L22 - GI Motility Flashcards
what is swallowing?
The passage of food bolus from the oral cavity to the stomach
What does swallowing do? (2)
- protect the airway
- prevent entry of air into the stomach
What does swallowing involve?
Co-ordinated activity of muscles in the oral cavity, pharynx, larynx and oesophagus
(Partly voluntar, reflexive in nature)
What are the 3 different phases of swallowing?
- oral
- pharyngeal
- oseophageal
What is the swallowing reflex stimulated by?
Food bolus stimulating pressure receptors in the back of the throat and pharynx
What are the steps in the swallowing reflex? (3)
- stimulation of pressure receptors
- signals swallowing centre in brain = nerve impulses
- involuntary contraction in pharyngeal muscles = material into oesophagus
How many muscles does the swallowing reflex involve?
25 pairs
What is swallowing a key role of? (4)
Oral drug administration
- pathway to digestive system
- convenient route
- wide range of dosage forms
- timing with food
What is the motility in the stomach? (6)
- mixing and churning
- role in digestion
- formation of chyme
- peristalsis
- gastric emptying
- depends on viscosity
What is gastric emptying?
Exit to the small intestine
How is stomach motility involved in drug administration? (3)
- mixing and dissolution of drugs
- gastric emptying influences drug absorption
- drug stability
What is the motility in the SI? (3)
- mixed by segmentation
- movement by peristalsis
(Sequential activity in muscle bands) - coordinated by the enteric nervous system
What are the steps in peristalsis? (3)
- contraction of circular muscles behind food mass
- contraction of longitudinal muscles ahead of food mass
- contraction of circular muscle layers forces food mass forwards
What is the intestinal and colonic motility controlled by?
ENS
(Enteric nervous system)
What are the 2 main branching networks in the intestines?
- auerbachs (myenteric) plexus
- meissners (submucosal) plexus
What are the steps in enteric neurons controlling peristalsis? (3)/(4)
- sensory neurons detect food pressure and stretch
- motor neurons trigger muscle contractions/relaxations
- influenced by neurotransmitter and autonomic input
= ensures smooth coordinated and movement through GI
What controls the ENS? (3)
- sympathetic nervous system
- parasympathetic nervous system
- hormonal control
How does the sympathetic nervous system control the ENS? (3)
- fight or flight
- inhibits ENS
- dec peristalsis, blood flow, secretion and absorption
How does the parasympathetic nervous system? (3)
- rest and digest
- stimulates ENS
- inc peristalsis, blood flow, secretion and absorption
How does hormonal control control ENS? (2)
- inc by cholecystokinin, gastrin, motilin, serotonin, insulin
- dec by secretin and glucagon
How is intestinal motility involved in drug administration? (2)
- bioavailability - dissolution
- absorption - transit time
- distribution
Migrating motility complex
What is within the migrating motility complex? (5)
- recurring motility pattern
- regulated by electrical activity
- occurs between feeeding
- stomach to LI
- cleansing mechanism
How is the migrating motility complex involved in drug administration? (4)
- drug absorption (emptying, motility, timing of administration)
- controlled release drugs
- drug efficacy
- pharmacokinetics (onset of action, half life, bioavailability)
What is the motility in the large intestine - segmentation? (6)
Haustral shuttling
- localised contraction and relaxation of haustra (segmentation)
- mixing contents
- optimise absorption
- efficient water absorption
- stool formation
- support microbiome
What is the motility in the large intestine - mass movement? (3)
- coordinated contraction = contents toward rectum
(Ascending colon and transverse colon) - triggered by gastrocolic reflex
- role in defaecation
What does defaecation do? (4)
- eliminate waste
- stored in rectum
- initiated by activation of stretch receptors
- involuntary and voluntary steps
What is constipation? (4)
- weak mass movement
- inc transit time
- too much water absorbed
- causes = lifestyle, medications, neurological issues
What is diarrhoea? (4)
- hyperactive mass movement
- dec transit time
- too little water absorbed
- causes = infection, medications, food intolerance
What is vomiting? (2)
- expulsion of gastric contents through mouth
- causes = GI irritation, toxins/drugs, pain/fear/stress, pregnancy, vestibular disturbances
What are the sequence of steps in vomiting? (2)
- Signals from body (Stomach, intestines, inner ear, brain)
- relayed to vomiting center in brainstem (coordinates complex process)
What is the vomiting timeline? (4)
- increased salivation
- relaxation of the lower esophageal sphincter
- contraction of the diaphragm and abdominal muscles
- opening of the upper oseophageal sphincter
What does increased salivation do in the vomiting timeline? (2)
- protects teeth from stomach acid
- prepares the body for vomiting
What does relaxation of the lower oesophageal sphincter do in the vomiting timeline?
Allows stomach contents to move up into oesophagus
What does contractionof the diaphragm and abdominal muscles do in the vomiting timeline?
Increase pressure in stomach, pushing its contents upwards
What does opening of the upper oesophageal sphincter do in the vomiting timeline?
Opens, contents expelled through mouth
