GIT motility

Question 1

what are the main functions of the GIT?

Answer 1

• propel ingested food along the entire length of the GIT
• mixing and grinding of the contenets of the GIT
• aid absorption of nutrients and water
• clear the stomac and intestines of luminal contents

Question 2

what is GIT motility?

Answer 2

this is the ability of the alimentary canal (tract) to contract and propel ingested substances along its length

timing of food movement is important for optimum processing

Question 3

what things does mastication aid in??

chewing

Answer 3

• teeth (incisors and molars)
• mixing food with saliva (lubrication - mucin is a glycoprotein that acts as a lubricant)
• reduces food size (facilitates swallowing)
• mixes food components with digestive enzymes (carbohydrate with salivary amylase for carbohydrate digestion and fat with lipases for lipid digestion)

Question 4

the muscles of the teeth are innervated by which nerve

Answer 4

trigeminal nerve

cranial nerve V

Question 5

what is the process of mastication controlled by?

Answer 5

it is controlled by brain stem nuceli
- reticular areas for rythmical chewing
- additional involvement from the hypothalamus/amygdala/cerebral cortex

Question 6

what are the 3 stages of Deglutition (swallowing)

Answer 6

1) voluntary stage = initaites the swalloing process
2) pharyngeal phase = involuntary passage of food through the pharynx into the esophagus
3) oesophageal phase = involuntary transport of food from the pharynx to the stomach

Question 7

what does deglutition require?

Answer 7

it requires the pharynx to be a tract for propulsion of food
- this is important so that respiration is not compromised

Question 8

describe the steps/movement of mouth muscles/ tongue in the voluntary phase (phase1)?

Answer 8

1- food is voluntarily moved posteriorly into the pharynx by the tongue
2- the trachae is closed
3- the oesophagus is opened
4- a fast peristaltic wave is initiated by the nervous system of the pharynx forces the bolus of food into the upper esophagus

happen in < 2 seconds

Question 9

the pharyngeal phase is a reflex arc (automatic), what is it initiated by?

Answer 9

it is initaited by the voluntary movement of food into the back of the mouth
- detected in a ring area around the pharyngeal opening.
- excitation of the involuntary pharyngeal sensory receptors to elicit the swallowing reflex.

Question 10

how is the oesophageal phase initiated?

Answer 10

This stage is iniated automatically by neuronal areas of the medulla and lower pons
- the motor impulses from the swalloing centre to the pharynx and upper eosophagus that causes swallowing are transmitted successively by CN V, CN IX, CN X, CN XII

Question 11

what is the effect of pharyngeal stage of swallowing on respiration?

Answer 11

• the pharyngeal stage occurs in < 6 seconds
• interuption of respiration is for a fraction of usual respirator cycle
• the swallowing centre will specifically inhibit the respiratory centre of the medulla during this time (respiration is arrested very breifly)

Question 12

stage 1 peristalsis?

Answer 12

• continuation of the peristaltic wave that begins in the pharynx and spreads into the eosphagus during the pharyngeal stage of swallowing
• this is a continous wave tht passes from the pharynx to the stomach in about 8-10 seconds

Question 13

stage 2 peristalsis?

Answer 13

• this is a result from distention of the oesophagus by retained food
• the waves continue until all food has emptied into the stomach

Question 14

what is stage 2 of peristalsis iniated by?

Answer 14

• intrinsic neural circuits in the myenteric nervous system
• reflexes that begin in the pharynx

Question 15

what are th 2 different types of muscle that are found in the oesophagus?

Answer 15

1) straited muscle in the upper 1/3rd. (they creates peristaltic waves)
2) smooth muscle in the lower 2/3rds

Question 16

what controls the 2 different types of muscle in the oesophagus?

Answer 16

straited = controlled by skeletal nerve impulses from the glosspharyngeal and vagus nerves

smooth = vagus nerve that acts through connections with the oesophageal myenteric nervous plexus.

Question 17

under normal circumstances, what hsould happen in the oesophageal phase and peristalsis?
what happens in abnormal circumstances?

Answer 17

primary peristalsis should happen, this is an automatic and singular wave of contraction that does not stop until food is in the stomach.

in abnormal circumstances, if there is a blockage, a second wave will occur= secondary peristalsis.

Question 18

what is receptive relaxation?

Answer 18

this is relaxation wave that precedes peristalsis
- it opens the oesophageal sphincter in preparation for food to allow the stomach to relax. for the stomach to expand it has to relax.
- it occur ahead of the peristaltic wave
- it allows easy propulsion of food into the stomach.

Question 19

what controls receptive relaxation

Answer 19

myenteric inhibitory neurons.

Question 20

in the last 3cm of the oesophageal circular muscle, what does it act as?

Answer 20

it acts as a lower oesophageal sphincter called the gastroesophageal sphincter
- it is normally tonically constricted.

Question 21

what happens to the food entering the stomach?

storage motor function of stomach

Answer 21

the food entering the stomach will form concentric circles in the stomach.
- newest food lying closest to the oesophageal sphincter
- oldest food lying nearest the outer wall of the stomach

Question 22

what are the 3 motor functions of the stomach?

