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HUBS192 Lectures 1-38 > HUBS192 Lecture 24 - Gastrointestinal Physiology > Flashcards

HUBS192 Lecture 24 - Gastrointestinal Physiology Flashcards

1
Q

what are the functions of GI tract?

A
  • obtain nutrients required for growth and energy needs

- replace fluid and salts lost in urine & faeces, sweating and breathing

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2
Q

what is mechanical digestion?

A

when food is broken into smaller parts

-mostly occurs in the stomach rather than the mouth

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3
Q

what is the basic principle of the function of the regulation of the GI system?

A

to regulate conditions in the intestinal lumen by receptors in the wall of the GI tract

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4
Q

what 2 changes do the receptors in the wall of the GI tract respond to?

A

1) stretch of the stomach caused by food in the lumen

2) change in composition by pH, osmolarity, amino acids, sugars and fats

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5
Q

what are the effectors of the receptors in wall of the GI tract?

A

smooth muscle and glands

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6
Q

what are the reflexes stimulated by the receptors in the wall of the GI tract?

A
  • smooth muscle contraction

- gland secretion

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7
Q

what are the effectors of GI tract regulated by?

A

regulated by nervous and hormonal regulation

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8
Q

what stimulates motility and secretion within the GI tract?

A

the parasympathetic nervous system

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9
Q

what inhibits motility and secretion within the GI tract?

A

the sympathetic nervous system

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10
Q

what are the 2 functions of the central nervous system associated with the GI tract?

A

1) co-ordinates activity over long distances

2) modulates the activity of enteric nervous system

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11
Q

does the central nervous system directly innervate the GI system?

A

no it only modulates the activity of the enteric nervous system which directly innervates the GI system smooth muscle and glands

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12
Q

what 2 components make up the enteric nervous system?

A

1) submucosal plexus

2) myenteric plexus

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13
Q

what is the function of the submucosal plexus?

A

regulates secretion through the epithelium layer of the small and large intestine and the stomach

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14
Q

what is the function of the myenteric plexus?

A

regulates motility by controlling the contraction or activity of the smooth muscle cells

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15
Q

what are the 2 characteristics of the enteric nervous system?

A

1) involved in the local reflexes of peristalsis and segmentation
2) is totally self contained

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16
Q

what is the largest endocrine organ in the body?

A

the GI tract

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17
Q

what are the 4 critical hormones secreted in the GI system?

A

1) gastrin
2) gastric inhibitory peptide (GIP)
3) secretin
4) cholecystokinin (CCK)

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18
Q

what are the 4 functions of motility within the GI tract?

A

1) movement at a controlled rate (rate that allows digestion and absorption to occur)
2) mechanical digestion
3) mixing
4) exposure to the absorptive surfaces

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19
Q

what are the motility patterns that allow movement at a controlled rate?

A
  • propulsion
  • storage
  • aids chemical digestion and absorption
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20
Q

what is the relationship between surface area and the rate of chemical digestion?

A

the greater the surface area the greater the rate of chemical digestion

21
Q

what is the function of mechanical digestion?

A

increases the surface area of food by breaking it down into smaller parts which is essential for chemical digestion

22
Q

what is the basis of the GI motility?

A

smooth muscle

23
Q

what the properties of the smooth muscle within the GI tract?

A
  • spontaneously active

- contracts without external input

24
Q

what is the strength of contraction regulated by?

A

by nervous and hormonal input

25
Q

what is the frequency of contraction of the stomach?

A

3 contractions per minute

26
Q

what is the frequency of contraction of the duodenum?

A

12 contractions per minute

27
Q

what is the frequency of contraction of the ileum?

A

9 contractions per minute

28
Q

what is the only motility pattern that occurs during fasting and describe this?

A

the migrating motor complex

  • occurs 4 hours after a meal
  • cycle of activity that repeats every 2 hours until, food is eaten again
29
Q

what is the only motility pattern that occurs during fasting and describe this?

A

the migrating motor complex

  • occurs 4 hours after a meal
  • cycle of activity that repeats every 2 hours until, food is eaten again
  • 1 hour inactivity
  • 50 minutes of uncoordinated activity
  • 10 minutes of coordinated activity
30
Q

what is the motility pattern that occurs during feeding that does not involve contraction?

