to produce saliva, this can be considered a site of assimilation.

Oesophagus:

The swallowing of food causes it to move from the mouth to the stomach through the oesophagus, by peristalsis.

I found a nice definition of peristalsis online, which I’ll put here:

the involuntary constriction and relaxation of the muscles of the intestine or another canal, creating wave-like movements which push the contents of the canal forward.

Stomach:

The stomach is an organ containing gastric juices (mainly hydrochloric acid and protease enzymes). The acidity (pH2) kills bacteria and the proteases digest proteins. The stomach also churns the food in it. It releases small amounts of food at a time into the duodenum, storing the rest.

Mechanical and chemical digestion occurs in the stomach.

Pancreas:

Secretes pancreatic juices to the duodenum.

As the pancreas uses nutrient molecules to do this, this can be considered a site of assimilation.

Gall bladder:

Stores bile which is produced by the liver, and secretes it to the duodenum.

Small Intestine:

The Pancreas and the gall bladder are connected to the duodenum by ducts. Pancreatic juices and bile (stored in gall bladder) are transported to the small intestine via these ducts. Pancreatic juices contain proteases, lipases (fat-digesting enzymes), amylases and sodium hydrogencarbonate (which neutralises the acid from the stomach).

Bile, produced by the liver and stored in the gall bladder, contains bile acids, also known as bile salts – which emulsify fats. Bile is also alkaline, which helps neutralise stomach acids.

The epithelial lining of the rest of the small intestine secretes yet more enzymes which breakdown maltose and peptides. The jejunum and ileum have a huge surface area due to the villi present, allowing a greater amount to be absorbed at a time.

The small intestine is a site of both chemical digestion and absorption.

The large intestine:

The main function of most of the large intestine is to reabsorb the water from the undigested food.

The last part of the large intestine, called the rectum, stores faeces until it is egested.

Anus:

The anus is the site of egestion – it has sphincter muscles that control when faeces is egested from the body.

 

 

Notes submitted by Sarah

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