GI Physiology 1 Flashcards
Regulation of the GI system - Endocrine
Regulation that utilizes the blood to send wide spread signals throughout the body
Hormones released
Regulation of the GI system - Paracrine
Regulation that targets cells in close proximity (neighboring cells) and results in a more localized effect
Allows for localized communication
Regulation of the GI system - Neurocrine
Regulation that occurs when neurons innervate endocrine, vascular, or muscle cells and modulate their function
Regulation of the GI system - Autonomic Nervous System involves
PNS
SNS
ENS (enteric)
Regulation of the GI system - Key features of the enteric NS
Branch of the ANS
100 million neurons (equal to spinal cord)
Located entirely in GI
Regulated by local stimuli and PNS and SNS
There is communication btw the PNS and SNS with the ENS
ENS functions
ALL BY ITSELF! But, it will function better when it is communicating with the CNS and other branches of the ANS
ENS - gut brain axis
Communication between the ENS and the CNS
Involves communication by efferent and afferent neurons of the ANS that allow for fine tuning of the GI regulatory functions
PNS - afferents and efferents
Afferents = nausea, distension, satiety Efferents = Stimulate motility, stimulate secretions, VD
SNS - afferents and efferents
Afferents = pain Efferents = Inhibit mobility, inhibit secretions, VC
ENS - what does it do
Motility regulation Secretory regulation Mechanical sensation Chemical sensation Pain sensation
Neuronal innervation of the GI tract - Intrinsic ENS neurons
Motor neurons
Sensory neurons
Associative neurons (interneurons)
Intestinofungal neurons (regulate symp ganglia)
Neuronal innervation of the GI tract - Intrinsic ENS neurons - Motor neurons
Stimulate and inhibit smooth mm
VD
Regulate electrolyte and water secretion
Regulate secretion of hormones, electrolytes, water…
Neuronal innervation of the GI tract - Intrinsic ENS neurons - sensory neurons
Nociceptive neurons
Mechanoreceptive neurons
Chemoreceptive neurons
Neuronal innervation of the GI tract - Extrinsic ENS neurons
Sympathetic
Parasympathetic
Sensory input
Neuronal innervation of the GI tract - Extrinsic ENS neurons - Sympathetic
Motility inhibiting neurons
VC neurons
Secretomotor inhibiting neurons
Neuronal innervation of the GI tract - Extrinsic ENS neurons - Parasympathetic
Motility stimulating VD neurons Secretomotor stimulating neurons ENS inhibitory ENS excitatory
Neuronal innervation of the GI tract - Extrinsic ENS neurons - sympathetic input
nociceptive neurons
mechoceptive
chemoceptive
NT of the GI tract - NT of the PNS and SNS
Ach
NE
NT of the GI tract - NT of the PNS and SNS - Ach
VD
Inc secretions
Smooth mm contraction
Primary NT of the PNS - can be released by both pre and post PNS to stimulate GI
NT of the GI tract - NT of the PNS and SNS - NE
VC
Inhibit smooth mm contraction
Dec secretions
Primary NT of the SNS - inhibit GI
NT of the GI tract - NT of the ENS
Ach Serotonin Dopamine Nitric Oxide Vasoactive intestinal peptide
NT of the GI tract - NT of the ENS - Ach
VD
Inc smooth mm contraction
Stimulate secretion
NT of the GI tract - NT of the ENS - Serotonin
VD
Inc smooth mm contraction
Stimulate secretion (interneurons)
NT of the GI tract - NT of the ENS - Dopamine
Inhibit ENS neuronal firing
NT of the GI tract - NT of the ENS - NO
Smooth mm relaxation (vascular and GI)
NT of the GI tract - NT of the ENS - VIP
Smooth mm relaxation (vascular and GI)
GI motility - what is BER
Basal electrical rhythm or slow waves
Spontaneous oscillating de and re polarization waves that do not elicit a contraction
GI motility - BER is initiated by
the interstitial cells of Cajal that serve as the pace packer cells and lie between the longitudinal and circular muscle
GI motility - spike potentials are
rapid depolarization events that occur at the peak of the slow wave and elicit a contraction
