Lecture 1: Structure + Innervation of Gastrointestinal Tract Flashcards
What is the linear sequence of the GIT
Mouth > Esophagus > Stomach > Small intestine > Large intestine > Anus
Mouth digestive processes and goal
Acquiring and mastication
Goal: To breakdown particles for absorption
Stomach digestive processes
Mixing and hydrolyzes protein
What does majority of absorption occur?
Small intestine
Small intestine digestive processes
Digests and absorbs protein, carbs, fat, absorbs vitamin and minerals
Large intestine digestive processes
Reabsorption of water, fermentation of fiber
What are the supportive structures of the GIT?
Salivary glands
Pancreas
Liver
Gallbladder
Salivary glands responsibilities
Saliva for lubrication and digestion of starch and fats
Pancreas responsibilities
Buffering, digestion of carbs, proteins, fat
Liver responsibilities
“First pass” metabolism
Receives all nutrients absorbed from gut before blood returns to heart (takes up some nutrients and sotres)
Makes bile for fat digestion
Where does “first pass” metabolism occur?
Liver
Gallbladder responsibiltiies
Stores all bile made by the liver
What are the two surfaces of the GIT wall?
Mucosal
Serosal
What does the mucosal surface of the GIT wall face?
Lumen
What does the serosal surface of the GIT wall face?
Blood
Name the layers of the mucosal layer
Epithelial cells
Lamina propria
Muscularis mucosae
Function of epithelial cells of mucosal layer
Important absorptive and secretory functions - sloughed and replaced often
Function of lamina propria of mucosal layer
Connective tissue, blood and lymph vessels
Function of muscularis mucosae of mucosal layer
Smooth muscle cells, change shapes + surface area of epithelium
What does the submucosal layer of the GIT wall contain?
Collagen, elastin, glands, blood vessels
What are the two layers of smooth muscle in the GIT wall?
Circular muscle
Longitudinal muscle
Which layer of muscle is very thick and has more nerves?
Circular muscle
Which layer of muscle and thin and has few nerves?
Longituindal muscle
Name layers of GIT wall starting with the lumen
Mucosal layer (lumen)
- Epithelium
- Lamina propria
- Muscularis mucosae
Submucosal layer
Circular muscle
Longitudinal muscle
Serosal layer
Where is the submucosal plexus (meissner’s plexus) located?
Between submucosa and circular muscle
Where is the myenteric plexus (auerbach’s plexus) located?
Between circular and longitudinal muscle
Name the components of the autonomic nervous system involved in innervation of the GIT
Extrinsic component
Intrinsic (enteric) component
What component of ANS involved in innervation of the GIT corresponds to sympathetic and parasympathetic innervation?
Extrinsic component
What component of ANS involved in innervation of the GIT corresponds to the enteric component?
Intrinsic component
Where does the intrinsic (enteric) component begin and end?
Begins in esophagus, extends to anus
What does the intrinsic (enteric) component communicate with / what is it influenced by?
Influenced by and communicates with extrinsics
How does the enteric nervous system control functions of GIT in the absence of extrinsic system?
Short reflex arcs
Define short reflex arcs
Fast internal response to digestive stimuli
Where is the enteric nervous system located?
In ganglia of myenteric and submucosal plexuses
The ganglia of the myenteric and submucosal plexuses not only receive input from digestive stimuli, but also from
Parasympathetic and sympathetic systems
The parasympathetic and sympathetic nervous systems putting input on the ganglia of the myenteric and submucosal plexuses are able to
Modulate the activity of the ganglia
The ganglia of myenteric and submucosal plexuses are able to receive sensory information from
Receptors in mucosa
The ganglia of myenteric and submucosal plexuses are able to send motor information directly to
Smooth muscle, secretory, and endocrine cells
What are some examples of sensory information that the ganglia of myenteric and submucosal plexuses are able to receive?
Wall stretch, changes in nutrient concentration, osmolarity, pH changes, irritation
Name the two enteric plexuses
Myenteric
Submucosal
Both enteric plexuses communicate with each other using innervations and with
CNS via vagal, pelvic, and splanchnic nerves
The enteric nervous system controls what functions of the GIT?
Contractile, secretory, and endocrine
Enteric nervous system can release
Neurotransmitters/Neuromodulators
Enteric nervous system can operate independent of
Brain and spinal cord
If the vagus nerve is severed, the enteric nervous system will
Still function!
The parasympathetic innervation of the GIT is supplied by the
Vagus nerve (CNX) and pelvic nerve
The vagus nerve innervates which portion of the GIT
Upper (Striated muscle in upper third of esophagus, wall of stomach, SI, and ascending colon)
The pelvic nerve innervates which portion of the lower GIT
Lower (Striated muscle of external anal canal, walls of transverse, descending, and sigmoid colon)
PSNS preganglionic fibers long or short?
Long
Where do PSNS preganglionic fibers synapse?
In ganglia in or near target organs
PSNS ganglia specific location in GIT
Myenteric and submucosal plexuses within walls of GIT
Postganglionic neurons of PNS are classified as
Classified as cholinergic or peptidergic
Cholinergic postganglionic neurons release
Acetylcholine
Peptidergic postganglionic neurons release
Substance P and Vasoactive inhibitory peptide (VIP)
Substance P and Vasoactive inhibitory peptide then release..
Neurotransmitters and neuromodulators
Vasovagal reflexes are
Reflexes in which both afferent and efferent limbs containtained in the vagus nerve
Afferent fibers in vagus nerve delivery sensory information from and to
Periphery (receptors in wall of GIT) to CNS
Efferent fibers in vagus nerve deliver motor information from and to
From CNS to target tissues (smooth muscle, secretory, endocrine cells)
Vagus nerve is what % afferent and what % efferent?
~75% afferent, 25% efferent
Neuromodulators are usually secreted with
Neurotransmitters
Neuromodulators and act to increase/decrease what?
Amount of neurotransmitter released
What can act to modify the response of the postsynaptic cell?
Neuromodulators
Neuromodulators target the slower
G-protein neuroreceptors
