Motility Of The GI Tract-1/21/16

Question 1

Phasic contractions are found where?

Tonic contractions are found where?

Answer 1

Phasic-Esophagus, stomach (antrum), SI, all tissues involved in mixing and propulsion

Tonic-Stomach (orad), lower esophagus, ileocecal and internal anal sphincters

Question 2

List 3 stimuli for depolarization of slow waves to generate an AP

List 2 stimuli for hyperpolarization of slow waves that result in no AP

Answer 2

Depolarization–> 1) stretch, 2) Ach, 3) Parasympathetics

Hyperpolarization –> 1) Norepi, 2) Sympathetics

Question 3

This functional layer consists of smooth muscle, its contractions change the surface area and shape of the epithelium:

These functional layers are made of smooth muscle and provide motility to the GI tract:

Answer 3

Muscularis mucosae

Muscularis propria or externa

Question 4

This ENS plexus mainly controls GI secretion and local blood flow:

This ENS plexus is between longitudinal and circular layers and mainly controls GI movements:

Answer 4

Submucosal

Myenteric (Auerbachs)

Question 5

Where do slow waves originate?

How do slow waves spread rapidly to smooth muscle?

Answer 5

Interstitial Cells of Cajal (ICC)

Via GAP JUNCTIONS

Question 6

What are the 3 phases of swallowing?

Answer 6

Oral phase (Voluntary)–> Initiates swallowing process

Pharyngeal phase (involuntary) --> passage of food through pharynx into esophagus
Soft palate pulled upward --> epiglottis moves --> UES relaxes --> peristaltic wave of contractions is initiated in the pharynx --> food is propelled through open UES

Esophageal phase (involuntary) –> passage of food from pharynx to stomach; controlled by the swallowing reflex and the ENS (primary and secondary peristaltic waves)

Question 7

Where is the swallowing center located?

Answer 7

The medulla

Question 8

Diagram the neural circuit involved the in the swallowing reflex:

Answer 8

Food in pharynx –> AFFERENT sensory input via CN VII/IX –> Swallowing center (medulla) –> brain stem nuclei –> EFFERENT input to pharynx

The swallowing center inhibits the respiratory center during the pharyngeal stage

Question 9

The primary peristaltic wave is a continuation of pharyngeal peristalsis, is controlled by the ____ and cannot occur after a ___

Answer 9

Medulla, Vagotomy

Question 10

A secondary peristaltic wave occurs if primary contraction fails to empty the esophagus or when gastric contents reflux into the esophagus. It is induced by distention of the esophagus itself by the retained food, repeats until the bolus is cleared, both swallowing center and ENS are involved, can occur in the absence of ____ and occurs even after a ____

Answer 10

Oral and pharyngeal phases, Vagotomy

Question 11

What type of muscle is found in the pharynx and UES?

What type of muscle is found in the rest of the esophagus, LES, and stomach?

Answer 11

Striated

Smooth

Question 12

What are the UES and LES doing between swallows? What about the body of the esophagus?

Describe the pressure in the UES compared to the pharynx and body of esophagus between swallows:

Answer 12

They are both CLOSED

Body of esophagus is flaccid

UES Pressure > pharynx and body of esophagus pressure

Question 13

What does the UES do during swallowing?

What does the body of the esophagus do during swallowing?

What does the LES and upper part of stomach do during swallowing?

Answer 13

UES relaxes (opens)=Low pressure

Body of esophagus undergoes peristaltic contraction=High pressure

LES and upper part of stomach relaxes=Low pressure

Question 14

After a food bolus enters the stomach, the LES ____

Answer 14

Contracts (Increase pressure)

Question 15

An abnormal relaxation of the LES as well as heartburn, chest pain, dysphagia, food regurgitation, a “lump” in the throat, and dry cough may indicative of ___

Answer 15

GERD

Question 16

Achalasia is a neurogenic esophageal motility disorder characterized by impaired peristalsis and a lack of LES relaxation during swallowing. WHat are some causes of Achalasia?

