G1 - Introduction to GI Tract and Mobility Flashcards
what is the series of hollow organs running from the mouth to the anus (oral to aboral)?
alimentary canal
What part of the GI system chops food, lubricates it, starts carbohydrate digestion and propels food to the oesophagus?
mouth and oropharynx
what is the function of the oesophagus?
muscular tube that propels food to the stomach
what part of the GI Tract stores food temporarily, continues carbohydrate digestion, initiates protein digestion and regulates delivery of chyme to the small intestine?
stomach
what is the function of the small intestine?
principle site of digestion and absorption of material s
what part of the GI tract reabsorbs fluids and electrolytes, stores faecal matter before delivery to rectum?
large intestine
what part of the Gi tract stroes and regulates expulsion of faeces?
rectum and anus
what are the accessory structures of the GI system?
- salivary glands
- pancreas
- liver and gall bladder
motility definition
Mechanical activity mostly involving smooth muscle
What is secretion required for?
digestion
protection
lubrication
What does digestive secretions contain?
Water, electrolytes and organic compounds
Digestion definition
chemical breakdown by enzymatic hydrolysis of complex foodstuffs to smaller, absorbable, units
What is the conversion of carbohydrates to monosaccharides mediated by?
amylase and disaccharide
What is the conversion of proteins to amino acids, dipeptides and tripeptides mediated by?
Proteases, dipeptidases and tripeptidases
What are fats converted to monoglycerides and free fatty acids mediated by?
lipases
What is the name for the transfer of the absorbable products of digestion from the digestive tract to the blood or lymph?
absorption
What seperates and controls the movement of alimentary canal?
sphincters
Where does protein digestion begin?
stomach
What movement sends food in a normal manner through the alimentary canal?
propulsive
What movements send chyme backwards and forwards to extend the time for digestion
mixing
What contractions are maintained for long lengths of time?
tonic
What process describes the chemical breakdown of complex foodstuffs into smaller, absorbable units?
Enzymatic Hydrolysis
What layer in the mucosa of the GI Tract wall contains epithelial, exocrine and endocrine cells?
Mucous Membrane
What is contained in the lamina propia of the GI Tract?
- capillaries
- enteric neurones
- immune cells
What is the layer of smooth muscle in the mucosa layer of the GI tract wall called and its function?
mucularis mucosae
- changes shape and surface area of the intestine
What nerve network does the submucosa contain?
submucous plexus
What are the fibres like in the smooth muscle of the inner layer of muscularis externa?
circular
What are the fibres like in the smooth muscle of the outer layer of muscularis externa?
longitudinal
What nerve network does the Muscularis Externa contain?
myenteric plexus
What is the outer connective tissue layer of the GI tract known as?
serosa
What does circular muscle contraction do to the lumen?
lumen becomes narrower and longer
What does longitudinal muscle contraction do to the intestine?
intestine becomes shorter and fatter
What does muscularis mucosae contraction do to the mucosa?
Changes absorptive and secretory area of mucosa and mixing activity
What is formed when many cells are depolarised and contract at the same time, acting as one?
Functional Syncytium
Adjacent smooth muscle cells are coupled by what to allow spread of electrical currents from cell to cell?
gap junction
What is spontaneous activity of the GI tract modulated by? (2)
- intrinsic and extrinsic nerves
- numerous hormones
What is the term describing rhythmic patterns of membrane depolarisation and repolarisation that occurs in the stomach, small intestine and large intestine?
slow waves
What pacemaker cells are electrically coupled to smooth muscle cells and cause slow waves?
Interstitial Cells of Cajal
When will contraction if of smooth muscle cells occur?
if the slow wave amplitude is sufficient to trigger SMC action potentials
Upstroke of the SMC potential is mediated by?
voltage- gated Ca2+ channels
downstroke of the SMC action potential is meditated by?
voltage gated K+ channels
Force of contraction of SMC is related to what?
number of action potential discharges
what determines the basic electrical rhythm (BER)?
slow wave
Whether slow wave amplitude reaches the threshold depends on what?
- neuronal stimuli
- hormonal stimuli
- mechanical stimuli
what is the BER frequency of the stomach?
3 waves per minute
what is the BER frequency in the small intestine?
duodenum - 12 waves
ileum - 8 waves
what is the BER frequency in the large intestine?
proximal colon - 12 waves
distal colon - 16 waves
What is considered the ‘brain of the gut’?
enteric nervous system
What are ganglia of the enteric nervous system connected by?
Interganglionic Fibre Tracts in the myenteric and submucous plexus
what regulates motility and sphincters?
myenteric plexus
what modulates epithelia and blood vessels?
submucosus plexus
The enteric nervous system co-ordinates muscular, secretive and absorptive activities via what?
- sensory neurons
- interneurons
- effector neurons
What do preganglionic fibres synapse at when parasympathetically innervating the GI tract?
Synapse with ganglion cells within the ENS
what are the excitatory influences of parasympathetic innervation?
- Increased gastric, pancreatic and small intestinal secretion,
- increases blood flow
- increased smooth muscle contraction
what are the inhibitory influences of parasympathetic innervation?
- Relaxation of some sphincters,
- receptive relaxation of stomach
What do preganglionic fibres synapse with when sympathetically innervating the GI tract?
Synapse in the prevertebral ganglia.
Postganglionic fibres innervate mainly enteric neurons but also other structures
what are the excitatory influences of sympathetic innervation?
Increased sphincter tone
what are the inhibitory influences of sympathetic innervation?
Decreased motility, secretion and blood flow
A wave of contraction that normally proceeds along the gut in the aboral direction? It is a local reflex
peristalsis
What triggers peristalsis?
distension of the gut wall
Name of a short reflex in the GI system?
Intestino- intestinal inhibitory reflex
Name of a long reflex in the GI system?
Gastroileal systema
Rhythmic contractions of circular muscle layer that mix and divide luminal contents?
segmentation
what is colonic mass movement?
powerful sweeping contraction that forces faeces into the rectum
What is the name for sustained contractions found in the sphincters of the GI tract?
tonic contractions
what is Migrating motor complex?
powerful sweeping contraction from stomach to terminal ileum
what is the function of sphincters?
essentially as one way valves by maintaining a positive resting pressure relative to two adjacent structures
what the the location andd function of the Upper oesophageal sphincter?
location
- upper end of oesophagus
function
- relaxes to allow swallowing
- closes during inspiration
what the the location andd function of the lower oesophageal sphincter?
location
- lower end of oesophagus
function
- relaxes to permit entry of food to the stomach
- closes to prevent reflux of gastric contents to the oesophagus
what the the location and function of the pyloric sphincter?
location
- between stomach and duodenum
function
- regulates gastric emptying
- usually prevents duodenal gastric reflux
what the the location and function of the Ileocaecal valve ?
location
- between small and large intestine
function
- regulates flow from ileum to caecum
- distension of ileum opens, distension of proximal colon closes
what is the location of the external and internal anal spinchters?
location
- anus
function - defaecation
