1.12 GI Smooth Muscle + Blood Flow

Question 1

Peristalsis in the GI tract is an example of what smooth muscle structural type?

Answer 1

single unit (unitary)

Question 2

What differentiates smooth muscle form skeletal muscle in the ways that it can receive signals to contract?

Answer 2

smooth muscle can be signaled via circulating hormones in the bloodstream (skeletal cannot)

Question 3

smooth muscle contractile activity type with rapid short contract and relax pattern?

Answer 3

phasic

Question 4

what is phasic contraction used for?

Answer 4

period, strong for mixing, propulsion, and emptying organs

Question 5

what is tonic smooth muscle used for?

Answer 5

continuous tension or tone to regulate lumen size (ex. blood vessels)

Question 6

What smooth muscle activity type with sustained stead-state contraction over long durations with min energy spent?

Answer 6

tonic

Question 7

electric properties of phasic smooth muscle?

Answer 7

slow waves

Question 8

electric properties of tonic muscle?

Answer 8

sustained to keep contracted

Question 9

what is the natural state of tonic activity?

Answer 9

normally contracted (ex. Lower esophageal sphincter)

Question 10

What are the (4) key sources of calcium into cell for muscle contraction?

Answer 10

Extracellular
(1) Voltage-gated L-type channels
(4) Store-operated Ca²⁺ channels (SOCC) - warning low

Intracellular
(2) Calcium-induced calcium release (CICR) from SR
(3) IP3-mediated release from SR

Question 11

What activates the L-type ca channel for smooth muscle contraction?

Answer 11

ICC (Interstitial cell of Cajal) chloride channels triggered via Ach or SubP from enteric motor neuron

Question 12

what activates the SK3 channel then L-type ca channel for smooth muscle relaxation?

Answer 12

PDGFR a+ cell via NO or VIP from enteric motor neuron

Question 13

Where are NT released in smooth muscle?

Answer 13

autonomic varicosities (not NMJ)

Question 14

what does increased intracell calcium activate to initiate contraction?

Answer 14

MLCK - myosin light chain kinase

Question 15

What has to happen to myosin heads for it to bind to actin and muscle to contract?

Answer 15

phosphorylated

Question 16

Once calcium is in the cell what does it need to bind to first in smooth muscle to activate the MLCK?

Answer 16

calmodulin to make CAM complex

Question 17

How does phosphorylated (ML20) myosin interact with thin actin filaments?

Answer 17

cross bridges

Question 18

what is the Latch State?

Answer 18

Mechanism of low energy sustained smooth muscle contraction to use less energy (ATP)

Question 19

What do you need to remove calcium or relax smooth muscle? (4)

Answer 19

sarcolemma membrane transporters
(1) Plasma membrane Ca²⁺-ATPase (PMCA)
(2) Na⁺/Ca²⁺ exchanger
(4) CRAC channels

intracellular
(3) SERCA pump

Question 20

which channel is NOT ATP dependent to remove calcium from the cell?

Answer 20

Na+/Ca2+ exchanger

Question 21

how is the CAM complex dissociated?

Answer 21

decreased intracell calcium

Question 22

what is activated to remove phosphate from the ML20?

Answer 22

MLCP myosin light chain phosphatase

Question 23

hypocalcemia clinical presentations? (<2.12 mmol/L)

Answer 23

decreased contractility = dysphagia, pain in abdomen since motility is reduced

Question 24

what is essential in skeletal muscle to expose the binding sites on actin?

Answer 24

troponin to activate tropomyosin

Question 25

does smooth muscle have a defines motor end plate?

Answer 25

nope

Question 26

what are the (3) regulatory pathways to control relax/contract in MLCP?

Answer 26

PKG, PKC, ROCK

Question 27

what reg pathways promote relaxation via the MLCP?

Answer 27

PKG

Question 28

what reg pathways promote contraction via the MLCP?

Answer 28

ROCK and PKC

Question 29

Where is PKG working?

Answer 29

LES and pyloric sphincters + relax peristalsis

Question 30

where is PKC working?

Answer 30

contraction, mixing, segmentation, secretion regulation

Question 31

ROCK where is it working?

Answer 31

bloods vessels & tonic contraction at sphincters

Question 32

What is NO activating to convert GTP to cGMP ?

Answer 32

guanylyl cyclase (GC)

Question 33

what does cGMP activate to increase the dephopshorylation of MLC20 for smooth muscle relaxation?

Answer 33

PKG

Question 34

What kind of receptor and activation triggers PKC to initiate smooth muscle contraction?

Answer 34

GPCR then indirect activation of PK

Question 35

What does PKC activate by phosphorylation?

Answer 35

CPI-17

Question 36

What does the phosphorylated CPI-17 do?

Answer 36

MLCP inhibition to increase the phosphorylation of MLC for smooth muscle contraction

Question 37

How is RhoA activated?

Answer 37

indirect activation via GPCR

Question 38

what does Rho-kinase do once phosphorylated?

Answer 38

MYPT1 inhibitory sites activated of MLCP to increase myosin light chain phosphorylation for contraction

Question 39

What hormones are implicated in constriction of GI circulation?

Answer 39

Catecholamines:
Angiotensin II (ANG-II)
Arginine vasopressin (AVP/ADH)

Question 40

What hormones are implicated in GI vasodilation?

Answer 40

Gastrin, CCK, Secretin

Question 41

What are catecholamines implicated in?

Answer 41

STRESS response

Question 42

What are ANG-II implicated in?

Answer 42

response to low BP

Question 43

What are AVP/ADH implicated in?

Answer 43

shock response

Question 44

What is gastrin implicated in?

Answer 44

gastric mucosa for digestion/secretion

Question 45

What is CCK implicated in?

Answer 45

intestinal circulation for nutrient absorption and enzymes delivery in digestion

Question 46

What is secretin implicated in?

Answer 46

pancreas and small intestine for bicarb secretion and digestive enzyme delivery