Overview of GI Tract Flashcards
functions of GI tract
- intake, digestion, and absorption of nutrients
- immune and endocrine organ
- regulates food intake and glucose homeostasis
- establishes gut microbiome
- largest interface between outside and inside world
components of GI tract
- esophagus
- stomach
- small intestine
- large intestine
- rectum & anus
- accessory organs
esophagus function
transport and protection
stomach function
storage and controlled delivery of digests to small intestine
small intestine function
mixing, digestion, and absorption
large intestine function
reclaim water, site of gut microbiota, storage
rectum & anus function
waste storage and defecation
accessory GI organs
liver
pancreas
gallbladder
layers of the GI tract
- mucosa
- submucosa
- muscularis
- serosa
mucosa
innermost layer; surface lining of the GI tract lumen
intestinal lumen
body cavity that communicates with the external environment
components of the mucosa
- epithelium
- lamina propria
mucosal epithelium
outer layer of absorptive and secretory cells
mucosal lamina propria
inner layers containing blood vessels, nerves, and immune cells
submucosa
loose connective tissue beneath the mucosa that provides support
- contains larger blood vessels, lymphatics, nerve plexus, and ganglion cells
submucosal plexus
ganglia of nerves of the enteric nervous system
muscularis
two layers of smooth muscle located beneath the submucosa
- extends from esophagus to anal canal
layers of muscularis
outer longitudinal muscle
inner circular muscle
myenteric plexus
enteric nerves located between muscle layers
serosa
outermost layer of epithelium and connective tissue
why does GI tract function need to be regulated
- initiate postprandial and inter-meal periods
- maximize nutrient absorption based on diet
- allows for communication between proximal and distal regions and accessory organs
control mechanisms of GI
- endocrine
- neural
- paracrine
enteroendocrine cells
process signals and respond to food intake
- have mechanoreceptors and chemoreceptors in lumen
- release peptides/hormones in response to changes in lumen environment
GI hormones
hormones synthesized by enteroendocrine cells; must be:
- present in the gut
- released by appropriate physiological stimulus
- produce an appropriate response
- have identified structure
- blocked by an antagonist
extrinsic nervous system
cell bodies are located outside of the gut wall
communicate with enteric nerves and CNS
- afferents: vagal and spinal
- efferents: vagus and pelvic nerves (parasympathetic)
what portion of the gut does the vagus nerve innervate
innervates proximal portion of the gut
what portion of the gut does the pelvic nerve innervate
innervates distal portion of the gut
function of visceral afferents
transmit information from gut to CNS for REFLEXES only (no consciousness)
allows for homeostatic regulation in response to external stimuli
enteric nervous system (ENS)
intrinsic; cell bodies are located inside the gut wall
most ENS nerves do NOT receive CNS input
contains neurotransmitters
where are the nerves of the enteric nervous system located
submucosal and myenteric plexus
function of submucosal plexus
regulates secretions and absorption
function of myenteric plexus
regulates motility and contractility
intrinsic primary afferent neurons (IPANs)
neurons that communicate afferent information within the ENS
cell bodies located in submucosal & myenteric plexus
function of IPANs
regulates contraction and secretions of the gut WITHOUT CNS input
- activates local secretory cells
- regulates blood flow
vago-vagal reflex
extrinsic reflex pathway that controls contraction of the GI muscle layer in response to distention by food
- regulates gut function
- vagal afferent stimulates vagal efferent to cause: receptive relaxation, acid/enzyme/hormone secretion/antral contraction
