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PA10315 > The GI physiology: Motility > Flashcards

The GI physiology: Motility Flashcards

1
Q

What is the scientific name for swallowing?

A

Deglutition.

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2
Q

What are the three stages of swallowing?

A

Oral, pharyngeal and oesophageal.

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3
Q

How is swallowing initiated?

A

When pressure receptors in the walls of the pharynx are stimulated by food or drink forced into the rear of the mouth by the tongue.
voluntary, oral step

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4
Q

What impulses are sent when pressure receptors are stimulated by food?

A

Afferent impulses to the swallowing centre located in the medulla oblongata of the hind brain.

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5
Q

What is the second impulse sent in the deglutition process?

A

The afferent impulse then causes efferent impulses to the muscles in the pharynx, oesophagus (for contraction) and respiratory muscles.

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6
Q

How is respiration inhibited during deglutition?

A

Impulses from swallowing centre.

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7
Q

How is food prevented from moving into the trachea?

A

Impulses from the swallowing centre close the glottis (area around the vocal cords and the space between them).

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8
Q

What does the epiglottis do?

A

It is forced down to cover the closed glottis to prevent food or liquid entering the trachea. ie aspiration

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9
Q

What surrounds the oesophagus, in terms of physiology?

A

The upper 1/3 of the oesophagus is surrounded by skeletal muscle and the lower 2/3 by smooth muscle.

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10
Q

How is food prevented from entering the nasal cavity?

A

The soft palate closes.

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11
Q

How is the ingress of air and reflux of acid into the oesophagus prevented when not swallowing?

A

The upper and lower sphincters close.

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12
Q

What happens to the sphincters when swallowing?

A

The upper remains closed and the lower remains open to allow food to enter the stomach.

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13
Q

How long does it take for a peristaltic wave to reach the stomach?

A

Approximately 9 seconds.

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14
Q

What is the role of the tongue in swallowing?

A

It pushes food back towards the pharynx.

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15
Q

What happens after swallowing has occurred?

A

The epiglottis will raise so that breathing can occur again.

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16
Q

What is the swallowing reflex controlled by?

A

It is initiated voluntarily and is controlled by the brain stem.

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17
Q

What is the pharyngeal reflex?

A

This is the gag reflex that occurs due to distension.

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18
Q

What is unusual about the upper part of the GI tract?

A

It is the only part of the GI tract is where there is some skeletal, striated muscle.

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19
Q

What are the two methods that mix the contents of the stomach?

A

Peristalsis within the walls of the stomach but muscular contractions within the body of the stomach.

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20
Q

What causes backwards movement of food in the stomach?

A

Retropulsion.

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21
Q

Why do these methods of mixing need to occur?

A

To break food into manageable sizes.

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22
Q

Why does liquid leave the stomach before solids?

A

Liquids are not a challenge to the small intestine whereas there is a threshold for the size of food that can enter the smll intestine.

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23
Q

How is the basic rhythm of the stomach maintained?

A

Pacemaker cells in the longitudinal smooth muscle layer of the stomach wall.

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24
Q

What is secondary peristalsis?

A

When a large food piece does not reach the stomach the maintained distension of the oesophagus activates receptors to cause more peristaltic activity.

25
Q

What is the first step of mixing and movement in the small intestine?

A

Contraction of the circular muscles behind the food piece.

26
Q

What is the second step of movement and mixing in the small intestine?

A

Contraction of the longitudinal muscles ahead of the food mass.

27
Q

What is the third step of movement and mixing in the small intestine?

A

Contraction of circular muscle layer forces the food mass forward.

28
Q

What do these muscle contractions result in?

A

The chyme is moved backwards and forwards to achieve mixing.

29
Q

What initiates these movements in the small intestine?

A

Pacemaker cells (interstitial cells of Cajal) in the circular smooth muscle.

30
Q

How does the rhythm vary along the small intestine?

A

In the duodenum it is greater than in the ileum, producing a slow migration of chyme towards the large intestine.

31
Q

What does orad mean?

A

The GI tract towards the mouth.

32
Q

What does aborad mean?

A

The GI tract towards the anus.

