Lecture 6 - Salivary Glands Flashcards
major salivary glands and ducts
are the parotid and sublingual glands
what comprises the secretory apparatus?
multiple salivons each composed of an acinus lined by a secretory cells and connected to a duct lined by cells that can modify the electrolyte content of the primary acinar secretion as it passes thru the mouth
what are electrolytes in saliva derived from?
serum
what are the two major types of salivary secretion?
- serous secretion containing electrolytes, lipase (fat digestion), and ptyalin (an alpha-amylase - an enzyme for digesting starches)
- mucous secretion for lubrication.
partoid gland secrete what type of saliva?
serous
submandibular and sublingual gland secrete what type of saliva?
serous and mucous
buccal gland secretes what type of saliva?
mucous
what is the pH of saliva? what type of digestion does htis favor?
6.0 - 7.4 which favors the digestive action of ptyalin
in what species is salivary amylase present?
pig, absent in horse, sheep, goat, cow, dog and cat
what compounds are dominant in ruminant saliva?
Na and HCO3
what compounds are dominant in equine saliva?
Cl and Ca
what compound is present in ruminant saliva and used by rumen microbes to synthesize protein?
urea! a portion of this protein can be digested in the small intestine to be used as an amino acid source and an effective means of removing and recycling ammonia
what are the volumes of saliva like in herbivores?
high - approx 200 liters/day in ruminants
functions of salivary glands
- mastication and deglutition
- evaporative cooling in dog and cat
- provision of fluid and buffer in ruminants for forestomach digestion
what are the major buffers in saliva?
bicarb and phosphate (mostly from parotid)
do salivary glands play a critical role in digestion?
no - you can remove one without a problem
what does primary secretion from the acinus consist of?
Na, Cl, and HCO3 which are actively transported from the blood
what happens as saliva passes down the collecting ducts?
its modified by exchange of Na, H and K ions and active resabsorption of NaCl.
does water osmotoically equilibriate in saliva?
no - the duct epithelium is tight so the water does not osmotically equilibriate with ions as they are absorbed so that the osmolality is hypotonic at low rates of flow in nonruminants.
what is the osmalality of ruminant saliva at all rates of flow?
isotonic
what does cholinergic stimulation cause?
an increase in flow rate
where does acetylcholine act?
at muscarinic junctions which is the site of parasympathetic postganglionic action
what does atropine block?
it selectively interferes with Ach action at muscarinic junctions to effectively block parasympathetic effects
this is used to suppress salivary secretions and ronchial secretions before surgery
what is the effect of adrenergic stimulation?
produces a more viscous fluid, high in protein
what do adrenal hormones have a marked effect on in the ruminant?
on the Na:K ratio in saliva.
what happens when a ruminant undergoes Na deprivation in the diet?
Na deprivation in the diet causes a fall in urinary and salivary excretions of Na and a reciprocal rise in K excretions
what causes a reflex excitation of parotid salivation in the ruminant?
mechanical stimulation of the mouth, thoracic esophagus, cardia, reticulo-omasal orifice, etc.
what inhibits salivation in the ruminant?
distention of the rumen
what glands secrete continuously?
the feline sublingual and ruminant parotid
in the horse when does saliva flow from the gland? clinical relevance
only during mastication - this can be used to diagnose parotid duct lacerations because clear, watery fluid can be seen draining from the damaged duct
what indicates parotid duct laceration in the heart clinical relevance
parotid saliva has a high calcium concentration and will leave a chalky white deposit on hair and skin below a parotid duct laceration
a horses’s saliva has a lower level of what compounds compared to sheep?
bicarb and phosphate
what are the 3 parts of the esophagus
- upper esophageal sphincter (UES)
- body
- lower esophageal sphincter (LES)
what makes up the UES?
at the pharyngoesophageal junction, circular muscle fibers from the esophagus combine with the cricopharyngeus muscle, 2 lateral longitudinal esophageal muscles, and the ventral longitudinal muscle
what is the LES?
a functional sphincter at the gastroesophageal junction
within the esophagus, what is the tunica adventitia?
the outermost layer of the esophagus which is rich in blood vessels, nerves and elastic fibers. its loosely applied to surrounding structures and thereby allows the esophagus considerable freedom of movement.
what is important about the LES?
it is physiologically and pharmacologically distinct unit that separates positive intragastric pressure from negative pressure in the distal esophagus
which part of the esophagus has a serosal covering and what is its role?
the short abdominal portion of the esophagus has a serosal covering
plays a role in healing of intestinal incisions
what is the esophagus next to in the neck?
common cartoid artery, vagosympathetic trunk and recurrent laryngeal nerve
what is the esophagus mucosa composed of?
moderately keratinized stratified squamous epithelium arranged in characteristic longitudinal folds that flattern to accommodate a passing bolus.
