Physio GI Motility (32)

• BITTER
• taste buds are composed of groups of between 50 & 150 columnar taste receptor cells bundled together

roughly 1 in 4 people is a that is several times more sensitive to bitter & other tastes

• Sphincters
• rope off (compartmentalize) different digestive areas of the GI tract
• they ensure there’s unidirectional movement of digestive material & meter what “moves on” in the digestive process
• they relax as food is swallowed → tighten up again as food passes

• Saliva: secrete ~1 L/day
• Liquid Ingestion: 2.3 L
• Gastric Juices: 2 L
• Bile: 1 L
• Pancreatic juice: 2 L
• Intestinal juice: 1 L
• TOTAL: 9.3 L
• the small intestine (SI) reabsorbs 8.3 L, while the large intestine (colon) reabsorbs 0.9 L
• a total of 9.2 L is reabsorbed, meaning that only 0.1 L (100 mL) is excreted in feces

• it’s important for the digestive process
• digestion would be SLOWED w/o the liquid environment b/c enzymes are more mobile in a fluid environment
• w/o water, they’d get stuck in “sludge” & couldn’t work as efficiently

• a. Upper Esophageal (UES): top part of the esophagus
• b. Lower Esophageal (LES): end of the esophagus, beginning of stomach
• c. Pyloric: end of the stomach, beginning of duodenum
• d. Oddi: duodenum
• e. Ileocecal: end of ilium, beginning of colon
• f. Internal Anal
• g. Externa Anal

• it can happen because the Lower Esophageal Sphincter (LES) doesn’t constrict fully after food has passed from the esophagus into the stomach
• stomach acid can splash up into the esophagus, causing burning pain

• unlike the esophageal sphincters that allow all swallowed material to pass through, THIS is a metering one
• it can restrict or selectively allow small amounts of material to pass into the SI
• allows stomach digestion to occur fully & limits SI epithelial cell exposure to the stomach’s highly acidic & destructive environment
• (the Ileocecal Sphincter at the entrance to the colon also meters digestive contents)

• the Oddi Sphincter
• it controls the flow of bile (from the liver) & pancreatic enzymes + fluid into the SI
• lies in the duodenum of the SI JUST after the stomach empties into the SI

• you have SOME control over the External Anal Sphincter; can relax it during defecation
• the rest of them are all controlled by the autonomic n.s.

• esophagus has 2
• 3 more in the middle
• anal has 2

1. tongue rises, closing the oropharynx

2. soft palate rises, shutting off the nasopharynx* so food doesn’t go into/come out your nose

3. hyoid rises & moves forward

4. esophagus anterior wall is drawn forward by the hyoid

5. esophageal lumen is pulled open

• 6. epiglottis tilts backward to shut off the glottis* so food doesn’t go into the airway

• made up of the enteric, sympathetic, & parasympathetic nervous systems
• SNS stimulation CONTRACTS GI sphincters & BVs and INHIBITS GI secretion & motor activity
• in contrast, PSNS stimulates these digestive activities

• GUIDES the functions of the GI tract - is the MAJOR controlling factor, even though there are SNS & PSNS innervations as well
• can be seen along the entire GI tract from the esophagus → the colon

• it controls movement of food along GI tract
• regulates temperature
• sensory regulation of enzyme secretion
• + it senses pH & the concentrations of amino acids, fats, & carbohydrates

• Acetylcholine (excitatory when food is present): stimulates SM muscle contraction, ↑ intestinal secretions + release of enteric hormones, & dilates BVs
• Norepinephrine: from extrinsic sympathetic neurons is almost always INHIBITORY & has the opposite effect of ACh
• might see in STOMACH after a large meal slowing things down

• circular & longitudinal
• circular muscles SQUEEZE, longitudinal muscles CONTRACT
• intestinal layers, outermost layer → lumen

• 1. Myenteric
• 2. Submucous
• both of these are embedded in the digestive tract wall & extend from esophagus → anus (these are the main components of the Enteric NS, control the “brain” of the GI tract)

• is buried in the Submucosa (closer to the lumen)
• its principal role is in sensing the environment within the lumen, regulating gastrointestinal blood flow, & controlling epithelial cell function
• it feeds the information it senses up into the myenteric plexus

• located between the longitudinal & circular layers of muscle in the Tunica Muscularis
• it exerts control primarily over digestive tract MOTILITY

1. Motor: control GI motility & secretion

2. Sensory: receive info from sensory receptors in the mucosa & muscle (includes mechanical, thermal, osmotic, & chemical stimuli)

• 3. Interneurons: integrate info from sensory neurons & transmit it to ("programming") enteric Motor neurons
• most of these are multipolar

• in the Esophagus
• everywhere else in the GI tract there is a single layer of epithelial cells that are just like any other epithelium
• there is also Striated Muscle in the 1st 3rd of the esophagus - throughout the rest of the GI tract there’s only smooth muscle

• when material moves through the GI tract, the tract in front of it RELAXES (eg. by Nitric Oxide, NO)
• behind the material muscles CONTRACT so the stuff is propelled through/keeps moving forward
• muscle tone relaxation (+NO) happens PRIOR to contraction (+ ACh)
• [usually you think of ACh functioning in the PSNS to relax BVs, but in the gut you have to REVERSE your thinking & remember that the PSNS STIMULATES GI function therefore ACh → CONTRACTION]

• activity/stomach muscle contractions get MORE intense as food moves down the stomach length-wise
• STOMACHINTES PICTURE

• Proximal Stomach (near LES): large, lazy contractions
• as you move down the stomach contractions become more NUMEROUS & sharp
• tracing in SI shows a LOT of activity & mixing happening
• stomach shows a progressive increase in the # of contractions seen as you move from its beginning to end

• LIQUIDS - they leave the stomach much faster than solids
• eg. to get a lot of energy or electrolyte into your system it will happen more quickly if given in liquid form (takes longer to get into SI & be absorbed if solid)
• takes 30 minutes for 1/2 of liquid to be gone, & takes 90 minutes for 1/2 of solid to leave the stomach

• there are mostly MASS (large volume*) movements in the colon as opposed to the small sharp movements that occur in the SI
• large movements happen 3-5x a day