Physiology Block 3 Week 13 02 GI Motility Flashcards
Mastication
Breaks down food into smaller particles (increases surface area)
Teeth of Mastication
Incisors–cutting/ 50 lbs P
Canine
Molars–grinding/ 200 lbs P
Nerve responsible for Mastication
Trigeminal Nerve
Responsible for muscles of mastication
Chewing is both voluntary and a reflex
Chewing Reflex
Bolus of food inhibits muscles of mastication and lower jaw drops
Stretch reflex is activated leading to rebound contraction
Voluntary Stage of Swallowing
Bolus is rolled up and posteriorly into pharynx by tongue
Once bolus thrown back, no longer voluntary
Pharyngeal Stage of Swallowing
Tonsillar pillars stimulated by bolus:
SENSORY RECEPTORS for CN 5 and 9 (trigeminal and glossopharyngeal) are located between the tonsillar pillars and are activated once food is propelled backwards–impulses transmitted to the swallowing reflex center in the brain
MOTOR IMPULSES from CN 5, 9, 10, and 12 (hypoglossal) provide input to the pharyngeal region
SOFT PALATE rises to prevent food from entering nares
Palatopharyngeal folds are pulled to form a slit–allows only chewed food to pass
Larynx pulled up allowing EPIGLOTTIS TO COVER TRACHEA
Esophagus opens and upper esophageal sphincter RELAXES
Bolus propelled into esophagus by PERISTALSIS
INHIBITS RESPIRATION
Esophageal Stage of Swallowing: Primary Peristalsis
Upper esophageal sphincter (UES)–striated muscle
Lower esophageal sphincter (LES)–smooth muscle
Pressure waves move down the esophagus is coordinated with the opening of the LES
Esophageal Stage of Swallowing: Secondary Peristalsis
Food stuck in esophagus
Waves initiate at that point
Contraction orad (from mouth) to bolus is followed by a descending pressure wave that is coordinated with lower esophageal sphincter opening
Role of Diaphragm with Lower Esophageal Sphincter
LES relaxation
- normally maintains tone
- -relaxes under influence of Myenteric plexus–Vasoactive Intestinal Peptide and Nitric oxide (dilators) produced
Diaphragm can tighten or relax on the LES to allow things to move thru to the stomach
Hiatal Hernia
Esophageal disorder
Diaphragm not tight
Portion of the stomach is up past the diaphragm
Z-line (connection from LES to stomach) is too high
Reflux–barrier to acid coming up is inhibited
Transient Lower Esophageal Relaxation–LES remains open for longer duration or opens more often
Gastroesophageal Reflux Disease (GERD)
Damage to the mucosa
LES is wide open
Acid is coming up from the stomach into the esophagus
Esophagus does not have protection from acid like the stomach
Achalasia
Smooth muscle disorder
Inflammatory changes affecting myenteric plexus (GI motility) damaging distal esophagus smooth muscle
Inhibits ability to produce VIP and NO
Lack of peristalsis and inability of LES to relax
Food is NOT moving thru
LES will not relax and UES will not contract
Barium swallow–looks like birds beak
Dysphagia
Difficulty swallowing
Oropharyngeal
- -difficulty INITIATING swallowing (can’t coordinate muscles)
- aspiration
- neuromuscular disorders
- video fluoroscopy
Esophageal
- luminal lesions, motility disorders
- endoscopy, barium swallow
Stomach Anatomy
Cardia--esophagus to stomach Fundus Body Antrum Pylorus--stomach to duodenum
Gastric Functions
Storage of food
–Vago-vagal reflex: reduces wall tone keeping P low
Mixing food and secretions to form chyme:
–weak peristaltic waves
Controls rate of chyme entering duodenum
- -weak contractions = mixing
- -strong contractions promote emptying thru pylorus
- -vago-vagal and myenteric plexus
Acidic environment kills bacteria and parasites
Begin breakdown of proteins (collagen breakdown)
Gastric Mixing and Emptying
Controls rate of chyme entering duodenum
- -weak contractions = mixing
- -strong contractions promote emptying thru pylorus
- -vago-vagal and myenteric plexus
Pacemaker region propels food toward the antrum
Gastric Motility Patterns contributing to mixing, grinding, and sleving of gastric contents
Pylorus
- tonically constricted
- fluids easily pass
- solids need to be broken down
- Circumferential contraction A sweeps toward the pylorus resulting in anterograde and retrograde propulsion of material
- As A ends, contraction B mixes contents further
- Contraction B (strong contraction) causes transient and partial opening of the pylorus, allowing small particles to exit the stomach
- Further cycles of contraction against a closed pylorus continue mixing and grinding until all the meal is emptied from the stomach
Factors Promoting Gastric Emptying
Mostly gastric factors
- increased gastric volume leads to myenteric reflexes
- parasympathetic stimulation
- GASTRIN: weak gastric contraction and acid production
Factors Inhibiting Gastric Emptying
Mostly duodenal factors
Enterogastric reflex
- duodenum slows gastric emptying thru myenteric plexus
- duodenum to sympathetic ganglia and back to stomach
- duodenum to spinal cord (thru vagus n) and back to stomach (vago-vagal reflex)–minor
Factors Activating Enterogastric Reflex
Over-distention of duodenum
Irritation or excess acidity
- -duodenum produces SECRETIN, which stimulates pancreas to secrete bicarbonate
- -secretin slows gastric emptying
Hyper or hypo-osmotic solutions
Breakdown products of proteins or fats
- -too much fat in duodenum = CHOLECYSTOKININ (CCK) released:
- gallbladder contraction = bile released
- pancreas stimulated = bile released
- blocks effects of gastrin= slows stomach motility
Breakdown products of fats and carbohydrates = production of GASTRIC INHIBITORY PEPTIDE (GIP)
Slowing gastric emptying results in inhibiting emptying contractions and the tone of the pylorus increases
Gastroparesis
