GIT Motility Flashcards
What is the GIT?
a long muscular 5m tube
What does the GI system consist of?
- luminal GIT lined by mucous membranes
- associated accessory organs
What are the associated organs of the GI system?
- salivary glands
- hepatobiliary-pancreatic GI system
What does the hepatobiliary GI system consist of?
- liver
- gallbladder
- bile ducts
What are general functions of the GIT?
- supplying nutrients to the body for bodily functions
- maintaining homeostasis
- integration with other systems
- defence against exposure to the external environment
What is the digestive system responsible for?
- ingestion
- digestion
- absorption
- defecation
What does processing food involve?
- motility
- secretion
- membrane transport
What is electrical activity in GI smooth muscle controlled by?
interstitial cells of Cajal (pacemaker cells)
Where do ICCs form networks?
within the submucosal, intramuscular, and intermuscular layers throughout the GIT
What does the electricity of ICCs account for?
the self-excitable characteristics of the muscle
Which parts of the GIT do not have their own BER?
oesophagus and proximal stomach
What is BER?
the spontaneous depolarisation and repolarisation of ICCs
How does the ANS affect contractile force of the GIT?
- parasympathetic activity increases contractile force
- sympathetic activity decreases contractile force
What does the amplitude of slow waves determine?
the strength of muscle contraction
What is the amplitude of slow wave altered by?
release of neurotransmitters from enteric neurons
What do agents that cause relaxation in smooth muscle cause?
contraction in skeletal muscles
What is the oesophagus responsible for?
transporting food from the mouth to the stomach; it prevents retrograde movement of oesophageal or gastric contents
What is the oesophagus closed at both ends by?
- upper oesophageal sphincter – made of skeletal muscle controlled by swallowing centre
- lower oesophageal sphincter – made of cardiac muscle modulated by swallowing centre
Why must reflux be prevented?
gastric contents are damaging to the oesophageal epithelium
What does tonic contraction in the upper and lower oesophageal sphincters do?
keep their lumens partially or completely closed to prevent reflux
What does lower oesophageal sphincter tone do?
prevent or minimise gastro-oesophageal reflux or regurgitation
How does lower oesophageal sphincter tone increase and decrease respectively?
- increase by cholinergic agonist, alpha-adrenergic agonist, gastrin and substance P
- decrease by beta-adrenergic agonist, dopamine, CCK, nicotine, tea, coffee and cola
What is the interdigestive period?
period following digestion that begins after the GIT is cleared of food
What happens during the interdigestive period?
gastric motility clears undigested debris and sloughed epithelial cells
What does gastric motility do after a meal?
relax to accommodate ingested food with little change in the intra-gastric pressure and grinds and disperses the meal into fine particles
How are contents delivered to the duodenum?
at a rate that affords optimal mixing with pancreatic-biliary secretions and maximal contact with the brush border of enterocytes
What is the duodenum?
first part of the small intestine that connects to the stomach