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Gastrointestinal - Physiology > Rao 3 - GI Motility > Flashcards

Rao 3 - GI Motility Flashcards

1
Q

ALL of the GI tract is ___________ muscle except:

A

All of the GI tract is SMOOTH muscle EXCEPT the pharynx, upper 1/3 of the esophagus and external anal sphincter

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2
Q

What method is used by smooth muscle to mediate coordinated contractions in GI motility?

A
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3
Q

How does the actin:myosin ratio differ between smooth and striated muscle?

A

Smooth Muscle has actin myosin ratio of 12-18:1 compared to 2:1 for straited muscle

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4
Q

Differentiate Phasic and Tonic Contractions.

A
  • *Phasic Contractions** are periodic contractions followed by relaxation.
  • *Tonic Contractions** maintain a constant level of contraction or tone without and regular periods of relaxation
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5
Q

Tonic Contractions
• Where do we see these occurring?
• When are they important?

A

These occur in:
• Upper Region of the Stomach
• Lower Esophageal, Ileocecal, and Internal Anal Sphincter

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6
Q

What determines the frequency of slow waves?
• What determines the amplitude and duration?

A

Frequency of Slow waves is predetermined by the Cajal Cells in the underlying Myenteric Plexus (these are pacemaker cells like SA nodal cells)

Amplitude and Duration is determined by Neural and Hormonal Stimuli

**Note that more action potentials and longer action potentials lead to a more forceful contraction with greater duration**

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7
Q

What are the two different types of Cajal Cells?
• how do they communicate with other cells and each other?

A

Communicate their signal to smooth muscle cells via Gap Junctions

2 types:
• Myenteric - Form network of ICC’s connect by gap junctions => THESE are responsible for SLOW WAVES

• Intramuscular ICC’s are activated by neurotransmitter released from varicosities

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8
Q

When does GI smooth muscle contraction ocur relative to APs?
• When is the only time that APs will trigger contraction?

A

Only at the Apex of a slow wave can a Spike Potential trigger muscle contraction right AFTER the sequence of spike potentials fire

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9
Q

T or F: even if action potential threshold is not met, a tonic contraction can occur.

A

True

**Phasic contractions ONLY occur when AP threshold is met

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10
Q

What is the role of the following proteins/ions in smooth muscle contraction:
• Calcium
• Calmodulin
• Myosin
• Myosin Light Chain Kinase (MLCK)
• Actin

A
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11
Q

What are the major and minor sources of Calcium in Smooth Muscle Contraction?

A

MAJOR:
• Extracellular Calcium is the major source that can influx after changes in electrical stimulation of the cell occur that lead to changes in voltage gated calcium channels leading to Ca influx

MINOR:
• Sarcoplasmic Reticulum (not as developed as skeletal muscle)

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12
Q

What are the 3 important functions of chewing?

A
  1. Lubrication - mixes food with Saliva
  2. Facilitates Swallowing - Reduces Particle Size
  3. Carbohydrate Digestion - Mixes Carbs with Amylase
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13
Q

What is involved in the oral phase of swallowing?
• Voluntary or Involuntary?

A

ONLY voluntary phase of swallowing
• Bolus of food is pushed back in the mouth until it touches somatosensory receptors that initiate an involuntary swallowing reflex in the medulla

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14
Q

T or F: swallowing in upper pharynx is voluntary and involuntary in the lower pharynx and esophagus

A

True

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15
Q

What are the 4 steps in the pharyngeal phase of swallowing?

A
  1. Soft Palate pulled upward to Close the Nasopharynx by Flexing the Upper Sphincter
  2. Epiglottis moves DOWNWARD to cover the larynx
  3. Upper Esophageal Sphincter Relaxes to allow food to pass from pharynx to esophagus and middle and lower constrictors contract
  4. Peristaltic contractions initiate in the pharynx and propel food through open sphincter to the esophagus
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16
Q

What aspects of the nervous system are involved in the pharyngeal phase of swallowing?
• What nerves are parts of the brain are involved?

A

BOTH PNS and CNS are involved in the pharyngeal Phase:
1. Somatosensory and Chemosensory receptors sent information up afferent nerves to the Nucleus Ambiguus in the Brainstem

  1. Impulses are sent via the Vagus n.
  2. Impulses travel along vagus n. and initiate muscle movement sequentially from the top down
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17
Q

What are the 2 aspects of Innervation in the Esophageal Phase of swallowing?

A
  1. Somatic - Nerves Directly Synapse with the Muscle
  2. Visceral - must synapse with enteric nn. 1st that can then synapse with the muscle
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18
Q

What are the 3 steps of the esophageal phase of Swallowing?

A
  1. Closure of Upper Esophageal Sphincter
  2. Primary Perstaltic Wave pushes food along
  3. Secondary Perstaltic Wave is intitiated by continued distention of the esophagus
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19
Q

How does the muscle change as you progress from the top of the esophagus downward?

