BASICS of ORAL PHYSIOLOGY (Part 1).docx

8/14/2019 BASICS of ORAL PHYSIOLOGY (Part 1).docx

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Balarabe Musa EL- HUSSAIN

Dental Therapy DepartmentFederal School of Dental Technology & Therapy P.M.B 01473,

Trans-Ekulu, Enugu state, Nigeria, WEST AFRICA.


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INTODUCTION & GENERAL OVERVIEW

In an attempt to make the understanding of oral physiology more simplified, interesting,

easier & appreciative. It is important or pertinent that one should & also must have an

understanding of the back ground knowledge of the history of physiology; origin of physiology;

general classification of physiology; broad based subdivisions of physiology; relation of physiology

to other sciences and human physiology.The History of Physiology

In ancient times the earliest information on physiology was obtained from the empirical

observations of naturalists and physicians and particularly through the dissection of animal and

human cadavers. For many centuries the accepted views concerning the body and its functions

were those of Hippocrates and Aristotle i.e. in the fifth and fourth centuries B.C., respectively. In the

middle ages, advances in medicine stimulated the development of biology, and the overall progress

achieved in the sciences during the Renaissance contributed to the development of physiology.

However, Physiology as a science founded by an English physician W. Harvey, with his

discovery of blood circulation in 1628, which in the words of F. Engels another scholar in

physiology, waswhat made the science of the physiology of man and animals a very significant tool

in medicine and other allied fields; of which the dental therapy arm in the field of dentistry is never

an exception or rather in isolation. Physiology however became an independent field as it was

removed or distinguished from anatomy in the 19th century, due to the developmentaladvancements in organic chemistry; the discovery of the laws of the conservation and transformation

of energy and of the cellular structure of the body; as well as the formulation of the theory of

evolution of organic life.This is because, it was in the early 19th century that it was believed established that the

chemical compounds in the living organism were fundamentally different from inorganicsubstances and could not be produced outside the body: and this believe is what ushered in a new

stage in the development of physiology that began in the 20th century , when the earlier,

narrowly analytic view of the bodys vital processes gave way to a synthetic view.

Origin of Physiology

The term physiology is derived from two Greek words, physis --- meaning nature and

logos -- meaning word.Physiology is a field of sciencethat involves studying various functions

of the component /structural parts of living organisms . It is a critically important basic science

because it is the foundation upon which we build our knowledge of what normal functioning is,

how disease states are developed and how to treat them, and how to best cope with stresses

encountered by our bodies due to the changes in our environment.

The study of human physiology was stimulated by the development of medicine, and it

embraces many chemical and physical principles. This is because physiological processes are

dynamic; just as cells contained in the human body do change their primary functions i.e. into

secondary function in response to changes in the composition of their local environment.

Meanwhile, as living organisms responds to alterations in both their external and internal

environment, the resultant effects are consequently

registered/denoted/classified/categorized/identified/named & or regarded as physiological

reactions significantly aimed at preserving a constant/neutral physical & or chemical internal

environment homeostasis.


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Relative to living organisms vizviz plants & animals mammals and man or humans

inclusive,physiology is being described as the branch of science that deals with the life functioning

processes of individual systems, organs & tissues as contained in a specified identifiable or rather

distinguishable living organism. It is also being described as the field of scientific study of all

regulatory functional processes involving the interaction of various structural components both

microscopic & macroscopic in a living organism, either within the living organisms internal

structures or in between the living organisms internal structures and the immediate externalenvironment.

Branches of Physiology

Physiology as one of the most important i.e. vital or significant branch of biology/biological

science as well as medical science, it is however interwoven with a large number of independent or

interdependent allied fields or disciplines because of the existing close relationship shared amongst

other various identifiable arms i.e. the fields of biological sciences or medical sciences. Generally &from a broader point of view, physiology is classified into:

a) General physiologyb) Applied physiologyc) Physiology of specific structureshere belongs Oral Physiology.General physiology:

This is a branch of physiology centered about the general studies & understanding of the

physiological interactive or reactionary principles common i.e. exhibited amongst different species

of living organisms; as well as the processes involved in the excitation and inhibition of

mechanisms, relative to how the different species of living organisms respond to certain stimuli;

and is further subdivided into: Comparative, Developmental, Ecological physiology& & Evolutionary

etc.

Comparative physiology: ----This is a sub-discipline of physiology that

studies as well exploits the existing diversity of functional characteristics of

various kinds of livingorganisms.

Developmental physiology: ----Studies the formation and development of

physiological functions in the course of ontogeny, from the fertilization

processes in living organisms until death, and is closely associated with

evolutionary physiology.

Ecological physiology (Environmental physiology): --- It is a sub-discipline

in physiologic-biological science which studies the functioning of

physiological systems in living organisms relative to their adaptation ability

as regards their basic surrounding habitat & immediate environmental

conditions.
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Evolutionary physiology:----This is a sub-discipline of physiological scienceaimed at studying, identifying & understanding the manner in which the

functional characteristics of variety of individual living organisms & or their

structural component parts (i.e. in a population of different living organisms or

amongst various structural component parts in a living organism) do respond to

selection across multiplegenerations during the history of the population.

Applied physiology:It is a branch of physiology centered about how the study, understanding and knowledge of

how the biological systems and other various structural component parts of systems as contained

in the body of living organisms can be applied into practice in order to help resolve any

physiological functional deficiencies i.e. functional anomalies that may arise from abnormal

functioning; as well as the best possible steps applicable in practice. This involves the applicationof the knowledge ofphysiologicalproperties to restore stability, which differs fromclinical practice.

Thus, applied physiology is often than not being described as a branch of physiologyconcerned with the studies of the general and specific principles that control the functioning of

living organisms, in relation to various aspects of life. Other sub-divisions of applied

physiology include the physiology of labor, sports physiology, the physiology of

nutrition, aviation physiology, space physiology, underwater physiology, High

altitude physiology and exercise physiologyetc.

Physiology of specific structures:

The physiology of specific structures is aimed at investigating the life & functional processes

in individual structural groups of tissue component parts in living organisms or specific tissues i.e.

specialized tissues component parts in living organisms in order to study, evaluates, understands aswell as appreciates the properties of such group of specialized tissues or specific individualized

tissue and the ways in which these structural tissue component parts help form specialized

functional systems that play significant role in the maintenance of complete & total body integrity

of a living organism.

Broad Based Divisions of Physiology

Physiology is also subdivided into:

a) Normal physiologyb) Pathological physiology

Normal physiology:

Primarily studies the functioning of the healthy organism, its interaction

with the environment, and the mechanisms by which it resists and adapts to a

variety of factors.

Pathological physiology:
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Studies altered functions of the diseased organism, the processes of

compensation and adaptation in disease, and the mechanisms of recovery and

rehabilitation. A branch of pathological physiology is clinical physiology, which

studies the origin and activity of such functions as blood circulation, digestion, and

higher nervous activity during disease in animals and man.

Relationship of Physiology to other sciences

Physiology as a branch of biological science is closely related to such morphological sciences

as anatomy, histology, and cytology; however physiology & morphology are significantly closely

interdependent. Furthermore, physiology as a branch of both biological & medical science also

utilizes extensive use of the principles and methods of physics, chemistry, cybernetics, and

mathematics in which the chemical and physical processes occurring in the organism are studied in

conjunction with biochemistry, biophysics, bionics, evolutionary laws that are studied in

conjunction with embryology. More so, whereas the physiology of higher nervous activity is

associated with ethology, psychology, physiological psychology, and pedagogy; however the

physiology of farm animals has direct significance for livestock breeding, zootechny, and veterinary

science.

Conclusively & from a general point of view, physiology is generally accepted to be most

closely associated with medicine, of which it plays significant i.e. vital role in the diagnoses,

prognoses, management involving prevention & or treatment of variety of diseases affecting living

organisms. In which Clinical medicine is what in turn, provides physiology with significant new

areas of investigation, as the data established by physiological studies are what constitute part of

the foundation of the natural sciences and are widely used in philosophy to substantiate the

materialist world outlook.

