L25

Question 1

what are examples of Phasic contractions

Answer 1

Phasic contractions
• Esophagus, gastric antrum (stomach), small intestine
• Contract and relax in seconds

• Tonic contractions
• Lower esophageal sphincter, orad (near mouth stomach, ileocecal and internal anal sphincters
• Sustained contractions that last minutes to hours

Question 2

what are examples of where tonic contractions happen

Answer 2

• Tonic contractions
• Lower esophageal
sphincter, orad (near
mouth) stomach, ileocecal
and internal anal
sphincters
• Sustained contractions that

eg you want the shinters to be constantly contracted and then relax when you need them to (which is opposite to normal)

Question 3

what is the main difference between phasic and tonic contractions

Answer 3

phasic = seconds 
tonic = minutes to hours

Question 4

there are 2 main stages of motility patterns. what are they

Answer 4

fasting and fed

Question 5

describe the fasting motility pattern

Answer 5

• Clearing undigested material & secretions
• Regulating intestinal microflora

Fasting is a period of time where you are not eating eg when you are sleeping at night

Fasting has many different functions, it is not a time of absolute rest of GI tract as there are motility patteren to help clear the GI tract and it also helps with the microflora in the gut

Question 6

what is the fed motility pattern used for

Answer 6

• Storage
• Movement at a controlled rate
• Mixing
• Exposure to absorptive surfaces

Question 7

what are some other names for the fasting motility pattern

Answer 7

Fasting Motility = Migrating Motor OR Myoelectrical Complex (MMC)

Question 8

when does the Fasting Motility pattern start and how long does it last

Answer 8

Starts 4-5 hours post meal absorption

Duration – 2 hours from the stomach to the end of the large intestine

Question 9

the MMC has 3 phases Coordinated in stomach then small intestine. what are they

Answer 9

(1) intense, (2) inactive, (3) intermittent

Question 10

what is the function of the MMC

Answer 10

Clears undigested material & secretions

Regulates intestinal microflora (makes sure you don’t get too much or that one bacteria doesn’t overpower others)

Epithelial cell turnover

last 2 part of immune response

Question 11

what is the MMC regulated by

Answer 11

Hormonal = Motilin released by intestinal m-cells

Neuronal = Motilin stimulates both the enteric and autonomic NS

hormonal and neural elements act on eachother

Question 12

fed state has 3 main functions. what are these

Answer 12

Reservoir/Storage Function
- Mainly stomach but also the Colon
- Relaxation of smooth muscle allows the volume of luminal
contents to increase without change in pressure

Peristalsis
- Lower esophagus, stomach
- Small & large intestine
- Propulsive (but also mixing as part of retropulsion in the
stomach)

Segmentation
• Small and large intestine
• Mixing & exposure to absorptive surfaces

Question 13

there are 2 types of reservoir functions in the stomach. what are these

Answer 13

receptive relaxation and accommodation

Question 14

what is receptive relaxation

Answer 14

1. Receptive relaxation
   An event, (e.g. swallowing in the case of the stomach) triggers reduced muscle tone as content is moved along the tract (less resistance as content
   arrives).

Allows food to enter and not be pushed back.

Question 15

what is accommodation

Answer 15

2. Accommodation
   Progressive relaxation in response to a volume
   change.

This is due to receptors in the stomach which detect distention and stretch which causes a locals and something long loop reflex which causes the stomach to stretch

Question 16

describe the muscle contraction responsible for peristalsis

Answer 16

Ascending circular muscle contraction behind bolus.

Descending circular muscle relaxation ahead of bolus.

Longitudinal muscle
shortening (contraction)

Causes intestine to bunch up meaning that the cyme only needs to travel a shorter distance

Combines with other motility to produce complex patterns
(e.g. retropulsion)

causes movement from the mouth towards the anus

Question 17

describe segmentation

Answer 17

Circular muscle contraction in alternating
segments.

Mixing function.

The major motility pattern in the small
intestine.

