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Block 3 Week 1 Meg > Sanders: Smooth muscle > Flashcards

Sanders: Smooth muscle Flashcards

1
Q

Regions such as sphincters and the fundus of the stomach produce this type of contraction

A

Tonic contraction (sustained contractions or periods of sustained relaxation)

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2
Q

Other regions, such as the distal stomach or small intestine, produce this type of contraction

A

Phasic contraction (periods of relaxation between contractions)

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3
Q

A third type of contraction with phasic contractions superimposed upon tonic contractions

A

Mixed contractions

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4
Q

Smooth muscle can become activated spontaneously in the absence of exogenous stimuli. This is considered a…

A

myogenic mechanism

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5
Q

Smooth muscles are also regulated by (blank) and (blank)

A

motor neurons; hormones

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6
Q

Another mechanism of activation of smooth muscles

A

humoral or paracrine (substances produced in the immediate environment of GI smooth muscle cells)

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7
Q

Analogous to the Z lines in skeletal muscles

A

Dense bodies

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8
Q

These are pockets found around the edges of smooth muscle cells that bind calmodulin

A

caveolae

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9
Q

These couple smooth muscle cells into an electrical syncytium

A

gap junctions

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10
Q

Discuss the biochemical mechanism behind smooth muscle contraction.

A

Ca+ rises in the cytoplasm, binds to calmodulin, activates MLCK, which phosphorylates the light chain of myosin allowing it to bind and form a cross-bridge with actin.

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11
Q

What is the major player that reduces cross-bridge cycling and leads to smooth muscle relaxation?

A

Myosin light chain phosphatase (MLCP)

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12
Q

So when the light chain of myosin is phosphorylated, what occurs? When it is dephosphorylated, what occurs?

A

contraction; relaxation

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13
Q

How does much of the Ca+ required for contraction of smooth muscle cells enter the cell?

A

voltage dependent calcium channels

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14
Q

Ca+ can also enter smooth muscle cells through these two mechanisms

A

GPCRs

Release of intracellular stores from the SR

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15
Q

What activates Ca+ channels in the G protein coupled receptor pathway?

A

IP3

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16
Q

Some GPCRs can lead to Ca+ desensitization. Discuss this pathway.

A

GPCR activates adenylate cyclase, produces cAMP, which activates PKA, which increases the activity of myosin light chain phosphatase. This causes relaxation.

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17
Q

Guanylate cyclase can also cause relaxation when bound by (blank)

A

NO

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18
Q

Another way to inhibit EC coupling and smooth muscle contraction is through activation of these channels, which decreases the opening of voltage gated Ca+ channels

A

K+ channels

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19
Q

Major excitatory neural receptors in smooth muscle

A

muscarinic receptors

neurokinin receptors

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20
Q

One inhibitory neural receptor in smooth muscle

A

Guanylate cyclase

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21
Q

Excitatory hormone receptors in smooth muscle

A

Gastrin receptors

CCK receptors

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22
Q

Inhibitory hormone receptor in smooth muscle

A

Secretin receptors

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23
Q

How is resting membrane potential set in GI smooth muscle cells?

A

The dominant resting permeability in smooth muscle cells is due to K+ channels.

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24
Q

This increases open probability of Ca+ channels

A

Slow wave depolarization

25
Q

Slow waves are depolarizations that increase the open probability of (blank) channels in smooth muscle cells

A

Ca+

26
Q

Pacemaker cells of the gut; these cells form a network through the GI tract to generate rhythmical electrical activity of the gut

A

Interstitial cells of Cajal

27
Q

There are at least (blank) classes of ICCs. Some lie between the circular and longitudinal muscle layers are are called (blank). Others lie between muscle bundles and are called (blank).

A

3; ICC-MY; ICC-IM

28
Q

If there is a loss of ICC-IM cells, what happens following motor nerve activation? What does this suggest about these cells?

A

a reduced response; ICC cells are innervated and play a role in the response to neural stimulation

29
Q

What cells make up the SIP syncytium?

