Smooth muscle function and mobility

Question 1

Organizations of layers of GIT

Answer 1

-Serosa
-Muscular Layer
-Submucosa
-Mucosa

Question 2

3 layers of muscle

Answer 2

1.submucosa muscularis mucosae
2.circular smooth muscle (inner)
3.longitudinal smooth muscle (outer)

Question 3

Submucosal musclaris mucosae

Answer 3

-muscle moves villi in the small intestine

Question 4

Circular smooth muscle

Answer 4

-layer closest to the lumen
-fibers run at right angles to the long axis of intestine
-helps with peristalsis

Question 5

Longitudinal smooth muscle

Answer 5

-outer layer
-fibers run parallel to the long axis of the intestine
-help with peristalsis

Question 6

Types of contractions in GI smooth muscle

Answer 6

1.segmental contraction
2. Peristalsis

Question 7

Segmental contraction

Answer 7

-mixing reaction that is carried out by the circular smooth muscle

Question 8

Peristalsis

Answer 8

-propels bolus down the GI tract aborally
-coordinated contraction of the outer longitudinal muscle and the inner circular muscle behind food bolus to push it along
»process requires entry of calcium from extracellular fluid (making this process sensitive to hypocalcemia)

Question 9

Smooth muscle contraction during peristalsis

Answer 9

-requires Ca from extracellular fluid
-contraction of cells is syncytium (possible due to gap junctions), therefore no need for nerve fibers to innervate every muscle fiber

Question 10

Smooth vs. striated muscle

Answer 10

-smooth contract slowly compared to striated
-smooth have longer actin filaments and can therefore contract 3-4 x the distance of striated muscle
-smooth muscle contraction requires entry of Ca into the cell from extracellular fluid
-smooth muscle contract as syncytium. Individual neurons not required to stimulate each cell

Question 11

Mechanotransduction in GI tract

Answer 11

-process by which cells convert mechanical forces into electrical and chemical signals that result in cellular responses
>smooth muscle cells have a wide array of membrane associated molecules to sense and process the mechanical stimuli
»mechanical stimuli then converted into short (changes in ion concentrations and voltage) and long (changes in gene expression) effects

Question 12

Membrane associated molecules used in mechanotransduction

Answer 12

-Surface receptors (ion channels, G protein coupled receptors, kinases
-specialized intracellular cytoskeletal proteins
-extracellular cell-cell connections

Question 13

Gi smooth muscle activity

Answer 13

-show spontaneous (myogenic) activity, conduction of electrical impulses from fiber to fiber, and sensitivity to stretch
-modulated by autonomic nerves

Question 14

Interstitial cells of Cajal

Answer 14

-smooth muscle cells within the GI tract that undergo rhythmic depolarization caused by variations in conductance of Na, Ca, Cl across the cell membrane at regular intervals (pacemakers of the gut)
like pacemaker cells/purkinje fibers of the heart

Question 15

Function of interstitial cells of cajal

Answer 15

-responsible for the basal or basic electrical rhythm (BER)
>the spontaneous depolarization and repolarization of these pacemaker cells in the smooth muscle of the stomach, small intestine, and large intestine

Question 16

Cajal resting membrane potential `

Answer 16

Negative 50 mV

Question 17

Depolarization of Cajal cells

Answer 17

1.Slow waves
2.Spikes

Question 18

Slow waves

Answer 18

-spontaneous, slow, transient depolarization, conducting varying distances along the tract (basic electrical rhythm)

Question 19

Spikes

Answer 19

-faster transient depolarization that can occur in burst at the periods of maximal depolarization of a slow wave
>proceed and initiate contraction of smooth muscle

Question 20

Parasympathetic stimulation of cajal cells

Answer 20

-increases the rate at which these potentials depolarize the membrane, thus increasing the rate of the spike discharge and contraction

Question 21

Sympathetic stimulation of cajal cells

Answer 21

-prolongs (slows) the rate at which the generator potential depolarizes the membrane and thus slows the rate of the spike discharge

Question 22

Slow Wave membrane potential

Answer 22

-resting membrane potential (-50 to -60 mV). Membrane potential fluctuations are spontaneous slow waves (moving from 5-15mV) in smooth muscle
>fluctuations appear to be an intrinsic property of smooth muscle, and does not depend on nervous stimuli

Question 23

Are slow waves action potentials?

Answer 23

-No, they are not action potentials and do not elicit contractions
**sometimes stomach may be considered an exception

Question 24

Slow Wave frequency in Small intestine vs. stomach and large intestine

Answer 24

-Small intestine: 10-20x per minute
-Large intestine and stomach: 3-8x per minute

Question 25

Spikes

Answer 25

-occur on top of a slow wave. AP’s caused by rapid entry of Ca ions
-occur when stretched by a bolus of food OR receptors activated by parasympathetic stimulation

Question 26

Smooth muscle contraction steps

Answer 26

1.L-type channels open, Ca enters
2. Ca binds to calmodulin, forming complex
3.Complex combines with Myosin light chain kinase which can act on myosin and actin and results in either contraction (phosphorylation) or relaxation

Question 27

Speed of contractions (slow waves and spikes)

Answer 27

-Slow waves take a few seconds
-Spikes are very quick, within a second

Question 28

What causes spikes/depolarizations?

Answer 28

1.stretch
2.acetylcholine
3.parasympathetics

Question 29

What causes hyperpolarizations?

Answer 29

1.NE
2. Sympathetics

Question 30

Contractile Activity patterns

Answer 30

-Tonic
-Phasic

Question 31

Tonic smooth muscle contractions

Answer 31

-normally contracted and generate a variable steady-state force
-Ex. sphincters, blood vessels, airways

Question 32

Phasic Smooth muscle contraction

Answer 32

-rhythmic contractions (Ex. peristalsis in GI tract) but may also contract intermittently during physiological activities under voluntary control (Eg. Voiding of urine or swallowing)

Question 33

Swallowing and relaxation

Answer 33

-swallowing through pharyngeal stimulation results in neural reflex relaxation of the lower esophageal sphincter and the proximal part of the stomach to allow entry of food

Question 34

Deoxynivalenol (DON)

Answer 34

-vomitoxin
-produced by Fusarium graminearum (fungi)
-commonly found in corn, barley, wheat
-develops in cool, damp weather
-negative effects begin at ~4 ppm, but inconsistent

Question 35

Fusarium Head Blight (FHB)

Answer 35

-disease caused by infection with Fusarium fungal species
-bleached heads and shriveled chalky/pinkish kernels
-during infection, a variety of mycotoxins can be produced (including DON)

Question 36

DON impact on weanling pigs

Answer 36

-growth effects greater than feed intake, proving that growth was not related just to feed intake
-thickness of smooth muscle in the jejunum and ileum decreased, which affects animals growth

Question 37

DON impact on mice

Answer 37

-small intestine shorter
-motility affected because mice given charcoal after DON and moved less compared to control
**direct effect on proteins involved in motility of small intestine. Which effects intake and therefore growth