Brent Cornell

    
There are two major groups of organs which comprise the human digestive system:

• The alimentary canal consists of organs through which food actually passes (oesophagus, stomach, small & large intestine)
• The accessory organs aid in digestion but do not actually transfer food (salivary glands, pancreas, liver, gall bladder)

Diagram of the Digestive System

⇒  Click on the diagram to show / hide labels

Alimentary Canal:

Oesophagus

•  A hollow tube connecting the oral cavity to the stomach (separated from the trachea by the epiglottis)

•  Food is mixed with saliva and then is moved in a bolus via the action of peristalsis

Stomach

•  A temporary storage tank where food is mixed by churning and protein digestion begins

•  It is lined by gastric pits that release digestive juices, which create an acidic environment (pH ~2)

Small Intestine

•  A long, highly folded tube where usable food substances (nutrients) are absorbed

•  Consists of three sections – the duodenum, jejunum and ileum

Large Intestine

•  The final section of the alimentary canal, where water and dissolved minerals (i.e. ions) are absorbed

•  Consists of the ascending / transverse / descending / sigmoidal colon, as well as the rectum 

Accessory Organs:

Salivary Glands

•  Release saliva to moisten food and contains enzymes (e.g. amylase) to initiate starch breakdown 

•  Salivary glands include the parotid gland, submandibular gland and sublingual gland

Pancreas

•  Produces a broad spectrum of enzymes that are released into the small intestine via the duodenum

•  Also secretes certain hormones (insulin, glucagon), which regulate blood sugar concentrations 

Liver

•  Takes the raw materials absorbed by the small intestine and uses them to make key chemicals

•  Its role includes detoxification, storage, metabolism, bile production and haemoglobin breakdown

Gall Bladder

•  The gall bladder stores the bile produced by the liver (bile salts are used to emulsify fats)

•  Bile stored in the gall bladder is released into the small intestine via the common bile duct

Drawing of a Human Digestive System

Key Features:

• Stomach should look like a ‘J’-shaped bag and be connected to the oesophagus and small intestine
• Liver should look like a right-angled triangle and be superimposed to the left of the stomach (right side of the human)
• Bile duct (connected to gall bladder) and pancreatic duct should both feed into a U-shaped bend of the small intestine
• Small intestine should be thinner in width than the large intestine