Please enable JavaScript.
Coggle requires JavaScript to display documents.
GI Motility - Coggle Diagram
GI Motility
Normal Motion of Swallowing
Actions
Chewing -> Pharyngeal phase -> Movement of Material in Esophagus -> Relaxation of stomach to receive ingested material
Initially voluntary buit once intiiated, swallowing proceeds as involuntary reflex
Minimal digestion/Absorption at this stage
Chewing
3 Major Functions
Facilitates swallowing by reducing size
Mixes food with saliva (exposes food to digestive enzymes, lubricates food for easier transit)
Increases surface area of ingested food
Pharyngeal Phase
Swallowing is initiated by propulsion of food into the oropharynx by movements of the tongue
Material is propelled by elevation and retraction of tongue against the palate
Nasopharynx closes as material is passed from oral cavity, respiration is inhibited
Laryngeal muslces close the glottis and raise the larynx
Bolus propelled by peristaltic contraction by constrictor muscles, upper esophageal sphincter relaxes
Anatomical Parts
UES
Tonically closed at rest due to continuous neural excitation (excitation ceases with swallowing, sleep, general anesthetic)
Thick circular muscle (cricopharyngeal muscle, striated muscle, pressure higher in anterior and posterior area)
LES
1-2 cm in length
No true separate sphincter muscle anatomically
Tonically closed
Via neuronal and humoral influences
Relaxation of LES occurs with swallowing via enteric nerves
Esophageal Body
Propels food from pharynx to stomach via coordinated contractions
2 Layers; inner circular layer, outer longitudinal layer:
Upper 1/3 of body is smtraited muscle, bottom 2/3 is smooth muscle
Innervated by vagus nervve and myenteric plexus
Esophageal Motility
Coordinated contractions by central and peripheral mechanisms
Innervated by vagus nerve (somatic motor from nucleus ambiguus, visceral from dorsal motor)
Somatic nerve synapse directly to striated muscle fibers
Visceral motor nerves do not synapse directly to smooth musle, but with nerve cell bodies between longitudinal and circular layters
Process
UES Opens to allow bolus from pharynx -> Esophagus
Body of esophagus undergoes peristalsis
Progresses to distal segments
Before wave reaches the LES, LES relaxes, and after passage to the stomach, LES is back to resting phase
Peristalsis
Primary: Esophageal contraction preceded by pharyngeal phase
Seocondary: Esophageal contraction in absence of oral or pharyngeal phases, when esophagus is distended, and primary contractions fails to empty esophagus or if gastric contents reflux into esophagus
Process of Defecation
Motility in Rectum and Anal canal
Rectum is usually empty, contractions occur regularly
Activity in proximal rectum will slow flow of contents into rectum
Anal canal
Usualaly closed to due contraction of internal anal sphincter
When rectum is distended, internal anal sphincter will relax due to rectosphincteric reflex
Defecation is prevented via external anal sphincter
Defecation
Rectosphincteric reflex is elicted when evacuation si convenient
Series of voluntary and involuntary actions
Muscles of descending and sigmoid colona nd rectum contract to propel contents towards anal canal
Internal + External sphincters relax to allow passage
Voluntary contractions raise intra abdominal pressure
Pelvic floor relaxes and allows increased abdominal pressure to force pelvic floor down
Contractility of Intestines
Small intestine
Optimized for digestion and absorption
Contraction have 3 functions: Mixing of food wiht digestive secretions, ciruclation of intestinal contents, net propulasion of intestinal contents
Anatomy
Contraction of small intestine are from activity of 2 layers of smooth muscles: outer layer of longitudinal muscles, inner layer of circular muscles (usually thicker
Innervation
Autonomic nervous via enteric nerves
Enteric forms plexuses between circular and longitudinal muscle layers
During contractions, luminal pressure = Intra-abdominal pressure, lumen is occluded and intraluminal pressure increases
Segmentation: Contractons are not coordinated, and contents are displaced proximally and distally
Patters of Contraction
Fasting Stage
Contractions that do not occur evenly overtime
Cycles of no or very few contraction followed by phase of intesnse contractions that end abruptly called migratory motor complex
Sweeps undigested contents from stomach through intestines to colon
Non Fasting Stage
No MMC, contractions are more uniform, and are separated by 5-20 seconds
Controlled by ICC, smooth muscle cells, nerves, and humoral substances
Large Intestine
Allow for optimal absorption of water, and electrolyte's, move aborally, store and evacuate feces
Anatomy
Longitudinal and Circular Muscle layers
Longitudinal: Concentrated into 3 flat bands called taeniae coli
Circular: Layers are continuous from cecum to anal canal
At anal canal: Layers thikcen to form internal anal sphincter
External Anal Sphincter: Overlapping and distal to internal anal sphincter - layers of striated muscle
Innervation
Innervated by autonomic nervous system
Enteric nerves lie between circular and longitudinal
Myenteric receive input from vagus nerve, and pelvic nerves from spinal cord
Contractions
Contraction: Flow of content from large intestines from small intestine is intemittent (Regulated by ileocecal valve that relaxes)
Contractions can last 12-60 seconds, move content back and fort to mix and expose them to colonic mucosa to absorb water and electrolytes
Segmental contractions propel contents over short distances aborally
Once reaching descending colon, material has changed from liquid to semisolid state