GI Innervations and Structure Flashcards
What is the function of the gastrointestinal tract?
digestion and absorption of nutrients
What are the general activities to accomplish digestion and absorption?
- motility (propel and mix)
- secretions (enzymes, bile, mucus, acid, bicarbonate)
- digestion (breakdown into absorbable molecules)
- nutrients absorbed
What is the linear sequence of the gastrointestinal tract?
- mouth
- esophagus
- stomach
- small intestine
- large intestine
- anus
What are the support structures of the gastrointestinal tract?
- salivary glands
- pancreas
- liver
- gallbladder
What does the gallbladder do?
Stores bile for breakdown of fats/lipids
What does it mean that the liver has “first pass” metabolism?
Liver receives ALL nutrients via portal vein before anything goes into peripheral circulation
What do salivary glands contribute to the GIT?
some enzymes, lubrication, buffering
What does the pancreas contribute to the GIT?
enzymes, bicarbonate
What occurs in the mouth for digestion?
some enzymatic breakdown and chewing to increase surface area
What occurs in the stomach for digestion?
HCl hydrolyzes protein, mixing
What occurs in the small intestine for digestion?
continued digestion with enzymes and absorption
What occurs in the large intestine for digestion?
water absorption, fermentation
What is produced by fermentation in the large intestine?
volatile fatty acids (VFAs)
What are the two surfaces of the GIT wall?
mucosal and serosal
The mucosal surface of the GIT faces where?
lumen
The serosal surface of the GIT faces where?
blood
What are the layers of the GIT?
- mucosal layer (lumen)
- submucosal layer
- two layers of smooh muscle
- serosal layer
The mucosal layer of the GIT is composed of what?
- epithelial cells
- lamina propria
- muscularis mucosae
The submucosal layer of the GIT is composed of what?
- collagen
- elastin
- glands
- blood vessels
What are the two layers of smooth muscle and give brief differences between them?
- circular muscle (thick and has more nerves)
- longitudinal muscle (thin and has less nerves)
What are the two types of ganglia in the GIT?
- submucosal (meissner’s) plexus
- myenteric (averbach’s) plexus
Where is the submucosal plexus?
between submucosa and circular layer
Where is the myenteric plexus?
Between circular and longitudinal layer
What are the functions of epithelial cells in the mucosal layer?
- secretory and absorptive functions
- sloughed and replaced frequently
What is the lamina propria of the mucosal layer composed of?
- connective tissue
- blood
- lymph nodes
What is the function of muscularis mucosae in the mucosal layer?
smooth muscle cells that change shape and surface area of epithelial cells
Which innervation component of the GIT contains sympathetic and parasympathetic innervation?
Extrinsic
Which innervation component of the GIT begins in the esophagus and extends to anus?
intrinsic (enteric)
The intrinsic (enteric) component of GIT innervation is contained within?
submucosal and myenteric plexuses
Does the intrinsic (enteric) component of innervation communicate with the extrinsic component?
Yes
Is the intrinsic (enteric) component of innervation influenced by the extrinsic component?
Yes
Which component of innervation can operate independent of the brain and spinal cord, meaning that it functions even if the vagus nerve is severed?
Enteric
How do plexuses communicate?
Interneurons
What does the enteric nervous system control?
contractile, secretory, and endocrine functions of GIT
What type of neurons release neurotransmitters/neuromodulators from vesicles and from synaptic terminals?
Enteric
The enteric nervous system can control functions of GIT in the absence of extrinsic system via?
short reflex arcs
What is the sensory information received directly from receptors in mucosa by myenteric and submucosal plexuses?
- wall stretch
- changes in nutrient concentration
- changes in osmolarity
- pH changes
- irritation to mucosa
Which ganglia can also send motor information directly to smooth muscle, secretory, and endocrine cells?
those of myenteric and submucosal plexuses
Most neurons of which nervous system can secrete two or more neurocrines?
Enteric
Neurocrines (neurochemicals) are found in neurons of which nervous system?
enteric
What can act to increase/decrease the amount of neurotransmitter released and/or act to modify the respone of the post-synaptic cell?
neuromodulators
What is usually secreted along with neurotransmitters?
neuromodulators
The parasympathetic innervation of GIT is supplied by?
- vagus nerve
- pelvic nerve
Which nerve supplies parasympathetic innervation to the upper GIT?
vagus nerve
Which nerve supplies parasympathetic innervation to the lower GIT?
pelvic nerve
What is included in the upper GIT?
striated muscle in upper third of esophagus, wall of stomach, small intestine, and ascending colon
What is included in the lower GIT?
striated muscle of external anal canal and walls of colon
Name two neurotransmitters.
- acetylcholine
- norepinephrine
Name five neuromodulators.
- vasoactive intestinal peptide (VIP)
- gastrin releasing peptide (GRP), or Bombesin
- enkephalins (opiates)
- neuropeptide Y
- substance P
The postganglionic neurons of parasympathtic nervous system are classified as?
cholinergic or peptidergic
Cholinergic neurons of PNS release?
acetylcholine
Peptidergic neurons of PNS release?
- substance P
- vasoactive inhibitory peptide (VIP)
- and other neuromodulators
What are vagovagal reflexes?
reflexes in which both afferent and efferent limbs are contained in the vagus nerve
Afferent fibers in vagus nervedeliver sensory information from?
periphery (receptors in wall of GIT) to CNS
Efferent fibers in vagus nerve deliver motor information from?
CNS to target tissues (smooth muscle, secretory, endocrine cells)
What is the mixture of afferent and efferent fibers of the vagus nerve?
- 75% afferent
- 25% efferent
The SNS has short preganglionic fiber that synapse in ganglia where?
outside the GIT
The PSNS has long preganglionic fibers synapsing in ganglia where?
in or near target organs
What are the four sympathetic ganglia that serve the GIT?
- celiac
- cranial mesenteric
- caudal mesenteric
- hypogastric
Postganglionic nerve fibers of the SNS (adrenergic) leave sympathetic ganglia and do what?
- synapse on ganglia in the myenteric and submucosal plexuses
OR - they can directly innervate smooth muscle, endocrine, or secretory cells
