Lecture 1: Functional Anatomy and General Principles of GI Regulation

Question 1

4 Major physiological processes of GI tract

Answer 1

1) Motility
2) Secretion
3) Digestion
3) Absorption

also excretion and immune function

Question 2

What is the name for the vasculature of the gut?

Answer 2

Splanchnic

Question 3

What are the 6 sphincters of the GI tract?

Answer 3

1) UES (between pharynx and esophagus)
2) LES (esophagus and stomach)
3) Pyloric
4) Sphincter of Oddi (pancreatic and bile duct)
5) Ileocecal
6) Internal and external anal

Question 4

What important nutrient travels in the lymph?

Answer 4

lipids and lipid-soluble molecules

they are too large to pass into capillaries

Question 5

What does the celiac artery supply?

Answer 5

liver, spleen, stomach

Question 6

What does the superior mesenteric artery supply?

Answer 6

pancreas, small intestine, proximal colon

Question 7

What does the inferior mesenteric artery supply?

Answer 7

distal colon

Question 8

What are the 4 layers of the gut?

Answer 8

1) Mucosa (innermost)
2) Submucosa
3) Muscularis externa
4) Serosa

Question 9

What 3 things is mucosa made of?

Answer 9

1) epithelium
2) lamina propria
3) muscularis mucosae

Question 10

What are the most abundant cells of the mucosal epithelium?

Answer 10

absorptive enterocytes (play vital role in digestion and absorption)

Question 11

What cells of the mucosal epithelium regulate GI function by releasing regulatory peptides?

Answer 11

Enteroendocrine cells

Question 12

What type of epithelial cells are found in the esophagus?

Answer 12

SQUAMOUS (no absorption, just food transport)

Question 13

What type of epithelial cells are found in the intestinal epithelium?

Answer 13

COLUMNAR (lots of absorption)

Question 14

What is the functional unit of absorption?

Answer 14

villus (increases surface area 600x)

Celiac disease has flattened villi leading to malabsorption

Question 15

What do parietal cells produce?

Answer 15

HCl

Question 16

What do chief cells produce?

Answer 16

pepsinogen

Question 17

What molecules are found in abundance in the lamina propria?

Answer 17

collagen and elastin fibrils

Question 18

Where are the lymph vessels, nodes, capillaries, and nerves found?

Answer 18

lamina propria

Question 19

What is the muscularis mucosae?

Answer 19

smooth muscle cells in folded shape due to contractions

Question 20

What follows the mucosal layer and what are some hallmarks of that next layer?

Answer 20

SUBMUCOSA - made of connective tissue (collagen and elastin) similar to lamina propria in that it has lymph nodes and nerves

Question 21

What is Meissner’s plexus and where is it located?

Answer 21

submucosal plexus of the enteric nervous system (nerve bundle in gut) found in the SUBMUCOSA

Question 22

What layer follows the submucosa and what role does it play?

Answer 22

Muscularis externa/propria - involved in CONTRACTIONS

Question 23

Where is the myenteric plexus?

Answer 23

in the muscularis externa layer

Question 24

What is the layer beneath the muscularis externa and makes up the outermost layer?

Answer 24

Serosa (made up of squamous mesothelial cells)

Question 25

What is the function of the serosa layer?

Answer 25

to secrete a viscous substance that reduces friction between abdominal organs during contractions. Also connected to mesentery to help suspend organs

Question 26

What is the name of the sensor cells of the GI system?

Answer 26

Enteroendocrine cells (EECs) respond to stimulus by secreting a hormone

Question 27

Are most EECs "open" (meaning in contact with GI lumen and near capillaries) or "closed" (no contact with GI lumen)

Answer 27

OPEN | ECL cells of gastric epithelium are closed

Question 28

What is the main function of gastrin?

Answer 28

to stimulate acid secretion by the ECL and parietal cells

Question 29

What is the main difference between endocrine and paracrine signaling?

Answer 29

Endocrine: goes INTO THE BLOODSTREAM Paracrine: diffuses thru interstitial space (not transported in circulation)

Question 30

What cells produce histamine?

