L22 - GI motility Flashcards
what is swallowing?
passage of a food bolus from ORAL CAVITY to STOMACH
why is swallowing important?
it protects airway and prevents entry of air into stomach
what does swallowing involve?
- coordinated activity of muscles in the oral cavity, pharynx, larynx and oesophagus
- partly voluntary control
- partly reflexive/ involuntary
3 phases of swallowing
Oral: voluntary
Pharyngeal: reflex
Oesophageal: reflex
describe the swallowing reflex
- stimulated when food bolus stimulates PRESSURE RECEPTORS in back of throat and pharynx
- signals to the swallowing centre in brain telling you to swallow
- this triggers N.I’s
- innervates (stimulates) skeletal muscle in pharynx and upper oesophagus
- involuntary contraction in pharyngeal muscles pushes material into the oesophagus
- epiglottis prevents passage of food into lungs
Swallowing occurs in around 20 seconds.
motility in stomach
- mixing and churning to dissolve food for absorption
- gastric emptying into SI
- drug stability
what happens if gastric emptying into SI occurs too fast?
minimises the amount of time drug is present in small intestine so drugs cannot be as efficiently absorbed
what is the rate of gastric emptying dependent on?
type of food, e.g. high carb content passes through fastest, high fat content = slowest.
motility in small intestine
- mixed by segmentation (circular one)
- movement through SI by peristalsis (wave like)
- coordinated by enteric NS
role of ENS in intestinal motility
- Auerbach’s (myenteric) plexus- muscle- neurones for movement
- Meissner’s (submucosal) plexus: in submucosal layer - neurons which detect chemical changes
what is the enteric NS?
solely exists in gut, works independently from other NS.
how do enteric neurones control peristalsis?
- sensory neurons detect food presence and STRETCH
- motor neurons trigger MUSCLE CONTRACTIONS/ RELAXATIONS
- influenced by NT’s and autonomic input
- ensures the smooth movement through GI
- contraction behind food bolus: release of ACh
- relaxation in front of food bolus: release of nitric oxide
control of ENS (sympathetic NS)
- fight or flight
- inhibits ENS
- decreased peristalsis, blood flow, secretion, absorption
control of ENS (parasympathetic)
- rest and digest
- stimulates ENS
- increased peristalsis, blood flow, secretion, absorption
control of ENS (hormonal control)
- increased by cholecystokinin, gastrin, motilin, serotonin, insulin: increase in activity in ENS
- decreased by secretin and glucagon: decrease in ENS
transit time
time taken for something to move through gi tract
greater transit time =
more drug absorbed
what does the migrating motility complex do?
regulates drug absorption
describe the migrating motility complex
- Recurring motility pattern
- Regulated by electrical activity
- Occurrs between feeding (when you haven’t eaten)
- Process from stomach to large intestine
- Cleansing mechanism (removes bad bacteria/ food particles)
- Responsible for “tummy” intestines rumbling
Migrating Motility Complex & Drug Administration
- timing of administration is important
- can use control release drugs
haustral shuffling (motility in large intestine)
- localised contraction + relaxation of haustra
- segmentation in haustra allows optimum water absorption
- mixes contents
- contents moved from intestine to gut to microbiome
- stool formation
motility in large intestine - mass movement
- coordinated contractions that propel the contents of the colon toward the rectum
- contractions that occur in the ascending colon and transverse colon
- triggered by the gastrocolic reflex: when take food into stomach, stomach sends signal to intestine to remove waste
- defection
defaecation
- temporarily stored in rectum
- activation of stretch receptors
- voluntary and involuntary steps
constipation
- weak mass movement
- increased transit time in gi tract
- too much water absorbed in large intestine due to slowed down movement
Causes:
- lifestyle
- medications
- neurological issues
diarrhoea
- hyperactive mass movement
- decreased transit time
- too little water absorbed
causes: - infections
- medications
- food intolerance
vomiting
- forcible expulsion of gastric contents through mouth
- initiated by signals from various parts of body (stomach, intestine, inner ear, brain)
- signals relayed to the vomiting centre in brain stem - coordinates complex process of vomiting
causes of vomiting
- GI irritation
- toxins/drugs
- pain/fear/stress
- Pregnancy
- vestibular disturbance: changes in your ear/motion sickness
vomiting timeline
- increased salivation due to sympathetic NS kicking in: protects teeth from stomach acid, prepares body for vomiting
- relaxation of LOWER oesophageal sphincter: allows stomach contents to move up to oesophagus
- contraction of diaphragm + abdominal muscles: muscles forcefully contract, increasing pressure in stomach and pushing contents upwards
- opening of upper oesophageal sphincter: sphincter opens, contents expelled through mouth
