GI 1 Flashcards
Duodenal Cluster (3)
- Duodenum
- Pancreas
- Biliary System
Biliary System
the organs and ducts (bile ducts, gallbladder, and liver) associated with production/transportation of bile
Sphincter of Oddi
at the jxn of bile ducts and duodenum, controls when bile and pancreatic sercretions are realeased into the lumen of the duodenum
3 Parts of the Small Intestine
- Duodenum
- Jejunum
- Ileum
Function of Jejunum
site of the majority of nutrient absoprtion
Function of the Colon
absorb water andd electrolytes, store wastes ad indigestibles
Flow of the GI tract
oral cavity –> esophagus –> stomach –> duodenl cluster –> jejunum –> ileum –> colon –> rectum –> anus
Pylorus
controls outflow from stomach
Upper and Lower Esophageal Sphincters
control swallowing and reflux
Ileocecal valve
at jxn of small intestine and colon; one way valve that keeps GI bacteria in the colon and allows other residues from the small intestine to pass through
Internal and External anal sphincters
control defecation
Mucosal Plica
the folds in the lumen of the GI tract
What sits on the folds of the mucosal plicae?
Villi and microvilli, to aid in efficient digestion and absorption
Label the layers of the GI Wall
Components of the Submucosa of the GI Wall
loose connective tissue, arteries, veins, lymphatics, submucosal plexus [ganglia] (at the base)
Components of the Muscularis Layer of the GI Wall
Internal Circular Muscle Layer
Myenteric Plexus (in the middle)
External Longitudinal Muscle Layer
What are the two main functions of the intestinal epithelium?
secretion and absorption
How often is all of the intestinal epithelium replaced?
every 2-5 days
Types of Cells in the Intestinal Epithelium (6)
- Intestinal stem cells
- Paneth cells
- Transit Amplifying cells
- Goblet cells
- Enteroendocrine cells
- Enterocytes
What type of cells make up the majority of the intestinal epithelium?
enterocytes (secrete enzymes and absorb nutrients)
Paneth cell function
secret antimicrobial peptides
What percent of the intestinal epithelium do enteroendocrine cells make up?
1%
Enteroendocrine cell function
secrete hormones
Crypt
an invagination of the intestinal lumen that has cells of primarily secretion capabilities
The enteric nervous system is a branch of what part of the peripheral nervous system?
autonomic (involuntary control)
What do we consider the extrinsic nervous system of the GI tract?
Autonomic Nervous System
The Two (2) Main Ganglia of the Enteric Nervous System
- Myenteric Plexus
- Submucosal Plexus
Since the enteric nervous system can function as a loop on its own, what do we call those loops?
microcircuits
What two nerves of the parasympathetic nervous system innervate the GI?
- Vagal nerves
- Pelvic nerves
What type of fibers of the parasympathetic system synapse on the GI - pre or post ganglionic?
preganglionic
Where do the fibers of the parasympathetic innervation of the GI originate from?
the medulla and the sacrolumbar region (mostly sacral)
Where do the fibers of the sympathetic innervation of the GI originate from?
thoracolumbar region
What type of fibers of the sympathetic system synapse on the GI - pre or post ganglionic?
postganglionic
Where do the preganglionic fibers of the sympathetic nervous system synapse?
prevertebral ganglia (sympathetic trunk)
Does the myenteric plexus extend the entire length of the gut?
yes (including striated muscle of the esophagus)
Primary function of the Myenteric Plexus?
motor innervation to the longtitudinal and circular muscle layers
Where along the GI tract will you find the most submucosal plexus?
small intestine, specifically the proximal duodenum
Main function of the Submucosal Plexus
secretory control
Explain the microcircuit of the intrinsic nervous system
Sensory (afferent) neurons receive input (chemo or mechano), sensory fibers communicate with interneurons along the myenteric plexus, motor neurons then carry the signal back to the lumen (result dependent on NTs whether stim or inhibits)
Varicosities
endings of nerve fibers similar to a motor plate in skeletal muscle, but more multiple swellings that contain vesicles with neurotransmitters
3 Main Functions of Submucosal Plexus
To Moderate:
1. Secretory Activity
2. Endocrine Activity
3. Blood Flow
2 Main Functions of the Myenteric Plexus
To Control:
1. Tonic Contractions
2. Rhythmic Contraction intensity
2 Types of Contractions in the GI Tract
- Tonic
- Rhythmic
Tonic Contractions
typically around sphincters, long lasting weaker contraction
Rhythmic Contraction
strong contractions to propel food along the GI tract and also mix food with digestive secretions
What nervous system has fibers that can synapse directly on target cells - pre or postganglionic?
Sympathetic postganglionic fibers
What nervous system contains 50% sensory and 50% motor?
sympathetic
Vagovagal reflex
both sensory and motor neurons of the vagus nerve communicate with the CNS to coordinate responses to gut stimuli
What NTs work with the parasympathetic fibers in the GI tract?
acetylcholine or peptides
What NTs work with the POSTganglionic sympathetic fibers of the GI tract?
norepinephrine
What NTs work with the PREganglionic sympathetic fibers of the GI tract?
Acetylcholine
Long loop reflex
the coordination of the enteric nervous system with the CNS in response to fight or flight response or anticipation of food
Short loop reflex
essentially a summary of all the microcicuits of the enteric nervous system (it communicates with itself to initiate a response)
What are some stimuli that can affect the GI tract?
CNS influence, physical environment (lumen pressure, distention), chemical environment (pH, nutrient conc.), microbes
