Exam 4- Small and Large Intestines

Question 1

What 3 things increase the surface area of the small intestines?

Answer 1

Folds of mucosa (Kerckring’s folds), villi on the folds, microvilli on the apical surface of the enterocytes (brush border)

Question 2

What structures exist between individual villi in the small intestine and produce mucus and other secretions?

Answer 2

Crypts of Lieberkuhn

Question 3

Where are new enterocytes produced from stem cells?

Answer 3

Crypts of Lieberkuhn

Question 4

What is a lacteal within a villi? What is its function?

Answer 4

Extension of lymph system used to help with digestion (chylomicron from intestines to lacteal)

Question 5

Basal electrical rhythym is dependent on location within GI tract. Where is it the fastest and where is it the slowest?

Answer 5

Fastest by duodenum and slowest towards end of GI tract (12-9 rhythms/min)

Question 6

What are the two types of movement within the small intestines?

Answer 6

Segmentation and peristalsis

Question 7

What is the action of segmentation in the small intestintes?

Answer 7

Mixes chyme w/ juices and exposed it to mucosa

Question 8

What is the action of peristalsis in the small intestines?

Answer 8

Peristaltic reflex initiated by distention of intestinal lumen and mediated by myenteric plexus, propels chyme towards colon

Question 9

What are simultaneous contractions of sections of circular muscle that divides the intestine into small segments?

Answer 9

Rhythmic segmentation

Question 10

What causes circular muscle relaxation in front of the bolus during perstalsis? (2)

Answer 10

VIP, NO

Question 11

What causes circular muscle contraction behind the bolus during peristalsis? (1)

Answer 11

ACh

Question 12

PNS preganglionic fibers synapse on neurons where?

Answer 12

Within the enteric NS

Question 13

Sympathetic postganlionic fibers synapse on neurons where?

Answer 13

myenteric plexus

Question 14

Where does vagal stimulation generally elicit contractions?

Answer 14

Intestines

Question 15

Where does sympathetic stimulation inhibit intestinal contractions?

Answer 15

Nonsphincteric sites

Question 16

What intestinal reflex will inhibit gastric emptying due to an increase in H concentratio of duodenal chyme?

Answer 16

Enterogastric

Question 17

What intestinal reflex will increase ileal motility in reponse to gastric secretion and motility (via gastrin & PNS)?

Answer 17

Gastroileal (keeps material moving towards rectum)

Question 18

Distention of the ileum relaxing the ileocecal sphincter occurs via what intestinal reflex?

Answer 18

Ileocecal

Question 19

Distenal of the stomach increasing colonic motility occurs via what intestinal reflex?

Answer 19

Gastrocolic

Question 20

What intestinal neurohumoral agents will increase motility? (4)

Answer 20

ACh, gastrin, CCK, motilin

Question 21

What neurohumoral factors decrease intestinal motility? (5)

Answer 21

NE, somatostatin, secretin, VIP, gastric inhibitory polypeptide

Question 22

How much intestinal juice is secreted by the small intestine per day?

Answer 22

1.5-2 L

Question 23

What 2 structures secrete mucus in the small intestine?

Answer 23

Submucosal glands of Lieberkuhn and goblet cells

Question 24

Intestinal secretions are under control of local neural reflexes and triggered by what? (4)

Answer 24

Entry of chyme into intestine, secretin, CCK, ACh

Question 25

What is the role of enterokinase in the small intestine?

Answer 25

Affects ability to digest protein (peptidase that converts tripsinogen into tripsin > activates inactive pro-proteases released from pancreas)

Question 26

What are the 3 conspicuous bands of muscle that separate the longitudinal muscles of the large intestines?

Answer 26

Taeniae coli

Question 27

What type of muscle forms the internal and external anal sphincter?

Answer 27

Internal = circular, external = striated

Question 28

What are the pockets formed by the wall of the colon?

Answer 28

Haustra

Question 29

What portion of the large intestine is composed of lymphoid tissue and hosues lymphocytes?

Answer 29

Appendix

Question 30

Are villi present on the mucosa of the colon?

Answer 30

No (little absorption and no secretion of enzymes)

Question 31

How is the mucosa layer in the large intestines different from the small intestines? (3)

Answer 31

Mucosa is thicker, crypts are deeper w/ more goblet cells, mucus provides lubrication and protection form irritating gases and acids from bacteria

Question 32

What is the function of the ileocecal valve?

Answer 32

Prevent backflow and bacterial contamination

Question 33

What portion of the intestines does not transport glucose or amino acids?

Answer 33

Colon

Question 34

What are the main functions of the colon? (2)

Answer 34

Absorption of water and electrolytes (most Na from chyme is reabsorbed), stoarge of fecal matter until explusion

Question 35

Of the 500mL of chyme entering the colon per day, how much is absorbed and how much is voided?

Answer 35

350mL absorbed and 150mL voided (100mL is water, remainder is solid)

Question 36

What is the oxygen status of the colon environment?

Answer 36

Anaerobic environment

Question 37

What are the byproducts of bacterial metabolism in the colon (5)

Answer 37

H2, N2, CO2, methane, and H2S gases

Question 38

What substances are synthesized in the colon? (2)

Answer 38

B complex vitamins and vit K

Question 39

The vagus nerve of the ANS (extrinsic NS) has an excitatory effect on what portions of the large intestines? (3)

Answer 39

Cecum, ascending and transverse colons

Question 40

The pelvic nerve of the ANS (extrinsic NS) has an excitatory effect on what portions of the large intestines? (3)

Answer 40

Descending colon, sigmoid colon, rectum

Question 41

The SNS (extrinsic NS) exhibits inhibitory effects via what 3 nerve complexes in the colon?

Answer 41

Superior and inferior mesenteric ganglia, hypogastric plexus

Question 42

Intrinsic regulation of the colon occurs via what plexus?

Answer 42

Enteric plexus

Question 43

Why is the "sluggish" colonic motility acceptable?

Answer 43

Very strong contractions are not necessary (but still engages in mixing and propulsive movements)

Question 44

What movement of the colon is very slow, mostly mixing, and aids in absorption of water and electrolytes?

Answer 44

Haustration

Question 45

What is the function of the haustration in the colon? (2)

Answer 45

Slow movement allows significant bacterial growth, aids in absorption of water and electrolytes

Question 46

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)?

Answer 46

Mass movements

Question 47

When is the gastrocolic reflex most evident?

Answer 47

After first meal of day (strong urge to defecate)

Question 48

What is defecation initated by?

Answer 48

Rectal filling by mass movement

Question 49

What 3 things occur when distension increases intraluminal rectal pressure great enough?

Answer 49

Active contraction of rectum, reflex relaxation of internal anal sphincter, constriction of external anal sphincter

Question 50

Contraction of what muscles will result in a valsalva maneuver and assist in the elmination of feces?

Answer 50

Abdominal muscles

Question 51

During defecation, what enhances contraction of descending and sigmoid colon and inhibits internal anal sphincter?

Answer 51

PNS pelvic nerves

Question 52

During defecation, what sphincter voluntarily relaxes?

Answer 52

External sphincter

Question 53

Arrival of the first bolus of fecal material causes what kind of increase in wall tension?

Answer 53

Passive (stretching of the rectum wall)

Question 54

How does the tone of the internal and external anal sphincters change during filling/ defecation?

Answer 54

Internal sphincter progressively decreased tone, external sphincter progressively increased tone

Question 55

Arrival of the second bolus of fecal material causes what kind of increase in wall tension?

Answer 55

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