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
The secretions of the GI system consist of enzymes and hormones for digestion, mucus
to provide protection and lubrication, water, and electrolytes.
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
Pharynx: a musculomembranous tube that is divided into the nasopharynx, oropharynx,
and laryngeal pharynx.
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.
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.
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
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.
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.
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.
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.
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