Exam 4- Small and Large Intestines Flashcards
What 3 things increase the surface area of the small intestines?
Folds of mucosa (Kerckring’s folds), villi on the folds, microvilli on the apical surface of the enterocytes (brush border)
What structures exist between individual villi in the small intestine and produce mucus and other secretions?
Crypts of Lieberkuhn
Where are new enterocytes produced from stem cells?
Crypts of Lieberkuhn
What is a lacteal within a villi? What is its function?
Extension of lymph system used to help with digestion (chylomicron from intestines to lacteal)
Basal electrical rhythym is dependent on location within GI tract. Where is it the fastest and where is it the slowest?
Fastest by duodenum and slowest towards end of GI tract (12-9 rhythms/min)
What are the two types of movement within the small intestines?
Segmentation and peristalsis
What is the action of segmentation in the small intestintes?
Mixes chyme w/ juices and exposed it to mucosa
What is the action of peristalsis in the small intestines?
Peristaltic reflex initiated by distention of intestinal lumen and mediated by myenteric plexus, propels chyme towards colon
What are simultaneous contractions of sections of circular muscle that divides the intestine into small segments?
Rhythmic segmentation
What causes circular muscle relaxation in front of the bolus during perstalsis? (2)
VIP, NO
What causes circular muscle contraction behind the bolus during peristalsis? (1)
ACh
PNS preganglionic fibers synapse on neurons where?
Within the enteric NS
Sympathetic postganlionic fibers synapse on neurons where?
myenteric plexus
Where does vagal stimulation generally elicit contractions?
Intestines
Where does sympathetic stimulation inhibit intestinal contractions?
Nonsphincteric sites
What intestinal reflex will inhibit gastric emptying due to an increase in H concentratio of duodenal chyme?
Enterogastric
What intestinal reflex will increase ileal motility in reponse to gastric secretion and motility (via gastrin & PNS)?
Gastroileal (keeps material moving towards rectum)
Distention of the ileum relaxing the ileocecal sphincter occurs via what intestinal reflex?
Ileocecal
Distenal of the stomach increasing colonic motility occurs via what intestinal reflex?
Gastrocolic
What intestinal neurohumoral agents will increase motility? (4)
ACh, gastrin, CCK, motilin
What neurohumoral factors decrease intestinal motility? (5)
NE, somatostatin, secretin, VIP, gastric inhibitory polypeptide
How much intestinal juice is secreted by the small intestine per day?
1.5-2 L
What 2 structures secrete mucus in the small intestine?
Submucosal glands of Lieberkuhn and goblet cells
Intestinal secretions are under control of local neural reflexes and triggered by what? (4)
Entry of chyme into intestine, secretin, CCK, ACh
What is the role of enterokinase in the small intestine?
Affects ability to digest protein (peptidase that converts tripsinogen into tripsin > activates inactive pro-proteases released from pancreas)
What are the 3 conspicuous bands of muscle that separate the longitudinal muscles of the large intestines?
Taeniae coli
What type of muscle forms the internal and external anal sphincter?
Internal = circular, external = striated
What are the pockets formed by the wall of the colon?
Haustra
What portion of the large intestine is composed of lymphoid tissue and hosues lymphocytes?
Appendix
Are villi present on the mucosa of the colon?
No (little absorption and no secretion of enzymes)
How is the mucosa layer in the large intestines different from the small intestines? (3)
Mucosa is thicker, crypts are deeper w/ more goblet cells, mucus provides lubrication and protection form irritating gases and acids from bacteria
What is the function of the ileocecal valve?
Prevent backflow and bacterial contamination
What portion of the intestines does not transport glucose or amino acids?
Colon
What are the main functions of the colon? (2)
Absorption of water and electrolytes (most Na from chyme is reabsorbed), stoarge of fecal matter until explusion
Of the 500mL of chyme entering the colon per day, how much is absorbed and how much is voided?
350mL absorbed and 150mL voided (100mL is water, remainder is solid)
What is the oxygen status of the colon environment?
Anaerobic environment
What are the byproducts of bacterial metabolism in the colon (5)
H2, N2, CO2, methane, and H2S gases
What substances are synthesized in the colon? (2)
B complex vitamins and vit K
The vagus nerve of the ANS (extrinsic NS) has an excitatory effect on what portions of the large intestines? (3)
Cecum, ascending and transverse colons
The pelvic nerve of the ANS (extrinsic NS) has an excitatory effect on what portions of the large intestines? (3)
Descending colon, sigmoid colon, rectum
The SNS (extrinsic NS) exhibits inhibitory effects via what 3 nerve complexes in the colon?
Superior and inferior mesenteric ganglia, hypogastric plexus
Intrinsic regulation of the colon occurs via what plexus?
Enteric plexus
Why is the “sluggish” colonic motility acceptable?
Very strong contractions are not necessary (but still engages in mixing and propulsive movements)
What movement of the colon is very slow, mostly mixing, and aids in absorption of water and electrolytes?
Haustration
What is the function of the haustration in the colon? (2)
Slow movement allows significant bacterial growth, aids in absorption of water and electrolytes
What movement of the colon is stimulaed by the gastrocolic reflex, occurs 1-3x/day, and simultanelously contracts the ascending and trasnverse colons driving feces 1/3-3/4 the length of the colons (in a few seconds)?
Mass movements
When is the gastrocolic reflex most evident?
After first meal of day (strong urge to defecate)
What is defecation initated by?
Rectal filling by mass movement
What 3 things occur when distension increases intraluminal rectal pressure great enough?
Active contraction of rectum, reflex relaxation of internal anal sphincter, constriction of external anal sphincter
Contraction of what muscles will result in a valsalva maneuver and assist in the elmination of feces?
Abdominal muscles
During defecation, what enhances contraction of descending and sigmoid colon and inhibits internal anal sphincter?
PNS pelvic nerves
During defecation, what sphincter voluntarily relaxes?
External sphincter
Arrival of the first bolus of fecal material causes what kind of increase in wall tension?
Passive (stretching of the rectum wall)
How does the tone of the internal and external anal sphincters change during filling/ defecation?
Internal sphincter progressively decreased tone, external sphincter progressively increased tone
Arrival of the second bolus of fecal material causes what kind of increase in wall tension?
Active
