digestive system

• phy sical breakdown of food 1. Begins in the mouth w chewing (mastication) 2. Swallowing has three phases • voluntary buccal phase • involuntary pharyngeal phase • involuntary esophageal phase

• muscle layer of the digestive tract that’s responsible for moving food along and mixing it during digestion. • 2 muscle layer 1. circular - squeezes the tube (like wringing it), narrowing the passageway. 2. longitudinal - shortens the tube, pushing food forward.

involuntary wave like muscle contractions that move through the digestive tract in one direction

involuntary back and fourth contractions in the intestines that mix food (chyme)

• food is moistened by saliva as soon as it enters the mouth • saliva is produced by 1. parotid glands 2. submandibular glands 3. sublingual glands

• salivary amylase - digestion of starches • lingual lipase - digestion of fats • lysozyme - kills bacteria • mucin - lubricates food • bicarbonate ions - maintains proper ph for enzymes • immunoglobin a - provides immune protection

25 cm tube connecting pharynx to stomach

• transports food (does not digest it) • secretes mucus to lubricate passage

• mucosa (actually touches the food, makes mucus) • submucosa • muscularis externa (pushes the food down, muscular) • adventitia (outer covering)

• upper third (top part) - made of skeletal muscle, you control it • middle part - mix of skeletal and smooth muscle, partly under ur control • lower third (bottom part) - smooth muscle only, completely involuntary - so basically you start swallowing voluntarily at the top and the rest of the esophagus takes over and pushes the food

• upper esophageal sphincter - opens to let food in • lower esophageal sphincter - prevents acid reflux

• storage and churning of food • mixes food w gastric juices to form chyme • 3 layers of muscle for mixing 1. circular 2. longitudinal 3. oblique (extra layer)

regulates chyme entering the small intestine

• the stomach lining (mucosa) has gastric glands that open into gastric pits • four main types of cells 1. mucous cells - secret mucus to protect stomach lining 2. parietal cells - secret hydrochloric acid 3. chief cells - secrete pepsinogen (converted to pepsin to digest proteins) 4. endocrine (G cells) - release hormones like gastrin into the blood to stimulate digestion

• release intrinsic factor needed to absorb vitamin B12 in the small intestine • release hydrochloric acid making stomach pH very acidic • acid helps activate digestive enzymes

• release pepsinogen (inactive) • acid HCl turns pepsinogen to pepsin which breaks proteins into smaller peptides • also release gastric lipase which helps digest fats (but most fat digestion happens in the small intestine)

• secrete mucus with bicarbonate • protects the stomach from its own acids and enzymes

• produce gastrin, a hormone that stimulates acid secretion

• where food enters • prevents reflux of acid back into the esophagus

• cardiac region - where food enters • fundus - dome shaped top part of the stomach • body - main central section • pylorus - funnel shaped bottom section that narrows into the pyloric canal

• controls release of chyme (partially digested food) into the small intestine • pyloric sphincter acts as a valve

folds in the stomach lining that allow the stomach to stretch when full

• produces bile • detoxification • nutrient metabolism • synthesis of important molecules (cholesterol, plasma proteins, etc)

yellow green fluid made of - bile salts (important for digestion) - bilirubin (pigment from breaking down hemoglobin) - cholesterol - electrolytes