Mastication, deglution and salivation

Mastication, deglution and salivation

1. Oral cavity

   • Cheeks: lateral walls. Covered externally by skin and internally by mucous membrane. They contain the buccinator muscle.
   • Lips: fleshy folds surrounding opening of mouth. Contain orbicularis oris muscle. Covered externally by skin and internally by mucous membrane. The labial frenulum keeps them attached.
   • Oral vestible: bounded by cheeks and lips, internally gums and teeth.
   • Palate: wall that separates oral cavity from nasal cavity. Is the roof of mouth.
     • Hard palate: anterior portion, formed by maxillae and palatine bones.
     • Soft palate: posterior portion, arch-shaped muscular portion.
   • Uvula: conical muscular process that hangs from the free border of the soft palate.
     • During swallowing, the soft palate and uvula are drawn superiorly, closing off the nasopharynx and preventing swallowed food and liquids enter to nasal cavity.
   • Teeth
     • accessory digestive organs located in sockets of the alveolar processes of the mandible and maxillae. Alveolar processes covered by gingivae.
     • Permanent: 32 teeth
     • Deciduous: 20 teeth
     • Crown: visible portion above the level of the gums
       • Enamel: covers dentin. Consists primarily of calcium phosphate and calcium carbonate
       • Pulpar cavity: inside crown. Filled with pulp, connective tissue with vessels and nerves.
     • Neck: constricted junction of the crown and root near the gum line.
       • Dentin: calcified connective tissue that gives the tooth its basic shape and rigidity
     • Roots: portion attached to the gum.
       • Cementum: covers dentin root and attaches it to periodontal ligament.

2. Salivary glands

   • Release secretions into the mouth, enough to moisture mouth & pharynx, and clean mouth & teeth. Is more released when eating.
   • Major salivary glands
     • Submandibular gland: in the submandibular triangle. Its duct, the submandibular duct (Wharton) pierces the buccinator and flows into each side of the lingual frenulum.
     • Parotid gland: biggest gland. In the infratemporal region. Its duct, the parotid duct (stensen) flows into the parotid papilla, in front of the 2nd upper molar.
     • Sublngual gland: below the tongue, several secretory ducts, some join with the submandibular duct and others flow directly to oral cavity.
   • Lesser salivary glands
     • In the submucosa of the oral cavity. They flow directly into oral cavity by its conducts. They are the bucal, labial, lingual and palatine glands. Von Ebner duct.
   • Saliva
     • Composition
       • It is 99.5% water and 0.5% solutes (Na, K, Cl, HCO3, PO3, disolved gasses, organic substances <urea, uric acid, mucus, IgA, lisozyme, salivary amylase>.
       • Salivary glands: mucous liquid with amylase.
       • Submandibular glands: mucous liquid with amylase.
       • Sublingual glands: very thick mucous liquid with less amylase.
     • Salivation
       • Controlled by ANS, it daily secrets 1-1.6 L.
       • Parasympathetic stimulation promotes salivation. during stress sympathetic stimulation dries mouth.
       • Most components are reabsorved.
       • Chemicals in food stimulate superior and inferior salivary nuclei in brain steem; it returns in parasympathetic impulses in CN VII and IX.

3. Tongue

   • Accesory digestive organ composed of skeletal muscle with a mucous membrane.
   • Muscles
     • Extrinsic muscles:Move tongue side to sie and in and out. hyoglossus, genioglossus, styloglossus.
     • Instrinsic muscles: Alter shape and size of tongue. Longitudinalis superior, transversus linguae, verticalis lnguae.
   • Papillae: gustatory corpuscules, make the specialized mucosa.
     • Filiform: smallest and most abundant. Long conic projections with simple stratified epithelium very keratinized. It DOESN'T HAVE gustatory corpuscules. In all dorsal surface.
     • Fungiform: fungiform projections, higher than filiform papillae. More abundant in the tongue tip. Simple stratified epithelium. They containt hte GUSTATORY CORPUSCULES.
     • Calciform: large dome-shaped. We have 8-12. Each surrounded by a deep groove lined by flat stratified epithelium that contains numerous taste corpuscles. The von Ebner ducts (ligual salivary glands) secret its fluid here.
     • Foliated: Parallel lower ridges separated by deep grooves of the mucosa. in lateral borders of tongue.

4. Temporomandibular joint and masticatory muscles

   • Temporomandibular joint: paired joints that conect the temporal bone with the mandibula.Is a Synovial articulation. Ith as 3 ligaments. temporomandibular, stylomandibular and sphenomandibular.
   • Masticatory muscles: masseter, temporalis, medial pterigoid, lateral pterigoid. CN V3.

