Chapter 23 the digestive system: the small intestin Flashcards
Where is the small intestine located?
extends in abdominal cavity from pylorus of stomach to cecum of
large intestine; longest part of alimentary canal
What are the main functions of the small intestine in digestion?
propulsion—muscularis externa moves chyme through by peristalsis
mechanical breakdown/digestion—by mixing/segmentation action of muscularis externa
chemical digestion—mainly by enzymes from the pancreas
absorption—most small chemicals into blood; most fats into lymph
how many sub divisions does the small intestine have?
3
How long is the small intestine?
about 20 feet long in cadaver
What are the 4 general layers of the the small intestine wall?
mucosa– simple columnar epithelium on inner surface of villi and intestinal crypts/glands
submucosa—mainly areolar connective tissue; along with mucosa form large circular folds
muscularis externa—2 layers of smooth muscle; inner circular layer and outer longitudinal layer
serosa—inner layer of areolar connective tissue and outer layer of simple squamous epithelium;
extensions called mesentery
what are the 3 sub divisions of the small intestine?
duodenum—shortest subdivision, first 5% of length; unique features are major duodenal papilla from hepatopancreatic ampulla and duodenal glands in submucosa
jejunum—middle subdivision, 35% of length
ileum—longest subdivision, last 60%; ileocecal valve/sphincter at junction with cecum
What are villi that are found in the mucosa layer of the small intestine wall?
villi are fingerlike projections; goblet cells secrete mucous; absorptive enterocytes with microvilli
absorb most water and nutrients into blood except for fats which are mainly absorbed into lacteals
What are intestinal crypts/glands found in the mucosa layer of the small intestine wall?
most cells secrete intestinal juice; enteroendocrine cells secrete hormones
