1 B: Anatomy of GI wall / Intro to GI regulation Flashcards
Describe the lumen of the GI tract? Where are the contents located?
It is continuos with the external environment
-The contents are located within the lumen are technically OUTSIDE the BODY.
Why is the GI tract lumen environment important?
B/c conditions essential to the digestive process can be tolerated in the GI tract lumen but are generally NOT TOLERATED in the BODY PROPER
What happens when the contents escape from the GI tract lumen?
Examples?
The can produce symptoms that often indicate GI dysfunction
EX: Peptic ulcer disease (PUD) & Acute pancreatitis
What is Peptic ulcer disease (PUD)?
Gastric juice that penetrates the gastric mucosal barrier, which injures the gastric wall with its “acidic & enzymatic contents”
What is Acute Pancreatitis ?
What can this cause?
Pancreatic juice that escapes the pancreas and/or duodenum.
-The pancreatic digestive enzymes can cause the widespread destruction of pancreatic tissue & possible hemorrhage.
What does the pathogenesis of Acute Pancreatitis involve?
Active secretion of pancreatic juice while the main pancreatic duct is obstructed at tis entrance into the duodenum.
What does the build up of obstructed secretion cause?
Greatly increases the pressure within the duct system, causes the ducts to rupture & the pancreatic juice to escape.
What occurs in the case of a ruptured appendix?
The colon wall tears open, allowing intestinal bacteria (flora) to escape to the abdominal & pelvic cavities, causing PERITONITIS or even DEATH.
What are the 4 layers of the GI tract wall? (inner to outer)
1) Mucosa
2) Submucosa
3) Muscularis Externa
4) Serosa (Visceral peritoneum)
How are some smooth muscle regulated (Autonomous Smooth muscle function) ?
Some are “pacemaker” cells that display rhythmic spontaneous variations in membrane potential
What is the prominent type of self-induced electrical activity in digestive smooth muscle called?
Slow-wave potential
or alternatively called, Basal electrical rhythm (BER) or pacemaker potential
What are the neurons of the submucosal & myenteric plexuses called?
The intrinsic nerve plexuses or enteric nervous system (ENS) “Brain in the GUT” (intrinsic nerves)
What are the two kinds of neurons in the ENS ? Explain
1) SENSORY: Posses receptors that respond to specific local stimuli (pain) in the GI tract
2) MOTOR: Innervate smooth muscle cells, exocrine cells & endocrine cells of the GI tract ( to directly affect GI tract motility, secretion of digestive juices & secretion of GI hormones )
What does the Motor neurons directly affect?
directly affects GI tract motility, secretion of digestive juices & secretion of GI hormones
What are the extrinsic nerves (parasympathetic innervation) ?
Nerves that originate outside the GI tract & innervate the various GI organs
***Nerve fibers from both branches of the autonomic nervous system
What innervates the upper GI tract?
The vagus nerves
What does the vagus nerves innervate?
1) Esophagus
2) Stomach
3) small intestine
4) ascending colon
The vagus nerves are mixed nerves in which 75% of the fibers are __________and 25% are ______________
75%= AFFERENT 25% = EFFERENT
The lower GI tract is innervated by ?
The pelvic nerves (Pelvic splanchnic)
What does the pelvic nerves innervate?
1) Transverse, descending & sigmoid colons
2) Anal canal
Where are the pelvic nerves derived from ?
Spinal nerve pairs S2, S3, and S4
What are the majority of parasympathetic post-ganglionic neurons servicing the GI system?
Cholinergic (acetylcholine) ; SOME are peptidergic (VIP, enkephalins, neuropeptide Y, substance P)
What are the 3 sympathetic ganglia that serve the GI tract? Where is it located (Extrinsic Nerves) ?
1) Celiac
2) Superior mesenteric
3) Inferior mesenteric
***Thoracolumbar region
What are these post-ganglionic fibers made up of?
Adrenergic (norepinephrine)
Approximately 50% of the sympathetic nerve fibers are _______ and 50 % are _____________
Afferent and Efferent
How does the Autonomic nerves influence GI tract motility and secretion by?
1) Modifying ongoing activity in the enteric nervous system
2) altering the level of GI hormone secretion
3) acting directly on smooth muscle and glands
What makes up the Enteric nervous system?
1) Myenteric plexus
2) Submucosa plexus
What do mucosa of certain regions of the GI tract contain?
Endocrine cells that secrete hormones
How are GI hormones transported?
What do they exert ?
Thru blood to other areas of the GI tract or accessory GI structures
***Exert excitatory/inhibitory influences on smooth muscle & exocrine cells
