Gastrointestinal System

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Biological Sciences
Stephen Reid

Chapter 39: Gastrointestinal System STRUCTURES AND FUNCTIONS  The main function of the gastrointestinal (GI) system is to supply nutrients to body cells.  The GI tract is innervated by the autonomic nervous system. The parasympathetic system is mainly excitatory, and the sympathetic system is mainly inhibitory.  The two types of movement of the GI tract are mixing (segmentation) and propulsion (peristalsis).  The secretions of the GI system consist of enzymes and hormones for digestion, mucus to provide protection and lubrication, water, and electrolytes.  Mouth: o The mouth consists of the lips and oral (buccal) cavity. o The main function of saliva is to lubricate and soften the food mass, thus facilitating swallowing.  Pharynx: a musculomembranous tube that is divided into the nasopharynx, oropharynx, and laryngeal pharynx.  Esophagus: o A hollow, muscular tube that receives food from the pharynx and moves it to the stomach by peristaltic contractions. o Lower esophageal sphincter (LES) at the distal end remains contracted except during swallowing, belching, or vomiting.  Stomach: o The functions are to store food, mix the food with gastric secretions, and empty contents into the small intestine at a rate at which digestion can occur. o The secretion of HCl acid makes gastric juice acidic. o Intrinsic factor promotes cobalamin absorption in the small intestine.  Small intestine: two primary functions are digestion and absorption.  Large intestine: o The four parts are (1) the cecum and appendix; (2) the colon (ascending, transverse, descending, sigmoid colon); (3) the rectum; and (4) the anus. o The most important function of the large intestine is the absorption of water and electrolytes.  Liver: o Hepatocytes are the functional unit of the liver. o Is essential for life. It functions in the manufacture, storage, transformation, and excretion of a number of substances involved in metabolism.  Biliary tract: o Consists of the gallbladder and the duct system. o Bile is produced in the liver and stored in the gallbladder. Bile consists of bilirubin, water, cholesterol, bile salts, electrolytes, and phospholipids.  Pancreas: o The exocrine function of the pancreas contributes to digestion. o The endocrine function occurs in the islets of Langerhans, whose beta cells secrete insulin; alpha cells secrete glucagon; and delta cells secrete somatostatin. GERONTOLOGIC CONSIDERATIONS  Aging causes changes in the functional ability of the GI system.  Xerostomia (decreased saliva production) or dry mouth is common.  Taste buds decrease, the sense of smell diminishes, and salivary secretions diminish, which can lead to a decrease in appetite.  Although constipation is a common complaint of elderly patients, age-related changes in colonic secretion or motility have not been consistently shown.  The liver size decreases after 50 years of age, but liver function tests remain within normal ranges. There is decreased ability to metabolize drugs and hormones. ASSESSMENT  Subjective data: o Important health information: the patient is asked about abdominal pain, nausea and vomiting, diarrhea, constipation, abdominal distention, jaundice, anemia, heartburn, dyspepsia, changes in appetite, he
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