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BIOM20002 - HSF > Lecture 45 - Control of Digestion > Flashcards

Lecture 45 - Control of Digestion Flashcards

0
Q

What are the major functions of the gut?

A
  • digestion
  • absorption
  • removal of waste products
  • fermentation: breakdown of cellulose
  • epithelial barrier to pathogens
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1
Q

How does fermentation occur in the gut?

A

Gut Microbiome / probiotics digest cellulose to deliver us with short chain fatty acids

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2
Q

Which is the largest immune system in the body?

A

The gut

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3
Q

Why is the epithelial barrier in the gut important?

A
  • protect us from invaders in food

* protect us from our own microbiome

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4
Q

Which is the largest endocrine system in the body?

A

The gut

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6
Q

Describe the gut as a chemical refinery

A
  • Mechanical crushing
  • Mixing vats
  • Solvents and catalysts
  • product separation
  • conveyor belt
  • waste disposal
  • control systems
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6
Q

What are the control systems of the gut?

A
  • CNS
  • ENS
  • hormones
  • muscle
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7
Q

Why is the pylorus important?

A

Separates with acid contents of the stomach and the base contents of the duodenum.

Controls the flow into the duodenum

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8
Q

How long is the gut in total?

A

7 metres

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9
Q

What are the basic elements of neural control of the GIT?

A

Local: ENS
Central: vagus and sympathetic pathways
• Cephalic phase

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10
Q

How is the smooth muscle of the gut controlled?

A

Pacemakers
which control:
• propulsion
• mixing

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11
Q

What is the longer distance, slow control of the GIT?

A

Endocrine

Controls:
• appetite (satiety, hunger)
• coordination

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12
Q

Describe the ENS

A

Network of neurons within the intestinal wall

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13
Q

Describe how the ENS changes along the length of the gut

A

Doesn’t change

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14
Q

What are the layers / plexuses of the ENS?

A
  • Submucous plexus

* Myenteric plexus

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15
Q

Where does the submucous plexus lie?

A

Between the mucosa and the circular muscle

16
Q

Where does the myenteric plexus lie?

A

Between longitudinal and circular muscle layers

17
Q

What happens when a part of the gut is cut out and out in a dish?

A

Can still produce many of the basic functions

The pacemakers and sensory neurons are still present

18
Q

What does the CNS do in the GIT ?

A
  1. Modulates
  2. Initiates
    … the activity of ENS
19
Q

What are the three basic functions of the ENS?

A
  • motility of gut
  • absorption of salt and water
  • release of enzymes and hormones
20
Q

Describe the motility pattern after a meal

A 
Fed state:
• stomach relaxation -- for storage
• segmentation
• peristalsis
(• retropulsion)
21
Q

What is segmentation?

A

Localised constrictions to mix up the contents

No propulsion

22
Q

How does vomiting occur?

A

Anesis / Retropulsion

23
Q

Describe the motility of the stomach when fasting

A

MMC: migrating motor complex

24
Q

Describe MMC

A

Slowly propagating constrictions through the intestines; ‘housekeeping’
Get rid of debris:
• epithelial cells
• bacteria

25
Q

Describe the motor patterns in the colon

A

Mass movement contraction

Defecation

26
Q

Why don’t we swim after a meal?

A

Exercise: blood flow to muscles

Not enough blood for digestion –> cramps

27
Q

Where are the pacemakers

A

Antrum of stomach : special cells

Also, the whole way along the stomach

28
Q

Why is it called slow wave?

A

Slow compared to what is seen in the rest of the nervous system

29
Q

What are ICC?

A

Interstitial cells of Cajal

Modified smooth muscle cells

30
Q

What is the catch mechanism?

A

Once the smooth muscle in GIT contracts, it remains contracted.

It need inhibitory stimulation to relax

31
Q

What are the stimuli of the ENS?

A

Products of digestion
(pH
Stretch
Osmolarity)

32
Q

What detects stimuli in the GIT

A

ENS sensory neurons

33
Q

What other stimuli affect the GIT?

How is this different from the others?

A

Sight
Smell
Memory of food

This is different, because they are sensed by the brain, not the ENS

34
Q

Describe the long reflexes that control digestion

A

CNS is involved
• Stimulus: products of digestion / extrinsic factors
• Receptor: sensory neurons of ENS
• Integration: Cephalic brain
• Efferent: para- and sympathetic neurons
• Effectors: smooth muscle and secretory cells

35
Q

Describe the short reflexes that control digestion

A

Within the ENS
• Stimulus: products of digestion
• Receptor: sensory neurons of ENS
• Integration: within ENS, sensory neurons
• Efferents: neurons of submucous and myenteric plexuses
• Effectors: smooth muscle and secretory cells of GIT

36
Q

What are some of the feed forward reflexes involved with digestion?
Describe them

A

Cephalic reflex
• Sight, smell etc. of food stimulates the cephalic phase (salivation, distension of stomach)

Gastro-colonic reflex
• ingestion of food stimulates defecation

37
Q

What are some of the feed back reflexes involved with digestion?

A

Acid in stomach stimulates release of:
• secretin
Protein in stomach stimulates release of:
• CCK

CCK and secretin feedback to reduce stomach motility and gastric acid secretion

BIOM20002 - HSF (60 decks)

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