PHYSIOLOGY OF NOSE,SMELL AND PATHWAY

Physiology of NOSE,OLFACTION and PATHWAYDr. SALEEM SAEED.AJunior Resident, Dept of E.N.T

INTRODUCTIONNose contains organ of smell and respiration. It warms ,cleans and humidifies the inspired air, cools and remove water from the expired air.

Also add quality to speech production.

ENT surgeon should distinguish normal nasal function from pathological symptoms to prevent unnecessary surgeries.

Although nose is a paired structure divided coronally in to two chambers, it act as a functional unit.

FUNCTIONS OF NOSEBreathingAir conditioning of inspired airProtection of lower airwayVentilation and drainage of p.n.sOlfactionNasal resistanceVocal resonanceNasal reflexes

1.BREATHING

Nose is the natural pathway for breathing ,mouth breathing is acquired through learning.

Newborn infant with choanal atresia may asphyxiate to death if urgent measures are not taken to relieve it.

Nose also permits breathing and eating to go on simultaneously.

Inspired air passes upward in a narrow stream medial to middle turbinate and then downwards and backwards in the form of an arc, and thus respiratory air currents are restricted to the central part of nasal cavity

During expiration ,air currents follows the same course as inspiration but the entire current is not expelled directly through the nares.Friction offered at limen nasi converts in to eddies under cover of inferior and middle turbinates and this ventilates the sinuses through the ostia.

Nasal cycleUnder autonomic nervous system nasal mucosa undergoes rhythmic cyclical congestion and decongestion, thus controlling the air flow through nasal chambers.

The changes are produced by vascular activity, particularly the volume of blood on the venous sinusoids (capacitance vessels).

When one nasal chamber is working, total nasal respiration, equal to that of both nasal chambers is carried out by it.

In modern western literature it was first described by German physician Richard Kayser in 1895. Cycle lasts 2-12 hours(average 2.5-4 hours).

FACTORS AFFECTING:Allergy, infection, exercise, hormones, pregnancy, fear and emotions, including sexual activity.

2.Air conditioningNose is called air conditioner for lungs.Adjusts temperature and humidity of inspired air before it passes on to the lungs.Temperature control of the inspired air is regulated by large surface of nasal mucosa ,particularly in region of middle and inferior turbinates and adjacent part of the nasal septum(highly vascular with cavernous venous spaces).This makes an efficient radiator mechanism to warm up the cold air .Inspired air which may be at 20C or 0 C or even at subzero temperature is heated to near body temperature in one fourth of seconds.

Similarly hot air is cooled to the body temperature.

HUMIDIFICATION:Humidity of atmospheric air varies depending on climatic conditions.

Nasal mucosa adjusts the relative humidity of the inspired air to 75% or more.

Moisture is essential for integrity and function of the ciliary epithelium.

Humidification also has a significant effect on gas exchange in the lower airways.

Water ProductionWater comes from serous glands which are extensive throughout the nose.

During nasal cycle, secretions are lower on the more obstructed side.

Additional water comes from the expired air, naso lacrimal duct and oral cavity.

Humidification is reduced by atropine probably acting on the glands rather than the vasculature.

Filtration and Purification:Particles >3m are trapped by nasal vibrissae.

Particles 0.5m and transports them to nasopharynx for swallowing.

Sneezing protects against irritants.3.Protection of Lower Airway:mechanical and chemical

Composed of two elements-mucus and water.Glycoprotein -produced by mucus glands.water and ions produced mainly from serous glands and indirectly from transudation from capillary network.2 secretory cell types in mixed nasal glands -mucus and serous cells.Glycoprotein found in mucous are produced in goblet cells(within the epithelium) and glandular mucus cells.Submucosal glands are mixed and arranged around ducts.

Nasal secretions

Anterior part of the nose contain serous gland only in vestibular region produce a copious watery secretion when stimulated.Sinuses has fewer goblet cells and mixed glands.

Composition of mucus

Water and ions from transudation.

Glycoprotein: sialomucins,fucomucins,sulphomucins.

Enzymes : lactoferrin,lysozymes.

Circulatory proteins: complement,-2 macroglobulin,c reactive protein.

Immunoglobulins: igA,igE,igG,igM,igD.

Cells:surfaceepithelium,basophils,eosinophils,leukocytes.

Rheology of mucusGlycoprotein give mucus viscosity and elasticity.

Movement of cilia produces shearing effects that the elasticity counter acts-if it is the right consistency-viscosity and elasticity complement each other and mucus moves.

Techniques to measure the rheology:micro sherometry and controlled stress technique.

Mucus viscosity can be measured by drawing up mucus in to a capillary tube under negative pressure and measuring flow relative to the pressure.

ciliaULTRA STRUCTUREFound on the surface of cells in the respiratory tract.Function:to propel mucus backwards in the nose towards the nasopharynx.All cilia have the same ultrastructure although nasal cilia are relatively short at 5m ,with up to 200 per cell.A cilium has a surface membrane.Nine paired outer microtubules surround a single inner pair of microtubules.Outer-paired microtubules are linked together by nexins and to the inner pair by central spokes.

Outer pair also have inner and outer dynein arms,which consist of an ATPase ,which lost in kartageners syndrome.

Microtubules become the basal body in the cell-the outer body become triplets and the inner pair disappear.

Nasal mucus film is in two layers, one upper more viscous layer and lower more watery layer in which cilia can move more freely.

MUCO-CILIARY BLANKET:Goblet cells in nasal mucosa secrete a mucous blanket; moves backward like a conveyer belt in to nasopharynxIt consist of Superficial mucus or gel layerDeep serous and sol layer

Ciliary actionBeat frequency is between 7 and 16Hz at body temperature,it remain constant between 32 and 40 C.

Beat consist of a rapid propulsive stroke and a slow recovery phase.