Answer 22

storage
mixing
emptying

Question 23

describe the ‘vagovagal reflex’?

Answer 23

this reflex is initated by food stretching the stomach.
- stomach -> brain stem -> back to the stomach

• this will cause a decrease in tone in stomach muscular wall
• the wall will then bulge outwards
• greater quantities of food will be accomated for.

limit = 0.8-1.5 litres

Question 24

describe the motor function ‘mixing’ of the stomach?

mixing motor function of stomach

Answer 24

• mixing of the food with gastric secretions forms a semifluid micture (chyme)
• there are mixing waves = peak peristaltic constrictor waves which begin in mid/upper portions of the stomach wall, they move forward every 15-20 secs.
• these waves become more intense

Question 25

describe how you get segmentation of the small intestine | mixing contractions and segmentation contractions

Answer 25

- chyme induced extension of the GI wall -> stretch -> localised concentric contractions (spaced along intestine, short lasting) -> segmentation - the frequency of segmentation will be determined by the frequnecy of the slow waves

Question 26

how can segmentation become weaker?

Answer 26

it can become weak when the excitator activity of the enteric nervous system is blocked by atropine

Question 27

what causes segmentation of the small intestine

Answer 27

slow waves in the smooth muscle however, it is not effective without the background excitation from the myenteric nerve plexus

Question 28

describe the activity of peristalsis after a meal?

Answer 28

- chyme entry into duodenum -> duodenal wall stretch - gastroenteric reflex (from stomach distension via the myenteric plexus) - gastrin, CCK, insulin, motilin, serotonin increases motility - secretin, glucagon decreases motility | activity is increased after a meal

Question 29

describe the propulsive movement of peristalsis?

Answer 29

- occurs in any part of the small intestine - moves towards anus at 0.5-2cm/s - it becomes weak and dies out after 3-5cm - the net movement of chyme is slow:1cm/min - the chyme movement from pylorus to iliocecal valve takes about 3-5 hrs

Question 30

where is the ileocecal valve? how does it close?

Answer 30

- it protudes into the lumen of the cecum - it forcefully closs when excess pressure builds up in the cecum.

Question 31

describe the structure of the ileocecal sphincter?

Answer 31

the wall of the terminal ileum is thickened circular muscle and this creates a sphincter - it normally remains mildly constricted and slows emptying of ileal contents into the cecum

Question 32

what happens to the ileocecal valve immediatly after a meal?

Answer 32

the gastroileal reflex intensifies peristalsis in the ileum and there will be emptying of ileal contents into the cecum

Question 33

what is the ileocecal sphincter regulated by?

Answer 33

the cecum to ileocecal sphncter and cecm ileum reflex is mediated by the myenteric plexus and extrinsic autonomic nerves.

Question 34

what are the mixing movements in the colon aided by? what are these?

Answer 34

mixing movemets in colon = haustrations - these are similar to segmentation movements in the small intestine - there is combined contraction of circular and longitudinal smooth muscle - it generates bag like sacs (30 seconds peak, then 60 secs disappear)

Question 35

what is the differance in function for the proximal and distal half of the colon?

Answer 35

proximal half = absorption distal half = storage

Question 36

what happens in modified peristalsis | mass movements

Answer 36

- a constrictive ring occurs (usually in the transverse colon) in response to distension - 20cm of colon distal to constrictive ring lose haustrations and contract as a unit - fecal material move in mass down the colon.

Question 37

describe the time frame for propulsive movements?

Answer 37

- contraction develops progressivly over 30 secs - relaxation occurs over the next 2-3 mins - another mass movement then occurs - a series of mass movements persists for 10-30 mins, then it stops. - it will return at variable time points (usually every 12 hrs- straight after breafast) - sensation oif need to poo is felt when poo is in the rectum. this is our body getting rid of excess food in preparation for more meals.

Question 38

describe gastrocolic and duodenal colic reflexes?

Answer 38

gastrocolic = reflex as food moves into stomach duodenal colic = movement as food moves into duodenum - this is facilaited mass movement after meals - due to distention of the stomach and duodenum

Question 39

describe the innervation of gastrocolic and duodenal colic reflexes? and how are they inhibited?

Answer 39

reflex from GIT to prevertebral sympathetic ganglia and back to GIT - the reflex will be inhibited when extrinsic autonomic nerves of the colon are removed

Question 40

what is the effect of iritation of the colon?

Answer 40

irritation of the colon can also cause mass movemnts eg - ulcerated condition of colon mucosa, mass movement persists almost all the time.

Question 41

describe defication and how does the anal canal change?

Answer 41

- the rectum is usually empty of faeces - the anal canal is tightly closed via the contraction of anal sphincters - gas or faeces in the rectum will stimulate stretch receptors in its wall initating the rectosphincteric reflex - defication is a reflex activity but it is subject to conscious control.

Question 42

describ the rectosphincteric reflex?

Answer 42

this reflex relaxation of the smooth muscle of the internal anal sphincter and contraction of the striated muscle of the external anal sphincter (this is what stops us from pooing ourselves all the time)