Question 18

which is the main motility pattern in the small intestine

Answer 18

segmentation

Question 19

Barium acts as a contrast die and then they have taken xray videos of the the motility patterns which is how you diagnose defects with motility patteren

Answer 19

4

Question 20

what is the difference between smooth muscle in the body and in the GI tract

Answer 20

Intestinal smooth muscle is different from other types of smooth muscles

The big difference is how the cells are interconnected and how they get their messaging

In the GI smooth muscle we call it signal unit or interconnected smooth muscle as they are are all connected via gap and adherence junctions therefore they contract all together fin a sinciduim

This differs from other smooth muscle where each individual cells is directly innervated

Question 21

describe the arrangement of intestinal smooth muscle

Answer 21

• Single unit or unitary smooth muscle
• Acts as a syncytium
• Extensive intercellular communication through Gap junctions (electrical)
• Cells physically connected through Adherens junctions

• Muscle cells are arranged in layers with a neural plexus between
• circular and longitudinal intestinal smooth muscle
sandwiching neural components of the myenteric plexus

There are also intestinal cells of cajal which are the pacemaker cells

They are long cells and each individual cell is going to interact with 10 or more cells

They have a very irregular arrangement they are not striated like skeletal mucles s

Question 22

what are the measurements of intestinal smooth muscle cells

Answer 22

Cells are 5 – 20 µM diameter and ~ 500 µM long

Question 23

how many other cells with a smooth muscle cell interact with

Answer 23

10 through gap and adherences junctions

Question 24

how does smooth muscle contract

Answer 24

You stil have actin and myosin filaments but they are not regulated my troponin or tropomyosin instead they are modulated by modulin and myosin like kinase

They still get modulated by action potentials and membrane depolerisation which causes voltage gated Ca channels causeing the entry of Ca. Ca binds to a molecule called calmodulin.

This complex activated a kinase (myosin like calcium kinase). This phosphorylates the myosin like chain. When this is phosphorylated it interacts with actin which leads to the contraction

Because all of these cels are linked electrical then all of these cells are going to contract as a syncytium

You can also remove the phosphate with a myosin like chain phosphatase (removes phosphate whereas a kinase adds it)

NO (neurotransmitter) will activated myosin like chane phosphatase which removes the phosphate causing relaxation

Question 25

The membrane potential of intestinal smooth muscle is not stable. what is its range

Answer 25

* Varies between -40 and -80 mV * Fluctuates in a pattern of Slow Waves or Basic Electrical Rhythm * Generated by Interstitial Cells of Cajal

Question 26

what is the MP of smooth muscle cells in the intestine generated by

Answer 26

• Generated by Interstitial Cells of Cajal Interstitial cells of cajal which spontainiously depolerisae and reploerise. These are connected to the smooth muscle cells therefore it causes them to contract and relax this facilitates a pattern of slow waves or basic electrical rhythm

Question 27

how do Interstitial cells of Cajal (ICC) Generate slow waves

Answer 27

Function as pacemakers by causing rhythmic changes in: | • Activity of Na+/K+ ATPase and Membrane K+ conductance

Question 28

where are interstitial cells of cajal located

Answer 28

Stomach and small intestine - In smooth muscle layer close to myenteric plexus • Colon - Boundary of muscle layer and submucosal layer

Question 29

describe the arrangement of ICC

Answer 29

• Send multiple branching processes to surrounding smooth muscle cells • Electrically linked to other ICC & muscle cells by gap junctions

Question 30

what would happen if you knocked out the ICC

Answer 30

If you take away the interstitial cells of cajal then you don't get the slow waves therefore you don't get the regular fluctuations of membrane potential

Question 31

what determins the frequency of contraction of smooth muscle

Answer 31

slow waves which are generated by ICC Therefore the frequency of contraction does not chane in different areas of the GI tract (except in pathological conditiins)

Question 32

Different areas of the GI tract will have different ICC with have different firing rates. This has a functional purpose. what is this

Answer 32

The higher up you go the more you want to digest therefore it is faster and the lower region is slower beacyse you want to give more time for absorption

Question 33

the firing rate of the ICC differs in different parts of the GI tract. what are these different rates

Answer 33

Faster in the proximal regions of the GI tract (digestion) = Duodenum 12 – 20 per minute Slower in the distal regions of the GI tract (absorption) = Colon 6-8 per minute

Question 34

describe how Action potentials determine the force (size/amplitude) of contraction in smooth muscle

Answer 34

* Small / no contractions occur in absence of action potentials * If the membrane potential does not reach threshold no contraction. • Greater the number of action potentials the greater the force of contraction • The longer the potential is above threshold, the more APs, the bigger the contraction. • Calcium also contributes – elevated Ca2+ = more calmodulin / myosin light chain kinase activation.