A

the storage pattern

  • occurs in the stomach and colon
  • the relaxation of smooth muscles allows volume to increase without a change in pressure (lumen increases)
  • controlled by nervous regulation by the vagus nerve
31
Q

what are the 2 motility patterns that occurs during feeding that does involve contraction?

A

1) propulsion
- occurs in the oesophagus, stomach, small and large intestine
- driven by peristalsis
2) mixing
a) occurs in the stomach
- driven by retropulsion
b) occurs in the small and large intestine
- driven by segmentation

32
Q

what is segmentation?

A

feature of the small and large intestine where there is alternate regions of contraction and relaxation which forces the food material together by collision (mixing it with the secretions)

33
Q

what is the function of chewing?

A
  • reduces the size of food
  • allows ingestion by reducing size
  • mixes food with saliva
34
Q

what is chewing controlled by?

A

controlled voluntarily by skeletal muscle that controls the reflex of strength, frequency and side of chewing

35
Q

what is swallowing?

A

the rapid transfer of material from mouth to stomach initiated voluntarily but proceeds involuntarirly

36
Q

what are the 4 functions of motility in the stomach and how do they carry out this function?

A

1) storage
- stored in the fundus and the body of the stomach
2) mechanical digestion
- involves muscular contractions in the antrum
3) mixing
- antrum
4) controlled delivery to the duodenum
- opening and closing of the pyloric sphincter

37
Q

what is the function of the fasting gastric motility pattern?

A

-house keeping of residual secretions and undigested material

38
Q

what is receptive relaxation of the storage motility pattern?

A

receptors which respond to stretch in lower oesophagus when food passes down the lower oesophagus the receptors are stimulated and then via the vagus nerve to the CNS and back down to the stomach allows the smooth muscles to relax to accomodate food

39
Q

what is gastric accomodation of the storage motility pattern?

A

receptors respond to stretch in the fondus and body of the stomach respond to the arrival of food because the muscles are being stretched, and the stretch receptors stimulate the vagus nerve via the CNS and back down to the stomach to allow for relaxation,

  • done by inhibiting the activity of the enteric nervous system
  • allows the volume of the stomach to increase without change in pressure
40
Q

what is the peristalsis motility pattern?

A
  • initiated on the greater curvature and spreads to antrum
  • 3 contractions per minute
  • first 60 minutes following meal is gentle activity (gentle ripping of the stomach walls)
  • 60 - 300 minutes more intense activity carries on until food material is processed
41
Q

what 2 motility patterns are involved with peristalsis?

A

1) propulsion
2) retropulsion
- combined with the pyloric sphincter that creates mechanical break down and mixing

42
Q

what is the relationship between rate and gastric emptying?

A

rate of gastric emptying matches the digestive capacity of the intestine

43
Q

how gastric emptying regulated?

A

regulated by feedback from the duodenum

44
Q

what are the factors that affect gastric emptying?

A
  • size of the meal (the larger the meal the faster the emptying)
  • composition of the meal: fluids deliver faster than solids, related to the role of stomach in digestion
  • fats slow gastric emptying (fats are difficult to digest)
45
Q

what are the 3 functions of small intestinal motility?

A

1) mixing with secretions from the pancreas, bilary system (liver/gallbladder) and intestine
2) controlled movement
3) exposure of products of digestion to absorptive surfaces

46
Q

what is the motility pattern of the small intestine between meals?

A

the migrating motor complex

47
Q

what is the motility pattern of the small intestine after a meal?

A

1) segmentation for mixing and exposure to absorptive surface (contributes to movement also)
2) limited peristalsis (in humans) for movement

48
Q

what is the primary function of the colon?

A

storage of faeces

49
Q

what are the 2 motility patterns of the colon?

A
  • large periods of inactivity
    1) segmentation
  • exposure to absorptive surfaces
  • absorption of fluid and salt from faeces
    2) mass movement
  • 1-2 times a day following meals
  • peristaltic wave that drives faeces into the rectum and initiates defection

HUBS192 Lectures 1-38 (38 decks)

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