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• Functions of the digestive system: – Ingest food and convert to energy. – Absorb nutrients – Eliminate waste • Alimentary Canal or GI tract: – Broken into sections with different jobs. – Mouth > Esophagus > Stomach > Small Intestine > > Large Intestine > Sigmoid Colon > Rectum > Anus – Many other organs help along the way. • Mouth: – Chief function is to receive food and begin digestion process. • Teeth: – Incisors-Cut – Canines-Tear – Pre-molars and Molars for grinding and crushing. • Tongue helps to manipulate food, move it, and taste it. • Salivary Glands: Saliva to soften and digest food. – amylase helps break down starch. • Salivary Glands: – Parotid – Sublingual – Sub mandibular • After food is softened and balled up it is called a bolus. • The bolus passes through the pharynx and goes into the Esophagus – Swallowing is a reflex action. • We start the process, but the food is pushed down the Esophagus tube involuntarily. – Peristalsis- Rhythmic contraction that pushes food along GI tract. – Esophagus connects mouth to stomach. • Entrance to stomach controlled by valve like muscle called esophageal sphincter. – “Heart Burn” •Stomach: – Diameter changes to accommodate food and fluid. • Folds called rugae that disappear as stomach expands. – Four sections: • • • • Cardiac Fundic Body Pyloric Fig. 15.4a • Stomach: – Functions to mechanically and chemically digest food. • Contraction of muscle helps separate food into small pieces and mix it with digestive enzymes. • Chemical digestion: – H Cl made by gastric cells in stomach-breaks down connective tissue and activates pepsin enzyme. » Also functions in protection from bacteria. – Pepsin breaks down protein. – Chyme: soupy liquid that leaves stomach. • Chyme leaves the stomach through the pyloric sphincter and enters into small intestine. • Small Intestine: – Roughly 6m in length but small in diameter. – Three sections: • Duodenum, jejunum and ileum – Site of chemical digestion of all food contents: • Receives input of digestive enzymes from liver and pancreas. – Bile from liver and pancreatic juice. • Absorption of nutrients. – Villa and micro villa help increase the surface area to maximize absorption. • Passes non-digestible products to large intestine. – Passes through the ileocecal valve. • Large Intestine: – Shorter in length, but wider in diameter compared to the small intestine. • Cecum • Colon: – – – – Ascending Transverse Descending Sigmoid • Rectum • Anal Canal Fig. 15.9a • Large Intestine: – Functions to absorb water and transport waste to rectum. – Also an important site or vitamin production by resident bacteria. (B and K) • Waste then leaves through the anal opening. Pancreas: – Functions as an endocrine and exocrine gland. – Pancreatic Juice contains: • • • • • Sodium bicarbonate: raises pH Amylase: digests starches Trypsin: digests proteins Lipase: digests lipids. Nucleases: digest nucleic acids • Liver: – Largest organ of the body (not counting skin) • Function of Liver: – Blood enters and toxins are removed and detoxified. – Stores vitamins and iron. – Helps regulate cholesterol level and aids in production of blood plasma proteins. – Produces bile which is stored in the gall bladder. • Bile is a fat emulsifier. • Removes excess glucose and stores it as glycogen. • Glycogen is broken down and glucose released when level is low. • Produces glucose if needed. •Disorders: – Jaundice – Hepatitis – Cirrhosis