Question 35

Elevation of intracellular Ca2+ initiates contraction – two mechanisms describe the one to do with depolerisation

Answer 35

Depolarisation of cell membrane potential Opens voltage gated Na+ and Ca2+ channels in sarcolemma (cell membrane) Results in an Influx of Ca2+ which activates contraction (calmodulin & MLCK) as well as activates the ryanodine receptor resulting in release of Ca2+ from the sarcoplasmic reticulum (Ca2+ induced Ca2+ release) This increases the contraction amplitude.

Question 36

Elevation of intracellular Ca2+ initiates contraction – two mechanisms describe the one via the Gq pathway

Answer 36

this is pharmomechanical contraction. is is caused when Hormones & neurotransmitters bind to a receptor to induce Ca2+ release. • Gαq - Signaling pathway activated • Receptor activation of phospholipase C • Production of IP3 • IP3 induces release of Ca2+ from sarcoplasmic reticulum This increases the contraction amplitude

Question 37

both mechanisms of Ca elevation lead to increased contraction amplitude and can occur at the same time.

Answer 37

6

Question 38

what 3 things down regulate smooth muscle contraction

Answer 38

hyperpolarisation increased activity of myosin light chain phosphatase inhibition of excitatory ENS neurotransmittion

Question 39

describe how hyperpolarisation of smooth muscle cell membrane (or decrease Ca2+) happens

Answer 39

* Slow waves do not pass threshold - No contraction | * Or Pass threshold but reduce the number of action potentials - Reduced force

Question 40

2. Increased activity of Myosin Light Chain Phosphatase

Answer 40

• Dephosphorylates myosin so reduced force of contraction

Question 41

describe hormone and neurotransmitters effect on regulating contractions

Answer 41

Hormones and neurotransmitters regulate contractions • Modulate magnitude/strength of contraction only • Little effect on frequency (this is determined by ICC and varies by region)

Question 42

describe an example here neural control can effect smooth muscle activity

Answer 42

increase in parasympathetic activity = increase in ACh binding to muscarinic receptors this activates the ENS which increases smooth muscle activity this causes More time above threshold means greater force of contraction and more GI tract motility if this was sympathetic activation noradrenalin would be released which would bind to the a1 receptor decreasing ENS activity therefore Less time above threshold means smaller force of contraction and less GI tract motility

Question 43

what receptor do opiods bind to

Answer 43

Opioids can be very specific for receptors in the GI tract called reperiomid or amodium which is used to treat diarrhea G alpha inhibbitory

Question 44

when opioids bind to their receptors what happens

Answer 44

These inhibit an expiratory signal which would normally tell the ENS to contract The smooth muscle doesn't contact and then it doesn't aid in the digestion and movemt of chime through the GI tract which halts a lot of the digestive processes. If you had diarrhea this would be a good thing as you would have more time to reabsorbe water and salts loosed In a healthy perosn however this would lead to constipation, constipation causes stretching damage to the GI tract which over time will cause pain and mellabsorbtion

Question 45

what is Impacted bowel

Answer 45

is when the facies is so hard that the intestine cant move it

Question 46

what did elvis presley's autopsy show

Answer 46

He had a heart attack but when they looked at his GI tract he as constipated and a megacolon (because it had been stretched) The enlarged colon mean that you needed more contraction to induce defecation. What he was doing in called Valsalva maneuver (what you do when you take a massive shit).

Question 47

what is the Valsalva menover and what does it cause (how does it cause a heart attack)

Answer 47

Valsalva menover (what you do when you take a massive shit). This increased the thoracic pressure, increasing the abdominal pressure which puts pressure on the bowl to force poop out the Valsalva menover it increases the intrathoracic pressure which created a compression on the aorta. This compression pushes everything on the aorta backwards. When the aortic pressure is higher then you ventricular pressure the openings to the coronary arteries are open. Therefore if you have anything that could cause blockage of the coronary arteries (clots) and you perform this Valsalva menover and they get pushed backwards then you are going to have a very large heart attack.

Question 48

Which of the following statements about the spontaneous contractions of intestinal smooth muscle is not correct? A. These are phasic contractions generated by interstitial cells of Cajal. B. Spread of spontaneous contractions depends on gap junctions between intestinal smooth muscle cells. C. The frequency of contractions is dependent on the region of the intestine. D. Spontaneous contractions are generated by the parasympathetic nervous system. E. Intestinal smooth muscle can contract independently of the central nervous system.

Answer 48

D