motility of the gut

Question 1

is GI muscle single or multi unit smooth muscle ?

Answer 1

coupling of cells to act as single unit

Question 2

what mechanism operates in smooth muscle to reduce the use of ATP

Answer 2

the latch bridge mechanism

Question 3

are actin + myosin arrangements highly structured in smooth muscle

Answer 3

no they arent arranged in rows

Question 4

which cells act as pacemakers in GI tract ?

Answer 4

interstitial cells of Cajal

Question 5

what is the term used to describe smooth muscle when it is able to function over a wide range of lengths

Answer 5

plasticity

Question 6

what effects do the following have on gastric motility ?
vagal stimulation 
CCK
GIP 
Secretin

Answer 6

increase
decrease
decrease
decrease

Question 7

which has the fastest rate of spontaneous activity 
stomach 
duodenum 
ileum 
colon

Answer 7

duodenum - 13 contractions per minute

Question 8

what are the functions of motility in the GI tract

Answer 8

mixing

propulsion

Question 9

what is motility dependent on ?

Answer 9

smooth muscle
enteric nervous system
autonomic nervous system
hormones

Question 10

describe the contractile activity of the visceral smooth muscle of Gi tract :

Answer 10

shows rhythmic cycles of activity through pacemaker cells ( interstitial cells of cajal)

Question 11

describe the contractile activity of peristalsis

Answer 11

waves that move bolus

Question 12

describe the contractile activity of segmentation

Answer 12

churn + fragment bolus

Question 13

what are 3 main factors influencing GI tract motility ?

Answer 13

• smooth muscle functional syncytium
• neural control
• hormonal control

Question 14

what is smooth muscle functional syncytium ?

Answer 14

electrical activity of muscle cells
slow wave of pacemaker potentials
spike potentials that result in contraction

Question 15

how does neural control influence GI tract motility ?

Answer 15

parasympathetic pathway excites + inhibits motility

sympathetic pathway inhibits effects of motility

Question 16

what are the 2 distinct areas of motor activity in the stomach ?

Answer 16

proximal

distal

Question 17

what is the migrating motor complex ?

Answer 17

when indigestible solids that have failed to pass through the pylorus can pass into the small intestine between meals
is a result of motor activity

Question 18

what is the bodies response to the stomach filing ?

Answer 18

stomach pressure remains constant until around 1l of food ingested due to plasticity of smooth muscles
peristaltic waves move toward pylorus at rate of 3 per minute
basic electrical rhythm initiated by pacemaker cells

Question 19

where does the most vigorous peristalsis + mixing occur

Answer 19

near the pylorus

Question 20

what happens to chyme at the pylorus ?

Answer 20

• delivered in small amounts into the duodenum

- or if to big forced backwards into stomach for further mixing

Question 21

what is gastric emptying regulated by ?

Answer 21

neural enterogastric reflex

hormonal mechanisms

Question 22

how do mechanisms work to regulate gastric emptying ?

Answer 22

inhibit gastric secretion + duodenum filling
carbohydrate rich chyme quickly moves through duodenum
fat-laden chyme is digested more slowly causing food to remain in stomach for longer

Question 23

how does secretin help regulate gastric activity ?

Answer 23

stimulates HCO3 secretion

inhibits stomach activity

Question 24

how does CCK regulate gastric activity ?

Answer 24

stimulates gallbladder contraction + emptying

inhibits stomach activity

Question 25

how does motilin regulate gastric activity ?

Answer 25

increase gastric motility | increases intestinal motility

Question 26

how does neuronal control regulate gastric activity ?

Answer 26

short reflexs operating in the enteric nervous system inhibit gastric secretions/ contractions long reflexes operating via the CNS alter autonomic nerve activity

Question 27

what is the enteric nervous system ?

Answer 27

intrinsic NS that controls different functions of GI tract

Question 28

why is the ENS describe as separate from the ANS ?

Answer 28

because it has its own independent reflex activity

Question 29

what are the 2 types of ganglia in the ENS ?

Answer 29

myenteric ( auerbach) | submucosal (meissner)

Question 30

where is the myenteric plexuses located ?

Answer 30

inner + outer layers of the muscular external

Question 31

where the submucosal plexuses located ?

Answer 31

in the submucosa

Question 32

what do neurons in the ENS respond to ?

Answer 32

mechanical deformation chemical stimuli temperature

Question 33

what do receptors in the duodenum + jejunum sense ?

Answer 33

acidity osmotic pressure certain fats amino acids + peptides

Question 34

what sympathetic nerves innervate the GI tract ?

Answer 34

coelic superior + inferior mesenteric hypogastric plexuses

Question 35

what parasympathetic nerves innervate the GI tract ?

Answer 35

preganglionic cholinergic fibres terminate on ganglion cells in the intramural plexuses