Ch. 25: The Digestive System (The Small and Large Intestines)
what does the small intestine include?
duodenum, jejunum and ileum
what is the ileum?
longest portion of small intestine
what supplies blood to the numerous branches of the small intestine?
superior mesenteric artery and vein
what does the mesentary proper support?
the branches of the superior mesenteric artery and vein, lymphatics and nerves that supply the jejunum and ileum
what are plicae circulars?
transverse folds contained in the intestinal mucosa
what does the mucosa of the small intestine form?
small projections called intestinal villi
what is the function of intestinal villi?
increase the surface area for absorption
what determines the primary functions of the regions of the small intestine?
characteristics of duodendum?
1. contains duodenal (Brenner's) glands that aid the crypts in producing mucus and 2. receives the secretions of the common bile duct and pancreatic duct
what do the lamina propria of the jejunum and ileum contain?
large groups of aggregated lymphoid nodules (Peyer's patches)
functions of intestinal juice?
1. moistens the chime; 2. helps buffer acids; 3. dissolves digestive enzymes and products of digestion
what are secretin and cholecystokinin (CCK)?
2 hormones important in the coordination of digestive activities
what do parasympathetic (vagal) innervations do?
stimulate digestive function
what does sympathetic stimulation do?
inhibits activity along the digestive tract
another name for large intestine?
where does large intestine begin and end?
begins as a pouch inferior to the terminal portion of the ileum and ends at the anus
main functions of the large intestine?
1. reabsorb water and compact feces; 2. absorb vitamins by bacteria; 3. store fecal material prior to defacation
divisions of large intestine?
cecum, colon, rectum
what does cecum do?
collect and stores materials arriving from the ileum
what does the ilium open into?
the cecum at the ileal papilla
what forms the ileocecal valve?
muscles encircling the opening of the ileum
what is appendix attached to?
what does appendix function as a part of?
how does colon differ in structure from small intestine?
it has a larger diameter and thinner wall than small intestine
four subdivisions of colon?
ascending, transverse, descending, sigmoid
where does rectum terminate?
in the anal canal leading to the anus
what do internal and external anal sphincters control?
passage of fecal material to the anus
what triggers defecation reflex?
distension of the rectal wall
what are major histological features of the colon?
1. lack of villi; 2. abundance of goblet cells; 3. distinctive mucus-secreting intestinal glands
how does movement from cecum to the transverse colon occur?
slowly, via peristalsis and haustral churning
how does movement from the transverse to the sigmoid colon occur?
several times each day, via mass movements
what might distention of the rectal wall from mass movement stimulate?
the conscious desire to relax internal and external anal sphincters to defecate