gut motility

Question 1

what are the types of cells found in the wall of the GI tract?

Answer 1

interstitial cells of cajal
smooth muscle cells
enteric neurons

Question 2

what do ICCs do?

Answer 2

spontaneously generate electrical slow waves –> phasic muscle contractions

Question 3

how are the electrical waves of ICCs transmitted through smooth muscle

Answer 3

gap junctions

Question 4

what is the advantage of smooth muscle being arranged as a functional syncytium?

Answer 4

allows waves to spread over large distances

Question 5

what are the two plexuses of the GI system and what do they control?

Answer 5

Myenteric plexus – controls movement of the gut

Submucosal plexus – controls secretion, absorption and mucosal function

Question 6

what does the ENS control?

Answer 6

GI motility, local blood flow and trans mucosal movement of fluids

Question 7

what neurones does the ENS contain?

Answer 7

sensory
interneurons
motor

Question 8

what modulates the ENS?

Answer 8

extrinsic nerves

hormones

Question 9

explain the intrinsic innervation of the gut

Answer 9

parasympathetic - vagus and pelvic nerves

sympathetic - prevertebral ganglia (greater splanchnic nerve, lumbar colonic nerve, hypogastric)

Question 10

describe which system controls each part of the GI tract?

Answer 10

oesophagus - CNS
stomach - myogenic, ENS and CNS
small intestine - ENS
large intestine - ENS and myogenic
rectum and anus - ENS and CNS

Question 11

what is the migrating motor complex?

Answer 11

large contraction every 90-120 minutes which occurs during hunger

Question 12

where does the MMC originate?

Answer 12

stomach - vagus dependent

small intestine - vagus independent

Question 13

what are the three phases of the MMC?

Answer 13

Phase I + II: build-up of irregular contractions

Phase III: high amplitude, big contraction

Question 14

what is the function of the MMC?

Answer 14

clears undigested material
prevents bacterial growth
gives sensation of hunger

Question 15

what are the three phases of food intake and when do they occur?

Answer 15

cephalic - prepares GI tract for food.

gastric - when food enters the stomach

intestinal - when food has been digested

Question 16

what occurs in the cephalic phase

Answer 16

MMCs abolished. saliva, gastric acid, pancreatic acid secreted.

Question 17

what is the gastric phase responsible for and what triggers it?

Answer 17

satiation, early digestion, gastric emptying

triggered by mechanical effect

Question 18

what triggers the intestinal phase and what occurs in it?

Answer 18

triggered by chemoreceptors in the small bowel

signals to stomach to stop eating - decreases appetite

Question 19

explain how the primary peristaltic wave occurs?

Answer 19

when bolus enters the oesophagus it hits the striated muscle

triggers vagus nerve –> primary peristaltic wave

Question 20

when does a secondary peristaltic wave occur in the oesophagus?

Answer 20

when the bolus moves down and gets stuck, triggering stretch receptors which trigger the ENS

Question 21

alongside peristalsis of the oesophagus, how is food movement into the stomach aided?

Answer 21

shortening of the longitudinal muscle

Question 22

what is the proximal area of the proximal area of the stomach?

Answer 22

funds and body

Question 23

what is receptive relaxation?

Answer 23

reflex in which the fundus relaxes to accommodate food triggered by the vago-vagal reflex

Question 24

what id adaptive relaxation?

Answer 24

the reflex which reinforces the reflective relaxation reflex. inhibitory NTS (NO) is released from the ENS so stomach dilates to accommodate food

Question 25

why may pressure build up in the stomach?

Answer 25

gas bubble forming from swallowing air

Question 26

how is pressure build up in the stomach relieved?

