Gastrointestinal: motility Flashcards
What is GI motility? (3)
- Movements of the wall of the GI tract
- Due to contractions of the muscular externa
- Function: to mix and propel
What are the different types of electrical activity in the GI smooth muscle? (4)
Slow waves of depolarisation
Frequency of waves: basic electric rhythm
BER vary in different areas of GI tract
Height of BER affected by neural and hormonal input
What are the parasympathetic and sympathetic roles in GI smooth muscle?
Parasympathetic: excitation
Sympathetic: inhibition
What cells act as pacemaker cells for the GI muscle and where are they located?
- Interstitial cells of Cajal - instigate slow waves
- Sit at boundary of longitudinal and circular smooth muscle layers
What is the relationship between electrical and mechanical activity in smooth stomach muscle? (2)
Larger depolarisations = stronger contractions
Action potentials = even stronger contractions
What is the relationship between electrical and mechanical activity in smooth intestinal muscle? (2)
Action potentials required for force
Strength of contraction varies with frequency of action potentials
What is peristalsis and segmentation? (3)
Peristalsis propels contents forwards
Segmentation mixes contents
Waves of contraction
How does peristalsis occur? (3)
Circular and longitudinal muscle contractions
- Proximal segment - circular contracts, longitudinal relaxes, diameter decreases
- Distal segment - circular relaxes, longitudinal contracts, diameter increases
How does segmentation occur? (3)
- Motility in the small intestine
- requires circular muscle
- mixes chyme
How do we chew? (4)
Chewing reflex - cyclical reflex
Jaw muscles active - mouth closed
Food enters and inhibits jaw muscles
Jaw dropping relieves pressure of food
What is saliva + chewed food called?
Bolus
How do we swallow? (3)
- Tongue moves bolus to pharynx
- Initiates swallowing reflex
- Integration center - swallowing centre of medulla oblongata
What are the steps of the swallowing reflex? (8)
- Bolus descends into pharynx - presses epiglottis
- Epiglottis covers glottis so food does not enter trachea
- inspiration inhibited
- bolus stretches oesophagus, triggering peristalsis
- Peristalsis propels bolus to stomach (9s)
- Bolus arrives at stomach
- triggers relaxation of lower eosophagul sphincter
- Bolus enters stomach
What are the functions and mechanisms of gastric motility?
Functions: Mix chyme, regulate gastric emptying
Mechanism: peristalsis, enteric nervous system
What are the patterns of gastric motility? (4)
- Waves of peristalsis - increase closer to pylorus
- Functions in mixing chyme - pyloric sphincter closed
- Functions in gastric emptying - pyloric sphincter opens with stronger contractions
- Emptying rate increases - vol. of chyme and strength of gastric peristalsis
What regulates the increase force of contractions?
Gastrin
What regulates the decrease in force of contractions? (3)
CCK
Secretin
GIP
What are the 4 phases of regulation?
Cephalic phase - excitations (anger, aggression)
Cephalic phase - inhibitions (pain, fear, depression)
Gastric phase - excitatory stimulus (distension of the stomach)
Intestinal phase - inhibitory stimuli (distension of duodenum)
How is vomiting stimulated? (3)
- Stimuli stimulate stretch receptors and chemoreceptors
- Afferent nervous impulses from GI lining sympathetic and vagal nerves to the brain
- Mediated through vomiting centre in medulla
How is the vomiting centre activated? (4)
- Triggers reverse peristalsis, pyloric sphincter relaxed
- Powerful efferent nervous impulses cause:
- contractions of diaphragm and abdominal muscles
- relaxation of gastro-oesophageal sphincter - Gastric and intestinal contents forcefully expelled through the mouth
- Glottis is closed temporarily
What are the 4 other ways vomiting can be caused?
- Activation of chemoreceptor trigger zone (drugs)
- Disturbance of vestibular labyrinths by movement (motion)
- Sensory stimuli - visual olfactory
- Psychic stimuli - cerebral cortex
What hormone stimulates motility?
Gastrin
What are the 3 motility reflexes?
Intestino-intestinal reflex - injury or stress
Ileogastric reflex
Gastroileal reflex
What is haustrations and where does it occur?
Mixing
Proximal colon
How is colon motility regulated? (2)
Colonocolonic reflex - distension in one area causes relaxation in the other
Gastrocolic reflex - food in stomach increases motility
What are the steps in defacation?
- Distension of colon
- Stretch receptors
- Rectum and smooth muscle contracts
- Increase pressure in the rectum
=5. Both sphincters relax - defecation
=5. Internal anal sphincter relaxes/external anal sphincter contracts