Answer 30

Enterochromaffin-like cells (ECL) in the stomach

Question 31

What does histamine do and where does it act?

Answer 31

histamine diffuses thru the interstitial space and binds to nearby parietal cells to secrete HCl

Question 32

What important neurotransmitter is released from enteric neurons, mucosal mast cells, and ECLs that is responsible for regulating contractile activity of smooth muscle cells in GI tract?

Answer 32

Seratonin

Question 33

Where is cholecystokinin produced?

Answer 33

I cells of the duodenum

Question 34

What hormones signal both endocrine and paracrine?

Answer 34

1) CCK 2) Secretin 3) Peptide YY 4) Proglucagon

Question 35

What two nervous systems feed the gut?

Answer 35

1) Extrinsic (cell bodies located outside gut wall - ANS) | 2) Intrinsic (cell bodies located inside gut wall)

Question 36

What are the 2 intrinsic or enteric nervous system cell bodies?

Answer 36

1) submucosal plexus | 2) myenteric plexus

Question 37

Which part of the autonomic nervous system is responsible for activating GI function?

Answer 37

PARASYMPATHETIC (via vagus)

Question 38

Postganglionic neurons of the parasympathetic innervation are either _________ or _________

Answer 38

cholinergic (Ach) or peptidergic (VIP vasoactive intestinal peptide)

Question 39

Vagus nerve is a mixture of afferents and efferents with the majority being _______

Answer 39

afferents (75%)

Question 40

What effect does sympathetic stimulation have on GI function?

Answer 40

INHIBITS (but activates sphincter contraction)

Question 41

True or false: enteric nervous system can act autonomously from extrinsic system?

Answer 41

true "little brain of the gut"

Question 42

Where is striated muscle located in the GI tract?

Answer 42

1) pharynx 2) upper 1/3rd of esophagus 3) external anal sphincter

Question 43

What type of muscle is contractile in the gut?

Answer 43

smooth

Question 44

What allows for rapid communication between smooth muscle cells?

Answer 44

gap junctions with interstitial cells of Cajal (ICCs) --> allows rapid transduction of action potentials

Question 45

Where are phasic contractions found and what are they employed to do?

Answer 45

esophagus, gastric antrum, small intestine mix and propel

Question 46

Where are tonic contractions?

Answer 46

orad (upper) region of stomach and lower esophageal, ileocecal, and internal anal sphincters

Question 47

What does the vagus nerve innervate?

Answer 47

esophaguse, stomach, gallbladder, pancreas, 1st part of intestine, cecum, proximal part of colon DOES NOT INNERVATE SALIVARY GLANDS

Question 48

What doe the pelvic nerves innervate?

Answer 48

the distal part of the colon and anorectal region

Question 49

What are Slow Waves?

Answer 49

unique feature of GI smooth muscle electrical activity (not large enough to elicit action potential) oscillations of depolarization and repolarization of membrane potential

Question 50

Where do slow waves originate?

Answer 50

Interstitial cells of Cajal (ICCs) between longitudinal and circulaf layers of muscularis externa (PACEMAKER CELLS)

Question 51

What are tonic contractions with respect to slow waves?

Answer 51

sub-threshold slow waves producing weak contractions without action potentials

Question 52

What are phasic contractions with respect to slow waves?

Answer 52

when action potentials occur on top of slow waves generating stronger, powerful contractions

Question 53

In GI smooth muscle, how do individual action potentials add?

Answer 53

summate into one long contraction

Question 54

What are segmentation contractions?

Answer 54

happen in intestines - split chyme and send it both directions, exposing more of it to enzymes. Then the chyme merges again and mixes

Question 55

What are peristaltic contractions?

Answer 55

propel chyme along GI tract, contraction occurs orad to bolus and caudad portion relaxes, sending bolus forward

Question 56

Where do peristaltic contractions occur?

Answer 56

pharynx, esophagus, gastric antrum, small and large intestines

Question 57

Which neurotransmitters stimulate orad contraction in peristalsis?

Answer 57

Ach and substance P

Question 58

Which neurotransmitters stimulate caudad relaxation in peristalsis?

Answer 58

VIP and NO