Answer 26

``` increased pressure picked up by the stretch receptors signals to vagus causes TLOSRs Burp reduces pressure inside stomach Avoids early satiety ```

Question 27

which has a thicker wall - distal or proximal stomach?

Answer 27

proximal

Question 28

what are the 3 phases of propelling food into the duodenum?

Answer 28

Phase 1: propulsion Phase 2: emptying Phase 3: Retropulsion - large particles are sent back into the antrum

Question 29

why is gastric emptying of liquids exponential?

Answer 29

no solids to grind or liquefy - no lag time

Question 30

how does the volume of liquid affect the gastric emptying time?

Answer 30

larger volume = emptied faster

Question 31

why do large solid particles suffer a lag phase?

Answer 31

need sufficient grinding first

Question 32

what does the rate of gastric emptying depend on?

Answer 32

physical properties neuronal and hormonal feedback nutritional content

Question 33

explain the duodenal and jejunal brake?

Answer 33

duodenum detects nutrients, osmolality and HCl levels CCK hormone is released to slow gastric emptying when too many nutrients enter the duodenum vagal afferents signal the motor nuclei which signal vagal efferents to reduce opening of pyloric sphincter, reduce contractions in antrum and enhance relaxation

Question 34

explain the ileal brake

Answer 34

Fats usually digested and absorbed in the duodenum Fats reach ileum Feedback slows gastric emptying and induces satiety

Question 35

what is the ileal brake mediated by?

Answer 35

peptide YY, Glucagon-like peptide-1, oxyntomodulin

Question 36

name some of the GI conditions associated with motility

Answer 36

Gastro-oesophageal reflux: failure to clear acid/dysfunctional lower oesophageal sphincter. Early satiety/nausea: incomplete gastric accommodation. Neuropathy: diabetes Dysrhythmia: nausea (gastroparesis) Obesity: poor feedback control.

Question 37

what kind of receptors do the enteric sensory neurons contain?

Answer 37

mechanical and chemical sensitive receptors

Question 38

what are the mechanical and chemical stimuli of peristalsis?

Answer 38

Mechanical stimuli – stretch, mucosal deformation Chemical stimuli – substances from endocrine cells (e.g. 5-HT), nutrients and low pH

Question 39

what do the sensory neurons of the GI tract do?

Answer 39

detect intraluminal stimuli initiate peristalsis, plus increased secretion & vascular flow

Question 40

how is information from sensory neurons transmitted to motor neurons?

Answer 40

Via interneurons ACh - secreted by excitatory nerves to the ascending wave of peristalsis NO - secreted by inhibitory neurons to the descending wave of peristalsis

Question 41

what are the functions of the ascending colon?

Answer 41

fermentation - rich in bacteria | absorption - of water and ions

Question 42

what is the advantage of haustra in the ascending colon?

Answer 42

increase surface area

Question 43

what are the movements of the ascending colon and what do they do?

Answer 43

propulsion and retropulsion - churn and slow transit | segmentation - mixes content and increases exposure to mucosa

Question 44

what controls movement in the colon and rectum?

Answer 44

ICCs, local mediators (5-HT) and local environment

Question 45

what occurs in the transverse colon?

Answer 45

absorption | relatively rapid transmit

Question 46

what occurs in the descending colon?

Answer 46

storage, slow, partly involuntary transit

Question 47

how does the colon decide which way to go?

Answer 47

interstitial cells, ENS and extrinsic nervous system

Question 48

explain how the conscious urge to defecate is triggered

Answer 48

contents distend rectum pressure increases passively (increases further by active contraction) accompanied by relaxation of internal anal sphincter and contraction of external sphincter contents continue to enter rectum triggers conscious urge to defecate

Question 49

what normally presents defecation?

Answer 49

tone of internal anal sphincter & puborectalis | mechanical effects of acute anorectal angle

Question 50

how is defecation initiated?

Answer 50

puborectalis muscle & external anal sphincter relax | intraabdominal pressure increased - facilitated by squatting

Question 51

what is water needed for?

Answer 51

Digestion and absorption – hydrolysis is main chemical reaction Facilitates propulsive movement of intestinal contents By liquefying intestinal contents, allows digested nutrients to be brought into close contact with absorptive microvilli surface

Question 52

name some conditions of the colon

Answer 52

pseudo-obstruction diarrhoea slow transit constipation - adult females chronic constipation - more common in elderly faecal incontinence