A

Upper 1/3 - Striated Muscle
Middle 1/3 - Mixed
Lower 1/3 - Smooth Muscle

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20
Q

Describe what is happening on Side A of the graph.

A

A - resting state of the esophagus
• Show High pressure in the upper and lower esophageal spincters with Lower pressure between the two sphincters (2-5)

B - Swallowing
1. Upper Esophageal Spincter relaxes to allow bolus entry
2-5. Peristaltic contractions move food down epiglottis
6. Lower esophageal sphincter opens

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21
Q

What are 3 causes of GERD?

A
  1. Hiatal Hernia
  2. Pregnancy
  3. Failure of Seconary Perstalsis
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22
Q

What happens if the pirmary perstaltic contraction does clear the food from the esophagus, wheat happens?

A

Secondary Peistaltic Contraction then occurs

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23
Q

What are the 3 important aspects of Gastric Motility?

A
  1. Relaxation of Orad (Receptive Relaxation)
  2. Contraction (Mixing and Digestion) - caudad region
  3. Gastric Emptying
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24
Q

What is Receptive Relaxation of the stomach?
• What part of the stomach is involved?
• What neuroendocrine mediators work at this?

A

This stage involves the ORAD of the stomach

Esophageal Sphincter opens the oral motility is needed to allow food into the esophagus

VIP mediated the relaxation via a VASOVAGAL REFLEX (afferent fibers detect distention and efferent fibers cause relaxation)

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25
Q

What are the Steps in the 2nd Part of Gastric Motility?
• what part of the stomach is involved?

A

Caudad is Needed for Mixing and Pushing Food into the Small Intestine

A. Contractions Start in the Middle then move out across the Caudad of the stomach and increase in Velocity and Amplitude as they near the pylorus. The Pyloric sphincter is closed by contraction and food is propelled back into the stomach = RETROPULSION

26
Q

What type of contraction causes Mixing and Digestion in the Stomach?

A

Phasic Contractions

Note: Slow waves in the stomach are not like those in the small intestine b/c they CAN cause contraction in the stomach

27
Q

What are the parasympathetic mediators that increase the force of contraction in the stomach?

A

Ach and Gastrin increase the forces of contraction

28
Q

What are the sympathetic mediators that decrease the force of contraction in the stomach and lead to trapping of food in the stomach?

A

• NE, GIP, Secretin all decrease gastric emptying

29
Q

What happens to stomach contractions in the fasting state?

A

Migrating Myoelectric Complexes start happening that Push anything that’s left in the stomach into the small intestine

This is process is mediated by Motlilin that causes contraction every 90 minutes via a BURST of Peristalsis

30
Q

What are some processes that may result in Failure to Empty to the Colon?
• what are some symptoms

A

Symptoms:
• Fullness, Loss of Appetite, Nausea

Processes:
• Obstruction - ulcer or cancer
• Vagotomy

31
Q

What are some processes that result in accelerated gastric emptying?
• Symptoms?

A

Causes:
• Inadequate Regulation

Symptoms:
• Diarrhea, Duodenal Ulcer

32
Q

T or F: liquids are eliminated from the stomach at the same rate as solid

A

False, liquids are eliminated faster

33
Q

T or F: An isotonic solution is elminated faster from the stomach than a Hyper/Hypotonic solution

A

True

34
Q

What are the two main factors that change gastric emptying time?

A

Fat
• Causes release of CCK an is released when fat gets to the duodenum (I-cells)
• Slowing down gastric emptying increases the ability to absorb fat

Acid
• H+ sensors in the stomach slow down emptying so that HCO3- is present in adequate amounts in the small intestine to neurtalize the acid

35
Q

T or F: contraction in the small intestine is local.

A

True, only one part constricts at once

36
Q

Are PHASIC contractions in the small intestine become more uniformly distributed in the fed or fasting state?

A

Contractions are more uniformly distributed in the Fed State (because there are no MMC’s? or because there is constantly an AP that will cause contractions at the peak of the slow waves?)

37
Q

What controls the rate of peristalsis in the small intestine?
• what accounts for the irregularities in contraction that we see?

A

Cajal Cells control the rate of contraction and keep the slow waves going at a rate of 12/min (or once every 5 seconds)

Action Potentials are not always triggered every 5 seconds so the rate can also occur at an interval of 5 (e.g. 10, 15, 30 seconds)

38
Q

What is a migrating myoelectric complex?
• what mediates this events?

A

Motilin mediates Migrating Myoelectic Complexes that occur every 90 minutes in a sweeping motion to empty the contents of the small intestine

39
Q

What are the two types of contractions that you can see in the small intestine?

A
  1. Segmentation Contraction - no forward movement, this just presses down on the food to mix it and expose it to pancreatic enzymes
  2. Peristaltic Contraction - propulsion of food foward
40
Q

What steps are involved in peristaltic contraction of the small intestine (including neurotransmitters etc.)?

