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PHSL233 > Lecture 25 - GI Tract Regulation > Flashcards

Lecture 25 - GI Tract Regulation Flashcards

1
Q

What is the distance ENS regulation can occur over in the GI tract?

A

Very short (cm)

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2
Q

What is the distance CNS regulation can occur over in the GI tract?

A

Long distances
(Via the autonomic nervous system)

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3
Q

What distance can hormonal regulation occur over in the GI tract?

A

Long distances

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4
Q

What are the ENS regulation action sites in the GI tract?

A

Very local, generally only effectors within one organ?

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5
Q

What are the CNS regulation action sites in the GI tract?

A

Coordinates fast and complex actions involving several sites of action (e.g. swallowing)

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6
Q

What are the hormonal action sites in the GI tract?

A

Each hormone regulates more than one cell type in more than one organ

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7
Q

What is the speed and duration of ENS response in the GI tract?

A

Fast and short duration

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8
Q

What is the speed and duration of CNS response in the GI tract?

A

Fast and short duration

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9
Q

What is the speed and duration of hormonal response in the GI tract?

A

Slow and sustained

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10
Q

What are the stimuli for ENS response in the GI tract?

A

Intrinsic - chemo/ osmo /mechano receptors within the GI tract

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11
Q

What are the stimuli for CNS response in the GI tract?

A

Extrinsic - Special senses, emotional responses.
Long reflex pathway - receptors within the GI tract

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12
Q

What are the stimuli for hormonal response in the GI tract?

A

Stimuli include both the GI tract luminal content and external / extrinsic stimuli

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13
Q

Can the ENS act independently of other systems in the GI tract?

A

Yes – ENS is sometimes called the brain of the gut

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14
Q

Can the CNS act independently of other systems in the GI tract?

A

No, only ENS directly innervates GI tract structures so must act via the ENS

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15
Q

Can hormones act independently of other systems in the GI tract?

A

Yes – some hormones released from the GI tract in response to GI tract luminal conditions act on the GI tract.

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16
Q

What are the ENS control signals/signal molecules in the GI tract?

A

Neural / action potentials
Neurotransmitters:
- Ach - stimulates
- NOS- inhibits

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17
Q

What are the CNS control signals/signal molecules in the GI tract?

A

Neural / AP’s
Neurotransmitters:
Parasympathetic: Ach - stimulates
Sympathetic: adrenaline - inhibits

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18
Q

What is the hormonal signalling pathway in GI tract?

A

Enteroendocrine cells
-> Peptide hormones
-> extracellular receptors.
Endocrine (Blood) and paracrine (diffusion)

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19
Q

What is the advantage of ENS regulation in the GI tract?

A

Fast local responses to conditions within a region of the GI tract

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20
Q

What is the advantage of CNS regulation in the GI tract?

A

Fast coordination of complex movements of short duration over long distances

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21
Q

What is the advantage of hormonal regulation in the GI tract?

A

Slow but sustained coordinated response over long distances / several organs of the GI tract

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22
Q

What does motility/motility pattern refer to?

A

Any pattern of contraction or relaxation of GI tract smooth muscle for a specific function.

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23
Q

What can motility patterns be?

A
  • Simple
  • Combination of two or more simpler patterns
  • Complex series of events
  • Relaxation
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24
Q

What motility patterns specifically move or propel GI contents along the tract?

