histology, physiology of prehension and mastication and swallowing Flashcards
deglutition
- the transport of a bolus of food or liquid from the mouth to the stomach
- normal deglutition requires precisely timed contraction and relaxation of numerous muscles of the oral and pharyngeal regions
voluntary deglutition
tongue pushes food bolus toward pharynx
involuntary deglutition
pharynx directs food towards digestive tract, not airway
mucosa
stratified squamous epithelium, includes lamina propria and mucularis mucosa
submucosa
dense collagenous stroma, contains large blood vessels, lymphatics, and nerves
tunica muscularis (muscularis externa)
2 layers: inner circular and outer longitudinal. variable muscle types between species
adventitia
consists of connective tissue with elastic fibers
how does the tunica muscularis propel food
the longitudinal muscle contracts and the circular muscle relaxes
what type of tunica muscularis do cats, horses, pigs, and humans have
primarily skeletal muscle with distal segments incorporating smooth muscle
what type of tunica muscularis do dogs and ruminants have
uniform skeletal muscle along the entire length
what type of tunica muscularis do avians have
uniform smooth muscle along the entire length
where is the upper esophageal sphincter (proximal)
at the back/lower end of the pharynx
where is the lower esophageal sphincter (distal) and what does it do
cardia, relaxes to allow food to pass into the stomach
what happens to the sphincters when deglutition is not occuring
both remain constricted
why is it important that the sphincters remain closed when deglution is not occuring
due to the differences in pressure along the esophagus
what cranial nerves are involved in coordination of swallowing
- trigeminal (CN V)
- facial (CN VII)
- glossopharyngeal (CN IX)
- vagus (CN X)
- hypoglossal (CN XII)
which cranial nerve provides only motor innervation during the control of deglutition
hypoglossal (CN XII)
what is primary peristalsis
esophageal peristalsis initiated by the pharyngoesophageal action
what is secondary peristalsis
occurs when material remains in the eosphagus
* initiated by receptive fields in the esophagus which are stimulated by the persistent material
a rapidly descending wave of ____ sequentially relaxes the UES, the body of the esophagus, and the LES, so that they are prepared for passage of an oncoming bolus
inhibition
the parasympathetic and sympatheric nervous systems forms a link between the CNS and __________ __________ _________
enteric nervous system (ENS)
how is innervation of the striated muscle of the esophagus provided by
special visceral efferent (motor) neurons from the bilateral nucleus ambiguus in the medulla oblongata
what nerve is the striated muscle of the esophagus controlled by
somatic (not parasympathetic) motor neurons in the vagus nerve
what is the ENS composed of
myenteric plexus and submucosal plexus
what is the myenteric plexus responsible for
generating and controlling peristaltic movements
where is the myenteric plexus located
sandwhiched between the two layers of the muscularis externa
what is the myenteric plexus
group of ganglia that run throughout the entire GI tract and innervate its multiple layers of smooth muscle
what does the submucosal plexus control
GI secretions and local blood flow
what is the submucosal plexus
a neural network located within the submucosa, transmits stimuli to the central nervous system through both parasympathetic and sympathetic pathways
what is eructation
expulsion of GI gas from the oral cavity
is it normal for some air to be swallowed during normal feeding
yes and amounts vary
what happens during regurgitation
- extra contraction of reticulum
- cardia/LES relaxes
- inspiratory excursion of ribs with glottis closed
- negative pressure in thorax allowing food into the esophagus
- reverse peristaltic wave pushes food into the mouth
- tongue expresses excess water
- water is swallowed
- remastication
how much gas can fermentation in the rumen generate in an adult and in sheep/goat
- adult cattle - 30-50 L of gas
- sheep or goat - 5 L of gas
what happens when there is a lack of eructation in ruminants
ruminal tympany which can lead to death via asphyxiation
