Introduction to the Structure, Functions and Control of the Alimentary Canal

Question 1

alimentary canal

Answer 1

series of hollow organs running from mouth to anus

Question 2

what do sphincters do

Answer 2

separate organs

control movement

prevent backflow

Question 3

mouth and oropharynx

Answer 3

eats
starts carbohydrate digestion - ligase
propels food to oesophagus

Question 4

oesophagus

Answer 4

propels food to stomach

Question 5

stomach

Answer 5

stores/churns food
carbohydrate digestion
initiates protein digestion
regulates delivery of chyme to duodenum

Question 6

small intestine

Answer 6

principle site of digestion and absorption of nutrients

duodenum, jejunum and ileum

Question 7

large intestine

Answer 7

colon reabsorbs fluids and electrolytes
stores faecal matter before delivery to rectum

caecum, appendix and colon

Question 8

rectum and anus

Answer 8

regulated expulsion of faeces

Question 9

accessory structures

Answer 9

salivary glands
pancreas
hepatobiliary system - liver and gall bladder

Question 10

digestive tract wall

Answer 10

mucosa, submucosa, muscular externa, serosa

Question 11

overall length of digestive tract

Answer 11

7-10m

Question 12

mucosa of digestive tract

Answer 12

mucous membrane (epithelial, exocrine and endocrine glands)
lamina propria (capillaries, enteric neurones , gut-associated lymphoid tissue)
muscular mucosae

Question 13

submucosa of digestive tract

Answer 13

connective tissue
larger blood and lymph vessels
submucosa plexus (neurone network)

Question 14

muscular externa of digestive tract

Answer 14

circular muscle layer
myenteric plexus
longitudinal muscle layer

Question 15

serosa of digestive tract

Answer 15

connective tissue

Question 16

major functions of the alimentary canal

Answer 16

motility, secretion, digestion and absorption

Question 17

gastrointestinal motility

Answer 17

mostly due to the activity of smooth muscle

some skeletal muscle

Question 18

circular muscle contraction

Answer 18

lumen becomes narrower and longer

Question 19

longitudinal muscle contraction

Answer 19

intestine becomes shorter and fatter

Question 20

muscularis mucosae contraction

Answer 20

change in absorptive and secretory area of muscosa, mixing activity

Question 21

smooth muscles in GI tract

Answer 21

electrically coupled - by gap junctions

Question 22

synchronous wave

Answer 22

hundreds of cells are depolarised and contract at the same time

Question 23

modulation of spontaneous activity

Answer 23

driven by specialised pacemaker cells

modulated by intrinsic and extrinsic nerves
numerous hormones

Question 24

slow wave electrical activity

Answer 24

determines the frequency, direction and velocity of rhythmic contractions

Question 25

what is it driven by

Answer 25

interstitial cells of Cajal (ICCs) pacemaker cells largely located between the circular and longitudinal muscle layers

Question 26

ICCs

Answer 26

form gap junctions with each other and smooth muscle cells electrically coupling them some form a bridge between nerve endings and smooth muscle cells

Question 27

slow waves in ICCs

Answer 27

drive slow waves in the smooth muscle cells to couple to them

Question 28

smooth muscle contraction

Answer 28

does not necessarily result from depolarising slow waves

Question 29

contraction in the intestine

Answer 29

occurs only if the slow wave amplitude is sufficient to reach a threshold to trigger smooth muscle cell calcium action potentials

Question 30

force

Answer 30

related to number action potentials discharged | driven in turn by the duration of the slow wave that is above threshold

Question 31

slow wave reaching threshold

Answer 31

neuronal stimuli hormonal stimuli mechanical stimuli generally act to depolarise smooth muscle cells rather than influence slow waves directly depolarisation shifts slow wave peak threshold

Question 32

parasympathetic innervation - most important

Answer 32

preganglionic fibres release ACh

Question 33

excitatory influences

Answer 33

increased gastric pancreatic and small intestinal secretion, blood flow and smooth muscle contraction

Question 34

inhibitory influences

Answer 34

relaxation of some sphincters, receptive relaxation of stomach

Question 35

sympathetic innervation - less important

Answer 35

preganglionic fibres release ACh synapse in the prevertebral ganglia