Exam #5: Intro to GI Flashcards
What is the UES? What two anatomical structures does this sphincter separate?
UES= Upper Esophageal Sphincter
This is the sphincter that segregates the mouth from the esophagus
What is the LES? What two anatomical structures does this sphincter separate?
LES= Lower Esophageal Sphincter
This is the sphincter the segregates the esophagus from the stomach
What is the pyloric sphincter? What two anatomical structures does this sphincter separate?
The pyloric sphincter is the sphincter between the stomach & small intestine i.e. pylorus of stomach & duodenum
What is the ileocecal sphincter? What two anatomical structures does this sphincter separate?
This is the sphincter muscle also known as the “ileocecal valve” between the ileum & cecum (small & large intestine)
What is the IAS? What two anatomical structures does this sphincter separate?
IAS= Internal Anal Sphincter
What is the EAS? What two anatomical structures does this sphincter separate?
EAS= External Anal Sphincter
What are the four layers of the GI tract?
1) Serosa= outer, connective tissue & squamous epithelium
2) Muscularis= longituindal & circular smooth muscle
- Neurons that innervate regulate peristalsis
3) Subumucsa= large blood vessels, glands, and connective tissue
4) Mucusa= inner & can be divided into:
- Lamina propria= capillaries, neurons, and immune cells
- Lamina muscularis muscoa= smooth muscle to coordinate GI motility
What are the three modes of cell communication in the GI system?
1) Endocrine= utilizes blood
2) Paracrine= localized
3) Neurocrine= neurons innervating endocrine, vascular, or muscle cells
Define the relationship between the parasympathetic, sympathetic, and enteric branches nervous systems.
The SNS, PNS & enteric nervous system (ENS) are all parts of the autonomic nervous system:
- ENS communicates with the SNS & PNS
- Enteric= intrinsic
- SNS & PNS= extrinsic
*****Note that the GI tract can function INDEPENDENTLY of the CNS b/c of ENS, but if works better with the SNS & PNS input
What is the function of PNS in GI tract?
Generally, think STIMULATION i.e. parasympathetic innervation:
- Stimulates motility
- Increases blood flow via vasodilation
- Increases release of GI secretions
What is the function of the SNS in GI tract?
Generally, think INHIBITION i.e. sympathetic innervation:
- Inhibits motility
- Causes a reduction in blood flow via vasoconstriction
- Inhibits release of GI secretion
- **Note direct vs. indirect effects:
- Indirect= ENS inputs
- Direct= input directly on GI
What is the function of the enetric NS in GI tract?
Generally, the ENS is an independent nervous system entirely for the GI tract that is contained in the tissue layers of the GI tract; it is modulated by SNS & PNS input. Functions:
1) Motor neurons stimulate or inhibit smooth muscle contraction
2) Promotion of vasodilation & increased blood flow
3) Regulation of water, electrolyte, and hormone secretion
4) Sensory neurons relay stretch, pain, and chemical to extrinsic fibers
Associative= interneuron
Intestinofugal= regulate sympathetic ganglia
What is the function of associative neurons in the ENS?
These are interneurons that communicate between ENS neurons
What is the function of intestinogufal neurons in the ENS?
These neurons leave the GI tract and termination on sympathetic ganglia; they regulate sympathetic input to the GI tract
What the effect of ACh on GI function?
Generally excitatory
- Vasodilation
- Increase secretions
- Smooth muscle contraction
*****This may be done indirectly via the ENS
What the effect of NE on GI function?
Generally inhibitory
- Vasoconstrictive
- Decrease secretion
- Inhibit smooth muscle contraction
What the effect of DA on GI function?
Generally inhibitory
- Vasoconstrictive
- Decrease secretion
- Inhibit smooth muscle contraction
*****Note that DA also inhibits ENS neuronal firing by interacting with pre-synaptic D2 receptors
What the effect of 5-HT on GI function?
Generally excitatory
- Vasodilation
- Increase secretion
- Smooth muscle contraction
*****Generally, this is a NT that is used by the interneurons
What the effect of NO on GI function?