Answer 16

Lack of VIP or the Enteric NS has been knocked out

Results from damage to nerves in the esophagus, preventing it from squeezing food into the stomach

May be caused by an abnormal IS response

Question 17

Receptive relaxation occurs in the ___ region of the stomach

The function of receptive relaxation is to ____

Receptive relaxation is a ____ reflex

Answer 17

Orad

Receive the food bolus in the stomach: Decrease pressure, Increase the volume of the orad region

Vagovagal

Question 18

Contractions of the ___ region of the stomach serve to both mix and propel gastric contents

Answer 18

Caudad

Question 19

____ regulates gastric contractions by increase AP’s and the force of contractions

____ regulates gastric contraction by decreasing AP’s and the force of contractions

Answer 19

Parasympathetic stimulation, gastrin, motilin

Sympathetic stimulation, secretin, GIP

Question 20

The rate of gastric emptying increases by (increase or decrease):
___ distensibility of the orad
___ force of peristaltic contractions of the caudad stomach
___ tone of the pylorus
___ diameter and inhibition of segmenting contractions of the proximal duodenum

Answer 20

Decreased
Increased
Decreased
Increased

Question 21

What are factors that inhibit gastric emptying?

Answer 21

• Relaxation of orad
• Decreased force of peristaltic contractions
• Increased tone of pyloric sphincter
• Segmentation contractions in intestine

Question 22

Complete the last step in the following pathways:

Acid in duodenum –> Stimulates secretin release —> ?

Fats in duodenum –> Stimulates CCK and GIP –> ?

Hypertonicity in duodenum –> (unknown hormone) –> inhibit ___

Answer 22

Acid in duodenum –> stimulates secretin release –> INHIBIT STOMACH MOTILITY VIA GASTRIN INHIBITION

Fats in duodenum –> stimulate CCK and GIP –> INHIBIT STOMACH MOTILITY

Hypertonicity in duodenum –> (unknown hormone) –> INHIBIT GASTRIC EMPTYING

Question 23

___ is a slow emptying of the stomach/paralysis of the stomach caused by damage to the vagus nerve.

Answer 23

Gastroparesis –> Type I diabetes at risk and can be caused by High blood glucose (diabetic gastroparesis)

Question 24

Large particles of undigested residue remaining in the stomach are emptied by ___

Answer 24

Migrating Myoelectric Complexes (MMC)

Question 25

MMC's are mediated by this hormone ___ Absence of MMCs in the stomach has been associated with this disorder ___

Answer 25

Motilin Gastroparesis

Question 26

Describe what circular muscle and longitudinal muscle do BEHIND THE BOLUS during peristalsis: Describe what circular muscle and longitudinal muscle do IN FRONT OF THE BOLUS during peristalsis

Answer 26

Behind the bolus--> Circular muscle CONTRACTS, Longitudinal muscle RELAXES In front of the bolus --> Circular muscle RELAXES, Longitudinal muscle CONTRACTS

Question 27

How does the Slow Wave frequency gradient change along the SI?

Answer 27

There is a decrease in frequency toward the iliocecal junction Duodenum=12 cycles/min Jejunum=10 cycles/min Ileum=8 cycles/min

Question 28

An excitatory motor neuron can cause peristaltic contractions in the SI with ___ An inhibitory motor neuron can inhibit peristaltic contractions in the SI with ___

