Lecture 5 - Motility Flashcards
How is feed procured?
lips, tongue, incisors
Molars
grind the feed
- vary in use depending on diet and species
Vertical vs lateral chewing
- vertical = carnivores and omnivores
- lateral = herbivores (better for grinding plant matter)
Floating
- teeth wear unevenly due to grinding and continue to erupt
Indications for floating
- dropping feed
- dropping wt
- head tossing
- balls of chewed hay coughed out
2 swallowing phases
- oropharyngeal phase
- oesophageal phase
Oropharyngeal swallowing phase
- bolus pushed back by tongue and triggers pressure receptors
- uvula blocks nose
- glottis and epiglottis blocks lung access
- swallowing center in medulla coordinates and inhibits respiratory center
- pharyngoesophageal sphincter opens
Oesophageal swallowing phase
- peristaltic waves
- skeletal muscle
- cardiac sphincter opens
Peristalsis motility
- waves of contraction
- peristaltic reflex (duodenum) programmed by enteric nervous system
- relaxation/contraction of longitudinal muscle and circular muscle
Gastric motility steps
- Fundus
- receptive relaxation = making room
- NO and VIP induced by ACh to induce relaxation - Corpus
- mixing vat for saliva, food, and gastric secretions - Antrum
- propulsion of food through pyloric sphincter to the duodenum
- controlled by distension and parasympathetic
Gastric emptying
- peristalsis
- pyloric sphincter opens and chyme enters duodenum
- regulated by force of contractions and signals from duodenum; rate dependent on physical and chemical state
- vagal component: vagotomy decreases contractions, stimulation of vagal nerve increats contrations
Factors increasing gastric emptying
- neural control
- distension of gastric wall
- increased parasympathetic - endocrine control
- gastrin
Factors decreasing gastric emptying
- neural control
- chemoreceptor, osmoreceptor, mechanoreceptor at duodenum
- increased sympathetic - endocrine control
- CCK, GIP, secretin
Most common form of motility
Segmentation
Segmentation
contraction of circular muscle where digesta is not propagated in one direction; alternating contractions for mixing
- frequency decreases distally
Segmentation in the colon
- haustration = clearing
Motility regulation duodenum
- stimulus = chyme distending duodenum
- sensors = stretch receptors in duodenal wall
- signal = nervous
- effector smooth muscle
- response = vigorous segmentation in duodenum
- effect = removal of chyme
Motility regulation in ileum/colon
- stimulus = protein/digesta causing gastrin release
- response =
1. gastro-ileal reflex: stimulates segmentation in ileum, gastrin inhibits the ileo-caecal sphincter so it opens
2. gastro-colic reflex: mass movements in colon
Tonic contraction
sustained contraction of muscle
Mechanism for contraction
Interstitial Cells of Cajal (ICC)
- pacemakers in circular and longitudinal muscle layers that set a constant pulse of depolarization/repolarization in ssmooth muscle cells
Basic electrical rhythm
smooth muscle cells have an intrinsic rhythm of depolarization/ repolarization frequency
When does contraction occur?
When depolarization goes above threshold to cause action potential
- Ach (parasympathetic) increases the basal membrane potential to stimulate APs and contraction
- Norepinephrine (sympathetic) decreases resting basal membrane potential and prevents generation of APs and contraction
small intestine motility in fed state
Segmentation reflex
- major type of motility
- mix luminal content
- regulated by ENS
small intestine motility in fasting state
Migrating Myoelectric Complex - to push things along
3 phases of migrating myoelectric complex
Phase 1: quiescent period
Phase 2: intermittent contraction
Phase 3: powerful propulsions to sweep intestinal content out
Motilin
stimulates stomach and duodenum
- intrinsic nerves stimulate distal duodenum and jejunum
large intestine motility
Fxns:
- microbial digestion
- reabsorption of H2O and electrolytes
Haustral contractions for mixing
Peristaltic contractions to clear
Antiperistaltic movement to fill cecum
Aboral mass movement
Antiperistaltic movement
motlilty in large intestine to fill cecum
Stomach worms
increase gastric emptying
vomiting center in the medulla
- activated by visceral afferents anywhere in GI; blockage or mucosal irritation = stimulus
- vestibular stimulation = motion sickness; signal from perception
- efferent nerves activate upper GI, diaphragm, and abdominal muscles
- closes glottis, LES relations, stops respiration, somatomotor signals, abdominal pressure
2 concerns with vomiting
- significant fluid and electrolyte
- acid-base imbalance
How are most signals sent in the gut?
- interneurons; not being sent up the spinal cord to the brain
Sympathetic effects
- inhibits digestion
- postganglionic neurons release norepinephrine to decrease:
1. GI tract smooth m. motility
2. exocrine secretion
3. endocrine secretion
Parasympathetic effects
- promote digestion
- postganglionic neurons release acetylcholine to increase:
1. GI tract smooth m. motility
2. Exocrine secretion
3. Endocrine secretion
Long reflex
- stimulus: distention, osmolarity, food, pH
- receptor cells: mechano and chemoreceptors
- CNS
- Ach (+) or Norep (-) released
- effector cells: smooth muscle and endocrine cells
- motility and secretion
OR
- Stimulus: smell, taste, sight
- activates CNS
- to enteric nervous system
- effector cells: smooth muscle and endocrine cells
- motility and secretion
Short reflex
- stimulus: distention, osmolarity, food, pH
- receptor cells: mechano and chemoreceptors
- enteric nervous system: myenteric plexus (sym and para) and Submucosal plexus (para)
- effector cells: smooth muscle and endocrine cells
- motility and secretion
Ileus
- caused by inhibition of motor activity
- increase activity upstream and decrease activity downstream
- if blocked too long = distention then sympathetic reflex enters CNS = pain
- common complication of inhibiting motor neuron activity
