GI motility Flashcards
Mastication
Breaks down food into smaller particles (increases surface area
prevents excoriation
incisors: cut at 50 lbs of pressure
molars: grind at 200 lbs of pressure
multiple muscles are involved in mastication
main nerve involved is trigeminal (tirCHEWminal) 5
Chewing reflex- bolus of food inhibits muscles of mastication and lower jaw drops, strech reflex is activated leading to rebound contraction and lower jaw comes up
Swallowing
3 phases:
1. Voluntary Stage- blous is rolled and and posteriorly into pharynx by tongue
- Pharyngeal stage: stimulation of tonsillar pillars by bolus, sensory receptors for cranial nerves 5 and 9 (trigeminal and glossopharyngeal) are located between tonsillar pillars and are activated once food is propelled back. Swallowing center of brain is activated. motor impulses from CN 5,9,10, 12 (hypoglossal) provide input to the pharyngeal region. Soft palate rises to prevent nasal swallowing, palatopharyngeal folds pulled to form a slit to prevent large chunks, vocal cords close, larynx pulls up allowing epiglottis to cover trachea. UES relaxes, bolus goes into esophagus, respiration is inhibited
- Esophageal phase:primary peristalsis- pushes bolus down, with a receptive relaxation of lower ES. Secondary peristalsis- housekeeping function, initiates at site of residual
lower esophageal sphincter
diaphragm helps to form barier against reflux
LES relaxation- allows for esophagus to stomach, normally maintains tone. relaxes under influence of NO and VIP from myenteric plexus
hiatal hernia- stoach threads throu hatus, no meds only surgical
achalasia: smooth muscle disorder- lack of perisalsis in LES so cant relax. Bird beak appearance, Food retained in esophagus, mega esophagus, halitosis, deficiencies in NO and VIP
GERD- acid damages the esophagus due to hiatal hernia, transient lower esophageal relaxation (TLER)
Stomach
Anatomy- Cardia, Fundus, Body, Antrum, Pylourus
gastric functions
Storage of food: vago vagal reflex- stomach to brain and back reduces tone to keep pressure low
Mix of food and secretion to form chyme: weak peristaltic contractions
Controls rate of chyme entering the duodenum: weak contractions promote mixing strong contractions (20% of waves) promote emptying Vagovagal as well as myenteric plexus
Acidic environment kills bacteria and parasites
Begin the breakdown process of proteins and breaking down collagen
gastric mixing and emptying
Weak mixing waves, then strong emptying waves approximately 20% of waves. Chyme is emptied through pylorus
control of gastric emptying
factors promoting emptying (mostly due to gastric factors)- increased gastric volume leads to myenteric reflex, parasympathetic stimulation, gastrin (weakly increases gastric contraction)- main role in acid production
factors inhibiting emptying- mostly due to duodenal factors) enterogastric reflex: duodenum slows gastric emptying through ENS (myenteric plexus). Duodenum to sypmathetic ganglia and back to stomach. Duodenum to spinal cord through sensory vagus and back to stomach through motor vagus (vago vagal -minor role)
Factors activating entero gastric reflex: over distension of duodenum, irritation or excess acidity, so the duodenum produces secretin (slows gastric emptying, stimulates pancrease to secrete bicarb), heper or hypo osmotic solutions, breakdown products of proteins or fats (too much fat in duodenum results in production of CCK (slows stomach by clocking gastrin, stimulates gallbladdr and pancrease), breakdown of fats and Carbs produces GIP (gastric inhib peptide)
the end result of slowing of gastric emtying is that emptyng contractions are inhibited and the pylous tightles
Pylorus
tonically constricted, fluid will pass easily and quicklym solids need to be broken down through mixing waves
Small intestines
Mixes content (myenteric plexus)- constriction of circular muscle results in sausage like small intestine allowing mixing and breaking of contents
Move contents (myenteric plexus)- 3-5 hours through small intestine (1cm/min), more nutrients=slower, fats are slowest, nutrient poor= faster. Stimulus for propulsion: distension, irritation, activation of chemoreceptors. Myenteric plexed produce Ach and substance P constrict proximal to bolus. And VIP and NO distal to blous to dialate
Autonomics (PS NS- stim, Sym NS- inhib)
Gastro-enteric reflex: enteric NS- gastric stretch stimulates small intestine motility.
Parasym NS- vago cagla
Symp NS: to ganglia and back. Inhibits symp activity and as a result there is greater motility
hormonal control of small intestine motility
Stimulatory: gastrin CCK, motilin (released during fasting and responsible for migrating motor complex)
inhibitory: secretin and glucagon
MMC and peristaltic Rush
MMC (migrating motor complex): produced during fasting state every 90 minutes in stomach and small intestine, movs undigestible material through small intestine rapidly as it is fecal matter( motilin)
Peristaltic rush- powerful rapid movement, moves from small intestine to colon like in diarrhea
ileocecal valve
prevents colonic bacteria from colonizing small intestine. increased cecum conent results in slowed emptying by valve through enteric NS and sympathetics
Right colon
1-2 days from cecum to rectum
Mixing movements: smooth muscle contractions, narrows lumen leading to haustrations, tinea coli also contracts
Propulsive movements: smooth muscle contractions with disappeatance of haustrations distally the entire earea remains constricted
Left colon
Storage: rectosigmoid angle acts as a barrier to keep rectum empty,
defecation reflex
mass movement push material through descending colon and sigmoid into rectum
2 major events follow
1. Enteric NS (weak defecatory reflex)- stimulates the descening colon and sigmoid to have more mass movement. inhibits the internal anal sphincter by VIP and NO
- parasympathetics (strong defecatory revlex) amplifies mass movements from descending colon and sigmoid and inhibits internal anal sphincters
futher amplified by clossing of glottis, deep breath and contracting abdomina muscles when socially acceppta to inhibit external sphincter