33
Q

What happens when sensory detect extension of the walls due to bulky food?

A

The sensory neurones synapse with an excitatory neurone that branches and sends a signal to an efferent nerve that sends a stimulus to a muscle to signal it to contract.

34
Q

What is the enteric nervous system?

A

It regulates what is going on through the GI tract.

35
Q

What controls the force of contraction?

A

It is influenced by hormones and ENS autonomic nerves.

36
Q

What is segmentation in the small intestine?

A

Rhythmic contractions that are simultaneous around food that ensures there is sufficient mixing an breaking down to increase the surface area for enzymes to act on.

37
Q

What is the migrating motility complex (MMC)?

A

The pattern of peristaltic activity that replaces segmentation in the post-absorptive state after a meal.
Propel undigested and liquified chyme into large intestine once absorption has occured

38
Q

What is the purpose of the MMC?

A

They flush undigested material and bacteria into the large intestine.

39
Q

How long does it take the waves from MMC to reach the large intestine?

A

2 hours.

40
Q

What causes stomach rumbling when hungry?

A

The waves from the migrating motility complex pattern.

41
Q

Where is faeces stored?

A

In haustra, small pouches (segments) in the large intestine.

42
Q

How is faeces moved towards the rectum?

A

Slow, rhythmic segmentation contractions of the circular smooth muscle every 30 minutes.

43
Q

What triggers defaecation?

A

The presence of faeces in the descending colon/rectum.

activates stretch receptors

44
Q

What does our health depend on?

A

The appropriate balance and mixture of microorganisms.

45
Q

What is a theory about the cause of depression?

A

Those with bad gut microorganisms (and/or number) may experience improved symptoms when their gut bacteria is improved.

46
Q

What experiment was done with mice and their faeces?

A

The removal of faecal matter from one mouth into another showed that symptoms of disease that the initial mouse had were passed to the second mouse.

47
Q

What is the basis of the defaecation reflex?

A

There is a contraction of the rectum and the relaxation of the internal anal sphincters, but contraction of of the external anal sphincter. There is increased motility in the sigmoid colon.

48
Q

What is the specific reflex that allows the faeces to be expelled after the initial stages of the reflex?

A

A pressure is reached in the rectum that triggers reflex relaxation of the external anal sphincter which allows the faees to be expelled.

49
Q

How can the defaecation reflex be overrided?

A

Descending pathways to somatic nerves to the external anal sphincter can override the signals that would relax the sphincter. This keeps the external sphincter closed and defaecation can be delayed.

50
Q

What happens to the faeces when conscious thought has overrided the defaecation reflex?

A

The distension of the rectum initiates a reverse movement that drives the rectal contents back into the sigmoid colon and the urge to defaecate is stopped until the next mass movement forces faeces into the rectum to increase its volume.

51
Q

How can the ability of voluntary anal sphincter control be lost?

A

Spinal cord damage.

52
Q

What is the difference between the internal anal sphincter and the external anal sphincter?

A

The internal is composed of smooth muscle whereas the external is composed of skeletal muscle and is under voluntary control.

53
Q

How is the defaecation reflex initiated?

A

The distension of the walls of the rectum due to the mass movement of faecal matter.

54
Q

What is accompanied by the distension of the rectum?

A

The urge to defaecate, mediated by mechanoreceptors due to the distension of the rectum.

55
Q

3 steps of swallowing

A

oral (voluntary)
pharyngeal (involuntary)
oesophogeal (involuntary)

56
Q

defaecation reflex detailed

A

an autonomic nervous system reflex where sensory impulses are sent to the control centre in the spinal cord
Parasympathetic impulses stimulate logitudinal contractions of the rectum, forcing faeces into the anal canal
Relaxation of internal anal sphincter allows faeces to move towards the external one
Voluntary relaxation of external anal sphincter- defaecation completed

57
Q

how is food stopped from going into nasal cavity

A

soft palate elevates

58
Q

what is the force of contraction in the stomach determined by

A

when food arrives how much it stretches the stomach, detected by mechanoreceptors

59
Q

what are digestive movements in the stomach stimulated by

A

parasympathetic nervous system

PA10315 (47 decks)

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