Tension correlates with the spike potentials
In the absence of spike potentials, the cell is at rest
GI motility - primary regulators of GI smooth mm
Ach (stimulate contraction)
VIP (inhibit contraction)
NO (inhibit contraction)
GI motility - 4 types of GI motor activity
Segmental contraction (mixing) Peristaltic contractions (moving) Reverse peristaltic contraction (storing and keeping empty) Migrating motor complex (MMC - during interdigestive period)
GI motility - Segmental contractions - describe
Toothpaste analogy
Intermittent spaced segments of contraction
All moves to middle and then there is a contraction in the middle of the tube and it all goes to outside - moves back and forth so you get mixing
GI motility - motility within the GI tract is coordinated by
Regulators that promote smooth muscle contraction (Ach) and regulators that induce smooth mm contraction (NO, VIP)
Need to appreciate the upstream contraction and the downstream relaxation to allow directional motility in the GI tract
GI motility - MMC - what is it
Migrating motor complex is a rhythmic motility pattern that occurs during the interdigestive period (between meals) approx every 90 min
GI motility - MMC - purpose
To maintain directional movement of undigested contents
GI motility - MMC - strongest contractions are in the
Upper GI tract (stomach, duodenum, jejunum) and fade in intensity in the ileum and colon
Loss of function of the MMC can lead to
Inc colonization of bacteria in the upper GI tract
GI motility - Also regulated by __ mm
Striated
- Upper esophageal sphincter
- Upper 1/3 of esophagus
- External anal sphincter
GI motility - directional movement is regulated by what? and name them
Sphincters! UES LES PS IS IAS EAS
GI motility - sphincters are ___ ____ mm and regulate ___ movements
Sphincters are specialized circular muscles and regulate antegrade and retrograde movements
Blood supply of the GI tract
Splanchnic circulation
Receives about 30% of the CO when the body is at rest
This reservoir can be shunted though to other regions (during ex for example)
Blood supply of the GI tract - Blood is delivered primarily by the ____
GI organs drain into the _____
Celiac and superior mesenteric arteries
The GI organs drain into the portal vein
Blood supply of the GI tract - The portal venous system delivers blood to the ____
Liver!
So contents absorbed by the GI tract have to pass through the liver!
Blood supply of the GI tract - factors that increase blood flow
8 fold inc in blood flow following a meal (postprandial hyperemia)
Sequential dilation of the GI tract (prox to distal)
Flow is regulated to muscularis layers and through villi and submucosa
VD is maintained for 2 to 4 hrs after the meal
PNS, NO, VIP, hormones like CCK, low oxygen, hyperosmolarity
Blood supply of the GI tract - factors that decrease blood flow
SNS innervation of vascular smooth mm
- NE, alpha adrenergic receptors
Endocrine/paracrine regulation of vascular smooth mm
- Somatostatin
- Analogues of somatostatin can be administered to dec GI bleeding
Some differences between the large and small intestine
Small intestine longer with larger apical area
Large intestine has no nutrient absorption and no villi
Enteric bacteria - what is the pattern
As you move away from the stomach (to a less acidic environment) the population/amount of bacteria is greater
Greater at the colon than at the stomach
Enteric bacteria - growth of GI bacteria
GI secretions (saliva, acid, fluid/electrolytes, bile)
Mucosal immunity
Intestinal motility
Pharmacological agents (antibiotics, CA chemo, immunosuppressants, motility inhibitors, acid inhibitors)
Enteric bacteria - functions of intestinal bacteria
Nutrient metabolism and salvage
Xenobiotic and drug metabolism
Antimicrobial protection and suppression of pathogenic organisms
Immunomodulation and development of gut immune system
