Movement of Food - Gut Motility and Control

Question 1

What are examples of controlled motility?

Answer 1

swallowing, mixing, emptying of stomach and defaecation

Question 2

Where are most nutrients absorbed?

Answer 2

small intestine

Question 3

What are the 4 layers of the GI tract?

Answer 3

mucosa, submucosa , muscularis externa, serosa

Question 4

What are GI sphincters?

Answer 4

Smooth muscle rings that act as valves

Question 5

What are main functions of the digestive tract?

Answer 5

motility, secretion of juices, digestion and absorption

Question 6

Describe motility?

Answer 6

propel ingested food from mouth to rectum

Question 7

Describe secretion of juices?

Answer 7

Aid in digestion and absorption

Question 8

Describe Digestion?

Answer 8

food broken down into absorbable molecules

Question 9

Describe Absorption?

Answer 9

nutrients, electrolytes and water are absorbed from lumen of GIT to blood

Question 10

What is Phasically?

Answer 10

smooth muscle cells in muscularis layer can cause rapid contractions and relaxation for e.g peristalsis and segmentation in oesophagus

Question 11

What is Tonically?

Answer 11

sustained contractions lasting minutes to hours e.g sphincters in fundus

Question 12

What can contractions be modulated by?

Answer 12

nerves, hormones, local factors

Question 13

What are effector units?

Answer 13

SMC’s arranged in sheets of bundles to contract synchronously

Question 14

What allows contractions to happen in the GI?

Answer 14

Smooth muscle cells connected by gap junctions allows AP to travel in all directions

Question 15

Where is there low electrical resistance? and why?

Answer 15

in SMC gap junctions so electrical activity can spread readily for synchronous contractions

Question 16

What is special about SMC’s in the GI tract?

Answer 16

polarised - negative inside respectively

Question 17

What is the level of polarisation in the GI set by?

Answer 17

cells of cajal - specialised non contractile pacemaker cells

Question 18

What do cells of cajal do?

Answer 18

generate slow wave potentials and are electrically coupled to SMC’s , lie between nerve fibres and smc’s

Question 19

What can electrical activity by stimulated by?

Answer 19

Stretch, gastrin, ACh

Question 20

What can inhibit electrical stimulation?

Answer 20

noradrenaline, CCK, secretin

Question 21

What does parasympathetic innervation do to GI?

Answer 21

increase gut muscle activity, relax sphincter

Question 22

What does sympathetic innervation do to GI?

Answer 22

inhibit gut movements and constrict sphincters

Question 23

What do Hormones do in GI?

Answer 23

motilin increase activity

CCK or secretin decrease activity

Question 24

What happens in peristalsis of phasic contractions?

Answer 24

adjacent segments of intestine alterate contract and relax to move food along distally

Question 25

What happens in segmentation of phasic contractions?

Answer 25

nonadjacent segments of intestine alternate and contract/relax moving food forwards and backward to mix food

Question 26

Where is peristalsis seen?

Answer 26

oesophagus, stomach, small and large intestine

Question 27

Where is segmentation seen?

Answer 27

small and large intestine

Question 28

What happens on an empty stomach?

Answer 28

contracts when blood glucose is low due to activation of vagus nerve

Question 29

What happens on filling stomach?

Answer 29

expands from 50ml to 1L without pressure rising, ruggae flatten, relaxation and plasticity of SMC

Question 30

What happens to food storage?

Answer 30

not much action in first 30 min then peristalsis

Question 31

What happens when mixing food with secretions?

Answer 31

Peristaltic contractions build towards antrum region for churning

Question 32

What happens with emptying of chyme intro the duodenum?

Answer 32

small 3ml of chyme goes into duodenum with each peristaltic wave most goes to antrum the pyloric sphincter closes to allow backflow of empying, stops reflux

Question 33

What occurs during stimulation of gastric phase?

Answer 33

Stretch of walls release gastrin and activate CNS, increase motility and emptying of stomach

Question 34

What occurs during inhibition of intestinal phase?

Answer 34

empty stomach contents to duodenum, releases hormones to inhibit gastric motility such as secretin and cck, inhibit nerve reflex

Question 35

What is housekeeping contractions?

Answer 35

sweep any contents secretions debris through colon and keep intestine clean

Question 36

What is the migrating myoelectric complex?

Answer 36

slow wave activity in duodenum as previous wave reaches terminal ileum

Question 37

When does segmentation contractions occur in s.intestine?

Answer 37

as chyme enters as it provide through mixing

Question 38

How is motility controlled in small intestine?

Answer 38

extrinsic and intrinsic nerves and hormones

Question 39

What is the ileocaecal sphincter?

Answer 39

controls rate of entry into large intestine , stops bacteria and other pathogens, normally closed

Question 40

What is the main function in the large intestine?

Answer 40

storage and release of faecal material, absorption of fluid and electrolytes has no villi

Question 41

What is the main motility of large intestine?

Answer 41

segmentation , strong peristalsis then defaecation

Question 42

What is diarrhoea?

Answer 42

passage of watery faeces in excess of 500ml a day from increased colonic fluid volume

Question 43

In diarrhoea why would fluid accumulate in the intestinal lumen?

Answer 43

defective ion transport, osmosis, hypermotility of intestine and active secretion

Question 44

What is constipation?

Answer 44

difficult in defaecation due to excessive dehydration, delayed transit inadequate dietary fibre and drugs

Question 45

What are disorders of motility?

Answer 45

damage to extrinsic nerves, damage to intrinsic myenteric nerve plexis and migraine - stomach inactive and IBS