Anatomy of the GI system – NOT ON STUDY GUIDE • Digestive system – enteric nervoussystem (extrinsic and intrinsic) o Autonomic (involuntary) and hormonal control [except chewing,swallowing, defecation] ▪Vagus nerve o Ingested substancestrigger hormonesthat stimulate or inhibit ▪Muscular contractions – GI motility; timely secretion of substancesthat aid in digestion o Located near the areasthat they innervate and control • Mouth o Reservoir for chewing and mixing of food with saliva o Taste buds(chemoreceptors) and olfactory nerves are stimulated – initiatessalivation and secretion of gastric juices in the stomach • Salivary glands o Submandibular,sublingual, parotid (largest;secretessaliva) o Saliva is composed of water with mucus, sodium, chloride, bicarbonate, potassium and salivary a-amylase (carb digestion) and is controlled by ANS ▪Cholinergic parasympathetic fibersstimulate salivary glands • Ex: anticholinergic medsinhibitsalivation ▪Sympathetic beta-adrenergic stimulation decreasessalivary secretion – none, little, orlittle with rich protein content ▪A pH of 7.4 which neutralizes bacterial acids aiding to prevent injection ▪ContainsIgA – prevents orally ingested microorganisms • Esophagus o Conductssubstancesfrom oropharynx to stomach o Upper esophagealsphincter prevents entry of air into the esophagus during respiration o Lower esophagealsphincter (cardiac sphincter) preventsregurgitation from the stomach