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Physiology > Lecture 29 - GI Motility > Flashcards

Lecture 29 - GI Motility Flashcards

1
Q

How many layers of muscle tissue does the GI wall have? What are they called?

A

3 layers of smooth muscle.

  1. Muscularis mucosa (small layer in the mucosa)
  2. Circular smooth muscle
  3. Longitudinal smooth muscle
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2
Q

What is the function of the muscularis mucosa?

A

Movement of villi.

Submucosal muscles contract: villi
shorten; submucosal muscles relax:
villi lengthen.

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3
Q

Muscle fibers in
the circular muscle
layer are oriented
_____, whereas
muscle fibers in
the longitudinal muscle
layer are oriented _____.

A

Muscle fibers in the circular muscle layer are oriented CIRCUMFERENTIALLY, whereas muscle fibers in the longitudinal muscle layer are oriented along the LONGITUDINAL AXIS OF THE TUBE.

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4
Q

How is food moved along the GI tract?

A

By the action of the muscle in its walls.

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5
Q

What is the function of sphincters?

A

To isolate one region from the next and provide selective retention of contents or prevent backflow, or both.

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6
Q

What are sphincters composed of?

A

Most sphincters consist of a greatly enlarged inner circular smooth muscle.

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7
Q

Is there any voluntary skeletal muscle in the GI tract?

A

Yes, at the pharynx and proximal esophagus (entire esophagus of ruminants and some other species) as well as the external anal sphincter.

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8
Q

What are the two types of contractions that the circular and longitudinal muscle layers conduct?

A
  1. Segmentation contraction
  2. Peristaltic wave
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9
Q

What is the function of segmental contractions?

A
  • Squeeze the food so it is continually mixed as it moves down the GI tract.
  • Facilitate contact between digestive enzymes and the ingesta through mixing and grinding action.
  • Moves material in the lumen along the mucosal cells that will absorb the nutrients.
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10
Q

What mediates segmental contraction?

A

Contraction and relaxation of the circular smooth muscle.

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11
Q

What is peristalsis?

A

Muscle contraction of the GI system that propels food down the tract.

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12
Q

What muscles are involved in peristalsis?

A

It is a coordinated contraction/relaxation pattern of the inner and outer muscle layers.

The inner and outer muscle layers behind the food bolus will contract and the muscles ahead of the bolus need to be relaxed.

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13
Q

What is a syncytium?

A

When one smooth muscle cell contracts, many others in the same area will also contract. This is possible in smooth muscle cells.

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14
Q

What mediates contraction as a syncytium?

A

Gap junctions between adjacent cells.

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15
Q

What are gap junctions?

A

Low‐resistance channels for ion movement between adjacent cells.

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16
Q

What are the gut pacemaker cells?

A

Interstitial cells of Cajal.

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17
Q

Which muscles of the GI tract do NOT undergo rhythmic depolarization?

A

Esophagus

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18
Q

How many times per minute do depolarization waves occur in the stomach?

A

16-20 times/min

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19
Q

How many times per minute do depolarization waves occur in the small intestine?

A

I don’t really know? just less than the stomach

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20
Q

How many times per minute do depolarization waves occur in the colon?

A

2-3 times/min

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21
Q

What is the resting membrane potential of Cajal cells?

A

-50 mV

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22
Q

What is the threshold potential of Cajal cells?

A

-35 mV

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23
Q

How does the membrane potential change during slow waves? What causes this change?

A

Changes from -50 mV (resting potential) to -40 mV. Due to leakage of sodium and calcium into the cell wall.

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24
Q

During slow waves, the leakiness of the membrane to sodium and calcium is …

A

short-lived.

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25
Q

The resting membrane potential of Cajal cells can be altered to become ___ which allows the slow wave to depolarize the cell to ___.

A

The resting membrane potential of Cajal cells can be altered to become -40 mV which allows the slow wave to depolarize the cell to -30 mV.

This is now above threshold!!

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26
Q

The greater the ______ stimulation, the longer the resting membrane potential remains ______ and the _____ action potentials that will be initiated during a slow wave of depolarization.

A

The greater the PARASYMPATHETIC stimulation, the longer the resting membrane potential remains CLOSE TO THRESHOLD and the MORE action potentials that will be initiated during a slow wave of depolarization.

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27
Q

More action potentials during a slow wave will result in …

A

stronger contraction strength for the smooth muscle cells within the syncytium.

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28
Q

Sympathetic nervous innervation can change the resting membrane potential of Cajal cells to about…

A

-60 mV

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29
Q

With sympathetic stimulation, slow wave depolarization increases the membrane potential to only …

A

–50 mV, well below the threshold and little muscle contraction will occur.

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30
Q

T or F: The interstitial cells of Cajal undergo rhythmic depolarization irrespective of their resting membrane potential.

A

True

31
Q

T or F: The pacemaker cells of the GI tract fire action potentials irrespective of their resting membrane potential.

A

False

32
Q

T or F: Smooth muscles in the GI wall contract irrespective of the resting membrane potential of Cajal cells.

A

False

33
Q

T or F: Smooth muscles in the GI wall only contract at the peak depolarized state of the resting membrane potential of Cajal cells.

A

False?????? I think

34
Q

Can skeletal muscle contract spontaneously?

A

No, they are under somatic control (voluntary).

35
Q

What is the function of the oral cavity?

A
  • Prehension of food
  • Mastication (chewing)
  • Swallowing (while preventing food from entering the airways)
36
Q

What is prehension?

A

The act of getting food into the mouth

37
Q

Most animals drink by…

A

drawing water into the oral cavity with suction.