Generally inhibitory
- Smooth muscle relaxation (vascular & GI)
What the effect of VIP on GI function?
Generally inhibitory
- Smooth muscle relaxation (vascular & GI)
What is the source, target, and action of cholecystokinin (CCK) in GI function?
Source= duodenum
Target
- Pancreas
- Gallbladder
- Stomach
- Sphincter of Oddi
Action
- Increase enzyme secretion
- Increase contraction
- Decrease emptying
- Increase relaxation
What is the source, target, and action of Gastrin in GI function?
Source= G-cells of stomach
Target=
- Parietal cells
- ECL
- D-cells
Action= promote gastric acid secretion
What is the source, target, and action of Motilin in GI function?
Source= upper GI
Target
- Stomach
- Duodenum
Action= increase smooth muscle contraction
What is the source, target, and action of Peptide YY in GI function?
Source= ileum & colon
Target= pancreas
Action= decrease enzyme & fluid secretion
What is the source, target, and action of Secretin in GI function?
Source= duodenum
Target=
- pancreas
- stomach
Action
- Increase bicarbonate secretion
- Decrease acid secretion
- Delay gastric emptying
What is the effect of Somatostatin on GI function?
Source=
- stomach
- duodenum
- pancreatic cells
Target=
- stomach
- intestine
- pancreas
- liver
Action=
- decrease acid secretion
- increase fluid absorption
- decrease smooth muscle contraction
- decrease secretions
- decrease bile flow
What is the effect of prostaglandins on GI function?
Source=
- stomach
- intestine/ immune cells
Target
- stomach
- intestines
Action=
- increase blood flow
- decrease acid secretion
- increase mucus/ bicarbonate secretion
- increase motility
- increase fluid secretion
What is the effect of histamine on GI function?
Source=
- stomach
- intestine/ immune cells
Target=
- stomach
- intestine
Action=
- increase acid secretion
- increase fluid secretion
Describe the blood supply to the stomach.
The blood flow to & from the stomach is known as the “splanchnic circulation”
- Blood from GI organs is carried to the portal vein
- Portal vein empties into the liver
- Liver returns blood to the body via the hepatic vein
GI–>portal vein–>liver–>hepatic vein–>body
How does ACh influence blood flow to the GI tissues?
Vasodilation & increase blood flow
How does CO2 influence blood flow to the GI tissues?
Vasodilation & increase blood flow
How does VIP influence blood flow to the GI tissues?
Vasodilation & increase blood flow
How does NE influence blood flow to the GI tissues?
Vasoconstriction & decreased blood flow
Describe the GI smooth muscle membrane potential.
Remember that GI smooth muscle has a “resting slow wave” potential i.e. continuous depolarization & repolarization that DOES NOT result in contraction
How are contractions initiated in GI smooth muscle?
“Spike potentials” i.e. a stimulus triggers a rapid depolarization on the up-slope of a slow wave potential–>contraction
What are the four types of contraction seen in GI smooth muscle? What is the general function of these different types of contraction?
1) Segmental= mixing
2) Peristaltic= moving
3) Reverse peristaltic= storing
4) Migrating Motor Complex= fasting state contractions to keep things clear
What are the three phases of the MMC?
Phase 1= quiescent period
Phase 2= increase in irregular action potentials
Phase 3= regular spike potentials–peak contraction
What regulates the MMC?
- Motilin plays a major role
- ENS
- Vagus nerve
What are the key stimuli that initiate GI contractions?
- Mechanical stretch
- ACh from PNS/ ENS
What are the key stimuli that inhibit GI contractions?
- NO
- VIP
- NE
What are the two sites in the GI tract that are under voluntary control?
1) Upper esophageal sphincter
2) External anal sphincter
What are sphincters?
Circular muscle that control anterograde & retrograde movements
What are the key NTs that relax sphincter muscle?
NO
VIP
What is counter-current blood flow? What are the pathologic implications of counter-current blood flow?
Mucosal surface of the GI/ villi:
- Blood supply is “counter current” i.e. arterial & venous blood pass each other, which facilitates diffusion of oxygen & nutrients
**Compromised blood flow= compromised health of villi–>shrink
