Gastrointestinal 1 - 3

Question 1

functions

Answer 1

digestion and absorption of nutrients
achieved through:
motility to propel food
secretions from glands
digestion/hydrolysis into absorbable molecules
absorption into bloodstream of nutirients, electrolytes and water

Question 2

structure of GI tract wall

muscosal layer

Answer 2

long muscular tube with variatiosn of structure for functions:
- muscosal layer = epithelial cells for sec/abs, lamina propia (connective tissue, contains blood and lymph vessels), muscularis mucosae (smooth muscle)

Question 3

GI tract wall

submucosal layer

Answer 3

collagen, elastin, glands. blood vessels

Question 4

GI tract wall

circular and longitudinal muscle layer

Answer 4

motility
circular - thick, more densley innervated - contraction = dec diameter
longitudinal - thin, mainly nerve fibres - contraction = dec in segment length

Question 5

GI wall

serosa

Answer 5

outer layer, made of connective tissue

may be surrounded by mesenthial layer to prevent friction in very active areas

Question 6

mesentry

Answer 6

connects to abdominal wall

Question 7

2 plexuses

Answer 7

contains enteric nervous system
submucosal and myenteric plexus
plexus = branched network of interconnecting nerves

Question 8

enteric nervous system

Answer 8

innverates GI tract
collection of nerve plexuses surrounding GI tract - inc pancreas and biliary system
more neurons than spinal cord
part of ANS

Question 9

neuronal control

Answer 9

regulated by ANS
extrinisic = sympathetic and parasympathetic innervation
intrinsic = ENS, primary mechanism, ganglia within submucosal and myenteric plexuses
can direct all function of GI tract in absense of extrinsic innveration

Question 10

parasympathetic control

Answer 10

ganglia within plexuses co ordinate info received from PNS and relay to smooth muscle, endocrine and secretory cells
post ganglionic neurons are either cholinergic or peptidergic

Question 11

sympathetic control

Answer 11

post gang nerve fibres are adrengeric
nerve fibres are mixed afferent and efferent
sensory and motor info relayed between GI tract and CNS, co-ord by plexuses

Question 12

GI regulatory substances

Answer 12

regulate contraction, sphincters
peptides classified as: hormones - from GI endocrine cells e.g. GIP
paracrines - from endocrine cells, act locally e.g. somatostatin
neurocrines - released from neuron following action potential

Question 13

motility

Answer 13

grinding, moving and fragmentation of food
msot contractile tissue is unitary smooth muscle - cells electrically coupled via gap junctions - rapid spread of action potential leading to co-ord contraction

Question 14

contractions

Answer 14

phasic - periodic contraction and relaxation (3-12/min)
tonic - constant level of contraction/tone
slow waves - subthreshold mem depolarisation (inward Ca trhough channel), repolarisation (outward K)
contraction is preceded by electrical activity

Question 15

GI pacemaker

Answer 15

interstitial cell of cajal ICC

Question 16

motility

Answer 16

subthreshold w
slow waves produce weak contraction - tonic
action potential on top - phasic
low pressure organs separated by sphincters - specialised circular muscles with positive resting pressure e.g. upper and lower oesophageal, pyloric, anal
regulated antegrade and retrograde movement

Question 17

mouth

Answer 17

teeth and tongue mechanically break down food
reduce particles and add saliva, results in smooth bolus of food ready for swallowing
saliva lubricates food, contains alpha amylase