5. Esphagus

   • Collapsible muscular tube, 25cm long. Posterior to trachea and anterior to vertebrae. It pierces the diaphragm thorugh the esophageal hiatus.
   • Histology
     • Mucosa: nonkeratinized stratified epithelium, lamina propria and muscularis mucosae. Near stomach it contains mucous glands (cardial glands).
       • Submucosa: areolar connective tissue, blood vessels and mucous glands.
         • Muscularis: superior 1/3 skeletal muscle <upper esophageal sphincter>, 2/3 skeletal and smooth, 3/3 smooth muscle <lower esophageal sphincter>.
           • Adventitia: superficial layer of esophagus, not convered by mesothelium.
   • It doesn't excrete product nor absorb.
   • cricopharyngeal part of the inferior pharyngeal constrictor muscle forms the superior esophageal sphincter, is the cervical esophagus.
   • Innervation
     • The nerves supply to the esophagus is somatic motor and sensory to the upper half and parasympathetic (vagal), sympathetic, and visceral sensory to the lower half. The cervical esophagus receives somatic fibers via branches from the recurrent laryngeal nerves and vasomotor fibers from the cervical sympathetic trunks through the plexus around the inferior thyroid artery
   • Irrigation: arteries to the cervical esophagus are branches of the inferior thyroid arteries. Each artery gives off ascending and descending branches that anastomose with each other and across the midline. Veins from the cervical esophagus are tributaries of the inferior thyroid veins
   • Topographical division
     • Cervical esophagus: part of the voluntary 1/3. starts from the upper border of the cricoid cartilage and ends at C6.
       • While it descends it inclines slightly to the left, enters to the superior mediastinum through superior thoracic aperture and becomes the thoracic esophagus. Lies between the trachea and the cervi- cal vertebral column

6. Deglution

   • Food goes from mouth to the stomach. It's facilitated by secretion of saliva and mucus. It occurs in 3 stages.
   • Food takes 4-8 secods and liquids take 1sec.
   • Stages
     • 1. Voluntary
       • Initiates swallowing process
       • The food is VOLUNTARILY squeezed or rolled posteriorly into the pharynx by pressure of the tongue upward and backward against the palate
     • 2. Pharyngeal
       • Passage of food from pharynx to esophagus. Less than 6 seconds
       • Food enters to posterior mouth and pharynx and EPITHELIAL SWALLOWING RECEPTOR AREAS are stimulated.
       • 2.1 Soft palate is pulled upward with the uvula to prevent reflux of food to nasal cavity.
         • 2.2 Palatopharyngeal folds are pulled medially to approximate to each other. They form a sagital slit through which food must pass in order to get to the pharynx. This is a selective action because it only allowed food enough chewed to pass. Lasts less than 1 second.
           • 2.3 Vocal cords of larynx are approximated and larynx is pulled upward and anteriorly by neck muscles + presence of ligaments that prevent upward movement of epiglotis, cause the epiglottis to swing backward over the opening of the larynx. This prevents passage of food to trachea.
             • 2.4 The upward movement of the pulls up and enlarges the opening of the esophagus. At the same time the upper esophageal sphincter relaxes. Between swallows the sphincter keeps contracted. The upward movement of the larynx also lifts the glottis out of the main stream of food flow, so the food mainly passes on each side of the epiglottis rather than over its surface
               • 2.5 Once the larynx is raised and the pharyngoesopha­ geal sphincter becomes relaxed, the entire muscular wall of the pharynx contracts, making the movement of peristalsis.
       • Nervous control
         • In the posterior mouth and pharynx, is the most sensitive tactile areas. The movement starts in a ring around the pharyngeal opening, which has greatest sensitivity.
           • Sends impulses through sensory portions of the CN V and XII into the medula oblongata to the tractus solitarius.
             • Successive stages of the swallowing process are then automatically initiated in orderly sequence by neu­ronal areas of the reticular substance of the medulla and lower portion of the pons called DEGLUTION AND SWALLOWING CENTER.
               • Motor impulses to pharynx and upper esophagus are cause by the CN's V,IX,X,XII.
     • 3. Esophageal
       • Passage of food from esophagus to pharynx. Gets to stomach in 8-10 seconds.
       • Primary peristalsis: is the continuation of the peristaltic wave that begins in the pharynx and spreads into the esophagu
       • Secondary peristaltic waves: distention of esophagus itself because of retained food. Continues until all food gets to stomach. The movement is initiated by INTRINSIC NEURAL CIRCUITS IN MYENTERIC N.S. and partly by REFLEXES that begin in the pharynx and are then transmit­ted upward through VAGAL AFFERENT FIBERS TO THE MEDULLA AND BACK through glossopharyngeal and vagal efferent nerve fibers.

7. Mastication

   • Incisors provide cutting action and molars provide grinding action.
   • Chewing muscles innerved by V3, and the process ins controled by the nuclei in the brains steem.
     • Stimulation in taste centers of brain steems may cause rythmical chewing movements.
     • Stimulation of areas in the hypotalamus, brain cortex and amygdala near sensory area for taste and smell may cause chewing.
   • Chewing process is caused by the chewwing reflex.
     • Presence of a bolus of food in the mouth at first initiates reflex inhibition of the muscles of mastica­ tion, which allows the lower jaw to drop
       • initiates a stretch reflex of the jaw muscles that leads to rebound contraction.
         • Raise the jaw to cause closure of the teeth,
           • Compresses the bolus again against the linings of the mouth --> inhibition of jaw muscles.

8. Pharynx

   • Food is swallowed and passes to pharynx. It extends from internal nares to the esophagus. Is composed of skeletal muscle and lined by mucous membrane.
   • Nasopharynx: functions only in respiration. Posterior to nose and superior to soft palate. Nose opens to nasopharynx through choanae.
     • Oropharynx: posterior to the mouth.
       • Laryngopharinx: posterior to larynx, connects to esophagus.

9. Ximena Sierra A01227884

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