HUMAN PHYSIOLOGY

The study of human physiology dates back to at least 420 B.C. and the time of Hippocrates,the

father of medicine.Physiology was first recognized in the early 1960s, due to the critical thinking of

Aristotle and his emphasis on the relationship between structure and function which marked the

beginning of physiology in Ancient Greece. However, it was Claudius Galenus (c. 126-199 A.D.),

known as Galen, who first use experiments to probe the function of the body ( otherwise called

experimental physiology). The medical world moved on from Galenism only with the appearance of

Andreas Vesaliusand William Harveyduring the middle ages, in which the ancient Greek and Indian

medical traditions were further developed by Muslim physicians.

Following from the middle ages, the renaissance brought an increase of physiologicalresearch in thewestern worldthat triggered the modern study of anatomy and physiology. It was in

the 19th century, that physiological knowledge began to accumulate at a rapid rate,due to the

advent of cell theory, concepts of cell environment & homeostasis. These were what made biologists

in the 20th century, to become more interested in how organisms other than human beings

function; which eventually brought about the existence of other fields of physiology such as

comparative physiology, ecophysiology & evolutionary physiology as distinct sub-disciplines. Thustoday, in Human Physiology we have molecular physiology, cell physiology, endocrine physiology,

cardiovascular physiology, respiratory physiology, oral physiologyand etc.

ORAL PHYSIOLOGY
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Oral Physiology is a branch of oral biological science that deals with the study of the

health and diseases of the oral cavity in the context of its proper biologic function . Thus, it is

often described as the physiology related to clinical manifestations in the normal and abnormal

behavior of oral structures, that deals with the scientific study of an human's oral cavity vital

functions, including growth & development, the absorption & processing of nutrients, the synthesis &

distribution of proteins and other organic molecules, as well as the functioning of different tissues,

organs & other anatomic structures that make up the oro-facial complex apparatus in humans. Ofwhich the principal clinical functions in which the oral structures participate are deglutition,

mastication, respiration, speech, and head posture.

Summarily, it can be said that oral physiology is a branch of biology that studies the normal

mechanical, physical, and biochemical processes of the functions of the structural components of the

mouth.


The oral cavity is derived from two Latin words Oralis ---i.e. pertaining to the mouth, and

Cavum ---i.e. referring to the cavity proper.The oral cavity is the space within the mouth, which isthe 1stportion of the alimentary canal, containing the tongue, teeth & other masticatory structures.

It is also the 1st portion of the mouth that which received food and begins food digestion by

breaking up food particles into smaller pieces while mixing them with saliva. It can as well be

described as the opening or hollow part of the mouth through which food is taken in; &

vocalizations emerge, which comprises of an externally visible part on the face and the system of

organs surrounding the orofacial opening. Furthermore, the oral cavity can also be described as the

part of the mouth behind the teeth and gums that is bounded above by the hard and soft palates and

below by the tongue and the mucous membrane connecting it with the inner part of the mandible.

More so, it is often described as the first space of the mouth, bounded laterally and in front by

thealveolar arches (containing theteeth), and posteriorily by theisthmus of the fauces.The oral

cavity is also known as an opening through which food is swallowed, that then goes down the

esophagus & finally into the stomach.Besides, it can also be described as a nearly an oval shaped
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hollow compartment in which food mastication takes place and is generally made up of two basic

anatomic parts that influences its significant physiologic functions. These basic component parts

are:

a) The vestibule oris i.e. oral vestibule.b) Cavum oris proprium i.e. oral cavity proper.Oral vestibule:

This is what forms the outer smaller portion of the oral cavity. It is a slit

like aperture bounded in front and laterally by the lips & cheeks; behind and

internally by the gums & teeth; above and below by the mucous membrane

reflection from the lips & cheeks to the gum covering the upper and lower alveolar

arches. The oral vestibule receives secretion from the parotid glands and

communicates with cavum oris proprium when the jaws are closed by an aperture

on each side behind the wisdom teeth.

Cavum oris proprium:

This is what forms the inner larger portion of the oral cavity, bounded

laterally and in front by the alveolar arch with their contained teeth; behind it

communicates with the pharynx by a constricted aperture (i.e. isthmus faucium). It is

roofedby the hard & soft palate, while the greater part of the flooris formed by the

tongue & mucous membrane reflection from the sides and under surface of the

tongue to the gum lining the inner aspect of the mandible. It receives secretions

from both sub maxillary and sublingual glands.

CONTENTS OF THE ORAL CAVITYThe oral cavity is an important component structural part of the human body; which from

the basic for assessing & evaluating various significant physiologic processes involved in

mastication up to the initial diagnosis of systemic diseases. The oral cavity also serves as an

important indicator i.e. a significant diagnostic parameter to the proper assessment & evaluation

of overall human general health. The structural component parts of the oral cavity are thus, the:

a) Lips.b) Cheeks.c) Teeth.d) Jaws maxillae and mandible.e) Gums i.e.gingivae.f) Tongue.g) Palate.h) Salivary glands.i) Jaw joint i.e. temporomandibular joint.


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Basic Physiologic & Morphologic component structures of the human oralcavity

The lips:

It is a muscular skeleton forming two fleshy folds surrounding the orifice of

the mouth. The lips are connected in the midline to the gingivae by a mucous

membrane fold (freanum labii superioris and inferioris). It also has red free margins

(vermillion). The lips are what outline the cavity externally and are the only visible

external part of the oral cavity, serving as an upper seal to the digestive tract.

Covered with skin on the outside and mucosa on the inner side, together they are

the gateway to the oral cavity.

Basic Physiologic & Morphologic component structures of the human lips


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Oral Physiologic actions/functions:These include:

Guiding food and water intake.

Helping in articulation of speech.

Helping mouth to chew and close on food i.e. by sealing the mouth

Assisting in speech and non- verbal communication.

Marking the transition from skin to mucous membraneEnhancing judgment on temperature & texture as it contains many sensory receptors

Aiding in exploring unknown object especially in babies & toddlers as a tactile organ

Playing crucial role in kissing & other acts of intimacy as an erogenous zone

Serving as a symbolic meaning for sensuality & sexuality

The cheeks:

Are what forms the sides of the face and are continuous in front with the

lips. The cheeks has a nonkeratinized mucosa tightly attached to the buccinators

muscles, reflected above and below upon the gum which continue behind with the

lining membrane of the soft palate.


Preventing food from escaping chewing action of the teeth

Helping in maintaining the teeth in positions

The Teeth:

They are derived from the embryonic dental organ, when the embryo is

about 3-4 weeks old in utero. They contain four significant tissues (enamel, dentine,

cementum and pulp). The enamel, cementum and dentine are hard tissues while

pulp is a soft tissue. Teeth are generally contained in the alveoli (teeth sockets) of

the alveolar bone. In overall human dentition, there are two different sets of teeth

(deciduous/milk/primary/babys teeth and adult/permanent/secondary teeth).


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Secondary dentition of the human adult

Primary teeth: ---Are the 1st sets of teeth formed. They are 20 in number,grouped from A-E on either side of the dental arches [upper and lower], with

the dental formulae of I- 2/2; C-1/1; M- 2/2. These set of teeth are replacedby secondary teeth. Physiologic eruption of these teeth into the oral cavity

begins in the mandibular arch with central incisors at the age of 6th-9th

month after birth. Unlike the secondary successors, primary teeth lack

premolars.

Secondary teeth: --- Are the 2nd group of human dentition, about 32 in

number arranged from 1-8 on either side of the midline of upper and lower

arches, with a dental formulae of I-2/2; C-I/1; Pm- 2/2; M-3/3. They are set

of teeth replacing the deciduous/primary teeth. Physiologic eruption of these

teeth in to the oral cavity begins in the mandibular region with the central

incisors at the age of 6-7yrs.


Improving esthetics, speech &mastication or mechanical breakdown of food ( involving

tearing, cutting and grinding of food)

Helping in deglutition

Providing protection for other internal oral cavity components

Helping to preserve & maintain the physiologic functional integrity of the oral cavity.

The Jaws:

The jaws in the oral cavity are two viz-a-viz upper and lower jaws

representing the upper and lower dental arches in the oral cavity.

Mandible jaw: ---It is also called inferior maxillary bone &is the largest and

strongest facial bone, which houses the lower teeth. It comprises of a body

(curved horizontal portion) and rami (two perpendicular portions) that joins

the body nearly at right angles. This bone also articulates with temporalbones through the gleinoid fossa as well as gives attachment to other facial

and masticatory muscles.


