Gastrointestinal motility Flashcards
Which part of the GI tract contains glands
Submucosa
What is the inner circular muscle function
Orientated in a circular pattern so mixing function
What is the outer longitudinal muscle function
Longitudinal so moving contents function
What plexus is responsible for secretions I the GI tract
Submucosal plexus
What plexus is responsible for movement in the GI tract
Myenteric plexus
What are the pacemaker cells in the GI tract called
Interstitial Cells of Cajal
How do Interstitial Cells of Cajal cause muscle tension
Initiate a spreading basal electrical rhythm (BER). There is a slow wave and the longer it spends above the threshold, the more spike potentials so there is a greater contraction force.
How does peristalsis occur
Chyme activates receptors. Sends a message upstream and downstream of food bolus.
Upstream: ACh is released which depolarises smooth muscle cells so they are closer to spoke potentials.
Downstream: Release VIP. Decreases slow wave production of ICCand hyperpolarisation of SM cells so further away from threshold so no contraction
What does parasympathetic nerve activation do to GI motility
Promotes increased motility
What does sympathetic nerve activation do to GI motility and how
Decreased motility
- > noradrenaline activates beta adrenoceptorson smooth muscle cells so cells hyper polarise and move further away from threshold
- > Indirectly by decreasing Ach release via A2 adrenoceptors
What is the zone of elevated pressure (ZEP)
prevents transit from one region to another
Where is the ZEP found in the oesophagus
In lower oesophageal sphincter of stomach (area of intense contraction)
What is the primary wave of oesophageal peristalsis controlled by
Vagus nerve
What initiates the peristaltic wave
Mechanoreceptors in pharynx detect food bolus initiates peristaltic wave
What happens if food is not projected to stomach after first peristaltic wave
Secondary wave of peristalsis is initiated by local ago-vagal reflexes
What are peristaltic waves like on an empty stomach vs a full stomach
Weak
1st hour- theiyre weak and the pyloric sphincter is closed
Later, peristaltic waves are associated with mixing of gastric contents and emptying some contents into the duodenum
What is the purpose of gastric contractions
Mixing of gastric contents and emptying some of the contents into the duodenum
Neural control of stomach
Vagal relaxatory fibres induce relaxation (stimulated by oesophageal and gastric distension)
- mediated by VIP
- Supported by action of sympathetic nerves so inhibits release of Ach
What increases gastric motility
Vagal fibres releasing ACh
Stimulatory hormones
Gastrin (antrum)
Motilin (small intestine)
Inhibitory hormones
gastrin (proximal stomach)
Secretin
CCK
NO
What does the rate at which gastric contents pass into the duodenum depend on
Meal composition Meal volume FRagment size Osmolarity (osmolarities of chyme greater and smaller than certain value slow gastric emptying) Acid (excess acid slows) Fat (in upper small intestine slows)
Two types of muscular contraction in small intestine:
Segmenting contractions
Peristaltic contractions
What is segmenting contraction
Occurs in circular muscle and serves a mixing function (secretions from pancreas and liver with chyme)
What are peristaltic contractions
More longitudinal
- occurs after meal
- MMC (strong wave of peristalsis typically after you’ve eaten to prepare room for food you’re just about to receive in small intestine)
