Physiology Block 3 Week 13 01 Overview of GI Physiology Flashcards
(46 cards)
Parotid Gland
Largest of the salivary glands
Small intestine relative lengths
Duodenum= 5% Jejunum= 40% Ileum= 55%
Sphincters and Valves (Tonic Contraction)
Upper Esophageal Sphincter Lower Esophageal Sphincter Pylorus Sphincter of Oddi Ileocecal Valve Internal anal sphincter External Anal Sphincter--under voluntary control
GI tract tends to move and contract–Phasic
Sphincters remain tight and maintain tone–Tonic
General Organization of the GI Tract
In to Out
Mucosa:
- Epithelium
- Lamina Propria
- Muscularis Mucosa
Submucosa: Meissner’s (Submucosal) Plexus
Muscularis Propria: Auerbach’s (Myenteric) Plexus
- Circular Muscle
- Interstitial cells of Cajal
- Longitudinal Muscle
Serosa or Adventitia
Submucosa Functions
Absorption
Secretion
Blood Flow
Invaginations
Interstitial cells of Cajal
In muscularis propria between circular muscle and longitudinal muscle
Determines the rate at which things contract (pacemaker)
Inflammatory Bowel Disease
Ulcerative Colitis (UC) Crohn's Disease (CD)
Ulcerative Colitis
Inflammatory Bowel Disease
- COLON ONLY
- mucosa and submucosa
- continuous starting in rectum
- pain, fevers, blood per rectum, weight loss, increased risk of colon cancer
Crohn’s Disease (Colitis)
Inflammatory Bowel Disease
- any portion of GI tract from MOUTH TO ANUS
- all GI tract layers
- may have skip areas
- pain, fevers, weight loss, STRICTURES (narrowing) due to all layers involved, FISTULAS (an abnormal connection between different organs)
**cobblestone like appearance because all layers involved
Enterocutaneous fistula–connection between GI and skin
Muscle Arrangement and Pacemaker cells
Action potential in 1 muscle fiber is easily transmitted to adjacent fibers, allowing multiple fibers to function as a syncytium
Each region of GI tract has underlying electrical activity that determines contraction rates:
- stomach: 3 contractions/min
- duodenum: 12/min
- ileum: 8/min
Interstitial cells of Cajal (pacemaker cells)–determines rate of contraction (between circular and longitudinal cells)
Myenteric (Auerbach’s plexus)
Responsible for mixing and propagation functions
Located between longitudinal and circular muslce layers in muscularis propria
Meissner’s Plexus (Submucosal plexus)
Responsible for secretion and absorption at the mucosal level
Responsible for blood flow at mucosal and submucosal levels
Influence on neuro-endocrine cells
Membrane potentials in intestinal smooth muscle
Resting:
Baseline slow waves do not cause contraction (except STOMACH)
Slow waves are not action potentials
Spikes:
Occur on top of slow waves and are what cause PHASIC contractions
Occur only when there is enough depolarization to reach threshold and continues
The more action potentials, the stronger the smooth muscle contraction
CALCIUM influx make contractions last longer than skeletal muscle
Factors that alter resting membrane potential:
Less negative = depolarization
-Stretch (a bolus from eating)
-Acetylcholine (released by parasympathetic NS)
-Parasympathetic NS activity
More negative = hyperpolarization–inhibits activity
- Norepinephrine
- Sympathetic NS activity
Autonomic Nervous System: Sympathetic
Stress, Fight or Flight
When active inhibits GI (slows it down)
Sympathetic nervous causes constriction of blood vessels to GI tract, diverting blood during times of stress
Originates between T5 and L2
Pre-Ganglionic fibers (short) enter sympathetic chain and release Acetylcholine
Post-ganglionic fibers (long) innervate the entire gut and release Norepinephrine
Ganglions:
- Celiac
- Superior Mesenteric
- Inferior Mesenteric
Autonomic Nervous System: Parasympathetic
Rest and Digest
Cranial Division via Cranial Nerve X (Vagus Nerve) Innervates: -Esophagus -Stomach -Pancreas -Small Intestine -Large Proximal Large Intestine -Sacral division via 2nd, 3rd, 4th sacral segments to pelvic nerves -Distal Colon: rectum and Anus
Pre-ganglionic fibers (long) END in Enteric NS (Myenteric and Meissner)
Parasympathetic NS increases GI activity and functions
Stimulatory Substances Produced by Myenteric Plexus
Myenteric Plexus = motility
- Acetylcholine
- substance P
Causes constriction to propel food forward
Inhibitory Substances Produced by Myenteric Plexus
Myenteric Plexus = motility
- Vasoactive Intestinal Peptide (VIP)
- Nitric Oxide (NO)
Things distal to bolus relax
Propulsive Movements
Forward movement of a contractile ring around the gut wall
Stimulus is distention of wall
Via ENS myenteric plexus, ring forms and PERISTALTIC movement is initiated
Responses in retrograde direction normally die out rapidly
Mixing Movements
Peristaltic against closed sphincter
Constrictive–attempt to break down to small components for easier absorption
Ileus
Decreased small bowel activity–No mixing in the small intestine
Many causes:
- post-op
- Narcotics
- electrolyte disorder (K+, Ca2+)
- severe illness
Avoiding post-op ileus:
- get patient out of bed ASAP after surgery
- turn patient every 2 hours
- more pain meds = longer to resolve
GI tract Reflexes
Intra-gut reflexes (ENS) have an effect on contraction and secretion
Gut to pre-vertebral sympathetic ganglia and back to another portion of the gut
Gut to CNS (spine or brain)
Intra-gut reflexes (ENS)
Have effect on contraction, secretion
-duodenal distension slows gastric emptying
Gastro-colic Reflex
Stomach distention causes increased colonic motility
Entero-Gastric Reflex
Duodenal distension inhibits gastric emptying
