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MD3002 - GI Physiology > Overview of GI Physiology > Flashcards

Overview of GI Physiology Flashcards

1
Q

What organ of the digestive tract is responsible for passage of food?

A

oesophagus

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2
Q

What organ of the digestive tract is responsible for temporary storage of food

A

stomach

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3
Q

What organ of the digestive tract is responsible for digestion and absorption

A

small intestine

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4
Q

What does the alimentary tract provide the body with a continoual supply of?

A
  • water
  • electrolytes
  • vitamins
  • nutrients
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5
Q

What are the 5 main functions of the digestive tract?

A
  1. Movement of food through the alimentary tract
  2. secretion of digestive juices and digestion of food
  3. absoprtion of water, various electrolytes, vitamins and digestive products
  4. Circulation of blood through the GI organs to carry away the absorbed substances
  5. Control all these functions by local, nervous and hormonal systems
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6
Q

Mucosa =

A

epithelium + lamina propria + muscularis mucosa

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7
Q

Describe the features of the epithelium in the mucosa

A
  • single cell layer forming continous lining of GI tract
  • shed and replaced every 2-3 days
  • apical side faces GI lumen; basolateral side faces interstitium and vasculature
  • extent of villi and crypts vary with GI secretion function e.g. absoptive vs motility
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8
Q

Describe the features of the lamina propria

A
  • Loose CT made up of elastin and collagen fibres
  • contain sensory nerves, blood and lymph vessels, secretory glands
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9
Q

Describe the the muscularis mucosa

A
  • thin layer of smooth muscle
  • increases SA by creating ridges and folds
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10
Q

Describe the submucosa

A
  • thicker layer with similar composition to lamina propria
  • incorporates blood vessels and nerve bundles that form a submucosal plexus (Meisnner plexus) - integral part of enteric nervous system
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11
Q

Muscularis externa =

A

circular muscle + myenteric plexus + longitudnal plexus (Auerbach plexus)

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12
Q

Describe the muscularis externa

A
  • muscle layers named based on orientation
  • ENS co-ordinates contractions to mix and move contents between compartments
  • Sphincters regulate flow from one compartment to the next
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13
Q

Describe the serosa

A
  • Outermost later of CT and squamous epithelial cells
  • some GI tract secretions do not have a serosal layer (e.g. oesophagus), but connect directly with the adventitia (CT that blends into the abdominal or pelvic wall
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14
Q

Give the layers of the GI wall in a typical cross section from the outer surface

A
  • serosa
  • longitudnal smooth muscle layer
  • circular smooth muscle layer
  • mucosa

AND

  • sparse bundles of smooth muscle fibres lie in deeper layers of muscoas
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15
Q

Describe how a syncytium is generated in GI smooth muscle

A
  • fibres connected via gap junctions
  • CT partly separates each bundle but at many points bundles fuse forming a branching network
  • Syncytium is created in each muscle layer (AP is evoked = it travels in all directions)
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16
Q

Give the length and breadth of a typical GI smooth muscle

A
  • 200-500μm long
  • 2-10μm diameter
  • in bundles of up to 1000 parallel fibres
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17
Q

What is GI smooth muscle excited by?

A

almost continual slow, intrinsic electrical activity

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18
Q

What are the two basic types of electrical waves in GI SM?

A
  • slow waves
  • spikes
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19
Q

How can the voltage of the resting membrane potential change?

A

change to different levels

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20
Q

What determines the rhythmical GI contractions?

A

slow waves

  • are not APS; are slow undulating changes in resting membrane potential
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21
Q

Between what values does the intensity of slow waves vary?

A

5 and 15mV

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22
Q

What is the range of frequency of slow waves?

A

3-12 per minute

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23
Q

Where are slow waves the fastest?

A

small intestine and duodenum

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24
Q

Are spike potentials true action potentials?

A

Yes

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25
Q

When do spike potentials occurs?

A

when resting membrane potential >~40mV

26
Q

What causes a greater frequency of spike potentials?

A

higher increase in slow wave potential

27
Q

How long does each spike potential last?

A

10-20ms

10-40x as long as APs in large nerve fibres

28
Q

What can spike potentials be stimulated by?

A
  • stretch
  • acetylcholine
  • parasympathetics
29
Q

Draw a diagram showing the changes in voltage of the resting potential of GI smooth muscle

A
30
Q

What is hyperpolarisation of GI smooth muscle stimulated by?

A
  • Noradrenaline
  • Sympathetics
31
Q

What is the neural control of GI function?

A

enteric mervous system

32
Q

Where is the enteric nervous system located?

A

in wall of gut from oesphagus to anus

important role in GI movements and secretion

33
Q

What are the main features of the myenteric plexus

A
  • linear chain of interconnecting neurons extending the entire length of the GI tract
  • controls muscle activity
  • some neurons are inhibitory;s ecrete an inhibitory transmitter (VIP)
34
Q

What are the main effectd og the myenteric plexus when stimulated?