A

smooth muscle cells
interstitial cells of Cajal
PDGFRa cells

30
Q

What does activation of inhibitory nerves cause in smooth muscle cells?

A

hyperpolarization; inhibition of phasic contraction for a few cycles

31
Q

Regions of the GI tract undergo this type of contraction to adjust organ volume and compliance and to maintain sphincter function

A

Tonic contraction

32
Q

Ring of contraction moving in the aborad (anal) direction

A

Peristaltic wave

33
Q

Ring of contraction that is stationary; pinches off a region separating it into two sections

A

Segmental contraction

34
Q

To make propulsion effective, there is contraction toward the (blank) end, and relaxation toward the (blank) end.

A

oral; anal

35
Q

Swallowing induces receptive relaxation in the (blank) and proximal (blank)

A

LES; stomach

36
Q

Region of the stomach that functions as a reservoir

A

proximal stomach

37
Q

region of the stomach that functions to grind solids

A

distal stomach

38
Q

This increases the compliance of the stomach, allowing it to store large volumes with little change in pressure

A

gastric accomodation; adaptive relaxation

39
Q

NO dependent inhibition of muscle

A

gastric accomodation; adaptive relaxation

40
Q

3 mechanisms regulate gastric accomodation

A

Adaptive relaxation
Receptive relaxation
Feedback relaxation

41
Q

The fundus (proximal stomach) gradually contracts so that a bit of food is passed along at a time. The tonic contractions that occur are stimulated by what?

A

ACh

42
Q

Which region of the stomach has the greatest frequency of contraction?

A

Body (corpus)

43
Q

Where is the dominant pacemaker located in the stomach?

A

in the orad corpus (body)

44
Q

Slow waves propagate in two directions across the stomach. Which direction is faster?

A

Around the stomach and down the stomach more slowly.

45
Q

Slow waves move toward the pylorus as smooth muscle cells (blank)

A

depolarize

46
Q

The frequency of the entire stomach runs at the frequency of the (blank)

A

dominant pacemaker in the body

47
Q

Also called adaptive relaxation; allows the stomach to accomodate and increase compliance in the fed state

A

Gastric accomodation

48
Q

3 mechanisms to regulate gastric reservoir function

A
  1. Feedback relaxation (from gut to vagal centers)
  2. Receptive relaxation (from vagal centers to gut)
  3. Adaptive relaxation
49
Q

Dominant pacemaker of the stomach is found in the (blank). Where is a “secondary” pacemaker located, which produces more infrequent contractions?

A

body; antral

50
Q

3 parts of motility in antrum and pylorus

A
  1. propulsion
  2. emptying
  3. repulsion (of larger particles) back into stomach
51
Q

Activated in response to nutrients, osmolarity, and pH of the stomach

A

vagal afferents

52
Q

Do liquid or solid meals empty first? Do isotonic/hypotonic/hypertonic meals empty first? Calorie dense or low calorie?

A

liquid; isotonic (hypertonic = slowest to empty); low calorie

53
Q

Lipids in the stomach cause this phenomenon (slow gastric emptying)

A

ileal break

54
Q

Excitation-contraction coupling in the small intestine occurs in a (blank) wave and is dependent on (blank)

A

slow; Ca+

55
Q

Segmentation involves both (blank) and (blank) inputs

A

stimulatory; inhibitory

56
Q

There is a cyclic contraction pattern overnight that occurs in III phases. What is the purpose of this? What phase is the most forceful?

A

To sweep all undigested material in the anal direction to prevent bacteria from building up; phase III is the most powerful

57
Q

Innervation to the colon

A

Right colon innervated by vagus nerve

The rest of the colon innervated by the pelvic nerves

58
Q

Which nerve controls the external anal sphincter?

A

poo-dendal

59
Q

3 contractile patterns of the colon

A
  1. mixing movement
  2. haustral migration
  3. mass movement

Block 3 Week 1 Meg (17 decks)

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