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The mandibular jaw

Morphologic features enhancing physiologic functions of the mandibular jaw

Mandible body:--- It is convex in general outline presenting a

somewhat horse shoe shape with external and internal surfaces, in

which the external surface is concave from side to side, while the

internal surface is concave from side to side too.

Mandible rami: ---These are quadrilateral in form with two surfaces

(external and internal) and two processes (coronoid and condyle)

marked with ridges.

The Maxillae jaw: --- Arealso called superior maxillary bones. They are the

most prominent bones of the face from a physiologic surgical point of view

on account of the number of diseases to which some of its parts are liable to.

Each of the maxillae bone does assist in the formation of three cavities (i.e.

the roof of the mouth; floor and outer walls of nasal fossae; and the floor of


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the orbit). It also enters in to the formation of zygomatic and sphenomaxillary

fossae as well as sphenomaxillary and pterygomaxillary fissures. The maxillae

are somewhat cuboidal and hollowed out to form a large cavity antrum of

Highmore.

Morphologic features enhancing physiologic functions of the maxillae jaw

Morphologic features enhancing physiologic functions of the maxillae jawOral Physiologic actions/functions:These include:

Providing for articulation with other facial bonesProviding for attachment to other facial and masticatory muscles.

The gum/gingivae:

It is the mucous membrane lining the lower part of the alveolus, closely

connected to the periosteum of the alveolar process. It is a specialized portion of


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mucosa that surrounds the necks of the teeth; covered by smooth and vascular

mucous membrane remarkable for its limited sensibility. The gum presents different

colours owing to its keratinization types as well as its proximity to underlying blood

vessels surface.

Morphologic features enhancing physiologic functions of the human gingivae gum


Helping in connecting each tooth at the neck and extends over the root and supporting

bone.Serving to anchors the teeth in position

Acting as a shock absorber to dissipate the forces of chewing


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The Tongue:

This is an organ of special sense (taste), made of mainly skeletal muscle

situated in the floor of the mouth and in the intervals between two lateral portions

of the body of the lower jaw. The tongue is a muscular organ (highly mobile,

flexible, and a muscular structure attached to the floor of oral cavity at one end and

free at the other projecting upwards from the floor of the mouth), partly invested by

mucous membrane and a sub mucous fibrous layer, consisting of two symmetrical

halves viz-a-viz an upper surface anterior 2/3rd and a lower surface posterior

1/3rd.

Morphologic features enhancing physiologic functions of the human tongue

Anterior 2/3rd:---This is also divided into two, i.e. the oral part-- that whichlies in the oral cavity and covered by tiny projections called papillae where

the four significant taste buds viz-a-viz sweet, salty, sour and bitter are

located; and the pharyngeal part--that faces backward to the oropharynx.

Posterior 1/3rd:--- This is the lower tongue surface covered with a smooth

mucous membrane that forms part of the pharynx (tongue root). It is

nonkeratinized and tightly bound to the underlying muscles. This portion of

the tongue contains such structures as frenelum linguae (freanum), sulcus

terminalis, freanum caecum and epiglottis and it is separated from the

anterior 2/3rdin the midline by a V-shaped groove fibrous septum.


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Helping in speech production.

Aiding in the formation of food bolus and swallowing of food (i.e. aiding food mastication)

Facilitating taste sensation, perception & appreciation of food

Helping in oral hygiene maintenance

Enhancing in esthetics and gestureServing as a sensory organ in babies

The palate:It forms the ceiling or roof of the oral cavity, consisting of two portions

viz-a-viz the hard palate (in front) and soft palate (behind). In which the front

portion of the palate is constructed of bone (specifically two bones called the

maxilla and the palatine) covered with a mucous membrane. Together these form

the hard palate. While further back in the mouth, behind the hard palate, lays the

soft palate. The hard and soft palate separates the oral cavity from the nasal cavity.


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Morphologic features enhancing physiologic functions of the human palatemouth roof


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Hard palate: It is the anterior part of the palate, consisting of the bony

plate covered above by the mucous membrane of the nose. Below this by

the mucoperiosteum the roof of the mouth, which constitutes an immovable

portion of the palate, with a bony skeleton bounded in front and at the sides

by the alveolar arches and gum/gingivae, while it continuous behind with the

soft palate. The hard palate is also furnished with palatal glands lying

between the mucous membrane and surface of the bone. On the hard palate

is a found linear ridge/raphe (palatine rugae); series of mucosa ridges and

irregular folds.

Soft palate: ---Continuous with the hard palate, lays the soft palate. It is also

called Velum pendulum palati, a movable fold suspended from the

posterior border of the hard palate that forms an incomplete septum

between the mouth and the pharynx. It also has a thin but firm fibrous layer

attached above to the posterior border of the hard palate. The soft palate is

made up of muscular tissue that is covered by epithelial tissue, and a

projection of tissue known as the (uvula).

Morphologic features enhancing physiologic functions of the human palatemouth roof


Aiding breathing and chewing at the same time

Aiding speaking and singing


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The Oral mucosa:It is a mucous membrane lining the oral cavity, composed of connective

tissues covered with stratified squamous epithelium. The oral mucosa is heavier and

more resistant to injuries than the mucous membrane of other more protected

cavities. It can withstand wear and tear of ordinary oral functions as well as resist

bacterial irritation or infection. The oral mucosa is made of three significant portions

viz-a-viz lining, masticatory and specialized (sensory) mucosae.

Lining oral mucosa: ---- It is a nonkeratinized mucosa, containing larger

blood vessels, nerves and lymphatics that cover the inner surfaces of the

cheeks, lips, floor of the mouth, ventral tongue surface, soft palate and

alveolar mucosa. The lining oral mucosa is not firmly attached to underlying

tissues.

Masticatory oral mucosa: --- It is tough epithelial surface membrane highly

keratinized to withstand masticatory forces/stress covering the hard palate

and the gingivae/gum. It is firmly attached to underneath tissues except on

the marginal gingivae.

Specialized (sensory) gingivae: ----It is keratinized epithelium that covers the

upper surface or dorsum of the tongue contributing to the special function of

taste sensation.Oral Physiologic actions/functions:This includes:

Helping in protecting the oral cavity against the daily wear and tear caused by eating

The salivary glands:These glands are found in and around your mouth and throat. There are

three pairs of major salivary glands (the parotid glands, the sub-mandibular glands

and the sub lingual glands). The parotid gland is the largest among the three major

glands followed by sub-mandibular and sub-lingual.


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Sub maxillary salivary glands: ---They are situated below the jaw in the

anterior part of the sub maxillary triangle of the neck. It is irregular in

form, covered by integuments, platysma, deep cervical fascia and the body

of the lower jaw. Its secretions get into the oral cavity via the Whartons

ductunder the tongue.

Submandibular/sublingual salivary glands: --- Are the smallest salivary

glands situated beneath the mucus membrane of the floor of the mouth at

the side of the freanum linguae in contact with the inner surface of the

lower jaw, close to the symphysis. Its secretions get into the oral cavity via

the duct of Rivini, though few others do join to open into the Whartons

duct via the duct of Bartholin.

Parotid salivary glands: ---Are the largest salivary glands placed near the

ear, lying upon the side of the face immediately below and in front of the

external ear. Its secretions get into the oral cavity via a dense, thick canal

about the size of a crow-quill the Stensons duct on the inner aspect of

the cheeks, near the upper teeth.


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The human salivary glands


Producing the saliva used to moisten (lubricate) the mouth, initiate digestion i.e. thephysical and chemical break down of food by solubulizing dry food in the mouthHelping in protecting the teeth from decay by providing alkaline buffering action

The temporomandibular joint (TMJ):

The TMJ is complex & flexible joint, composed of muscles, tendons and

bones. It connects the lower jaw (mandible) to the temporal bone at the side of the

head.


