Physiology Block 3 Week 13 02 GI Motility Flashcards Preview

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Flashcards in Physiology Block 3 Week 13 02 GI Motility Deck (40)


Breaks down food into smaller particles (increases surface area)


Teeth of Mastication

Incisors--cutting/ 50 lbs P
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



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



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



Difficulty swallowing

--difficulty INITIATING swallowing (can't coordinate muscles)
-neuromuscular disorders
-video fluoroscopy

-luminal lesions, motility disorders
-endoscopy, barium swallow


Stomach Anatomy

Cardia--esophagus to stomach
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

-tonically constricted
-fluids easily pass
-solids need to be broken down

1. Circumferential contraction A sweeps toward the pylorus resulting in anterograde and retrograde propulsion of material

2. As A ends, contraction B mixes contents further

3. Contraction B (strong contraction) causes transient and partial opening of the pylorus, allowing small particles to exit the stomach

4. 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



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:
-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

-MOTILIN--released during fasting and responsible for migrating motor complex

-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


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

-Rectosigmoid angle: acts as a barrier to keep rectum empty



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



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