A
  • increased tonic contraction/”tone” of gut wall
  • increased intensity of rhythmical contractions
  • slightly increased rhythm of contraction
  • increased velocity of conduction of excitatory waves along the gut wall, causing more rapid movement of the gut peristaltic waves
35
Q

What are the main features of the submucosal plexus?

A

mainly controls function within small segments of the intestine

**control local intertisital secretion, absoprtion and contractions of submucosal muscle that causing infolding of GI mucosa

36
Q

Effects of PSNS on control of GI Tract

A
  • increase activity of enteric NS
  • almost all fibres are in the vagus nerve
37
Q

Effects of SNS on the GI Tract

A
  • Inhibits GI tract activity
  • almost all fibres originate between T5 and T12
38
Q

What are the possible locations of afferent sensory nerve fibres of the gut

A
  • cell bodies in the ENS
  • dorsal root ganglia of the spinal cord
39
Q

What can sensory nerves be stimulated by?

A
  • irritation of the gut mucosa
  • excessive distention of the gut
  • presence of specific chemical substances in the gut
40
Q

What are the 3 types of gastrointestinal reflex?

A
  • Reflexes integrated within the enteric nervous system
  • Reflexes from the GI tract to prevertebral sympathetic ganglia and then back to the GI tract
  • Reflexes from the GI tract to the brain stem or spinal cord and then back to the GI tract
41
Q

Describe :

Reflexes integrated within the enteric nervous system

A

Reflexes controlling secretion, peristalsis, mixing, local inhibitory actions

42
Q

Describe :

Reflexes from the GI tract to prevertebral sympathetic ganglia and then back to the GI tract

A

Reflexes that transmit signals to other areas of the GI tract – gastrocolic reflex (stomach – colon); enterogastric reflexes ( stomach and colon inhibiting gastric motility) ; colonoileal reflexes (inhibition of ileal emptying)

43
Q

Describe:

Reflexes from the GI tract to the brain stem or spinal cord and then back to the GI tract

A
  1. Reflexes from stomach and duodenum to brain stem and back to stomach to control gastric motor and secretory activity
  2. Pain reflexes causing general inhibition of entire GI tract
  3. Defecation reflexes from the colon and rectum that travel via the spinal cord back to produce powerful colonic, rectal and abdominal contractions
44
Q

What is the stimuli for the secretion of:

Gastrin

A
  • protein
  • distention
  • Nerve
  • (acid inhibits release)
45
Q

What is the stimuli for the secretion of:

Cholecytokinin

A
  • Protein
  • Acid
  • Fat
46
Q

What is the stimuli for the secretion of:

Secretin

A
  • Acid
  • Fat
47
Q

What is the stimuli for the secretion of:

Gastric (inhibitory and peptide)

A
  • protein
  • fat
  • carbohydrate
48
Q

What is the stimuli for the secretion of:

Motilin

A
  • Fat
  • Acid
  • Nerve
49
Q

What is the site of secretion of:

Gastrin

A

G cells of the antrum, duodenum and jejunum

50
Q

What is the site of secretion of:

Cholecystokinin

A

I cells of the duodenum, jejunum and ileum

51
Q

What is the site of secretion of:

secretin

A

S cells of the duodenum, jejunum and ileum

52
Q

What is the site of secretion of:

Gastric (inhibitory and peptide)

A

K cells of the duodenum and jejunum

53
Q

What is the site of secretion of:

Motilin

A

M cells of the duodenum and jejunum

54
Q

What is the action of:

Gastrin

A

Stimulates

  • Gastric acid secretion
  • Mucosal growth
55
Q

What is the action of:

Cholecystokinin

A

Stimulates

  • Pancreatic enzyme secretion
  • Pancreatic bicarbonate secretion
  • Gallbladder contraction
  • Growth of exocrine pancreas

Inhibits

  • Gastric emptying
56
Q

What is the action of secretin

A

Stimulates

  • Pepsin secretion
  • Pancreatic bicarbonate secretion
  • Biliary bicarbonate secretion
  • Growth of exocrine pancreas

Inhibits

  • Gastric acid secretion
57
Q

What is the action of gastric (inhibitory and peptide)

A

Stimulates

  • Insulin release

Inhibits

  • Gastric and secretion
58
Q

What is the action of motilin?

A

Stimulates

  • Gastric motility
  • Intestinal motility
59
Q

What are the functional movements of the GI tract?

A
  1. propulsive movements - peristalsis
  2. mixing movements
60
Q

What is an increase in blood flow to the GI tract likely to be caused by?

A
  • vasodilators released from GI mucosa (CCK<vip>
    </vip><li>from GI glands - bradykinin</li><li>via decreased oxygen conc in gut wall due to increased metabolism</li><li>adenosine release</li>

</vip>

MD3002 - GI Physiology (4 decks)

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