SALIVARY GLANDS Overview

o Produced by a collection of three major (parotid, submandibular, lingual) and a number of minor (lingual, buccal) glands

o Acinar-ductular glands Acinar cells are classified as either serous or mucous Surrounded by contractile myoepithelial cells

o Serous acinar cells Secrete a watery fluid containing soluble proteins such as salivary

amylaseo Mucous acinar cells

Secrete a viscous fluid containing mucus Contents of saliva

o H2Oo Ions (HCO3-)o Enzymes (amylase)o Antibacterial compounds (lysozyme, lactoferrin, IgA), Mucus

Functions of salivao Lubrication for food (mucins)o Partial digestion of polysacchardies

Salivary amylase Cleaves internal alpha-1,4 bonds in starch Can break down up to 50% of starch before being

inactivated by gastric acido Moisten mouth and wash away dissolved foodo Mild antibacterial (lysozyme, lactoferrin)o Neutralize acids in food and regurgitated stomach acido Maintanence of teeth (Ca2+, fluoride)

Xerostomiao Absence of salivao Causes: drug side effects, head and neck radiation therapy, systemic

diseases (Sjogrens syndrome)o Absence leads to infections, tooth decay, and sever discomfort

Control of Salivary Secretionso Primarily by autonomic nervous system

Only area of GI tract not regulated by GI hormones Parasympathetic innervation

Predominant control begins in the salivatory nuclei of medulla which is stimulated by taste, smell, and chewing and is inhibited by sleep, fatigue, and fear

Sympathetic innervation

Reaches glands through superior cervical ganglia and acts on glandular beta-adrenergic receptors (Ach is the major neurotransmitter)

Production of Salivao Saliva glands have a high resting blood flow due to high rate of fluid

secretion Further increased upon secretion by parasympathetic innervation

of blood vesselso Fluid secreted by acinar cells is plasma like in compositiono Finished hypotonic

As it moves down ducts Na and Cl are reabsorbed and K is secreted due to abundant Na-K ATPase activity in duct cells

Cl-HCO3 exchanger in apical membrane is responsible for alkalinization of salvid

o Increase in flow leads to decrease in hypotonicity of saliva Less time for ductular modulation

ESOPHAGUS Chewing and Swallowing

o Under voluntary neuromuscular control Controlled by the swallowing center in the brainstem Begins as a voluntary action but proceeds reflexively

Anatomyo Muscular tube about 25 cm long with a sphincter at each end

Upper sphincter anatomical Lower sphincter is functional

o Swallowing followed by a wave of primary peristalsis which moves 2-4 cm/sec

When the wave reaches the LES, it relaxes to let food enter the stomach

Secondary peristalsis can be initiated by distension in the absence of swallowing

Esophageal Pressureso Between swallows

Pressure at upper and lower sphincter is positive due to intrinsic muscular tone

In thoracic cavity reflect intrathoracic pressure so is negative In abdominal cavity reflect intra-abdominal pressure (positive)

o Upon swallowing UES relaxes and then contracts contraction followed by

peristaltic contraction of the body of the esophagus LES and fundus relax before contraction arrives

Receptive relaxation Neural Innervation

o Efferent innervation through Vagus Nerve

o Visceral somatic fibers directly innervate the striated muscle of the upper 1/3 of the esophagus

o Vagal preganglionic fibers synapse on ganglion cells which then innervate lower portion of smooth muscle

Regulation of LESo Contraction regulated by intrinsic properties of smooth muscle, nerves,

and hormoneso Basal tone is myogenic but increased by ACh and Gastrino Transient relaxation mediated by inhibitory neurons that use VIP or NOo Sphincter tone lacking in newborns and decreased during pregnancyo Abnormalities

Failure of LES to function as a sphincter leads to reflux esophagitis GERD—Gastroesophageal Reflux Disease Failure of LES to relax results in achalsia (over time will lead to

dilation of esophagus)

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