BIOL 244 1st EditionLecture 3Outline of Current LectureChapter 23: part 3Current Lecture Saliva Secreted by serous and mucous cells Composition of saliva: 97-99.5% water Electrolytes: Na+, K+, Cl-, HCO3- Salivary amylast & lingual lipase Mucin  Metabolic wastes Lysozyme, IgA, defensins- to protect against microorganisms Control: Intrinsic glands continuously keep the mouth moist Extrinsic glands produce secretions when- Ingested food stimulates chemoreceptors & mechanoreceptors in mouth Strong sympathetic stimulation inhibits salivation & results in dry mouth (xerostomia) Pharynx: allows passage of food, fluid, & air Stratified squamous epithelium lining 3 regions: Nasopharynx- Not involved with ingestion Oropharynx  Laryngopharynx Esophagus: flat muscular tube from laryngopharynx to stomach Pierces diaphragm at esophageal hiatus Joins stomach at the cardiac orifice Stomach Mucosa Simple columnar epithelium composed of mucous cells- Layer of mucus traps bicarbonate-rich fluid beneath it Damaged epithelial cells are quickly replaced by division of stem cells every 2-3 days Gastric pits lead into gastric glands Gastric Glands Glands in the fundus & body produce most of the gastric juice Mucous neck cells  Parietal cells- Secretions: HCL pH 1.5-3.5 denatures protein in food, activates pepsin, & kills many bacteria Glycoprotein required for absorption of vitamin B12 in small intestine Chief cells- Secretions: Inactive enzyme pepsinogen Activated to pepsin by HCL & by pepsin itself (positive feedback mechanism) Enterocendocrine cells- Secretions: Secrete chemical messengers into the lamina propria Paracrines: serotonin and histamine Hormones: somatostatin & gastrin Gastritis: inflammation caused by any agent that breaches the mucosal barrier Peptic or gastric ulcers: erosion of the stomach wall Caused by Helicobacter pylori bacteria Digestive Processes Physical digestion Denaturation of proteins Enzymatic digestion of proteins by pepsin (and rennin in infants) Secretes intrinsic factor required for absorption of vitamin B12- Lack of intrinsic factor  pernicious anemia Delivers chyme to small intestine Response to stomach filling Stretches to accommodate incoming food- Reflex-mediated receptive relaxation: coordinated by the swallowing center of the brain stem- Gastric accommodation Plasticity (stress-relaxation response) of smooth