Stomach motility inhibited
Patient on narcotics–stomach does not empty
Small Intestine Functions
Mix Contents (myenteric Plexus) -constriction of circular muscle results in "sausage like" small intestine (segmentation) allowing mixing and breaking of contents
Move Contents (Myenteric Plexus)
- 3-5 hours from duodenum to ileocecal valve
- more nutrients in chyme = slower (very slow with fats)
- poor nutrient chyme = fast
Small Intestinal Propulsion
Stimulus for Porpulsion:
- Distension
- Irritation
- Activation of chemoreceptors
Myenteric Plexus produces:
- ACh and Substance P = contraction proximal to bolus
- VIP and NO = relaxation distal to bolus
Hormonal Control of Small Intestinal Motility
Stimulatory:
- GASTRIN
- CCK
- MOTILIN–released during fasting and responsible for migrating motor complex
Inhibitory:
- SECRETIN
- GLUCAGON–released when hypoglycemic
Autonomic NS Control of Intestinal Motility
Parasympathetic = stimulatory Sympathetic = inhibitory
Gastro-ileal Reflex
- ENS: gastric stretch stimulates small intestine motility
- Parasympathetic: vago-vagal
- Sympathetic: Inhibits sympathetic activity and results in greater motility
Migrating Motor Complex (MMC)
Small Intestine Movement
Produced during fasting state (every 90 minutes) in stomach and small intestine
Moves undigestible material through small intestine rapidly as it is fecal matter (MOTILIN)
Peristaltic Rush
Small Intestine Movement
Powerful, rapid movements
Moves from small intestine to colon–infectious diarrhea
Ileocecal Valve and Small Intestine Empyting
Prevents colonic bacteria from colonizing the small intestine (terminal ileum)
Increased cecal content results in slowed emptying by ICV
Pressure and chemical irritation relax sphincter and excite peristalsis
Pressure or chemical irritation in cecum inhibits peristalsis of ileum and excites sphincter
Colonic Motility
Right Ascending Colon: Fluid Hepatic Flexure: Semi-fluid Transverse colon: Mush Splenic Flexure: Semi-mush Left Descending Colon: Semi-solid Rectum: Solid
Poor motility causes greater absorption
Hard Feces in transverse colon causes constipation
Excess motility causes less absorption and diarrhea or loose feces
Right Colon Function
ABSORPTION
Mixing movements:
Smooth muscle contractions narrows lumen, leading to haustrations
-TINEA COLI (longitudinal muscle) also contracts
Propulsive Movements:
Smooth muscle contractions with disappearance of haustrations distally
Entire area remains constricted for 20 cms
Left Colon Function
Storage
-Rectosigmoid angle: acts as a barrier to keep rectum empty
Defecation
Defecation Reflex
Mass movements push material through descending colon and sigmoid into rectum–>
Weak Defecatory Reflex (Enteric NS):
- stimulated descending colon and sigmoid to have more mass movements
- inhibits the internal anal sphincter (smooth muscle) by VIP and NO
Strong Defecatory Reflex (Parasympathetic NS from S2-S4):
- amplifies mass movements from descending colon and sigmoid INTO rectum
- inhibits internal anal sphincter through PUDENAL NERVE
External anal sphincter under voluntary control
Further amplified by closing of glottis, deep breath, and contracting abdominal muscles to inhibit external anal sphincter
Constipation
2 or more of the following:
- straining during 25% of defecations
- lumpy or hard stools in at least 25% of defecations
- sensation of incomplete evacuations in at least 25% of defecations
- anorectal obstruction/blockage for at least 25% of defecations
- manual maneuvers to facilitate at least 25% of defecations
- fewer than 3 defecations per week
What contributes to normal bowel movements?
Extrinsic Innervation–parasymp and symp Right colon
Hormones and Drugs–narcotics slow down bowels at hepatic flexure
Luminal Factors–mass in transverse colon
Intrinsic Motility–myenteric NS at left colon
Sitz Mark Study
Not all constipation is the same
Patient swallows capsule with rings and x-ray where the rings are:
Decreased motility–diffuse–rings throughout Large intestine
Rectal Outlet obstruction–damage to nerves there, forget to have bowel movements
Tx: Surgery or biofeedback (retrain how to have bowel movements)
True facts regarding ingestion and motility include all of the following except?
A. Primary innervation responsible for mastication is through CN 5
B. Incisors are able to generate the greatest pressure per inch of all types of teeth
C. Secondary esophageal peristalsis is continuation of primary peristalsis
D. The upper esophageal sphincter fails to relax in patients affected by achalasia
B. Incisors are able to generate the greatest pressure per inch of all types of teeth
Molars provide 200 lbs
Incisors 50 lbs
D. The upper esophageal sphincter fails to relax in patients affected by achalasia
LES sphincter fails to relax in patients affected achalasia
What prevents ingested food from entering the nares?
Elevation of the soft palate
Factors promoting gastric emptying include all of the following except?
A. Increased gastric volume
B. Parasympathetic stimulation
C. Gastrin
D. Secretin
D. Secretin
Which of the following is function of the ileocecal valve?
A. Allows carbohydrates to enter the colon for absorption
B. Allows fluids to enter cecum to neutralize infections
C. Prevents colonic bacteria from entering small intestine
D. Allows the right colon to store fecal matterr
C. Prevents colonic bacteria from entering small intestine
Which of the following is false regarding the migrating motor complex?
A. Occurs every 90 minutes
B. Occurs during the fasting state
C. Responsible for transporting fats to the site of absorption
D. Mediated by motilin
C. Responsible for transporting fats to the site of absorption