38
Q

Dogs and cats drink by…

A

lapping water with the tongue.

39
Q

How do birds drink?

A

They fill their oral cavity with water then raise their beak which allows the water to drain into the pharynx.

40
Q

What is mastication?

A

The mechanical breakdown of food that allows mixing with saliva.

41
Q

What is the function of deglutition?

A

To deliver ingesta or fluid to the esophagus while keeping it out of the respiratory tract.

42
Q

Deglutition is a ______ reflex.

A

highly complex

43
Q

When not eating, the ____ is open and the soft palate is ____. The upper esophageal sphincter is kept ____.

A

When not eating, the GLOTTIS is open and the soft palate is DOWN. The upper esophageal sphincter is kept CLOSED.

44
Q

What are the steps of swallowing? (sorry this is a long one xoxoxo)

A
  1. The animal pushes the food to the back of the tongue (voluntary).
  2. This information is sent to the medulla (becomes involuntary).
  3. Respiration is inhibited by the medulla, reducing the danger of food inhalation.
  4. The soft palate is elevated dorsally to close the nasopharynx, preventing food from exiting via the nose.
  5. The glottis closes over the trachea. At this point the upper esophageal sphincter relaxes allowing the bolus to enter the esophagus.
45
Q

The presence of a bolus in the esophagus stimulates…

A

peristaltic contractions that move the bolus toward the stomach.

46
Q

How does the lower esophageal sphincter open?

A

It opens with a peristaltic wave at the same time as the stomach relaxes so food is not pushed back into the esophagus.

47
Q

The lower esophageal sphincter is normally in what position?

A

Tightly shut - prevents stomach contents and acid from entering the esophagus.

48
Q

What does stomach distention stimulate?

A
  1. ENS and vagal afferent
  2. ENS and vagal efferent
  3. Stomach muscle contraction
49
Q

How does the stomach contract?

A

It contracts as a peristaltic wave that propels ingesta towards the small intestine.

50
Q

What happens as the peristaltic wave reaches the end of the stomach?

A

The pyloric sphincter relaxes momentarily and a small amount of chyme enters the duodenum before the sphincter closes again.

51
Q

What happens when the pyloric sphincter shuts after letting some chyme through?

A

The more solid material in the stomach hits the pylorus and is shunted back, creating a churning motion that helps break down the solids.

52
Q

What increases gastric motility?

A
  • Increased stomach distension
  • Increased vagus nerve stimulation
53
Q

Increased gastrin in the stomach results from…

A

Increased stomach distension

54
Q

What decreases stomach motility?

A
  • An increase in duodenum distension
  • An increase in duodenal osmolarity
  • More fats and amino acids in the duodenum
  • Decreased pH in duodenum
55
Q

Duodenum distension or osmolarity results in…

A

Decreased vagal nerve stimulation.

56
Q

Fats and amino acids in duodenum increases…

A

Cholecystokinin (CCK, duodenum)

57
Q

A decreased pH in the duodenum increases…

A

Secretin in the duodenum.

58
Q

What do CCK and secretin act on?

A

The pyloric sphincter - causing it to constrict more which reduces chyme entering the duodenum.

59
Q

What is eructation?

A

Burping

59
Q

What is the process of eructation?

A

A peristaltic contraction leads to increased gas pressure which overcomes the lower esophageal sphincter and leads to air escaping into the esophagus.

At the same time, the animal consciously contracts its abdominal muscles which can force the escaped gas out of the mouth.

60
Q

What is the vomiting center?

A

A collection of nerve cells in the medulla that receive sensory information directly from the GI tract.

61
Q

What is the chemoreceptor trigger zone (vomiting)?

A

A second collection of neurons within the floor of the fourth ventricle that recognize blood‐borne chemicals or toxins.

62
Q

The vomiting center initiates widespread parasympathetic and sympathetic discharges, resulting in…

A

sweating, nausea, and salivation.

63
Q

Which animals are unable to vomit?

A
  • Rat
  • Rabbit
64
Q

Shortly after meals, what contractions predominate in the small intestine?

A

Segmental (mixing)

65
Q

What is the primary stimulus for small intestine contraction?

A

Distension of the small intestine.

66
Q

How is peristalsis of the small intestine mediated?

A

Short distances - ENS afferent and efferent neurons.

Long distances - Require coordination from parasympathetic fibers.

67
Q

What increases motility in the small intestine?

A
  • Increased stomach distension
  • Additional fats and amino acids in the duodenum
68
Q

What controls motility in the colon?

A

Both the ENS and ANS.

69
Q

What contractions occur in the large intestine?

A

Both segmental and peristaltic contractions.

70
Q

What is the defecation reflex?

A
  1. Sensory afferent fibers sense contact of feces with internal anal sphincter. Efferent fibers cause relaxation of the internal anal sphincter.
  2. The fecal matter now contacts the external anal sphincter composed of skeletal muscle. This information is conducted back to the spinal cord and brain by sensory afferent fibers.
  3. The animal will either consciously relax the external anal sphincter and defecate or make a conscious effort to tighten the external anal sphincter to delay defecation.
71
Q

What mediates the relaxation or contraction of the external anal sphincter?

A

Somatic motor neurons

72
Q

What structure allows the choice to halt the defecation reflex?

A

The external anal sphincter.

73
Q

What happens if an animal consciously tightens the external anal sphincter?

A
  • The animal can resist defecation during a rectal peristaltic wave.
  • The rectum relaxes and the internal anal sphincter regains normal tone until the next rectal peristaltic wave.
  • Eventually, the pressure within the rectum becomes greater than the animal can bear and defecation will ensue.

Physiology (52 decks)

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