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Uni year 1 > DRS - smooth muscle and motility > Flashcards

DRS - smooth muscle and motility Flashcards

1
Q

Where is smooth muscle found in the GIT?

A

In most regions of GIT

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2
Q

Where is skeletal muscle found in the GIT?

A

pharynx
top third of oesophagus
external anal sphincter

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3
Q

What are the two types of smooth muscle in the GIT and where are they?

A 
Phasic:
- rapid contraction and relaxation
- body of oesophagus, stomach antrum, small and large intestines
Tonic:
- sustained contractions
- sphincters, upper stomach
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4
Q

What are the pacemaker cells of smooth muscle in the GIT?

A

Interstitial cells of CAJAL

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5
Q

How does smooth muscle contract?

A

An action potential spreads along the sarcolemma down the T-tubules. Depolarisation by Na+ entry causes L-type calcium channels to open. Calcium will bind to RyR2 on the SR causing them to open to release more calcium from stores in the SR. The calcium binds to calmodulin to activate myosin light chain kinase. This phosphorylates MLCs allowing myosin-actin cross bridges to form.

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6
Q

What does the activation of the myenteric plexus cause?

A

Increases tonic contraction

Increases intensity of rhythmic contractions

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7
Q

What causes muscles of the GIT to relax?

A

VIP and NO

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8
Q

What causes muscles of the GIT to contract?

A

ACh

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9
Q

What are the sensory neurones in the smooth muscle of the GIT stimulated by?

A

Mechanoreceptors in the submucosal layer detect stretch due to the presence of food
Chemoreceptors in the myenteric plexus detect the chemical composition of food

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10
Q

What is Hirschprung’s disease?

A

Lack of neuronal ganglionic cells in the ENS plexi
Results in a megacolon
Submucosal and myenteric plexi are absent

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11
Q

What is Chaga’s disease?

A

Infectious disease of a parasitic nature

significant reduction in number of ganglionic cells in the ENS

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12
Q

What is achalasia?

A

Dramatic reduction in number of neuronal cells in the lower oesophageal segment
failure of gastrooesophageal shpincter to relx
disease of the oesophagus
Due to lack of inhibitory motor neurones in the lower part of the oesophagus

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13
Q

What is regulation in the fundus regulated by?

A

The vagovagal reflex

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14
Q

Where does sieving occur and what does it do?

A

Sieving in the pylorus ensures only small particles can enter the duodenum

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15
Q

Where does grinding occur and what does it do?

A

The antrum wall is thick because this where grinding occurs
Liquids and small particles are emptied
Large particles retained in bulge of terminal antrum
Grinding involves the churning of a bolus to reduce its size

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16
Q

Functions of the pylorus

A
  • allows regulated emptying of gastric contents
    Prevents reflux of duodenal contents into the stomach
  • Regulates amount of contents going into the small intestine
17
Q

Phases of gastric emptying

A
  1. Cephalic
    - sight, smell
    - food in mouth
    - relaxation of stmach enables it to store larger volumes
  2. Gastric
    - food in stomach
    - empties at rate proportional to the volume in it
    - due to myogenic reflex (stretching of smooth muscle causes contraction), activation of pressure receptors send impulses in nerve plexi and vagus nerve, gastrin release in response to peptides
  3. Intestinal
    - inhibitory phase, allows more time to digest and absorb nutrients
    - fats - increase CCK
    - low pH - secretin
    - amino acids - gastrin
    - carbohydrates - GIP
18
Q

3 functions of motor activity in the GIT

A
  1. segmental contractions
    - mixes chyme with secretions
    - non-propulsive
  2. peristaltic contractions
    - propulsion in caudal direction
  3. Allows some organs to acts as reservoirs for holding luminal content
    - stomach
    - allows stomach to function effectively
19
Q

Types of motility in small intestine

A

Segmentation

  • rings of circular movement, muscles contract and relax
  • results in mixing

Peristalsis

  • sequential contractions of longitudinal and circular muscle
  • results in propulsion of chyme
20
Q

What is the migrating motor complex

A

A pattern of electromechanical activity that occurs in GI smooth muscle during periods between meals

21
Q

Phases of MMCs

A
  1. Prolonged quiescent period
  2. Period of increasing action potential frequency and contractility
  3. Period of peak electrical and mechanical activity that lasts a few minutes
  4. Period of declining activity that merges into next quiescent period
22
Q

What are the functions of MMCs?

A
  • propels particles greater than 2mm from stomach to duodenum
  • cleansing of gut
  • clears small intestine of residual content
  • ensures cells that have been shed are flushed out
  • ensures bacteria don’t migrate up into small intestine
  • allows non-digestible material to be expelled
23
Q

Where do MMCs originate and where do they travel?

A

The stomach and often travel to the distal end of the ileum

24
Q

What does feeding cause?

A

Termination of MMCs and initiation of fed motor pattern segmentation and peristalsis

25
Q

What regulates MMCs?

A

ENS, humoral factors and extrinsic innervations

The hormone motilin is a major determinant of the MMC pattern

26
Q

What is released when a bolus is detected and what do they cause?

A

Acetylcholine released from myenteric plexus causes contraction of circular muscle behind the bolus and causes contraction of longitudinal muscle in front of bolus
VIP and NO cause relaxation of longitudinal muscle behind the muscle and relaxation of circular muscle in front of the bolus

27
Q

What is the iloecaecal sphincter?

A

The sphincter that separates the ileum from the colon. A stimuli proximal to the sphincter will cause relaxation and distal will cause contraction

28
Q

What are the functions of the colon?

A
  • Absorption of large quantities of fluid and electrolyes converting liquid to solid
  • absorb product of carbohydrate fermentation
  • storage
  • regulated release of faecal material
  • provides environment for beneficial bacteria which synthesis vitamins
  • secretes mucus and ions
29
Q

What are the two types of motility in the colon?

A

Colonic rhythmic phasic contractions

Giant migrating contractions

30
Q

What are colonic rhythmic phasic contracts?

A
  • Similar to segmentation
  • turning stuff over
  • small amount of propulsion

Short duration RPCs - 2/3 seconds, no propagation
Longduration RPCs - 15-20 seconds, contracts may propagate over short distances

31
Q

What are giant migrating contractions?

A
  • equivalent to MMCs
  • large amplitude contractions that propagate rapidly
  • occurs independent of being fed or fasted
  • propels matter towards rectum
32
Q

What are osmotic laxatives?

A

Create a hyperosmotic environment to draw water in from interstitial spaces into the lumen. Water is drawn into the bowel by osmosis.
Lactulose is an example

33
Q

What are bulk laxatives?

A

Bulk laxatives increase motility in the gut. They use molecules which act as bulking agents which swell and draw water into the lumen.

34
Q

What are stimulant laxatives?

A

Stimulate the ENS to increase motility by chemoreceptor activation
eg castor oil

35
Q

What parts of the colon does the vagus nerve innervate?

A

cecum and ascending and transverse colon

Vagal stimulation causes RPCs of the proximal part of the colon

36
Q

What does the pelvic nerve and nerves from the sacral spinal cord innervate and what does stimlation cause?

A

Sigmoid colon, rectum and anal canal

Causes GMCs of distal colon and sustained contraction of some segments

37
Q

What type of muscle does the inner anal sphincter consist of?

A

Involuntary smooth muscle

38
Q

What type of smooth muscle does the external anal sphincter consist of?

A

Striated voluntary muscle

Uni year 1 (19 decks)

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