Week 4a Gastrointestinal Physiology Flashcards
How much body mass is the GI system?
5%
What are the functions of the GI system?
- motility
- digestion
- absorption
- excretion
- circulation
All regions of the GI system work together to:
regulate the intake, processing & absorption of ingested nutrients & the disposal of waste products
What does the intestines interface with?
the immune system, with a diverse array of antigens present in food and gut microbes
What are the two primary movements of the GI system?
- mixing
2. propulsive (peristalsis)
What are the layers of the GI wall?
Serosa Longitudinal muscle layer Circular muscle layer Submucosa Mucosa Epithelium
Define the serosa
smooth membrane of thin connective tissue
What does the longitudinal muscle layer do?
contracts in order to shorten the length
What does the circular muscle layer do?
contracts to decrease the diameter
What does the submucosa do?
contains the submucosal (Meissner) plexus, which
transmits information from the epithelium to the enteric
and central nervous systems (CNS)
What is the mucosa layer?
functions to move the villi and contains blood vessels,
nerve endings, and immune and inflammatory cells
What layer of the GI system contains the immune and inflammatory cells?
mucosa
What is the GI system epithelium layer?
contents are sensed and where secretion of enzymes, absorption of nutrients, and excretion of waste products
occur
How is the GI system innervated?
- Extrinsic
SNS (primarily inhibitory)
PSNS (primarily excitatory) - Enteric (controls motility, secretion, & blood flow)
What does the SNS do in the GI system?
primarily inhibitory as stimulation can decrease or cease GI motility
primary neurotransmitter is norepinephrine
What does the PSNS do in the GI system?
- primarily excitatory as it activates GI motility and function
• primary neurotransmitter is acetylcholine
What does the enteric nervous system do in the GI system?
independent nervous system of the GI tract, which controls motility, secretions, and blood flow
What do vagus nerve fibers innervate in the GI system? (5)
[celiac plexus]
- esophagus
- stomach
- pancreas
- small intestine
- first half of large intestine
What do pelvic nerve fibers innervate in the GI system? (3)
[inferior hypogastric plexus]
- second half of the large intestine
- sigmoid
- rectal/anal regions
What is myenteric (Auerbach’s) plexus?
Linear chain of many interconnecting neurons that
extends the entire length of the gastrointestinal tract
→ Lies between the longitudinal and circular layers of the
intestinal smooth muscle
What does stimulation of myenteric plexus result in?
- Tonic contraction
- Increased intensity of rhythmic contractions
- Slight increase in rate of rhythmic contractions
- Increased velocity of peristaltic waves
What is the submucosal (Meissner’s) plexus?
• Controls inner wall of each minute segment of the intestine
• Originates in the epithelium
• Helps control local secretions, absorption, and contraction of the
submucosal muscle
What is Meissner’s plexus also called?
submucosal plexus
What is Auerbach’s plexus called?
myenteric plexus