023 Physiology of the GI tract: Motility Flashcards
Which cells generate the slow wave rhythm?
Cells of Cajal
Where is slow wave frequency highest?
In duodenum > Ileum > Colon > Stomach
What does the propagation of slow waves generate?
Segmental and peristaltic contractions
Outline the 3 stages of the swallowing reflex
- Oral
- Pharyngeal
- Oesophageal
What is achalasia? What are the symptoms?
The failure of lower oesophageal sphincter to relax. This causes difficulty in swallowing, food sticking on the way down, solids worse than liquids
How is food moved down the oesophagus?
Gravity and peristaltic waves
Where is the swallowing center in the brain?
Medulla
When do hunger pangs occur?
> 8 hours of the stomach being empty
What are hunger pangs?
Rhythmic peristaltis contractions that can last 2-3 minutes
What are treatments of achalasia
Physical distention of the lower esophageal sphincter or surgically cutting the sphincter.
Which part of the stomach causes regulation of gastric emptying?
Distal motor unit (antrum and pyloric sphincter)
What is the effect of cholecystokinin on the stomach?
Inhibition of gastric emptying and decreased stomach motility
Which part of the stomach acts as a temporary reservoir?
Fundus and body of the stomach
Why is there minimal increase in intragastric pressure?
Because stretching of the muscles in the stomach does not change muscular tone
Which part of the stomach is responsible for mixing chyme with gastric secretions and why?
Muscle wall in distal unit induces stronger contractions and forces food in pyloric sphincter. The rapid closure of sphincter causes mixing. This causes retropulsion.
What is emesis?
Vomiting
Why does hypersalivation occur during vomiting reflex?
Protection of epithelium from the acid in the vomit.
Why does reverse peristalsis occurs in the vomiting reflex?
Stomach and pyloric sphincter relaxes, causing change in pressure and the reverse peristalsis of chyme back from duodenum.
What does the muscularis mucosa do?
When it contracts, it agitates unstirred water layer rich in nutrients, allowing it to get in contact with epithelium for adsorption. This ‘piston like movement’ also allow chylomicrons to move down the lacteal.
When does segmentation occurs strongest?
Duodenum
What is the purpose of segmentation?
Mixing movements with no net forward movement. It is the contraction of circular smooth muscle that faciliates mixing.
Which movement is responsible for the net forward movement of chyme?
Peristalsis at the rate of 1cm/min
What are the movements of muscles during peristalsis?
Waves of contraction and relaxation of circular and longitudinal smooth muscle.
When does the migrating motor complex occur?
During interdigestive phase; initiated during hunger pangs
What does the migrating motor complex do?
Responsible for clearing out undigested products into the colon. It also stops the overgrowth of microorganisms.
Which hormone increases the migrating motor complex?
Motilin
Which hormone decreases the migrating motor complex?
Gastrin, CCK etc.
What is function of the ileal brake reflex?
This prevents unabsorbed nutrients from entering the colon. Slows down movement of GI tract to allow adsorption; maintains gut microbe environemnt.
How does the ileal brake reflex work?
Delays gastric emptying, jejunal transit and suppresses hunger
Which sphincter is responsible for moving food into the caecum?
Ileocecal sphincter
Which movements occur in the colon?
Mixing (haustrations)
Propulsive (peristalsis)
What stimulates the defaecation reflex?
Sudden distension of the rectal wall (stretch receptors)
Why might a diet high in fibre speed up intestinal motility?
Fibre retains water which increase bulk of contents and stimulates motility
Why would prior ingestion of oil or milk reduce neural effects of alcohol?
Alcohol is partly absrobed in stomach but more rapidly absorbed in the SI. Fat reduces gastric emptying (CCK mediated), which delays intestinal uptake of alcohol.
What mechanisms minimise changes in wall tension and intraluminal pressure in proximal stomach?
Release of inhibitory transmitters from parasympathetic nerve fibres e.g. VIP, NO.
What nerve reflexes are involed in defaecation?
i. somatic nerves - voluntary control of external anal sphincter.
ii. autonomic - stimualtion of stretch receptors in sigmoid colon/rectum results in relaxation of sphincter.
What is Hirschsprung disease?
Congenital absence of enteric neurons causing poor mixing and transit. Accumulation causes colonic distension.
What are nerve varicosities?
Nerve (swellings) that release transmitters that diffuse into the syncytium.
How does the GI smooth muscle act as a syncytium?
Nerve transmitters are rapidly transmitted through the gap junctions.
Which nerves stimulate the ileocaecal sphincter?
Myenteric plexus and prevertebral sympathetic ganglia.
