Exam 4 Study Guide GASTROINTESTINAL PHYSIOLOGY
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Exam 4 Study Guide GASTROINTESTINAL PHYSIOLOGY
Anatomy of the GI system – NOT ON STUDY GUIDE
• Digestive system – enteric nervous system (extrinsic and intrinsic)
o Autonomic (involuntar
...
y) and hormonal control [except chewing, swallowing, defecation]
▪ Vagus nerve
o Ingested substances trigger hormones that stimulate or inhibit
▪ Muscular contractions – GI motility; timely secretion of substances that aid in digestion
o Located near the areas that they innervate and control
• Mouth
o Reservoir for chewing and mixing of food with saliva
o Taste buds (chemoreceptors) and olfactory nerves are stimulated – initiates salivation and secretion of gastric juices in the stomach
• Salivary glands
o Submandibular, sublingual, parotid (largest; secretes saliva)
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 fibers stimulate salivary glands
• Ex: anticholinergic meds inhibit salivation
▪ Sympathetic beta-adrenergic stimulation decreases salivary secretion – none, little, or little with rich protein content
▪ A pH of 7.4 which neutralizes bacterial acids aiding to prevent injection
▪ Contains IgA – prevents orally ingested microorganisms
• Esophagus
o Conducts substances from oropharynx to stomach
o Upper esophageal sphincter prevents entry of air into the esophagus during respiration
o Lower esophageal sphincter (cardiac sphincter) prevents regurgitation from the stomach
Increase tone by cholinergic vagal stimulation and the digestive hormone gastrin
Decrease tone/relax by non-adrenergic, non-cholinergic vagal impulse and the hormones progesterone, secretin, and glucagon
o Vagus nerve allows relaxation of esophagus during swallowing
o Swallowing: complex event mediated by the swallowing center in reticular formation of brainstem
Phases: oropharyngeal (voluntary) and esophageal (involuntary)
Must coordinate with respiratory center
• Respiration is inhibited – epiglottis slides downward to prevent food from entering larynx and trachea
o Peristalsis:
Primary: immediately follows oropharyngeal phase of swallowing
Secondary: bolus of food becomes stuck – wave of contraction and relaxation occurs that is independent of voluntary swallowing
• Stomach
o Hollow muscular organ – stores food, secretes digestive juices, mixes food with juices – propels chyme into duodenum
o Muscle layers – outer (longitudinal), middle (circular), inner (oblique)
o Sphincters – lower esophageal (chyme enters from esophagus into stomach), pyloric (chyme exits stomach into duodenum of small intestine
o Functional portions – upper (fundus), middle (body), lower (antrum)
o Blood supply via branch of celiac artery; drainage via splenic vein and tributaries
o Few substances absorbed in stomach – can absorb alcohol, aspirin, NSAIDS
o Innervated by sympathetic and parasympathetic
o Gastric motility
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