PHS 3342 Lecture Notes - Lecture 17: Salivary Gland, Cellulase, Horse Length
28 Apr 2018
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April 3, 2018
Movement of Food through GI Tract
Chewing
Mastication (chewing): combined action of muscles of jaws, lips, cheeks, tongue
-Muscles can be controlled voluntarily, but chewing is usually reflex in nature
-Functions:
•Major function is to decrease particle size and increase surface area
•Chewing also breaks down cellulose walls of plant cells (we don’t have cellulase)
•Chewing, by moving food around in the mouth, stimulates receptors for taste and small —> appreciation of food
and stimulation of saliva secretion
-Mechanism:
•Pressure increases when jaws close following introduction of food bolus
•Reflex inhibition of jaw-closing muscles and contracting of jaw-opening muscles
•Mouth opens, producing a drop in pressure
•Reflect contraction of jaw-closing muscles and relaxation of jaw opening muscles
•Mouth closes and cycle repeats
Salivary Secretion
Saliva:
-Cleanses mouth - contains lysozyme (antibacterial enzyme)
-Dissolves food chemicals —> taste
-Moistens and compacts food (bolus)
-Begins digestion of starch (amylase)
-Bicarbonate neutralizes acid of oral bacteria
-Decreased saliva production alerts you of dehydration —> thirst
Salivary secretion:
-1-2 L of saliva produced per day (0.5 mL/min resting, max ~4 mL/min)
-3 pairs of extrinsic salivary glands + small intrinsic buccal glands
•Salivary glands: extrinsic because they’re outside the oral cavity
-Parotid glands: serous cells only (25%)
•Serous cells: produce watery secretion containing enzyme
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PAROTID
SUBMANDIBULAR
SUBLINGUAL
April 3, 2018
-Submandibular glands: serous and mucus cells (70%)
•Mucus cells: produce mucus
-Sublingual glands: serous and primarily mucus cells (5%)
•Buccal glands: within the lining of the oral cavity, produce small amounts of saliva to maintain moisture levels
Regulation of saliva secretion: long reflexes
-Salivary centre in medulla can be activated in multiple ways:
•Cerebral cortex: thinking of food, seeing food, smelling food
-Laying out food that you know you like activates saliva production
-Conditioned reflex - won’t produce much saliva in response to food you don’t like
•Pressure receptors and chemoreceptors in mouth
-Lets you know that there’s food in your mouth to increase saliva production
-Simple reflex
-Salivary cortex sends the signal through autonomic nerves (parasympathetic NS) to the salivary glands in order to
stimulate salivary secretion
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Deglutition (Swallowing)
Mouth and pharynx:
-Swallowing centre coordinates sequential muscle movements via long reflexes
•Want to contract behind the food but relax in front of it in order to push it forwards
-Coordinated activity of tongue, soft palate, pharynx, esophagus, and 22 separate muscle groups
-Swallowing process:
•Front of tongue pushed up against hard palate - rolls food mass towards the back of the tongue
•Bolus forced into pharynx by contractions of skeletal muscles in back of the throat (voluntary up until this point)
-After this point, esophagus is increasingly composed of smooth muscle
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•Respiration inhibited briefly as all routes to lungs blocked off - want to stop breathing because pharynx is
common to digestive and respiratory tracts
•Soft palate raises uvula - closes nasal passages
•Larynx rises - epiglottis covers opening to trachea
•Bolus presses on epiglottis
•Constrictor muscles force bolus into esophagus
Esophagus:
-Collapsed muscular tube (~25 cm)
•Upper esophageal sphincter (voluntary)
•Body: upper ⅓ skeletal muscle, lower ⅔ smooth muscle
•Lower esophageal sphincter (involuntary)
-Pressure gradients in esophagus created by contractions are important for movement of bolus down to stomach
and keeping sphincters closed when food not being ingested
-At lower GE sphincter, intragastric pressure is greater than atmospheric pressure but lower than contracted lower
sphincter —> causes stomach contents to stay there
•Heartburn: sphincter opens a bit and acidic stomach contents escape
-Alcohol and caffeine decrease lower GE sphincter tone
-Obesity or pregnancy can increase intragastric pressure
•Hiatus hernia: stomach slightly slips out of place, stomach protrudes slightly above diaphragm
-Diaphragm pushes on the stomach and causes acidic contents to escape out of the esophagus
Swallowing: initiated when pressure in pharynx increases due to muscle contraction
-Sphincters relax, brining pressures in these areas down to atmospheric pressure
-Food enters esophagus (following pressure gradient)
-Upper sphincter closes, glottis opens, and respiration resumes
•Pressure rises from above to below in esophagus
-Directional pressure rise is due to peristaltic wave of contraction, which propels food mass down
•2-4 cm/sec, 9 seconds to traverse esophagus
-Food in stomach causes the lower GE sphincter to contract, preventing gastric reflux
The Stomach
Anatomy of the stomach:
-Fundus: area extending above the gastroesophageal sphincter
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Document Summary
Mastication (chewing): combined action of muscles of jaws, lips, cheeks, tongue. Muscles can be controlled voluntarily, but chewing is usually re ex in nature. Cleanses mouth - contains lysozyme (antibacterial enzyme) Decreased saliva production alerts you of dehydration > thirst. 1-2 l of saliva produced per day (0. 5 ml/min resting, max ~4 ml/min) 3 pairs of extrinsic salivary glands + small intrinsic buccal glands: salivary glands: extrinsic because they"re outside the oral cavity. Parotid glands: serous cells only (25%: serous cells: produce watery secretion containing enzyme. Submandibular glands: serous and mucus cells (70%: mucus cells: produce mucus. Sublingual glands: serous and primarily mucus cells (5%: buccal glands: within the lining of the oral cavity, produce small amounts of saliva to maintain moisture levels. Salivary centre in medulla can be activated in multiple ways: cerebral cortex: thinking of food, seeing food, smelling food. Laying out food that you know you like activates saliva production.
