THE HUMAN DIGESTIVE SYSTEM!

You are about to go on a journey through time and space – travel through a human body – you start as a sandwich – you end up as manure! We start our journey, as any journey should, at the beginning…

SALIVARY GLANDS produce saliva – contains amylase to break down starch – lubricates food for swallowing. …the MOUTH Function: Food enters your body here! The TEETH are used for mechanical breakdown of food. The TONGUE pushes food towards the teeth and to the back of the mouth for swallowing.

You are now ground up, some starches breaking down and you are called a BOLUS… The PHARYNX, connecting the nose and throat, allows breathing while mouth is full. The tongue pushes you to the back of the throat to be swallowed… The EPIGLOTTIS covers your trachea so food does not enter your airways.

The bolus enters the ESOPHAGUS, a tube that connects the mouth to the stomach. PERISTALSIS is the motion of the muscles pushing food along the esophagus. (So you can swallow standing on your head!) SPHINCTERS are muscles that open and close in a circular motion – the one that separates the esophagus from the stomach is the CARDIAC SPHINCTER.

The STOMACH is a muscular bag full of HCl that: Stores food, slowly releases it to SMALL INTESTINE Breaks food down mechanically by smooshing it Breaks food down chemically through enzymes and HCl Only water, ethanol and certain drugs are absorbed into blood here. The PYLORIC SPHINCTER separates the stomach from the SMALL INTESTINE.

The LIVER has many functions in the body: Stores GLYCOGEN (glucose that can be used later) Breaks down amino acids into urea Filters out non-food molecules from blood (drugs) Produces BILE which acts like a detergent to break down FATS The GALL BLADDER stores BILE made by the LIVER and secretes it into the DUODENUM, the first part of the SMALL INTESTINE.

The PANCREAS also has many functions: Secretes pancreatic juices (enzymes) into the DUODENUM. Neutralizes stomach acid by secreting sodium bicarbonate solution into DUODENUM. Produces INSULIN and GLUCAGON into blood to regulate blood sugar levels.

The SMALL INTESTINE is where most of the digestion and absorption of nutrients occurs. DUODENUM: Accepts digestive secretions – most of digestion occurs here. JEJUNUM and ILEUM – some digestion – most of absorption of nutrients occurs here. Highly folded surface covered in villi and microvilli to maximize surface area. Its more than 6 metres long in adult humans!

The CECUM is the first part of the LARGE INTESTINE – it absorbs fluids and salts, and coats dry waste with mucous to lubricate it. The LARGE INTESTINE or COLON contains bacteria to continue breaking down food, producing B vitamins and vitamin K Fluids and salts absorbed Feces (dry waste not used by body) is formed here. FIBRE feeds the bacteria and cells lining colon. The LI is about 1.5 m long in adult humans! The APPENDIX is possibly a resevoir for bacteria – but it doesn’t really seem to have a purpose!

The RECTUM stores feces until it is ready to leave the body. The ANUS excretes the feces…and our journey is over.