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Morphologic features enhancing physiologic functions of the human TMJ


Providing for smooth up & down movement of the jaws

Providing for smooth side-to-side movement of the jaws

Enhancing chewing i.e. masticatory actions

Aiding in speech & yawning

Providing for muscles attachment to & from the surrounding joint

Helping in controlling the mouth precise position & movement

Summary on the oral cavity

The oral cavity i.e. mouth is an important part of the body that has

variety of oral physiologic actions or functions, of which some of these actions or

functions are vital, socialand or asocial. However, in order to effectively fulfill thesefunctions, the oral cavity is made up of a number of structures that perform specific

functions. These varieties of physiologic oral actions or functions are as summarily

charted below:-


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The human saliva though referred to in various contexts as either spit, spittle, drivel, drool, or

slobber; is a component of oral fluid & a watery substance produced in themouths of humans and

mostanimals.In mammals, saliva is produced in and secreted from the three pairs of major salivary

glands, which are the parotid, sublingual, submandibular glands as well as fromhundreds of other

minor salivary glands, referred to as the accessory salivary glands.

NOTE:-Saliva just like the blood also serves like a bloodstream to the mouth, whose chemical nature

evolves along with the oral flora & the teeth. Thus as does blood, saliva as well helps in building &

maintaining the health of the soft and hard tissues.

It also helps in removing waste products as well as providing disease-fighting substances

throughout the mouth, thereby offering first line protection against microbial invasion or

overgrowth that might lead to disease.

The secretion of saliva is under control of the autonomic nervous system, which controls both the

volume and type of saliva secreted. This is because all the salivary glands are innervated by both

sympathetic & parasympathetic nerve fibers, in which various neurotransmitters and hormones

stimulate different receptors, different salivary glands, and different responses.

However, the parasympathetic stimulation from the brain is what results in greatly enhanced

secretion, as well as increased blood flow to the salivary glands. While the salivary secretion isregulated by a reflex arch under influence of higher centers in the brain comprising of afferentreceptors and nerves that which carry or convey impulses as induced by actions on gustation and

or on mastication, via a central connection i.e. salivation center, and an efferent part consisting

of parasympathetic and sympathetic autonomic nerve bundles that separately innervate the

glands.

Daily salivary output

A considerable volume of saliva is produced over a day. About 0.5or 0.75to

1.5 liter of fluid is usually secreted in a day (which drops to almost zero during

sleep).This represents about 1/5of the total plasma volume. This fluid is not lost asmost of it is swallowed and reabsorbed by the gut.However, the relative proportion

contributed to the whole saliva by each of the gland pairs depends on the degree of

stimulation. Thus:

Under resting conditions: ---The submandibular glands contribute 69%, the

parotid glands 26%, and the sublingual glands 5%mean values of the total

secretion derived from these three major gland pairs.

Under conditions of increased exogenous stimulation:--- The submandibular

glands again account for the largest and the sublingual glands for the

smallest fraction of the total secretion from the major glands, but the relative

proportion of the total secretion contributed by the parotid glands increases.

Thus, the submandibular glands contribute 63.7%, the parotid glands 34%,

and the sublingual glands only 2.8%.
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NOTE: -Salivary flow can vary between 800mililiters and 2 liters, but this is regulated by a number of

factor especially nervous control by the brain stem. It has also been established that the mucosal and

labial glands in the oral cavity make some contribution to the total volume of saliva under stimulated

conditions.

Salivary secretion

As food is broken up by the teeth, it is lubricated with salivary secretions

saliva, in order Ithelps get food to the right consistency to be swallowed. Salivary

secretion is a combination of a serous and mucoid fluid.

The serous fluid:

Is watery and contains the enzyme ptyalin which the starts the

digestion of carbohydrates. It is secreted by all three paired salivary glands parotid,

submandibular and sublingual.

The mucoid fluid:

Is viscous or thick secreted throughout the day to moisturize the lining

of the mouth which increases during eating to lubricate the food in the mouth and

assist with swallowing. It also contains ptyalin high in potassium & bicarbonate ions.

It is secreted by the buccal glands of the mouth as well as the sublingual and

submandibular glands.

Characteristics of normal saliva

Amongst the characteristics of normal saliva are:

Saliva is rich in proteinsDue to the serous salivary cells it contains.

Saliva is hypotonic Due to the less solute contents it has, that drives the

osmotic pressure of water into the

cytoplasm of its mucosal cells for hydration of oral

tissues.

Saliva has a resting pH 6.7-7.4 Due to its ability of keeping oral environment

pH neutral to avoid dental erosion.

Physiologic classification of saliva

Saliva is broadly classified into three and these are atomar, molecular & normal

saliva.

Atomar salivasaliva atomaris----It gives rise to molecular saliva.


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Increasing lubricating qualities (i.e. providing film strength).3) Helping in aggregation of bacterial cells:By

Enhancing bacterial adherence to mucins.

Inhibiting mucin-coated bacteria from being attached to oral

mucosa surface.

4) Helping in encourages bacterial adhesion:ByReacting with bacterial adhesins, thereby blocking bacteria from

being attached to oral mucosa surface.

Amylases:Though there are several salivary isoenzymes, however, alpha-Amylase

is the major digestive salivary digestive enzyme. Of which about 70% -- 80%is

synthesized by the parotid salivary glands; while 20%-- 30% is derived from the

sub-mandibular glands, in which 60-120mg/100mlis found in the parotid saliva,

while 25mg/100ml is from the submandibular saliva, with molecular weights

ranging from 5457kDa, depending on the degree of salivary glycosylation.

Oral Physiologic Action/Functions:These include:

1) Helping in digestive function:ByConversion of starch to maltose.

Hydrolyzing starches into either amylose ,amylopectin, maltose &

or glucose,

2) Helping in the production of other bodily fluids:ByProducing tears.

Producing serum.

Producing bronchial secretions.

Producing male & female urogenital secretions.

3) Helping in modulating bacterial adherence.

Lingual Lipase:This is a highly hydrophilic salivary enzyme that readily enters fat

globules. It is secreted by the sublingual and parotid salivary glands & it is

significantly involved in the first phase of digestion as well as in the hydrolysis of

medium triglycerides into long-chain triglycerides.

Oral Physiologic Action/Functions: It is important in:

1) Infants digestion:ByEnhancing proper digestion of milk fat in new-born.


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Lactoferrins: They are Iron-binding proteins found in saliva providing nutritional

immunity against iron starvation. Lactoferrin with or without iron can be

degraded by some bacterial proteases.

Oral Physiologic Action/Functions: They are important in:

1) Providing anti-bacterial effects:ByTheir ability to bind to salivary ferric ions & produce an antibacterial

effect.

Lysozomes (muramidase):They are present in numerous organs and most body

fluids and are also called muramidase. They hydrolyses b (1-4) bond between N-

acetylmuramic acid (MurNAc) and N-acetylglucosamine (GlcNAc, or NAG) in the

peptidoglycan layer of bacteria.


1) Attacking & destroying bacteria cell walls to protect the oral cavity from invadingpathogens: By

Inhibiting bacterial adhesion to tooth surfaces.

Inhibiting glucose uptake and acid production.

Lysing of peptidoglycan layer.

Lactoperoxidase:There are two major types of lactoperoxidase produced in the

saliva called salivary peroxidase systems. These are the sialoperoxidase (SP)

produced in the parotid glands & submandibular gland acinar cells which is readily adsorbed to

various surfaces of the oral cavity, including the enamel, salivary sediment, bacteria and dental

plaque; & myeloperoxidase (MP) derived from leukocytes entering via gingival crevice in

the oral cavity.

Oral Physiologic Action/Functions:They are important in:

1) Controlling established oral flora:ByControlling bacterial metabolism.

Histatins: They are groups of small, histidine-rich, cationic salivary peptides

comprising of HIS 1; HIS 2 & HTN 3 contained in human saliva which are

either antibacterial and or antifungal; due to their ability to either bind to a

receptor on either the cell wall membrane of a bacteria or a fungal cell &


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consequently be transported across the cytoplasm of affected cells & unto the

mitochondrion of the cells concerned.


1) Controlling bacterial & fungal infections:ByInhibiting bacterial & fungal growth.

Statherins: They are produced by acinar cells in salivary glands as Calcium

Phosphate salts of dental enamel, & which are soluble under typical conditions of

pH and ionic strength.

Oral Physiologic Action/Functions: This includes:

1) Maintenance of tooth enamel integrity:ByPreventing or inhibiting the precipitation & or crystallization of

supersaturated calcium phosphate in ductal saliva and oral fluid.

