Motility
chewing and swallowing (5th cranial nerve) esophageal motility gastric motility small intestinal motility large intestinal motility
Peristalsis
initial stage - object enters (bolus), touching circular muscle
step 1 - contraction of circular muscles behind bolus
step 2 - contraction of longitudinal muscles ahead of bolus
step 3 - contraction in circular muscle layer forces bolus forward
Deglutination (Swallowing)
3 stages - vagus stimulation
1) voluntary - initiates swallowing
2) pharyngeal - passage of food through pharynx to esophagus
3) esophageal - passage of food from pharynx to stomach
Vagotomy
partial cut of vagus nerve affecting striated muscle
- primary peristalsis (continuation of pharyngeal peristalsis via swallowing center) CANNOT OCCUR
- secondary peristalsis (induced by distention, stretch is related to afferent sensory input from ENS and swallowing center) DOES OCCUR after vagotomy
Increase Emptying
increase tone of orad stomach, forceful peristaltic contractions, decreased tone of pylorus, absence of segmental contractions in intestine
Decrease Emptying
activation of receptors in intestinal mucosa initiates enterogastric reflexes. This decreases emptying by:
- relaxation of orad stomach, decreased force of peristaltic contractions, increased tone of pyloric sphincter, segmentation contractions in intestine
Acid, Fat/Protein: CCK
Intestinal Receptors
receptors trigger entreogastric reflexes
- Fat/protein: CCK release increases gastric distensibility which decreases gastric emptying
- Acid: decreases gastric emptying via intrinsic neural reflex
Gastric Motility
gastric smooth muscle
- Orad (upper stomach) - receptive to relaxation to accommodate food
- Caudad (lower stomach) - retropulsion mixes food with gastric juicee
- Antral Pump - propels chyme from ciudad to duodenum
Dysphagia
Swallowing disorders
1) CVA (stroke)/cranial nerves damaged
- aspiration - UES and pharyngeal contractions are not coordinated
* ** Secondary peristalsis is still functional
2) Muscular diseases - myasthenia graves, polio, botulism
3) Anesthesia - aspiration of stomach contents
GERD
Gastroesophageal Reflux Disease
- heartburn/acid ingestion (1/10 people)
- Backwash of acid, pepsin and bile into esophagus
Leads to: stricture of esophagus (scar tissue) asthma (aspiration) chronic sinus infection (reflux into throat) Barrett's esophagus
Barrett’s Esophagus
- damage to lower portion of esophagus as a result of GERD
Disorders of Gastric Emptying
1) Slow Gastric Emptying
- fullness, loss of appetite, nausea, sometimes vomiting
- causes include ulcer (scar tissue), cancer, scleroderma, eating disorders, vagotomy
- treat via pyloroplasty or balloon dilation
2) Fast Gastric Emptying
- diarrhea, hypotension, reactive hypoglycemia, duodenal ulcer
- causes include dumping syndrome (respective gastric operations) and pyloroplasty
Pyloroplasty
- surgery to widen lower stomach (pylorus)
- increases gastric emptying
Small Intestine Motility
1) Peristalsis - “law of gut” propulsive movement recall
2) Segmentation - a mixing movement (beads on a string)
Nervous factors:
- peristalsis reflex (ENS)
- intestine-intestinal reflex (severe distention inhibits bowel)
- gastroileal reflex (ileocecal sphincter relaxes, illeal peristalsis increases)
Hormonal factors:
- epinephrine
- motilin
- serotonin (ALOT)
- prostaglandins (ALOT)
- others??? Gastrin, CCK, insulin (stimulate contraction)
secretin, glucagon (inhibit contraction - don’t know exact roles of these)
Migrating Motility Complexes (MMC)
housekeeping function that sweeps undigested residues toward colon to maintain low bacteria in upper intestine
VERY coordinated, rapid peristalsis (between meals)
takes 90 min to go from stomach to colon and is mediated by motion and enteric nervous system
Large Intestine
- slow motility causes greater absorption and HARD feces in transverse colon cause constipation
- excess motility causes less absorption and diarrhea and loose feces
- recto sphincteric reflex: rectal distention triggers smooth muscle relaxation of internal anal sphincter
IF defecation is NOT desired?? skeletal muscle of external anal sphincter contracts through involuntary reflex
Diverticulosis
Diverticula = small sacs of intestinal lining that bulge outward to weak spots
- caused by excess colon pressure
- incidence increases with age
- treat through diet and lifestyle change
Diverticulitis
- diverticula pouches become inflamed
- INFECTION: caused by stool or bacteria getting into diverticula
- can lead to infections, tears, blockages or bleeding
