6.1 Digestion

The main purpose of the digestive system is to break down large molecules into smaller subunits due to the fact: • Large molecules are typically chemically inert and need to be broken down and reassembled into usable products. -Large molecules are typically insoluble and cannot be easily absorbed into cells, whereas smaller sub subunits are in soluble.

The digestive system is composed of the alimentary canal and a variety of supporting accessory organs

Directly Transfers food - Oesophagus- Food Tract from moth to stomach - Stomach- Storage tank with low pH (protein digestion) -Small Intestine - Site of nutrient absorption - Large intestine - Absorbs water and dissolved minerals

Supports Digestive processes - Salivary gland - Moistens food bolus (starch digestion) -Pancreas - Secretes key enzymes into small intestine - Liver - Metabolizes absorbed nutrient’s (produce bile) - Gall Bladder - Stores and secretes bile (emulsifies fats)

Peristalsis - Unidirectional movement of food along alimentary canal - Caused by contractions of sequential longitudinal muscles

• Bidirectional mixing of food within the small intestine. • Caused by contraction of non-sequential circular muscles.

The breakdown of food via physical actions - Chewing (grinding food using teeth) - Churning (squeezing stomach contents) -Segmentation (intestinal contrations)

The breakdown of food via chemical agents - Stomach acids (low pH environment) - Bile (emulsification of fats into droplets - Enzymes (catalysen hydrolysis reactions)

Starch is composed of glucose monomers - Is linear (amylose or branched (amylopectin) Amylase (salivary or pancreatic) digestion starch - It digests amylose into maltose disaccharides -It digests amylopectin into dextrin chains The Pancreas regulates the upstate of glucose - Insulin increases glucose uptake by cells - Glucagon decreases glucose uptake by cells The liver is responsible for glucose storage. - Glucose is stored as glycogen (polysaccharide)