Introduction to the Structure, Functions and Control of the Alimentary Canal Flashcards
alimentary canal
series of hollow organs running from mouth to anus
what do sphincters do
separate organs
control movement
prevent backflow
mouth and oropharynx
eats
starts carbohydrate digestion - ligase
propels food to oesophagus
oesophagus
propels food to stomach
stomach
stores/churns food
carbohydrate digestion
initiates protein digestion
regulates delivery of chyme to duodenum
small intestine
principle site of digestion and absorption of nutrients
duodenum, jejunum and ileum
large intestine
colon reabsorbs fluids and electrolytes
stores faecal matter before delivery to rectum
caecum, appendix and colon
rectum and anus
regulated expulsion of faeces
accessory structures
salivary glands
pancreas
hepatobiliary system - liver and gall bladder
digestive tract wall
mucosa, submucosa, muscular externa, serosa
overall length of digestive tract
7-10m
mucosa of digestive tract
mucous membrane (epithelial, exocrine and endocrine glands) lamina propria (capillaries, enteric neurones , gut-associated lymphoid tissue) muscular mucosae
submucosa of digestive tract
connective tissue
larger blood and lymph vessels
submucosa plexus (neurone network)
muscular externa of digestive tract
circular muscle layer
myenteric plexus
longitudinal muscle layer
serosa of digestive tract
connective tissue
major functions of the alimentary canal
motility, secretion, digestion and absorption
gastrointestinal motility
mostly due to the activity of smooth muscle
some skeletal muscle
circular muscle contraction
lumen becomes narrower and longer
longitudinal muscle contraction
intestine becomes shorter and fatter
muscularis mucosae contraction
change in absorptive and secretory area of muscosa, mixing activity
smooth muscles in GI tract
electrically coupled - by gap junctions
synchronous wave
hundreds of cells are depolarised and contract at the same time
modulation of spontaneous activity
driven by specialised pacemaker cells
modulated by intrinsic and extrinsic nerves
numerous hormones
slow wave electrical activity
determines the frequency, direction and velocity of rhythmic contractions
what is it driven by
interstitial cells of Cajal (ICCs)
pacemaker cells largely located between the circular and longitudinal muscle layers
ICCs
form gap junctions with each other and smooth muscle cells electrically coupling them
some form a bridge between nerve endings and smooth muscle cells
slow waves in ICCs
drive slow waves in the smooth muscle cells to couple to them
smooth muscle contraction
does not necessarily result from depolarising slow waves
contraction in the intestine
occurs only if the slow wave amplitude is sufficient to reach a threshold to trigger smooth muscle cell calcium action potentials
force
related to number action potentials discharged
driven in turn by the duration of the slow wave that is above threshold
slow wave reaching threshold
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
parasympathetic innervation - most important
preganglionic fibres release ACh
excitatory influences
increased gastric pancreatic and small intestinal secretion, blood flow and smooth muscle contraction
inhibitory influences
relaxation of some sphincters, receptive relaxation of stomach
sympathetic innervation - less important
preganglionic fibres release ACh synapse in the prevertebral ganglia
