Mammalian Digestive System

Oral Cavity, Pharynx, & Esophagus Digestion Starts in the Oral Cavity Mechanical digestion occurs here Increased surface area and makes easier to swallow Salivary glands secret saliva Saliva begins chemical digestion Composed of enzymes, buffers, & antibacterial agents Tongue distinctions food and pushes bolus Bolus- ‘ball’ of food swallowed

Oral Cavity, Pharynx, & Esophagus Food is pushed to the Pharynx (a.k.a. throat) Composed of the esophagus and trachea Separated by the Epiglottis Moves down the esophagus via peristalsis movement Rhythmic movement off the muscles

Digestion in the Stomach Stomach- pouch where food is stored and digested Secrets fluid called gastric fluid which aids in digestion of the food Mixture of juice and food called Chyme Fluid is composed of two components: Hydrochloric Acid (HCl) 2ph environment in the stomach Kills bacteria and denatures protein to expose petite bonds

Digestion in the Stomach Fluid is composed of two components: Protease (pepsin) Breaks peptide bond, cleaving proteins into small polypeptides Fluid created by the gastric glands Parietal cells release H & Cl ions Chief cells release pepsin in inactive form of pepsinogen Stomach protected from fluid via mucus and lining replacement

Digestion in the Small Intestine Small intestine- 6m long tube where most hydrolysis of molecules occurs First 25cm forms the duodenum Chyme mixes with additional digestive juices Juices secreted by the liver, pancreas, and gallbladder Pancreas secretion Alkaline solution containing enzymes Acts as a buffer

Digestion in the Small Intestine Liver secretion Called bile Stored and concentrated in the gallbladder Breaks down fats and other lipids Absorption Nutrients absorbed and distributed throughout the body Increased surface area increases absorption Aided by villi and mircovilli

Digestion in the Small Intestine Absorption Can be active or passive When absorbed, it is transported to the liver via blood Transported to the liver for two reasons: Detoxification Nutrient balance

Large Intestine Large intestine- consists of colon, cecum, and rectum Connected to small intestine via T junction One arm of junction is colon Leads rectum and anus Major function water recovery Other arm leads to cecum Pouch for fermenting ingested material

Large Intestine Feces forms in large intestine Feces stored in rectum until elimination