Lecture 20

Question 1

Length of adult GI tract

Answer 1

9m or 30ft mouth to anus
- shorter in vivo due to tonic contractions

Question 2

Digestion

Answer 2

Caused by enzymes released by the systems exocrine glands

Question 3

Amylase

Answer 3

Polysaccharide digestion

Question 4

Lipase

Answer 4

TAG digestion

Question 5

Proteases

Answer 5

Protein digestion

Question 6

Method of enzyme released into lumen

Answer 6

From exocrine cells via exocytosis into a duct that connects to the GI tract

Question 7

Peristalsis (peristaltic waves)

Answer 7

Wavelike muscular movements in one direction

Question 8

Stomach function

Answer 8

Storage, dissolution and partial digestion of food
- regulates the rate at which food moves into the small intestine

Question 9

3 sections of small intestine

Answer 9

1) Jejunum
2) Duodenum
3) Ileum

Question 10

Is the digestive system responsible for the homeostatic control of nutrients?

Answer 10

No, that is controlled by hormones from the endocrine system and kidneys

Question 11

What makes up feces?

Answer 11

Bacteria and ingested material not digested or absorbed

Question 12

Empty vs full stomach sizes

Answer 12

Empty: 50 mL, diameter the size of the small intestine
Full: 1.5 L

Question 13

Receptive relaxation

Answer 13

Relaxation of smooth muscle in stomach wall via parasympathetic innervation
- vagal input from stomach
- efferent input from swallowing center
- mediated by NO and serotonin

Question 14

Fundus

Answer 14

Uppermost part of the stomach

Question 15

Antrum

Answer 15

Lower portion of stomach
- thicker layer of smooth muscle
- responsible for mixing and grinding stomach contents

Question 16

Pyloric sphincter

Answer 16

Junction between antrum and small intestine
- ring of contractile smooth muscle

Question 17

Intrinsic factor function

Answer 17

Binds and allows absorption of vitamin B12

Question 18

What do Parietal cells secrete

Answer 18

Acid and Intrinsic Factor

Question 19

Canaliculi

Answer 19

Maximize SA and thus secretion of parietal cells into lumen

Question 20

G cells

Answer 20

Secrete Gastrin
- located in antrum

Question 21

ECL cells

Answer 21

Enterochromaffin-like
- secrete Histamine (paracrine)
- in tubular glands

Question 22

D cells

Answer 22

Secrete somatostatin
- in tubular glands

Question 23

Stomach peristaltic wave

Answer 23

Begins in body as ripple
- larger wave as it approaches Antrum
- mixes luminal contents
- pyloric sphincter muscles close as wave arrives

Question 24

Retropulsion

Answer 24

Food bouncing backwards from pyloric sphincter

Question 25

What produces peristaltic waves

Answer 25

Pacemaker cells in longitudinal smooth muscle layer

Question 26

Peristaltic wave rate

Answer 26

~3 per min

Question 27

Basis electrical rhythm of the stomach

Answer 27

Spontaneous depolarization-repolarizatio cycles (slow waves) of smooth muscle cells - through gap junctions - also affect circular layer above it

Question 28

Are the slow waves enough to bring smooth muscle to threshold

Answer 28

No, needs excitatory NTs or hormones

Question 29

What determines the force of contraction

Answer 29

Neural and hormonal input - determined by number of APs fired with each slow wave

Question 30

Effect of increased Gastrin on antral smooth muscle contraction

Answer 30

Increases force of astral smooth muscle contractions

Question 31

Effect of stomach distension

Answer 31

Increase force of antral contractions - via long and short reflexes triggered via mechanoreceptors in stomach wall

Question 32

4 things that trigger enterogastric reflex

Answer 32

1) Duodenum distension 2) Presence of fat 3) Low pH (high acidity) 4) hypertonic solutions in duodenum

Question 33

Enterogastric reflex

Answer 33

Inhibition of gastric emptying by multiple factors - prevents overfilling of duodenum

Question 34

Most potent inhibitor of gastric emptying

Answer 34

Fat

Question 35

Effect of fat rich meal on drug absorption

Answer 35

Slows it down, due to delay of drug entering small intestine through pyloric sphincter

Question 36

Effect of hypertonic solution on gastric emptying

Answer 36

Prevents duodenum from becoming too hypertonic - slows rate of entry of chyme - decreases delivery rate of large molecules to be broken down

Question 37

Effect of ANS on gastric motility

Answer 37

- increase in para increases gastric motility - increase in sympa decreases gastric motility

Question 38

Segmentation

Answer 38

Produces a continuous division and subdivision of intestinal contents

Question 39

MMC

Answer 39

Migrating myoelectrical complex - ceasing of segmenting contractions - occurs after absorption of meal - migrates about 2 ft each time down intestine

Question 40

Function of MMC

Answer 40

1) Moves undigested material into large intestine 2) Prevents harmful accumulation of bacteria

Question 41

Mass movement

Answer 41

3-4 times a day - wave of intense contraction - transverse section of large intestine towards rectum

Question 42

Effect of para and sympa on large intestine

Answer 42

- Para increases segmental contractions - sympa decreases colonic contractions

Question 43

Internal anal sphincter

Answer 43

Smooth, involuntary

Question 44

External anal sphincter

Answer 44

Skeletal, voluntary

Question 45

Initiation of Defecation reflex

Answer 45

Sudden dissension of rectum walls from mass movement

Question 46

Urge to defecate

Answer 46

Occurs due to mechanoreceptors activating with rectum distension

Question 47

Mechanism of defecation reflex

Answer 47

1) contraction of rectum, relaxation of internal anal sphincter 2) contraction of external, increased colon motility 3) high pressure triggers reflex relaxation of external

Question 48

Valsa maneuver

Answer 48

Closure of glottis, contraction of abdominal/thoracic muscles, transmits pressure to large intestine and rectum