Gastrointestinal System: Motility Flashcards
Swallowing Reflex
Stimulated when a food bolus stimulates pressure receptors in the back of the throat and pharynx
Signals to the swallowing centre located in the medulla
Swallowing centres triggers nerve impulses
Innervates skeletal muscles in the pharynx andupper oesophagus
Involuntary contraction in the pharyngeal muscles pushes material into the oesophagus
Involves more than 25 pairs of muscles
Swallowing
The passage of a food bolus from the oral cavity to the stomach
Involves the co-ordinated activity ofmuscles in the oral cavity, pharynx, larynx and oesophagus
Partly under voluntary control and partlyreflexive in nature
Gastric Motility - Stomach
Peristalsis and mixing (churning)
Movement depends on viscosity
Retropulsionforces solids back
Liquids exit faster than solids
Production of chyme
Motility in the Small Intestine
Mixed by segmentation
Movement by peristalsis
Sequential activity in muscle bands
Co-ordinated by the enteric nervous system
Intestinal Motility: Role of the Enteric Nervous System (ENS)
Intestinal and colonic motility is controlled primarily by the ENS
Two main branching networks:
Auerbach’s (myenteric) plexus
Meissner’s (submucosal) plexus
Contraction of GI Smooth Muscle
Activated/inhibited by many neurotransmitters
Acetylcholine induces contraction through activation of muscarinic receptors
Histamine induces contraction through activation of H1 receptors
Control of theENS
Sympathetic nervous system
- “fight or flight”
- inhibits ENS
- decreased peristalsis,blood flow, secretion andabsorption
Parasympathetic nervous system
- “rest and digest”
- stimulates ENS
- increased peristalsis,blood flow, secretionandabsorption
Hormonal control
- increased by cholecystokinin, gastrin, motilin, serotonin and insulin
- decreased by secretin and glucagon
The Migrating Motility Complex
Recurring motility pattern
Regulated by electrical activity
Occurs between feeding
Progress from stomach to large intestine
Cleansing mechanism
Motility in the Large Intestine–
Haustral Shuttling
Faeces stored in haustra
Haustra collapse to cause bulk movements
Defaecatory reflex triggered by faeces in descending colon/rectum
Defaecation
Eliminate waste
Temporarily stored in rectum
Process initiated by activation of stretch receptors
Involves involuntary and voluntary steps
Vomiting
Vomiting reflex
Vomiting centrein medulla oblongata
Forcible expulsion of gastric contents through the mouth
Gastrointestinal irritation – mechanical or chemical
A Vomiting Timeline
Pre-Ejection Phase:
Nausea often occurs
Autonomic changes such as tachycardia and increased salivation
Food contents move into the stomach due to reverseperistalsis
Pyloricsphincter relaxes allowing food content to fill the stomach
Ejection Phase:
Involuntary reflex called retching
Rhythmic contraction of the muscles of the chest wall, diaphragm andabdomen
Intense contraction forces the contents of the stomach into the oesophagus
Epiglottis closes to prevent food travelling down to the lungs
Vomiting occurs
Post-Ejection Phase:
Feeling of fatigue and muscle weakness
Epiglottis remains closed
mobility overview
mouth and esophagus: chewing, swallowing and peristalsis
stomach : filling, churning, peristalsis , emptying
small intestine: segmental contractions, peristalsis
large intestine: haustral shuttling, mass movement, defecation
sphincter: regulation of movement
secretion in the stomach
parietal cell: secrete HCl
denatures protein
pepsinogen to pepsin
chief cell: secrete pepsinogen
converted to pepsin
protein digestion
mucous cell: protection
lubrication
G cell: produce gastrin
controls HCl, motility, pepsin, mucous
Gastric Acid Secretion
Hydrochloric acid (~ 2.5 L/day)
Stomach pH 2-3
Optimal for activity of pepsin
Role of parietal cells, enterochromaffin cells & G-cells
Stimulated by histamine, gastrin & acetylcholine