Answer 28

Ach and Substance P --> cause contraction VIP and NO -> Cause relaxation

Question 29

``` Describe the actions of the following hormones as they relate to contractions of the intestine: A) Serotonin B) Prostaglandins C) Epinephrine D) Gastrin, CCK, motilin, and insulin E) Secretin and glucagon ```

Answer 29

A) Serotonin --> stimulates contractions B) Certain PGs--> stimulates contractions C) Epi-->inhibits contractions D) gastrin, cck, motilin, insulin-->tend to stimulate contractions E) Secretin and glucagon --> tend to inhibit contractions

Question 30

The vomiting reflex is coordinated by the ___

Answer 30

Medulla

Question 31

Describe the order of events in REVERSE PERISTALSIS of the vomiting reflex: How are nerve impulses trasnmitted in the vomiting reflex?

Answer 31

Reverse peristalsis in the SI --> Relaxation of stomach and pylorus --> forced inspiration to increase abdominal pressure --> movement of larynx --> relaxation of LES --> Closure of the glottis --> Forceful expulsion of gastric contents By both Vagal and Sympathetic Afferent nerve fibers to multiple distributed nuclei in the brain stem

Question 32

Distention of the ileum causes ___ of the ileocecal sphincter Distention of the colon causes ___ of the iliocecal sphincter

Answer 32

Relaxation-Allows flow of contents from the ileum into the colon Contraction-Prevents passage of contents from the colon to the ileum

Question 33

The internal anal sphincter is composed of ____ muscle The external anal sphincter is composed of ____ muscle

Answer 33

Smooth Striated

Question 34

Where is the Myenteric plexus located in the LI? List the main Parasympathetic innervation of the LI: List the main Sympathetic innervation of the LI:

Answer 34

Concentrated beneath teneae coli, innervates muscle layers Vagus n.--> cecum, ascending and transverse colon Pelvic splanchnic nerves (S2-S4)--> descending and sigmoid colon, rectum Superior mesenteric ganglion--> Proximal regions Inferior mesenteric ganglion --> distal regions Hypogastric plexus--> distal rectum and anal canal Somatic pudendal nerves --> external anal sphincter

Question 35

____ occur in the cecum and ascending colon, cause little propulsion, and serves to mix the contents of the LI

Answer 35

Segmentation contractions

Question 36

___ occur in the colon, over large distances such as from the transverse colon to sigmoid colon, occurs 1-3 times/day and move the contents of the LI and stimulate defecation reflex.

Answer 36

Mass movements

Question 37

Fluid to semi-fluid is found in the ___ of the LI Mush is found in the ___ of the LI Semi-mush to semi-solid is found in the __ of the LI Solid is found in the __ of the LI

Answer 37

Ascending colon Transverse colon Descending colon Rectum

Question 38

___ motility causes greater absorption, and hard feces in transverse colon cause constipation ___ motility causes less absorption and diarrhea or loose feces

Answer 38

Poor Excess

Question 39

In paraplegic patients lacking tonic contraction of the external anal sphincter, the ___ reflex results in defecation

Answer 39

Rectosphincteric

Question 40

The sensation of rectal distention, as well as the voluntary control of the external anal sphincter, is mediated by pathways within the spinal cord that lead to the ____

Answer 40

Cerebral cortex--> destruction of these pathways causes a loss of voluntary control of defecation

Question 41

___ contraction decreases the diameter of the segment ___ contraction decreases the length of the segment

Answer 41

Circular muscle Longitudinal

Question 42

This long reflex is generally stimulatory and increases motility, is secretomotor, and has vasodilatory activities

Answer 42

Vago-vagal reflex--> vagus carries both afferents (75%) and efferents (25%)

Question 43

This short reflex is generally inhibitory, involving only the ENS and completely independent of the ANS

Answer 43

Intestino-intestinal reflex --> Ileocecal sphincter acts by this reflex and Atropine has no effect on it

Question 44

___ reflex is when negative feedback from the duodenum will slow down the rate of gastric emptying

Answer 44

Enterogastric

Question 45

___ reflex is when gastric distention relaxes the ileocecal sphincter

Answer 45

Gastroileal (gastroenteric)

Question 46

Gastrocolic and gastroduodenal reflexes are when distention of the stomach/duodenum initiate mass movements and are transmitted by way of the ___ nervous system

Answer 46

Autonomic

Question 47

___ reflex initiates defecation and is caused by rectal distention

Answer 47

Rectosphincteric