Lubricating the oral mucosa.

Cystatins:They are ubiquitous in many human body fluids and are inhibitors of

cysteine-proteases that have an effect on calcium phosphate precipitation.

Oral Physiologic Action/Functions:This includes:

1) Protecting unwanted proteolysis such as bacterial proteases & lysed leucocytes:ByInhibiting proteases in periodontal tissues.

Proline-rich proteins (PRPs): They constitute a significant fraction of the total

salivary protein though possess important biological activities, and are

subdivided into three groups as: - 45% Acidic prolines; 30% Basic prolines; &

25%Glycosylated prolines.


1) Inhibiting the growth of calcium phosphate crystals: ByEncouraging adhesion of selected bacteria to the tooth surfaces.

Salivary immunoglobulins: They are a group of predominantly largeheterogeneous proteins i.e. glycoproteins secreted by salivary blood plasma

cells which comprises of such immunoglobulins as: IgA, IgD, IgE, IgG, & IgM.

However, the IgA category that comprises of IgA1& IgA2 subclasses are the


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most commonly identified in human saliva; of which IgA1 is the most

predominant.


1) Prevention of oral infections: ByProducing human body antibodies.

The major component parts of saliva and their respective oral physiologic actions/functions

The Minor Salivary Organic Substances:

Salivary acid phosphatases A+B: Are types of enzyme, used to free attached

phosphate groups from other molecules during digestion. It is basically a

phosphomonoesterase stored in lysosomes and functions when these fuse with

endosomes, which are acidified while they function; therefore, it has an acid pH

optimum.

NAD (P) H dehydrogenase (quinone): It is an enzyme that catalyzes the

removal of hydrogen from a substrate and the transfer of the hydrogen to an
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acceptor in an oxidation-reduction reaction. A NAD (P) H dehydrogenase

(quinone) is an enzyme that participates in biosynthesis of steroids.

NAD (P) H + H+ + a quinone NAD (P) + + a

hydroquinone

Superoxide dismutase:Are enzymes that catalyze thedismutationofsuperoxide

into oxygen and hydrogen peroxide. Thus, they are an important antioxidant

defense in nearly all cells exposed to oxygen. One of the exceedingly rare

exceptions is Lactobacillus plantarum and related lactobacilli, which use a

different mechanism.

Glutathione transferase (GST):Are composed of many cytosolic,mitochondrial,

and microsomal (now designated as MAPEG) proteins. GSTs are present in

eukaryotes and in prokaryotes, where they catalyze a variety of reactions and

accept endogenous and xenobiotic substrates.

Glucose-6-phosphate isomerase: Alternatively known as phosphoglucose

isomerase or phosphohexose isomerase, is an enzyme that catalyzes the

conversion of glucose-6-phosphate into fructose 6-phosphate in the second step

of glycolysis.

Tissue Kallikreins: Are a subgroup of serine proteases enzymes capable of

cleaving peptide bonds in proteins. Kallikreins are responsible for the co-

ordination of various physiological functions including blood pressure, semen

liquefaction and skin desquamation. They act on blood vessels and capillaries of

salivary glands to generate vasodilatations and increased capillary permeability,

thus resulting in increased production of more saliva due increased blood flow

to the salivary glands.

NOTE: - All these enzymes play a role in preventing infections in the mouth by destroyingmicroorganisms and digesting any food particles that are stuck between the teeth and which may be

used by the bacteria as a food source.

Inorganic Saliva Substances i.e. Components:
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The major inorganic saliva substances include the Calcium ions (Ca++);

Phosphate ions (PO4 ); Hydrogen Carbonate ions (HCO3 ); Hydrogen ions (H );Fluoride ions (F ); and Thiocyanate ions etc.

Calcium ions (Ca++): About 50%of Calcium ions are present in saliva, with a pH

of less than 4; in which about 1,4mmol/l to about 1,7mmol/l is contained in

stimulated saliva, and it is higher in sublingual saliva that in submandibular saliva,

while the parotid saliva contains less of calcium ions in its secretion. The Calcium

ions, serve to:

Help to prevent dissolution of dental enamel.

Contributes to solubility product of calcium phosphate, which is crucial in maintaining

tooth structure.

important as a buffer an essential nutrient for oral microflora for metabolic pathways

Maintain the integrity of teeth by providing minerals for newly erupted teeth which

helps with the post-eruptive maturation of enamel and prevents tooth dissolution by

enhancing the remineralisation of enamel.

Phosphate ions (PO4 ): There is about 90% (ie 6mmol/l) of phosphate ions inthe overal human saliva (in form of hydroxyapaptites), out of which about

4mmol/lis due to stimulated saliva secretion, which is unlikely to dissolve at a

pH around 6. However increase in the pH can lead to the precipitation of calcium

salts and subsequent formation of dental calculus.

NOTE: -The inorganic phosphate ions in saliva are basically found as conjugates of phosphoric

acid (H3PO4), which include H2PO4 , HPO4,2 and PO4,3 whose concentrations areaffected by salivary flow rate as well as salivary pH, and also to a smaller extent compared

to calcium i.e. circadian rhythm:

Also, the concentrations of each ionic type is dependent on salivary pH just as

decreased pH leads to decreased concentration of the tertiary ions, while increased flow

rate decreases total inorganic phosphate concentration.

Depending on pH, inorganic phosphate can be complexed to inorganic ions or proteins.

Hydrogen Carbonate i.e. Bicarbonate or Hydroxidodioxidocarbonate ions(HCO3 ): It is an intermediate anion from the deprotonation of carbonic acid. It isderived actively from CO2by carbonic anhydrase, and it is low in unstimulated

saliva, but increases with flow rate. Bicarbonate generally serves a crucial

biochemical role in the physiological pHbuffering system, as it helps:


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Neutralizes acid produce in the mouth by plaque bacteria whencarbohydrate is fermented.

Maintain the pH in the mouth to near neutral (i.e. 6.3) for normal tooth

maintenance.

Hydrogen Ions (H+): Hydrogen ions are derived from secretions via salivary

glands, oral microbiota owing to the intake of acidic drinks into the oral cavity by

individuals and Hydrogen ability to complex with many substances, whose

resultant effect is seen or observed as making the saliva acid-base balance a

complex & mutable process.

NOTE: -

The concentration of H+in saliva has the greatest influence on the chemical reactions in the oral

cavity: ByFacilitating the equilibria between calcium phosphate in dental hard tissue and surrounding

liquid phase solubility, as well as activity, of important salivary enzymes

Fluoride Ions:The concentration of fluoride in saliva depends on fluoride in the

environment, such as fluoridated drinking water and dental products used for

caries prophylaxis. Basal concentration of fluoride is less than 1 micromol per

liter, but can be much higher in places where levels of fluoride in drinking water

are high. Fluoride also enters saliva via facilitated transport over membranes of

salivary gland tissue. Clearance rate of inorganic phosphate is dependent on

salivary flow rate.

Thiocyanate: This is an antibacterial (oxidated to hypothiocyanite OSCN- by

active oxygen produced from bacterial peroxides by lactoperoxidase). Higher

concentration of this substance in saliva results in decreased or lower incidence

of dental caries. Its concentration is higher in the saliva of smokers than that of

non-smokers.

Others: Other inorganic substances in saliva are contained in small amounts, and

they include the followings. Sodium; Potassium; Chloride; Lead; Cadmium;

Magnesium; Iodine & Copper.

Glands of saliva secretion


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There are three major glands and other numerous minor glands

responsible for the production of saliva. The major glands are made up of large

glands with longer excretory ducts. They are paired and symmetrical, distributed

along the body and ramus of the mandible. This group includes the parotid, sub-

mandibular and sublingual glands. The minor glands are formed of numerous, small,

mucosal or sub-mucosal glands with short excretory ducts. They are classified

according to their location into labial, zygomatic, palatine and lingual.

NOTE: -

1) The major and minor salivary glands secrete their products into the oralcavity.

2) The saliva from the parotid gland is a rather thin, watery fluid.3) The saliva from the sublingual and the submandibular glands are much

thicker due to mucus content.

Structure of the salivary glands

The salivary glands are solid structures composed of millions of secretory cells.