A

Movement or Propulsion

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25
What are the two types of contraction in the GI tract?
Phasic Tonic
26
Where do phasic contractions occur in GI tract?
Esophagus, gastric antrum (stomach), small intestine
27
Where do tonic contractions occur in GI tract?
Lower esophageal sphincter, oral (near mouth) stomach, ileocecal and internal anal sphincters
28
How long are phasic contractions?
Several seconds
29
How long are tonic contractions?
Minutes-hours
30
What are the two main stages of motility patterns in the GI tract?
Fasting and fed
31
What is the function of fasting motility patterns?
- Clearing undigested material & secretions - Regulating intestinal microflora
32
What is the function of fed motility patterns?
- Storage - Propulsion and Movement at a controlled rate - Mixing (and exposure to absorptive surfaces)
33
In what stage does MMC occur?
Fasting
34
What is the MMC?
Migrating Motor Complex
35
When does MMC start?
Starts 4-5 hours post meal absorption
36
What is the duration of MMC?
Duration – 2 hours from the stomach to the end of the large intestine
37
What are the 3 phases of the MMC?
(1) intense (2) inactive (3) intermittent
38
Where is the MMC coordinated?
Coordinated in stomach then small intestine
39
What is the function of the MMC?
Clears undigested material & secretions Regulates intestinal microflora Epithelial cell turnover
40
What is the regulation of the MMC?
Hormonal - Motilin released by intestinal m-cells Neuronal - Motilin stimulates both the enteric and autonomic NS
41
What does storage involve in the GI tract?
Relaxation of smooth muscle allows the volume of luminal contents to increase without change in pressure
42
Where does storage occur in the GI tract?
Occurs in the stomach and the colon
43
What is receptive relaxation in the stomach?
Swallowing triggers reduced muscle tone as food is moved down the esophagus. Allows food to enter the stomach without a change in pressure in the stomach - Prevents gastric reflux in the stomach
44
What is the accommodation in the stomach?
Progressive relaxation in response to a volume change
45
Where does propulsion occur?
Occurs in the oesophagus, stomach, small intestine and large intestine
46
What are the steps of propulsion in the GI tract?
1) Arrival of bolus 2) Ascending circular muscle contraction behind bolus. Descending circular muscle relaxation ahead of bolus. 3)Longitudinal muscle shortening (contraction)
47
What is segmentation?
Circular muscle contraction in alternating segments. Mixing function.
48
Where does segmentation occur?
Small intestine
49
Describe the GI tract smooth muscle
Single unit or unitary smooth muscle Act as a syncytium (cells contract together) Extensive intercellular communication - Gap junctions (electrical) Cells physically connected - Adherens junctions Arranged in layers with a neural plexus between
50
What is the arrangement of intestinal smooth muscle?
Cells are 5 – 20 µM diameter and ~ 500 µM long Individual muscles interact with ~10 surrounding cells - Gap junctions and Adherens junctions Contain actin and myosin filaments - irregular arrangement (not striated as in SKM)
51
Describe the MP of intestinal smooth muscle
The membrane potential of intestinal smooth muscle is not stable - fluctuates cyclically Varies between -40 and -80 mV Fluctuates in a pattern of Slow Waves or Basic Electrical Rhythm - Generated by Interstitial Cells of Cajal
52
What do the Interstitial cells of Cajal (ICC) do?
Generate slow waves Function as pacemakers Rhythmic changes in: - Activity of Na+/K+-ATPase - Membrane K+ conductance
53
Where are the Interstitial cells of Cajal (ICC) located?
Stomach and small intestine - In smooth muscle layer close to myenteric plexus Colon - Boundary of muscle layer and submucosal layer
54
What is the arrangement of Interstitial cells of Cajal (ICC)?
Send multiple branching processes to surrounding smooth muscle cells Electrically linked to other ICC & muscle cells by gap junctions
55
What determines frequency of contraction in GI tract?
Slow waves ALWAYS determine the frequency of contraction Frequency of slow waves is a property of the ICC in each region
56
What is the frequency of contraction in different areas of the GI tract?
- Faster in the proximal regions of the GI tract (digestion) - Duodenum 12 – 20 per minute - Slower in the distal regions of the GI tract (absorption) - Colon 6-8 per minute
57
What determines the force of contraction in the GI tract?
Action potentials Small / no contractions occur in absence of action potentials Greater the number of action potentials the greater the force of contraction
58
What is mechanism 1 of contraction in GI tract smooth muscle?
AP and membrane depolarisation Opening of voltage gated calcium channels Increased cytosolic Ca2+ Ca2+ binds to calmodulin Ca2+ /calmodulin complex activates myosin light chain (MLCK) MLCK uses ATP to phosphorylate myosin Actin and myosin interact and cross bridge cycles produce tension
59
What is mechanism 2 of contraction in GI tract smooth muscle?
Pharmomechanical contraction. Hormones & neurotransmitters bind to a receptor to induce Ca2+ release. Gαq - Signalling pathway activated - Receptor activation of phospholipase C - Production of IP3 - IP3 induces release of Ca2+ from sarcoplasmic reticulum
60
What is the down-regulation of smooth muscle contractions in the GI tract?
1. Hyperpolarisation of smooth muscle cell membrane (or decrease Ca2+) 2. Increased activity of Myosin Light Chain Phosphatase 3. Inhibition of excitatory ENS neurotransmission
61
How does increased activity of Myosin Light Chain Phosphatase down-regulate GIT smooth muscle contraction?
Dephosphorylates myosin so reduced force of contraction – Nitric Oxide inhibitory neurotransmitter

PHSL233 (32 decks)

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