Flashcards in Lecture 1: Functional Anatomy and General Principles of GI Regulation Deck (58):
4 Major physiological processes of GI tract
also excretion and immune function
What is the name for the vasculature of the gut?
What are the 6 sphincters of the GI tract?
1) UES (between pharynx and esophagus)
2) LES (esophagus and stomach)
4) Sphincter of Oddi (pancreatic and bile duct)
6) Internal and external anal
What important nutrient travels in the lymph?
lipids and lipid-soluble molecules
(they are too large to pass into capillaries)
What does the celiac artery supply?
liver, spleen, stomach
What does the superior mesenteric artery supply?
pancreas, small intestine, proximal colon
What does the inferior mesenteric artery supply?
What are the 4 layers of the gut?
1) Mucosa (innermost)
3) Muscularis externa
What 3 things is mucosa made of?
2) lamina propria
3) muscularis mucosae
What are the most abundant cells of the mucosal epithelium?
absorptive enterocytes (play vital role in digestion and absorption)
What cells of the mucosal epithelium regulate GI function by releasing regulatory peptides?
What type of epithelial cells are found in the esophagus?
SQUAMOUS (no absorption, just food transport)
What type of epithelial cells are found in the intestinal epithelium?
COLUMNAR (lots of absorption)
What is the functional unit of absorption?
villus (increases surface area 600x)
Celiac disease has flattened villi leading to malabsorption
What do parietal cells produce?
What do chief cells produce?
What molecules are found in abundance in the lamina propria?
collagen and elastin fibrils
Where are the lymph vessels, nodes, capillaries, and nerves found?
What is the muscularis mucosae?
smooth muscle cells in folded shape due to contractions
What follows the mucosal layer and what are some hallmarks of that next layer?
SUBMUCOSA - made of connective tissue (collagen and elastin) similar to lamina propria in that it has lymph nodes and nerves
What is Meissner's plexus and where is it located?
submucosal plexus of the enteric nervous system (nerve bundle in gut) found in the SUBMUCOSA
What layer follows the submucosa and what role does it play?
Muscularis externa/propria - involved in CONTRACTIONS
Where is the myenteric plexus?
in the muscularis externa layer
What is the layer beneath the muscularis externa and makes up the outermost layer?
Serosa (made up of squamous mesothelial cells)
What is the function of the serosa layer?
to secrete a viscous substance that reduces friction between abdominal organs during contractions. Also connected to mesentery to help suspend organs
What is the name of the sensor cells of the GI system?
Enteroendocrine cells (EECs)
respond to stimulus by secreting a hormone
Are most EECs "open" (meaning in contact with GI lumen and near capillaries) or "closed" (no contact with GI lumen)
(ECL cells of gastric epithelium are closed)
What is the main function of gastrin?
to stimulate acid secretion by the ECL and parietal cells
What is the main difference between endocrine and paracrine signaling?
Endocrine: goes INTO THE BLOODSTREAM
Paracrine: diffuses thru interstitial space (not transported in circulation)
What cells produce histamine?
Enterochromaffin-like cells (ECL) in the stomach
What does histamine do and where does it act?
histamine diffuses thru the interstitial space and binds to nearby parietal cells to secrete HCl
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?
Where is cholecystokinin produced?
I cells of the duodenum
What hormones signal both endocrine and paracrine?
3) Peptide YY
What two nervous systems feed the gut?
1) Extrinsic (cell bodies located outside gut wall - ANS)
2) Intrinsic (cell bodies located inside gut wall)
What are the 2 intrinsic or enteric nervous system cell bodies?
1) submucosal plexus
2) myenteric plexus
Which part of the autonomic nervous system is responsible for activating GI function?
PARASYMPATHETIC (via vagus)
Postganglionic neurons of the parasympathetic innervation are either _________ or _________
cholinergic (Ach) or peptidergic (VIP vasoactive intestinal peptide)
Vagus nerve is a mixture of afferents and efferents with the majority being _______
What effect does sympathetic stimulation have on GI function?
INHIBITS (but activates sphincter contraction)
True or false: enteric nervous system can act autonomously from extrinsic system?
true "little brain of the gut"
Where is striated muscle located in the GI tract?
2) upper 1/3rd of esophagus
3) external anal sphincter
What type of muscle is contractile in the gut?
What allows for rapid communication between smooth muscle cells?
gap junctions with interstitial cells of Cajal (ICCs) --> allows rapid transduction of action potentials
Where are phasic contractions found and what are they employed to do?
esophagus, gastric antrum, small intestine
mix and propel
Where are tonic contractions?
orad (upper) region of stomach and lower esophageal, ileocecal, and internal anal sphincters
What does the vagus nerve innervate?
esophaguse, stomach, gallbladder, pancreas, 1st part of intestine, cecum, proximal part of colon
DOES NOT INNERVATE SALIVARY GLANDS
What doe the pelvic nerves innervate?
the distal part of the colon and anorectal region
What are Slow Waves?
unique feature of GI smooth muscle electrical activity (not large enough to elicit action potential) oscillations of depolarization and repolarization of membrane potential
Where do slow waves originate?
Interstitial cells of Cajal (ICCs) between longitudinal and circulaf layers of muscularis externa (PACEMAKER CELLS)
What are tonic contractions with respect to slow waves?
sub-threshold slow waves producing weak contractions without action potentials
What are phasic contractions with respect to slow waves?
when action potentials occur on top of slow waves generating stronger, powerful contractions
In GI smooth muscle, how do individual action potentials add?
summate into one long contraction
What are segmentation contractions?
happen in intestines - split chyme and send it both directions, exposing more of it to enzymes. Then the chyme merges again and mixes
What are peristaltic contractions?
propel chyme along GI tract, contraction occurs orad to bolus and caudad portion relaxes, sending bolus forward
Where do peristaltic contractions occur?
pharynx, esophagus, gastric antrum, small and large intestines
Which neurotransmitters stimulate orad contraction in peristalsis?
Ach and substance P