Between the cells run tiny ducts which collect the saliva and channel it into a single,

much larger, duct. This large duct carries the saliva away from the gland and into

the mouth.

The position of each of the three pairs of large major salivary glands is indicatedby their names.

Parotidmeans "near the ears".

Sublingualmeans "under the tongue".

Submandibularmeans "under the mandible" (i.e. under the jaw-bone).


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Relative locations for the 3 major human salivary glands

Major Salivary Glands

There three major salivary glands contained in the human oral cavity mouth &

they are:

The parotid salivary glands

The submandibular salivary glands

The sublingual sub-maxillary salivary glands

The Parotid Salivary Glands glandulaparotidea:

They are the largest paired salivary glands, found wrapped around the

mandibular ramus, lying just under beneath the skin & one in front of each human

ear; whose duct orifice opening is located i.e. situated on the inside of the

cheek, just opposite the crown of the upper second molar tooth.The saliva secreted

by the parotid glands is mainly serous i.e. thin, watery & amylase-rich fluid. On

stimulation, the parotid salivary glands accounts for up to 50%of the mouth volume

of saliva, whereas under un-stimulated conditions, they contributes much less 20%

i.e. when the glands are at rest. The parotid gland saliva secretion is carried to the

mouth in a small vessel called Stensons duct, andare usually felt by individuals asit is in the upper neck and feels like a rounded ball.


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The human parotid salivary glands

The submandibular gland glandulasubmandibularis:The submandibular glands are a smaller pair of glands i.e. smaller than

parotid glands located beneath the lower jaws, superior to the digastrics muscles,

whose saliva secretion is mixed i.e. a mixture of both serous fluid and mucus.

About 65% - 70% of the total saliva in the human mouth secreted by the

submandibular salivary glands is as a result of un-stimulated conditions i.e. at rest;

while about 30% -35% of the saliva fluid in human mouth is derived under

stimulated conditions. Each submandibular gland has a duct which runs forward

through the structures in the floor of the mouth, and opens by an easily seen orifice

at the base of the frenelum of the tongue. The paired submandibularglands enter

theoral cavityvia Wharton's ducts.

The human submandibular salivary glands

The sublingual glandglandula sublingualis:

The sublingual glands are a pair of glands located beneath the tongue,

anterior to the submandibular glands. Which contribute only about 1% 2%volume


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of the un-stimulated saliva secreted i.e. at rest & produces approximately about

5%volume of whole stimulated saliva secreted in the human mouth. The sublingual

saliva secretion is mainly mucous in nature.

The human sublingual salivary glands

The human sublingual salivary glandsMinor Salivary Glands

The minor glands are distributed throughout the oral mucosa (including the

labial, buccal, lingual, palatinal mucosa). These are mixed glands largely comprising

mucous acinar cells. However, the palatinal glands are strictly mucous, whereas the

lingual von Ebners glands are strictly serous. They produce less than 10% of the

total volume of saliva rich in lingual lipase--even in the absence of local stimuli);

which play an important role in lubricating the mucosa.

Physiologic processes of saliva secretion

The process of saliva secretion from the salivary glands into the oral cavity is

divided into three stages, which include the following:

Stimuli to secretion

Formation of initial acinar fluid


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Ductal modification of acinar secretion

Stimuli to secretion:

The stimulation to saliva secretion stage occurs in three phases, which include

Cephalic; Intra-organ and Inter-organphases.

Cephalic phase-------This phase is brought about by the following factors:-

a) Psychological phase (thinking of food).b) Visual phase (sight of food).c) Olfactory phase (smelling food).

Intra-organ phase------- This phase is the most important phase of salivasecretion and it is enhanced by the following:-

a) Mechanical stimulation--- Involves stimulation of touches &pressure receptors leading to mandibular movement and activation

of masticatory muscles.

b) Chemical stimulation ----Involve stimulation of taste receptors and itis more effective than mechanical stimulation, especially with acids.

c) Direct olfactory stimulation-----In which smell receptors are directlystimulated.

Inter-organ phase------- This is the third phase of saliva secretion that mayresult from irritation to the oesophagus or vomiting reflex.

Formation of initial acinar fluid:

The formation of initial acinar fluid for saliva secretion is initiated, controlled

and enhanced by parasympathetic and sympathetic stimulations.

Parasympathetic stimulation------This involves cascade of biochemical reactions

leading to release of calcium from calcium stores. The intracellular calcium

so released has three basic functions, and these are to:-a) Open basal Potassium (K) channels--- for outward diffusion of

Potassium (K). This initiates outward

b) Open apical Chlorine (Cl) channels--- for inward diffusion ofChlorine (Cl).


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c) Facilitate movements of secretory granules towards the apicalmembrane & exocytosis protein and mucoprotein.

Sympathetic stimulation------- This also involves cascade of biochemical

reactions that would lead to mobilization of Calcium (Ca) ions. A

proportion of intracellular increase in Calcium (Ca) ions so mobilized is due

to opening of Calcium (Ca) channels as well as rapid opening of Potassium

(K) channels. This is what initiates the salivary fluid secretion. Major result

of sympathetic stimulation is secretion of protein & mucoprotein that

gives thick viscous saliva.

NOTE: -

Outward diffusion of Potassium (K) is characterized by initial high Potassium (K) content in the

1stfew drops of saliva collected after stimulation. And as the Potassium content (K) is raised in basalextracellular fluids, there is activation of Sodium-Potassium-Chlorine (Na-K-Cl) transporter that

carries these ions intracellularly in the ratio of 2K & 3Cl ions: 1Naion. With Potassium (K) influx, it

replaces the Potassium (K) lost by outward diffusion. Further increase in intracellular Chlorine (Cl)

brings is what brings water down in an osmotic gradient and make the cell swells. The Sodium (Na) is

however excreted from the cell by Sodium-Potassium (Na-K) pump, while the Chlorine (Cl) in acinar

lumen dragged Sodium (Na) to the acinar lumen to balance the negative charge of Chlorine (Cl).

Ductal modification of acinar secretion:

At this stage, there is modification of intercalated ducts in which IgA from

lymphoid plasma cell follicles become depressed throughout the salivary glands

stroma, proteins and Kallikreins are secreted. Lysozymes, lactoferrins, carbonic

anhydrase, serum albumin, salivary amylase, some addition of potassium

Composition of primary acinar fluid.

Physiologic stages of salivary secretion

Salivary fluid secretion appears to be a two-stage process, involving:

Primary secretion stage.

Secondary secretion stage.

First stage primary secretion:At this stage saliva is initially formed as a near isotonic plasma-like primary

secretion in the acinar lumen upon stimulation. The acinar cells forming the

secretory end piece of the salivary gland actively pump sodium ions from the blood

into the lumen of the end piece. The resulting osmotic pressure difference between


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the blood and the fluid in the end piece causes water to flow from the blood,

through the tight junctions between the acinar cells, and into the lumen of the end

piece. Thus, the primary secretion as it leaves the end piece is thought to be

almost isotonic with plasma.

Second stage secondary secretion:It commences when the fluid in the first stage passes along through the duct

system it is modified by selective and energy-dependent reabsorption of sodium

and chloride without water, as the salivary ducts are impermeable to water and

secretion of potassium and bicarbonate the latter especially occurring under

stimulated conditions. The resulting saliva becomes increasingly hypotonic as it

moves down the ductal system: the final saliva secreted to the oral cavity containsconcentrations of sodium and chloride much below that of primary saliva.

Control of salivary secretion

The control of salivary secretion is ensured in two basic ways, which include:

Non-hormonal control

Neural control

Non-hormonal Control:

This is due to increased circulation of aldosterone in the human body.

Neural:

The neural control of saliva secretion is under control of the autonomic nervous

system, comprising of sympathetic & parasympathetic nerves which controls both

the volume and type of saliva secreted as stimulation of one receptor often

enhances and complements another receptor. Besides, the salivary glands are

innervated by both sympathetic and parasympathetic nerve fibers. In which various

neurotransmitters and hormones stimulate different receptors, different salivaryglands, and different responses. And as the various parasympathetic impulses travel

from the salivatory nuclei in the brain stem salivation centers, to reach the salivary

glands via the facial and glossopharyngeal nerves, saliva production and flow is

stimulated. Amongst the impulses that stimulate the salivation centers are:


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Impulses from the higher brain example thinking of food that one finds

delectable.

