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HUBS192 > Lecture 24- Introduction and motility > Flashcards

Lecture 24- Introduction and motility Flashcards

1
Q

What are the key functions of the GI tract?

A

Obtain nutrients required for
• Growth (constantly recycling cells)
• Energy needs

Replace fluid and salts lost
• In urine & faeces
• Sweating
• Breathing

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2
Q

What is the GI tract regulated by?

A

Combination of centric nervous system, enteric nervous system and hormones which regulates motility and secretion.

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3
Q

What is the chain of events that need to occur for ingested food to become waste?

A
  • Ingested
  • Mechanical digestion
  • Chemical digestion
  • Absorption
  • Waste
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4
Q

Which events in the GI tract does motility help with?

A
  • Carries out mechanical digestion

- Aids chemical and absorption

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5
Q

Which events in the GI tract does secretion help with?

A
  • Carries out chemical (enzymes)

- Aids mechanical and absorption

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6
Q

How are conditions in the intestinal lumen regulated?

A

Via stretch receptors in the wall of the GI tract:

  • When food comes in stretch occurs
  • Change in composition detected. Act as ‘tasters’ for luminal content
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7
Q

What are things the stretch receptors detect in regards to luminal composition?

A

pH, osmolarity, amino acids, sugars, fats

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8
Q

In the regulation of GI function what are the effectors and what do they do in response to stimulation?

A
  • Glands, secretion

- Smooth muscle, contraction

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9
Q

What is the role of the central nervous system in regulation GI function?

A
  • Co-ordinates activity over long distances
  • Parasympathetic (rest + digest) nervous system stimulates motility and secretion
  • Sympathetic (fight or flight) Nervous system inhibits motility and secretion
  • Modulates activity of enteric nervous system
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10
Q

What is the role of the enteric nervous system in regulation GI function?

A

-Is the guts own self-contained nervous system that takes care of most local reflexes such as peristalsis and segmentation

Consist of the:
-Submucosal plexus – regulation of secretion
-Myenteric plexus – regulation of
motility

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11
Q

How do hormones work to regulate GI function?

A
  • The GI tract is the largest endocrine organ in body
  • Hormones work at both the endocrine (released into the blood) and paracrine (localised in a small section of the GI tract itself) levels
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12
Q

What are the critical hormones invovled in regulating the GI tract function?

A
  • Gastrin
  • Gastric inhibitory peptide (GIP)
  • Secretin
  • Cholecystokinin (CCK)
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13
Q

What are the general functions of motility in the GI system?

A
  • Ensures movement is at a controlled rate via regulating things such as propulsion, storage and aiding chemical digestion and absorption
  • Mechanical digestion to increase surface area of food and thus making chemical digestion possible
  • Mixing which maximizes the contact of food with enzymes therefore aiding chemical digestion
  • Increases exposure to absorptive forces and therefore aids absorption
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14
Q

What is in charge of motility? How does this behave?

A
  • Smooth muscle

- Works spontaneously and so contracts without external input

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15
Q

In motility does the frequency of smooth muscle contraction stay the same across all regions of the GI tract?

A
  • No, varies according to region
  • Stomach is 3 per min while in the duodenum 12 per min and the Ileum 9 per min
  • We need a fast rate in the duodenum as we want the mixing with bicarbonate to occur whereas in the ileum absorption means contractions are slow to give more time
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16
Q

What is the strength of contraction in motility regulated by and how does this varies to how the frequency of contraction is regulated?

A
  • Strength regulated by Nervous and hormonal input

- Frequency regulated by enteric nervous system (self-contained)

17
Q

What generalized motility pattern is seen in fasting?

A

Migrating motor complex:

  • 4 h after a meal
  • Repeats every 2 h until eat again
  • Housekeeping (flush contents through)
18
Q

What generalized motility patterns are seen in feeding?

A

-Storage in the stomach and colon. Happens via the
relaxation of smooth muscles allowing volume to increase without a change in pressure

  • Propulsion occurs in the Esophagus, stomach, small and large intestine (pushes food so we are not dependent on gravity). This includes peristalsis which has different objectives and patterns in different regions.
  • Mixing + retropulsion in the stomach
  • Segmentation in the small and large intestine
19
Q

What is peristalsis? What is an example of where it occurs?

