alimentary mechanisms

Question 1

number of neurones in GIT wall

Answer 1

10-100 million (100 billion in brain)

Question 2

what nervous system do neurones in GIT communicate with

Answer 2

autonomic

Question 3

how are GIT neurones arranged

Answer 3

rich plexuses of nerves and supporting cells and ganglia

Question 4

what do ganglia consist of

Answer 4

nerve cells to carry signals, and glial cells which provide insulation, protection and nutritional and structural support

Question 5

what interconnect ganglia

Answer 5

tracts of fine, unmyelinated nerve fibres

Question 6

main feature of enteric nervous system

Answer 6

integrating centre to specific stimuli independent of CNS for coordinating function

Question 7

4 things which cause enteric nervous system disruption

Answer 7

inflammation (ulcerative colitis, Crohn’s disease), following invasive abdominal surgery, irritable bowel syndrome, ageing (constipation)

Question 8

2 plexi in gut wall which communicate directly with each other to make “local” decisions based on “local” signals

Answer 8

myenteric (Auerbach’s), submucosal (Meissner’s)

Question 9

where is myenteric plexus located

Answer 9

between circular and longitudinal smooth muscle layers

Question 10

innovation of myenteric plexus

Answer 10

efferent of both layers of smooth muscle

Question 11

what does myenteric plexus control and what does this allow

Answer 11

controls entire activity of muscularis externa, allowing for coordinated control of motor function and motility

Question 12

afferent function of submucosal plexus

Answer 12

senses environment within lumen using mechanoreceptors, chemoreceptors and osmoreceptors

Question 13

efferent function of submucosal plexus

Answer 13

fine tune local blood flow, epithelial transport and secretory, paracrine (diffusion) or endocrine cell function (circulation)

Question 14

4 key functions of enteric nervous system (SPAM)

Answer 14

secretion, perfusion, absorption, motility

Question 15

what areas of gut are heavily perfused

Answer 15

VSMCs, submucosal glands, absorbing enterocytes

Question 16

what is absorbed and how is this controlled

Answer 16

nutrients, vitamins, minerals and ions by adjusting expression of luminal transport proteins

Question 17

what causes effective gut transit

Answer 17

SMCs in circular and longitudinal muscle layers contract and relax at different rates

Question 18

what type of neurones are most present

Answer 18

multipolar (one axon, multiple dendrites)

Question 19

what do sensory neurones respond to

Answer 19

mechanical, thermal, osmotic and chemical stimuli

Question 20

where do motor cells terminate

Answer 20

SMCs, secretory cells of GI blood vessels

Question 21

function of interneurones

Answer 21

integrate sensory input and effector output

Question 22

where are SNS preganglionic neuronal cell bodies located

Answer 22

in spinal cord in lower thoracic and upper lumbar spinal cord

Question 23

where are SNS postganglionic neuronal cell bodies located

Answer 23

in pre- and paraverterbal ganglia

Question 24

where are PNS preganglionic neuronal cell bodies located

Answer 24

in brainstem and sacral spinal cord

Question 25

where are PNS postganglionic neuronal cell bodies located

Answer 25

very close to target organs

Question 26

length of SNS preganglionic and postganglionic nerves

Answer 26

preganglionic short, postganglionic long from sympathetic chain

Question 27

length of SNS preganglionic and postganglionic nerves

Answer 27

preganglionic long, postganglionic short

Question 28

SNS preganglionic innervation

Answer 28

preganglionic neurones are in splanchnic nerves from thoracic and lumbar regions

Question 29

what do thoracic branches of SNS innervate

Answer 29

foregut and associated organs

Question 30

what do lumbar branches of SNS innervate

Answer 30

hindgut

Question 31

PNS innervation

Answer 31

most GIT innervation in branch of ANS arises from vagus nerve; structures from descending colon onwards from pelvic splanchnic nerves (S2-S4)

Question 32

SNS neurotransmitters between SNS and enteric nervous system

Answer 32

norepinephrine

Question 33

SNS neurotransmitters in sympathetic chain

Answer 33

acetylcholine

Question 34

PNS neurotransmitter

Answer 34

acetylcholine

Question 35

effect on gut function of SNS and PNS

Answer 35

SNS reduces activity (innovation of VSMCs allows rapid shut down of gut perfusion in high stress situations), PNS increases activity

Question 36

examples of minor plexuses

Answer 36

deep muscular plexus (inside circular muscle), ganglia supplying biliary system and pancreas

Question 37

what does sympathetic control directly

Answer 37

blood vessels for vasoconstriction (coeliac, superior and inferior mesenteric)