Impulses from the mouth and throat taste sensations (sour and umami) and tactile

sensations (smooth objects in the mouth stimulate flow while rough objects

inhibit salivation).

Impulses from the stomach and proximal part of the small intestine irritation of the

lining of these parts of the alimentary tract.

None-the-less the impulses that stimulate salivary secretion, there are three

types of specific triggers to the stimulation of the impulses. And these triggers

include:

Mechanical---Example the act of chewing.

Gustatory ---The most stimulating trigger for sweet and or the least stimulating

trigger for bitter.

Olfactory ----A surprisingly poor stimulus.

Others--- Such as psychic factors e.g. pain, certain types of medication, and

various local or systemic diseases affecting the glands themselves.

NOTE: -

The parasympathetic stimulation from the brain results in greatly enhanced secretion, as well

as increased blood flow to the salivary glands. Also, stimulated saliva is what contributes to as

much as 80%to 90%of the average daily salivary production.

As parasympathetic stimulation increases salivation, it also increases blood flow to the

salivary glands.

Conversely, increased blood flow to the gland, for reasons other than parasympathetic

stimulation of the gland, also increases salivation.

The production of saliva is stimulated both by the sympathetic nervous system and the

parasympathetic.

The saliva stimulated by sympathetic innervations is thicker, and saliva stimulated

parasympathetically is more watery.

Sympathetic stimulation of saliva is to facilitate respiration, whereas parasympathetic

stimulation is to facilitate digestion.

Regulation of salivary secretion

Salivary secretion is regulated by a reflex arch involving conditioned &

unconditioned reflexes comprising afferent receptors and nerves carrying impulses

induced by actions on gustation and mastication, a central connection (salivation

center), and an efferent part consisting of parasympathetic and sympathetic

autonomic nerve bundles that separately innervate the glands. The secretory reflex
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arch is also under influence of higher centers in the brain. Saliva may be secreted in

the absence of exogenous stimuli referred to as the resting or un-stimulated salivary

flow. The regulation of salivary secretion is achieved by two basic means as:

Initiation of salivation by unconditioned reflex.

Initiation of salivation by a conditioned reflex.

Initiation of salivation by an unconditioned reflex:

Here the afferent part is activated by stimulation of various sensory receptors

including chemoreceptors in the taste buds and mechanoreceptors in the

periodontal ligament. The afferent nerves carrying impulses to the salivary nuclei

(salivation center) in the medulla oblongata are the facial, glossopharyngeal and

vagal nerves (taste) and the trigeminal nerve (chewing). Olfaction and stretch of thestomach are other afferent inputs that can initiate formation of saliva.

Initiation of salivation by a conditioned reflex:

In this reflex, the sight and thought of food may lead to some formation of

saliva. The salivary nuclei also receive impulses from other centers of the brain

resulting in facilatory or inhibitory effects on salivation depending on, for example,

the emotional state.

NOTE: -

The release of neurotransmitters from postganglionic neurons of both branches of the autonomic

nervous system is what elicits secretion of saliva to the oral cavity. In which the facial nerve provides

parasympathetic control of the submandibular, sublingual, and minor glands (except von Ebners

gland), whereas the glossopharyngeal nerves control the parotid glands.

Higher control of salivation

These include:

Excitement or inhibition.

Control of hypothalamus.

Excitement or inhibition:

Due to patterned reflexes i.e. preparatory stimulation of salivatory flow before

vomiting; Stimulation of regional parts of the cortex due to increased flow;


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Decreased salivation during sleep and progressive reduction in unstimulated flow

rate especially of infants between birth 5 years.

Control of hypothalamus:Due to an over-riding control and direct connection with sympathetic system,

for example in such conditions like fear, rage, excitement, dryness of the mouth and

excess salivation in certain circumstances.

Normal physiologic variation in salivary composition

The normal physiologic variation in salivary composition occurs in relation to such

conditions as:

Flow during sleep:

Submandibular glands produce (72%).

Sublingual glands+ minor glands produce (14%).

No measurable secretion from Parotid glands.

Unstimulated flow:

Submandibular glands produce (70%).

Parotid glands produce (20%).

Minor/accessory glands produce (7%).

Sublingual glands produce (


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The factors affecting influencingsaliva composition include:

Source of saliva

Flow rate

Duration of stimulation

Nature of stimulus

Time of day

Source of saliva :

This determines the concentration of main electrolytes in human saliva

which are sodium, potassium, calcium, chloride, bicarbonate, and inorganic

phosphate, because the saliva secreted from different salivary glands have

differences in composition; For instance, parotid saliva is relatively low in calciumand high in phosphate as compared with submandibular and sublingual secretions.

Types of proteins and their concentrations are different in the different secretions,

eg, most of the salivary amylase is derived from the parotid glands.

Flow rate:

Flow rate has a decided influence on salivary composition, because as the flow

rate is increased slightly above the unstimulated rate, the concentration & pH of

some electrolytes such as sodium and bicarbonate increases, whereas the

concentrations of other electrolytes like potassium, calcium, phosphate, chloride,

urea, and protein decreases.

Sodium (Na) & Chlorine (Cl) concentration.

Bicarbonate (HCO3) raises in high flow rates.

Amylase raises in high flow rates (esp. stimulated).

Urea, IgAfall in high flow rates.

Diffused through the ductal system

Duration of stimulation:

When flow rate of stimulated saliva is maintained constant for several

minutes, the composition of the saliva tends to change considerably with duration of

stimulation. For instance, there is an increase in the total concentrations of protein,


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These include the followings:

Unstimulated rate in infants is higher than in adults

Ca, Mg, K are higher in infants

Phosphate are low in infants but rises to adult level over the first year

Rate of parotid gland is not significantly affected by age

Sublingual glands secretion + Submandibular glands secretion show some

decreased flow with age.

Relationship between unstimulated and stimulated Saliva

The unstimulated saliva:

Basal production.

Confers most protection.

Importance of minor and submandibular output.

Low output during sleeping hours.

The stimulated saliva:

Protection during mastication.

Assists in deglutition.

Importance of parotid output.

Functions of saliva

Although, there are so many interrelated functions of the saliva is to protect the

oral cavity. However, these numerous salivary functions can be organized into 5

major categories that serve to maintain oral health and create an appropriate

ecologic balance:

Lubrication and protection,

Buffering action and clearance,

Maintenance of tooth integrity,

Antibacterial and antifungal activity,

Taste and digestion.

NOTE: - Salivary components work in concert in overlapping, multifunctioning roles, which can be

simultaneously beneficial and detrimental.


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Lubrication & protection:

The lubricating and protective functions of saliva are seen in the

following ways:

The seromucous coating of saliva lubricates and protects oral tissues, acting as a

barrier against irritants. These irritants include, but are not limited to, proteolytic

and hydrolytic enzymes produced in plaque, potential carcinogens from smoking

and exogenous chemicals, and desiccation from mouth breathing.

NOTE: -The best lubricating components of saliva are mucins ----they have the

properties of low solubility, high viscosity, high elasticity, and strong adhesiveness.

Mastication, speech, and swallowing all are aided by the lubricating effects of

mucins.

Mucins also perform an antibacterial function by selectively modulating the

adhesion of microorganisms to oral tissue surfaces, which contributes to the

control of bacterial and fungal colonization.

Mucins as a part of the enamel pellicle, help initiate bacterial colonization by

promoting the growth of benign commensals oral flora, forming a protective

barrier and lubrication against excessive wear, providing a diffusion barrier

against acid penetration, and limiting mineral egress from the tooth surface.

Buffering action & clearance:

The buffering and clearance functions of saliva are seen in the

following ways:

Saliva dilutes and removes substances (oral debris, noxious agents) from the oral

cavity which is referred to as salivary or oral clearance. Both the act of swallowing

and the salivary flow rate are important to this process, and these are the

principal ways by which oral bacteria and injurious, noxious agents are eliminatedfrom the mouth.

Saliva also clears dietary acids and thereby protects the teeth against erosion.

The higher the flow rate, the faster the clearance and the higher the buffer

capacity. Dental caries is probably the most common consequence of

hyposalivation.