A
  • Is the movement of food through the GI tract
  • Contraction of smooth muscle before the bolus pushes it forward
  • A common example of where it occurs is the small intestine
20
Q

What is segmentation? What is an example of where it occurs?

A
  • Used to mix food together by alternate patterns of smooth muscle contraction pushing food back and forth
  • This also helps to maximize exposure of different food to the epithelial lining for absorption
  • Occurs in the small intestine
21
Q

What is the purpose of chewing?

A
  • Reduce size of food
  • This allows ingestion
  • Food is mixed with saliva which makes it wet and aids the action of taste cells on the tongue to detect taste
22
Q

Is chewing voluntary?

A

Yes, it is controlled by skeletal muscle with reflex control over strength, frequency, side. However, can consciously override this if we choose

23
Q

What does swallowing allow? How is it controlled?

A
  • Rapid transfer of material from mouth to stomach

- Initiated at will, proceeds reflexly

24
Q

What are the functions of gastric (stomach) motility?

A
  • Storage in Fundus and body of stomach
  • Mechanical digestion + mixing in Antrum
  • Controlled delivery to duodenum via the Pyloric sphincter
25
Q

Why does the delivery of chyme to the small intestine need to be controlled?

A

Limited capacity for food in SI, also dependent on other factors such as osmolarity, pH and presence of fats in the stomach

26
Q

What happens to the stomach in fasting?

A
  • Shrinks to ≈ 50 ml in volume
  • Initiate migrating motor complex (Occurs 4 h after a meal and continues until eat, goes through 2 hour cycle, 1 h of inactivity, 50 min uncoordinated activity, 10 min coordinated activity)
27
Q

What is the functions of the migrating motor complex in the stomach during fasting?

A

House keeping to get rid of residual secretions and undigested material (don’t want hanging around to long)

28
Q

What happens in feeding gastric motility with regards to storage?

A
  • Receptive relaxation (Nervous regulation via the vagus nerve)
  • This relaxation allows an increase in volume with minimal change in pressure
  • Occurs in the Fundus and body to allow greater storage (gastric accommodation)
29
Q

What happens in feeding gastric motility with regards to propulsion?

A
  • Peristalsis
  • Initiated on greater curvature & spreads to antrum
  • 3 contractions per min, First 60 min following meal is gentle then 60 - 300 min after is more intense activity
30
Q

What happens in feeding gastric motility with regards to mixing and mechanical breakdown?

A
  • Retropulsion
  • This is the combination of peristalsis and closure or the pyloric sphincter which means that all the food mixes/ churns together causing mechanical breakdown
31
Q

What does the rate of gastric emptying match?

A

Digestive capacity of intestine, it is thus regulated by feedback from the duodenum

32
Q

What are some factors affecting the rate of gastric emptying?

A

-Size of meal: The larger the meal faster the
emptying
-Composition of meal: Fluids are faster than solids as particles don’t need to be broken down further whereas food does to increase surface area. Fats slow gastric emptying as they are difficult to digest.

33
Q

What are the functions of small intestine motility?

A
  • Mixing with secretions from pancreas, biliary system (liver/gallbladder) and intestine
  • Controlled movement
  • Exposure of products of digestion to absorptive surfaces
34
Q

How do the motility patterns in the small intestine differ between and after meals?

A

Between meals:
-Migrating motor complex (mostly at night as we snack in the day and it takes 4 hours to kick in)

After meal:

  • Segmentation for mixing and exposure to absorptive surfaces and contributes to movement
  • Limited peristalsis (in humans) for movement
35
Q

What is the motility of the colon or large intestine like?

A

-Storage of faeces
-Large periods of inactivity
-Segmentation increases exposure to absorptive surfaces. Important for fluid and salt absorption that occurs here.
-Mass movement occurs 1-2 time a day following meals
in a Peristaltic wave this drives faeces into rectum
and initiates defecation

HUBS192 (38 decks)

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