Gastrointestinal Motility

GASTROINTESTINAL MOTILITY

Q. 1

Which of the following is related with ‘gastrocolic reflex’?

 A

Mass peristalsis

 B

Segmental movement

 C

Pendular movement

 D

Colonic disorder

Q. 1

Which of the following is related with ‘gastrocolic reflex’?

 A

Mass peristalsis

 B

Segmental movement

 C

Pendular movement

 D

Colonic disorder

Ans. A

Explanation:

Gastrocolic reflex is a long reflex arc that is initiated by gastric distension. The reflex produces a generalized increase in colonic motility (peristalsis) with mass movement of feces. Mechano- and chemo sensitive components of the gastrocolic reflex are present, and 5-HT and ACh appear to be important mediators of the response. The function of this reflex is to clear the colon to ready it to receive the residues of the new meal. 

Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 27. Gastrointestinal Motility. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong’s Review of Medical Physiology, 24e.


Q. 2

‘Gastrocolic reflex’ is related with?

 A

GERD

 B

Mass peristalsis

 C

Duodenual reflex

 D

Rectoanal refelx

Q. 2

‘Gastrocolic reflex’ is related with?

 A

GERD

 B

Mass peristalsis

 C

Duodenual reflex

 D

Rectoanal refelx

Ans. B

Explanation:

Mass peristalsis

Gastrocolic reflex:

  • Facilitates appearance of mass movements after a meal.
    • Ex., For gastrocolic reflex –
    • Seen in early infancy.

Q. 3

Which cells are referred as “Pacemaker cells” with relation to ‘BER’?

 A

SA node 

 B

AV node

 C

Interstitial cells of Cajal.

 D

Pyramidal cells

Q. 3

Which cells are referred as “Pacemaker cells” with relation to ‘BER’?

 A

SA node 

 B

AV node

 C

Interstitial cells of Cajal.

 D

Pyramidal cells

Ans. C

Explanation:

Interstitial cells of Cajal.

Basic Electrical Rhythm (BER):

  • Smooth muscle cells of the gastrointestinal tract have spontaneous rhythmic fluctuations in membrane potential between about -65 and -45 mV.
  • BER initiated by Pacemaker cells called “Interstitial cells of Cajal”.

Pacemaker cells –

  • Interstitial cells of Cajal.
  • Stellate mesenchymal cells with smooth muscle-like features.
Location:
  • Are absent in esophagus & proximal stomach.
  • In distal stomach & small intestine – Located in outer circular muscle layer near myenteric plexus.
  • In colon – Located at the submucosal border of circular muscle layer.
Frequency:
  • In Stomach & small intestine –
  • Pacemaker frequency is in descending gradient.
  • Pacemaker with the highest frequency usually dominates (Eg., In Heart).

Q. 4

What is the rate of BER in the stomach?

 A

 About 1.5/min in the stomach.

 B

 About 15/min in the stomach.

 C

 About 4/min in the stomach.

 D

 About 0.4/min in the stomach.

Q. 4

What is the rate of BER in the stomach?

 A

 About 1.5/min in the stomach.

 B

 About 15/min in the stomach.

 C

 About 4/min in the stomach.

 D

 About 0.4/min in the stomach.

Ans. C

Explanation:

About 4/min in the stomach.

Basic Electrical Rhythm (BER):

  • Smooth muscle cells of the gastrointestinal tract have spontaneous rhythmic fluctuations in membrane potential between about -65 and -45 mV.
  • BER initiated by Pacemaker cells called “Interstitial cells of Cajal”.

Events:

  • During these cyclic fluctuations, if resting membrane potential crosses the threshold for excitation, an action potential or a burst of action potential may develop.
  • Hence, BER itself does not cause muscle contraction
  • But when spike potentials (action potentials) superimposed on most depolarizing portions of BER, muscle contraction occurs.
  • Tone of contraction depends on,
    • The frequency of stimulus rather than amplitude.
Metrics:
  • The threshold for the action potential is -50 mV.
  • The rate of BER:
    • About 4/min in the stomach.
    • About 12/min in duodenum 
    • About 8/min – distal ileum (falls down)
  • In Colon:
  • Rate rises from about 2/min at Cecum ———–> about 6 min at the Sigmoid colon.


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