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The buffer capacity of both unstimulated and stimulated saliva involves three

major buffer systems: the bicarbonate (HCO3), the phosphate, and the protein

buffer systems. These systems have different pH ranges of maximal buffer

capacity, the bicarbonate and phosphate systems having pK values of 6.1-6.3

and 6.8-7.0, respectively.

Maintenance of tooth integrity:

The maintenance of tooth integrity is facilitated by saliva in the

following ways:

Demineralization occurs when acids diffuse through plaque and the pellicle into

the liquid phase of enamel between enamel crystals. Dissolved minerals

subsequently diffuse out of the tooth structure and into the saliva surrounding

the tooth. The buffering capacity of saliva greatly influences the pHof plaque

surrounding the enamel, thereby inhibiting caries progression.

Remineralization is the process of replacing lost minerals through the organic

matrix of the enamel to the crystals. Super saturation of minerals in saliva is

critical to this process. Human salivary secretions are supersaturated with respect

to calcium and phosphate, but spontaneous precipitation from saliva to dental

enamel does not normally occur.

Antibacterial & antifungal activity:

The antibacterial/antifungal activity of saliva is due to:

Its fluid contains immunologic and nonimmunologic agents for the protection of

teeth and mucosal surfaces. Immunologic and nonimmunologic antibacterial

salivary content come from two different sources namely, plasma and ductal

cellswith different responses to stimulation and different content levels.

Taste & digestion:

The saliva enhances taste and begins the digestive process in the

following ways:


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The sense of taste is activated during the initial stage of ingestion of foodparticles allowing for identification of essential nutrients and of harmful and

potentially toxic compounds. Taste is a main stimulant for formation of saliva. On

the other hand, presence of saliva in the oral cavity is also essential for taste

perception, first of all because food particles need to be in solution in order to

stimulate taste receptor cells in the taste buds within the lingual papillae

(fungiform, foliate, and vallate papillae).

The hypotonicity of saliva enhances the tasting capacity of salty foods and

nutrient sources. Saliva has an early, limited role in total digestion by beginning

the breakdown of starch with amylase, a major component of parotid saliva that

initially dissolves sugar. The contribution of saliva to starch breakdown is limited

because most of the digestion of starch results from pancreatic amylase, not

salivary amylase. Salivary enzymes also initiate fat digestion. More importantly,

saliva serves to lubricate the food bolus, which aids in swallowing.

Summary of saliva functions

Summarized below are the concise functions of saliva in the mouth.

Amongst these functions are:

Cleansing function:

By cleansing action on the teeth.

Lubrication function:

By lubricating the mouth lining during mastication.

By moistening the mucosa of the mouth.

Protection function:

By physical protection of oral mucosa.

Taste sensation & perception function:

By dissolving certain molecules so that food can be tasted. Antibacterial and immunity function:

By producing antibodies eg IgA-produced by saliva plasma cells

especially against bacteria, thereby avoiding mouth infections or slowing

decay in a tooth cavity.


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Digestion function:

By producing chemical digestive enzymes eg amylase that begins the

digestion of starches breaking it downpolysaccharides intodisaccharides.

By moistening & lubricating food during mastication & swallowing.

Buffering function:

By producing minerals & electrolytes that help maintains optimum pH

value in the mouth.

By helping in maintaining the integrity of enamel.

Wound healing and maintenance of upper GI mucosal integrity function:

By producing Epidermal Growth Factor secreted by the submandibular

salivary glands.

By producing blood coagulation factors.

Abnormal Saliva Conditions in the Mouth

Although saliva is drained out of the mouth cavity by swallowing as it

passes down the throat and esophagus and into the stomach. However, when this

sequence is disrupted it results in abnormal saliva presence in the mouth. There are

two major abnormalities in the quantity and quality of saliva present in the mouth

and they are either:

Hypersalivation i.e. Sialorrhea

Hyposalivation i.e. xerostomia

Hypersalivation Sialorrhea:

Hypersalivation also called driveling, drooling, slobbering, ptyalism,

sialorrhea, hyperactive salivary flow, polysialia, and sialism, is a condition of

excessive production of saliva. It can be defined as salivary incontinence or the

involuntary spillage of saliva over the lower lip i.e. saliva beyond the margin of the

lip, due to increased amount of saliva in the mouth, which may also be caused by

decreased clearance of saliva. It is a condition characterized by the secretion of

drool in the resting state, which is often the result of open-mouth posture.
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Hypersalivation could be caused by excessive production of saliva, inability to retain

saliva within the mouth, or problems with swallowing.

Patients with hypersalivation

NOTE: -This condition is normal in infants but usually stops by 15 to 18 months of age. Sialorrhea

after four years of age generally is considered to be pathologic which could lead to functional and

clinical consequences for patients, families, and care-givers.

Pathophysiology of hypersalivation

Pathophysiology of hypersalivation is multifactorial, due to either:

Psychological factors.

Local factors.

Systemic factors.

o Psychological factors: Pregnancy

o Local factors:These include:1) Oral inflammation


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2) Teething Infection3) Oral cavity infection4) Dental caries5) Dental prosthetics Such as new and ill-fitting implants, bridges &

dentures

6) Mouth pains (i.e. stomatodynia).7) TMJ dysfunction8) Bruxism9) Tonsillitis10)Peritonsillar abscess11)Poor head control12)Constant open mouth13) Infrequent swallowing14) Inefficient swallowing15)Retropharyngeal abscess16)Epiglottitis17)Mumps18)Problems with jaw i.e. fracture or dislocation

o Systemic factors:These include:1) Toxin exposure- Pesticides, Insecticides, Mercury, Capsaicin, Snake

poisoning & Copper etc.

2) Medication Such as Tranquilizers, Anticonvulsants, Anticholinesterases &Lithium etc.

3) NeuromuscularSuch as Cerebral palsy, Parkinsons disease, Motor neurondisease, Bulbar/ pseudobulbar palsy, Bilateral facial nerve palsy i.e. Bells

palsy, Hypoglossal nerve palsy, Trigeminal neuralgia & Geniculate

neuralgia etc.

4) Stroke Infection- Such as Rabies5) Gastric- Such as Gastroesophageal reflux6) Dental malocclusion


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7) Decreased tactile sensation8) Macroglossia9) Nasal obstruction10)Poor lip control11)Disorganized tongue mobility12)Lack of awareness of saliva build up in the mouth

Side effects of hypersalivation:

The side effects of hypersalivation are most noticeable when hypersalivation is

left untreated; and these effects are also referred to as complications which are

classified into two major groups as:

Physical complicationsPsychosocial complications

o Physical complications:They include1) Perioral chapping i.e. skin cracking2) Maceration of skin around the mouth with secondary infection3) Dehydration4) Foul odour5) Aspiration pneumonia6) Speech disturbance impairment7) Interference with feeding8) Increased risk of inhaling saliva, food, or fluids into the lungs especially

when body's normal reflex mechanisms, such as gagging and coughing are

also impaired.

9) General difficulties to perform oral motor activities during eating andspeech with repercussion in quality of life

o Psychosocial complications: They include1) Isolation2) Barriers to education damage to books or electronic devices3) Increased dependency & level intensity of care


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4) Decreased self esteem5) Difficult social interaction i.e. impairment of social integration6) Social stigmatization

Management for hypersalivation:

Hypersalivation is a challenging oral condition to manage. However,

successful management of sialorrhea can alleviate the associated hygienic problems,

improve appearance, enhance self-esteem, and significantly reduce the nursing care

time of these sufferers, bearing in mind that the goal of managing hypersalivation is

a reduction in excessive salivary flow, while maintaining a moist and healthy oral

cavity as well as putting measures in place to help avoid the onset of xerostomia

i.e. dry mouth in affected patients. However, because of the numerous approachesthat could be utilized in the management of hypersalivation, which ranges from

conservative including observation, postural changes, medication & biofeedbackto

more aggressive measures such as surgical & radiation therapy; there is no single

approach that is totally accepted as being most effective in the management of

hypersalivation. None-the-less, a combination of two major approaches is being

widely accepted in an effort to help manage hypersalivation in patients and these

are:

Non invasive modalities e.g. oral motor therapy, p

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