where are submucosal mucus glands present?
at the pharyngeoesophageal junction ONLY
in what species is the muscle wall totally striated?
canine, porcine, ruminant
in what species is the muscle wall of the esophagus striated proximally and smooth distally?
feline
what does the muscle wall of the esophagus look like in a horse?
cranial 2/3 consists of 2 helical layers striated muscle with the caudal third composed of smooth muscle
define peristalsis
a propagating ring of contraction that travels aborad (sp?)
define orad (reverse) peristalsis
occurs in ruminants upon rumination (regurgitation of a “cud”)
what are the two forms of peristalsis
- primary contractions - induced by a swallow, traverse the whole body length, and can be propagated with or without a bolus
- secondary contractions - not induced by a swallow but by presence of contents anywhere along the body or after relief of esophageal distension or after reflux from the stomach
where is the velocity of peristaltic propagation most rapid?
through striated muscle (vs. smooth muscle)
the function of the UES
opens briefly after swallowing then closes through sustained contraction of the cricopharyngeus muscle
when does the LES relax?
when primary and secondary peristaltic waves are initiated to allow the transported contents to enter the stomach
what factors work together and/or independently to integrate esophageal peristalsis and lower esophageal sphincter relaxation?
the CNS
intrinsic and extrinsic nerves
myogenic factors
is the pharyngeal component of deglutition a voluntary act?
yes - totally dependent on the swallowing center in the medulla
what is the nucleus ambiguous the origin of?
the origin of vagal fibers to the striated muscle segment of the esophagus
the dorsal motor nucleus of the vagus is the origin of what?
the vagal fibers to the esophageal smooth muscle
where is the myenteric (Auerbach’s) plexus found?
in the smooth muscle coats and is sparse in the esophagus. sympathetic innervation is sparsely provided through fibers arising from sympathetic ganglia and included in motor fibers in the vagi.
nicotinic receptors are found where? what do they respond to?
in all autonomic ganglia. they respond to Ach released from both sympathetic and parasympathetic preganglionic fibers
where are muscarinic receptors found? what do they do?
on effector cell membranes. they bind with Ach released from parasympathetic postganglionic fibers.
does atropine affect nicotinic receptors?
nope!
what is the major agonist when it comes to controlling LES tone?
postganglionic Ach
what is the major ANTAGONIST of contraction with regards to controlling LES tone?
NO
what inhibits vagus-induced contractions in the striated muscle segments of the esophagus?
curare and succinylcholine
but not atropine
what augments the amplitude and duration of normal peristaltic contractions of normal esophageal smooth muscle?
bethanechol and edrophonium
what reduces the amplitude of peristaltic contractions in esophageal smooth muscle?
atropine and other cholinergic antagonists
are adrenergic alpha receptors excitatory or inhibitory?
excitatory! :)
are beta receptors excitatory or inhibitory?
inhibitory :(
do adrenergic agents (like adrenergic alpha and beta receptors) have a great effect on esophageal function?
no!
what causes a dose-dependent increase in contraction of the distal esophagus?
IV dopamine
what do you sometimes use to treat esophageal obstrution or choke?
oxytocin - but this is controversial
define vomiting
a reflex act in response to afferent impulses arriving through the vagus and sympathetic nerves or to emetic drugs.
how is the act of vomiting accomplished?
through relaxation of the LES and fundus of the stomach.
explain the process (steps) of vomiting
- contractions in the duodenum are reversed so that duodenal contents are driven by antiperistalsis into the stomach.
- the distal part of the stomach contracts, forcing gastric contents into the relaxed fundus and esophagus.
- at the same time, a deep breath is taken, the glottis is closed and the larynx raised to open the UES.
- soft palate is elevated to close off the posterior nares.
- the negative intrathoracic pressure created by sharp downward contraction of the diaphragm facilitates opening of the esophagus and LES.
- this causes the abdominal muscles to contract vigorously, squeezing the stomach and thus generating sufficient force to expel gastric contents.
what animal does not vomit
the rat
what animals rarely vomit?
horses and cattle
what has the horses’s inability to vomit been attributed to?
NOT because of a powerful LES
what drug has a central emetic effect in animals except horses?
apomorphine
what activity is related to vomiting but different because it is a normal component of digestion in ruminants?
what is it also referred to as?
regurgitation aka “chewing the cud”
what does the regurgitation process require?
reticular contraction, followed by relaxation of LES and reverse esophageal peristalsis
what is esophageal compaction caused by?
impaction with normal food material or a foreign body. it is considered a medical emergency
in what species is choke a common problem? what is caused from?
horses
caused by food impaction of the proximal esophagus
what are predisposing causes of choke?
stricture, diverticulum and ulcer
many times there is no apparent cause
