Mastication & Swallowing PDF

Mastication & Swallowing  Mastication & Swallowing Mastication (Chewing) To grind and break food into small particles Function 1) Facilitate swallowing (Reduce the size of the ingested particles)...

Mastication & Swallowing  Mastication & Swallowing Mastication (Chewing) To grind and break food into small particles Function 1) Facilitate swallowing (Reduce the size of the ingested particles) 2) Mix food with saliva (Expose the food to digeative enz. & lubricates it) 3) Stimulate taste buds 4) Increases surface area of the ingested mater Mechanism  Can occur voluntary.  But most mastication is reflex due to pressure of food in the mouth.  Most of muscles of mastication are supplied by motor branch of the 5 th Cr. n. Controlled by nuclei in the brain stem The incisors Cutting action The molars Grinding action Reflex Mastication  Closure of the teeth compress the bolus against the lining of the mouth inhibits the jaw ms. resulting in drop of the jaw.  This initiates a stretch reflex in the jaw muscles raising the lower jaw with closure of the teeth & contact of food with mouth lining.  Reflex relaxation of the muscles & this process is repeated rhythmically. 1 Mastication & Swallowing Swallowing Movement of food from mouth into stomach  Initiated voluntarily, but continued involuntary (once initiated, it can not be stopped)  Divided into 3 stages 1) Oral Stage 2) pharyngeal Stage 3) Esophageal Stage Oral (buccal) stage  Is voluntary passage of food from mouth to the pharynx  Swallowing is initiated when a bolus is voluntarily forced by tongue into pharynx.  Once the bolus reaches the pharynx, the process will be involuntary. 2  Mastication & Swallowing Pharyngeal stage  Is Involuntary  Initiated when food Reaches the back of mouth, stimulating the pressure receptors at the pharyngeal opening, that stimulate swallowing center  This triggers swallowing reflex:  Afferent: 5& 9  cranial nerves Centre: Swallowing center in MO  Efferent: 5, 9 , 10 & 12 Swallowing Reflex  When a bolus enters Pharynx  Stimulate Pressure receptors in pharynx  Stimulate Swallowing Center  Stimulate Highly Coordinated Motility in Pharynx aimed to 1) Push bolus into esophagus By peristalsis 2) Prevent bolus from entering mouth, nose, trachea Pharyngeal phase of wallowing is accompanied by 1) Closure of the larynx by the epiglottis 2) Peristaltic waves in the esophagus 3) Opening of the upper esophageal sphincter (UOS) 4) Momentary inhibition of respiration (Swallowing apnea) 3 Mastication & Swallowing Swallowing center 1) Inhibits respiration during pharyngeal stage but not in esophageal stage 2) Initiates peristaltic contraction in pharynx Fast Pharyngeal peristaltic wave to increase Intra-pharyngeal pressure. It is a primary peristalsis. Push bolus into esophagus Upper esophageal sphincter relax. Esophageal stage  Is involuntary  Bolus is propelled by Peristalsis (primary and secondary) to the stomach Which is a ring like contractions of circular smooth muscle N.B  The type of muscle (striated or smooth) in the esophagus varies along its length.  The UES and LES are formed by thickening of striated or circular smooth muscle, respectively. Stages of esophageal phase 1) A bolus in pharynx 2) Stimulate Pressure receptors in pharynx 1) Stimulate Swallowing Center in MO , 2) stimulate Vagus n. Relaxation of LOS (why?) 1) Primary Peristalsis in esophagus , Push bolus toward stomach , bolus enters stomach 4 Mastication & Swallowing Vagus nerve Site Neurotransmitter Action neurons in esophagus Ach Primary Peristalsis In esophagus neurons in LOS NO / VIP Relaxation of LOS Muscles of the pharynx & esophagus Type Site Nerve supply 1) somatic nerve fibers in striated muscle pharynx and upper 1/3 of the glossopharyngeal esophagus 2) vagus nerves 1) parasympathetic fibers in smooth muscle lower part of the esophagus vagus nerves 2) myenteric nerve plexus Cutting the vagus to esophagus No swallowing reflex (as it Secondary peristalsis in lower is mediated by vagus) &No part of Esophagus is still Primary peristalsis working Via Intrinsic plexuses N.B  Cutting of the vagus to esophagus (no swallowing reflex) Therefore, feeding can be done by introducing food by tube into the lower esophagus  Secondary peristalsis That pushes food into stomach  Except during swallowing Upper Esophageal Sphincter is always closed to Prevent Air Entry  Except during swallowing Lower Esophageal Sphincter is always closed to Prevent Acid Reflux 5  Mastication & Swallowing Disorders of LOS Disorder Causes Result  Gastric Acid enters Esophagus LOS (Esophageal Reflux) Reduced Tone of Lower  Clinical picture :Heartburn incompetence Esophageal Sphincter  May occurs during pregnancy or in (decrease tone ) presence of diaphragmatic hernia 1) Some food enters Trachea 1) Damage to Myenteric Plexus (Aspiration Pneumonia) in LOS 2) Some food enters Trachea 2) VIP or NO Deficiency (Aspiration Pneumonia) Achalasia 3) LOS Failed to Relax (increase tone ) Treated by 1) antispasmodic drugs 2) dilation of the sphincter. 3) incision of the esophageal muscle (myotomy). Esophageal Secretion Function of Mucus 1) Facilitate swallowing 2) Protect Esophagus from gastric Acid & enzymes N.B No food or H2O absorption and no digestion in the esophagus 6