A

Enterochromaffin-like Cells Sense Food => 5-HT Released => IPANs Activated => Peristaltic Reflex activated =>

Behind Bolus:
• Excitatory Neurotransmitters like Ach, Substance P, and NPY are released into the circular muscle
• Longitudinal muscle is relaxed

In Front of Bolus:
• Relaxation of Circular Muscle with NO and VIP to Widen the bowel
• Longitudinal Muscle Flexes to Shorten the Bowel

*5-HT = 5-hydroytryptamine
* IPAN = Intrinsic Primary Afferent Neuron

41
Q
A
42
Q

What are 4 ways in which vomitting can be triggered?

A
  1. Information from the Vestibular n.
  2. Base of Throat
  3. GI Tract
  4. Chemoreceptors in the 4th Ventricle
43
Q

What are the steps involved in Vomitting?

A

Reverse Peristalsis (sm. intestin) => Relaxed Stomach Pylorus => Inspiration to increase intraabdominal pressure => Larynx moves up and forward => Lower Esophageal Sphincter is relaxed => Glottis Closes => Forceful Expulsion

44
Q

What is Retching?

A

Same as Vomitting, but the upper esophageal sphincter doesn’t open

45
Q

What are the physiologic outcomes of intense vomitting?

A

Metabolic Alkalosis and Hypokalemia

46
Q

What Stimuli control the action of the ileocecal sphincter?

A

Distention from food in the ileum leads to IC valve OPENING
Distention from food in the Cecum leads to IC valve CLOSING

47
Q

What creates the haustra in the Colon?

A

Contraction of the Circularis Muscles

48
Q

What is the name of the longitudinal muscle in the colon and how is it arranged?

A

Longitudinal Muscle => Contracted into 4 bands called Teniae Coli

49
Q

Where in the colon does water absorption occur?

A

Distal Colon

50
Q

What is the Gastrocolic Reflex?
• is this a short or long arc reflex?

A

Gastrocolic Reflex:
• Stomach Distention increases Motility in the Large Intestine
• Efferent Limb is mediated by CCK and Gastrin

51
Q

The colon is still controlled by BOTH the ENS and ANS. What nerves supply parasympathetic innervation to the colon?

A

Vagus n.
• Cecum, Ascending Colon, Transverse Colon

Pelvic n.
• Descending Colon, Sigmoid Colon, Rectum

52
Q

In what part of the Colon do Mass Movements occur?
• what process is analogous to mass movement?
• what happens to haustrations in this time?

A

Mass Movements occur in the Ascending colon and cause LOSS of haustrations. These occur 1-3x per day similar to MMC’s but are much less frequent.

53
Q

Where do segmental contractions occur in the colon?
• where are these most intense?
• what about organized segmentation contractions?

A

Segmentation Contractions occur throughout the colon but are more frequent in the descending colon.

ORGANIZED segmentation is ONLY in the Ascending colon

54
Q

Where does mass movement happen in the colon?

A

This happens throughout the colon

55
Q

What is the rectosphincteric Reflex?

A

Smooth muscle contracts and internal anal sphincter relaxes in response to distention in the rectum

56
Q

Describe what is happening in this graph.

A
  1. Rectum gets passively distended until enough stool is present and the rectum contracts
  2. Internal Sphincter Relaxes in Response to the Pressure (Rectosphincteric Reflex)
  3. External Sphincter contracts to counteract the contractio nof the Rectum and Relaxation of the Internal Sphincter
  4. When Voluntary Defecation occurs the external sphincter is Conciously Relaxed
57
Q

NOTE:
• Ray Refers to Segmental Contractions as Long and Short in Megacolon lecture

I think Short Segmental = Roa’s Segmental and Long Segmental = Rao’s Organized Segmental

  • *Short Segmental** = Less than 15 seconds for mixing and H2O extraction
  • *Long Segmental** = Mixing + Propulsion distally
A
58
Q

T or F: Mass Movements may be precipitated by Colonic Distention

A

True, colonic distention may cause mass movments

59
Q

T or F: in the Gastrocolic Reflex the amount of contraction is proportional to the fat content of the meal only.

A

FALSE, the gastrocolic reflex is PROPORTIONAL THE THE CALORIC INTAKE in the meal

60
Q

What 4 hormones are key in Colonic Motility?
• What do they do?

A
  1. CCK - increases the frequency and amplitude of contractions
  2. PGF - stimulates LONGITUDINAL muscle contraction
  3. PGE - INHIBITS circular muscle contraction
  4. Serotonin - increases peristalsis and secretion in the GI tract and MODULATES PAIN preception
61
Q

Where is serotonin produced in the GI tract?
• How much of the total body serotonin is found in the GI tract?

A

Serotonin is released from Enterochromaffin cells and 80% is localized to the GI tract

62
Q

What is the use of 5-HT3 antagonists?
• 5-HT4 agonists?

A

5-HT3 antagonists - decrease pain in IBS and Functional Dyspepsis
5-HT4 Agonists - Prokinetic Effect

Gastrointestinal - Physiology (8 decks)

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