The Digestive System

The breakdown of large food molecules into smaller components. Once digested, nutrients can be absorbed. Vitamins, minerals, water can be absorbed without being digested.

The physical breakdown of food into smaller pieces (e.g. teeth)

The breakdown of macromolecules by enzymes (e.g. enzymes in saliva, amylase)

• simple sugar (1 unit) E.g. glucose, fructose, galactose

• sugars (2 units) E.g. sucrose, lactose, maltose

• many sugars E.g. starch, cellulous (Most common)

Accessory Organs and The Digestive Tract

structures that aid digestion but food doesn’t go through

organs that contain food

• humans get two sets of teeth • 20 deciduous (“baby” teeth) • 32 permanent that are covered in enamel, beneath is dentin with sensory cells, root attached tooth to the bone

• 8 of them • used for cutting

• 4 of them • used for tearing/ripping

• 8 of them • used for grinding

• 12 of them • used for grinding

• strong muscle containing taste buds (sweet, sour, salty, bitter) • helps mold and smooth out food into a soft mass called a bolus, which is then pushed to the back of your mouth (pharynx) towards the esophagus

Ball of chewed food

produce saliva the begin chemical digestion of food (3 salivary glands)

• the enzyme amylase which starts to breakdown starch into simpler sugars • mucus for lubrication, making it easier to swallow • dissolves water-soluble food particles • stimulates the taste buds

• muscular tube between mouth and stomach (25cm long)

• during swallowing the soft palate moves up to close off the nasal cavity, epiglottis close off the trachea (or windpipe), muscles above the bolus push it through the esophagus by a series of rhythmic contractions peristalsis, the esophagus is unrivalled by cells that secrete mucins (triglycerides)

• the entrance to the stomach is controlled by a ring of muscle called the esophageal sphincter • usually closed to prevent acidic stomach contents from rising into the esophagus • relaxes to allow food to enter stomach

• muscular, J-shaped organ where food is temporarily stored while further chemical and mechanical digestion takes place • walls are folded (called rugae) like an accordion, which allows the stomach to expand after a meal

• lined with millions of gastric glands that secrete gastric juice when simulated by presence of food • approximately 400 to 800ml of gastric juice are released per meal

• used for chemical digestion of food • gastric juice is made up of HCl acid, enzymes, salts, water and mucus