Propulsive phase: cilia is straight and tip points in to the viscous layer of the mucous blanket.

Recovery phase: cilia is bent over the aqueous layer.

Energy is produced by conversion of ATP to ADP by ATPase of the dynein arms dependent of mg2+ ions.

ATP is generated by the mitochondria near the cell surface next to the basal bodies of the cilia.

Mucus blanket is propelled backwards by metachronous movement of cilia-only those at the right angles to the direction of flow are in phase.

Mucus flows from the front of the nose posteriorly.

Mucus from the sinuses joins that flowing on the lateral wall ,with most mucus going through the middle meatus.

Most passes around the eustachian orifice and it is then swallowed.

Transportation of trapped particles to nasopharynx

Factors compromising the mucociliary functionDry atmosphere(absence of humidity)SmokingAir pollutants and nasal irritantsInfections Excessive summer above 45c and excessive cold below 10cHypoxiaSolutions above 5% and below 0.2%Drugs

4.Ventilation of PNS

Inspiration creates negative pressure in nasal cavity thus sucks the air out from paranasal sinuses via their ostium.

Expiration creates positive pressure in nasal cavity thus ventilates the para nasal sinuses via there ostium.

5.Nasal resistance

6.Vocal resonance

Nose forms a resonating chamber for certain consonants in speech.In phonating nasal consonants(M/N/NG) sound passes through the nasopharyngeal isthmus and is emitted through the nose.Many nasal condition affect the quality of voice by blocking the passage of air in expiration.

When nose( or nasopharynx) is blocked,speech become denasal, i.e, M/N/NG are uttered as B/D/G respectively.

Rhinolalia clausa-too little air escapes from the nose.

Rhinolalia aperta too much air escapes.

Sinuses have no effect on modifying voice.

7.Olfaction

This function of nose is less developed in human beings, plays most important role in behavior and reflex responses of lower animals.

man concentrate on audiovisual aspects,and yet much money is spent modifying body odors.

Olfactory compound need high water and lipid solubility.

Solute in the mucus is presented to the sensory mucosa.

OLFACTORY AREAOlfactory mucosa is located in roof of nasal cavity and adjacent area of superior turbinate and upper part of septum.

Area :200-400mm with a dencity of approx 510 receptor cells/mm Receptor cells have modified cilia which increase surface area and project like normal cilia in to the mucus. They are derived from basal cells ,regenerating every month.

STIMULUSOdoursreact with lipid bi layer of receptor cells at specific sitescauses outflow of k+ and cl-causes depolarization of cells.RECEPTORSOlfaction is mediated by G-protein coupled receptors in the cells which interact with a specific adenyl cyclase within neuroepithelium.Adrenergic and muscarinic antagonists block some odours.THRESHOLD AND ADAPTAIONOlfactory responses show both variations in thresholds and adaptation.

Threshold concentration can vary depending on the chemical nature of the stimuli.

The threshold of perception is lower than identification: a smell is sensed before it is recogniszed.

Threshold depend on level of inhibitory activity ,which are generated by higher centres.(some animals ,particularly dogs ,have lower thresholds).ADAPTATIONOlfactory responses shows marked adaptation.

Adaptation is peripheral and central phenomenon.

Other factors affecting threshold:Change in nasal mucus and its pH.Age decreases the threshold.Hormones (sex hormones)-increases the threshold.

DISCRIMINATIONMan is better at detecting the pleasantness of an odour rather than recognizing it.If two odours are mixed, resulting intensity is always less than the sum of the individually perceived intensities and dominated by the stronger component.

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Olfactometry(odour measurement)

QUALITATIVE OLFACTOMETRY:Olfactory sense is assessed by taking a solution or extract before the patients nose.Following primary odours are usually tested.Etherial etherCamphoraceous-camphorFlora(l)-salicyldehydeMusky-phenyl acetic acidMinty-mintPungent-formalinPutrid-thiophenol

QUANTITATIVE OLFACTOMERYMeasurement of olfactory sense done with an olfactometer.Gives an idea about qualitative defects of olfaction.Reading is taken as number of olfacts.

Olfactometry gives information about following

The extent of the field of smell.Gives an idea about pts acuity of smell.Possible parosmia(perverted smell)

Several standardized and practical psychophysical tests have been developed over the last several years, including a number of brief self-administered tests ranging from the ,three-item Pocket Smell Test to the 40-item University of Pennsylvania Smell Identification Test (UPSIT).

The UPSIT is commercially known as the Smell Identification Test and is the most widely used olfactory test.

The UPSIT can be self administered in 10-15 minutes by most patients in the waiting room, and scored in less than a minute by nonmedical personnel.

This test consists of four booklets containing ten microencapsulated (scratch and sniff') odourants .

Test results are in terms of a percentile score of a patient's performance relative to age- and sex-matched controls, and olfactory function can be classified on an absolute basis into one of six categories: normosmia, mild microsmia, moderate microsmia, severe microsmia,anosmia and probable malingering.

Clinical imp of testing is to distinquish patients who have a disorder from those who malinger and seek compensation.

Disorder of smell.

Anosmia :inability to detect qualitative olfactory sensations(Absence of smell function).Causes areObstructive lesions in the nose and nasopharynx.Lesions of mucosa.Trauma surgical or accidental.Neuritis .Central lesions in the brain.

Partial anosmia:ability to perceive some not all odours.

Hyposmia/microsmia: Decreased sensitivity to odourscauses areOld age (presbyosmia)Hypogonadal women,menopause.Tobacco smoker,radiation theapy of nose.Surgical removal of the mucosa.Hyperosmia: Increased sensitivity to common odours.Causes areEpilepsyPregnancy,hunger,strychnine poisoning.General paralysis of insane.Cystic fibrosis.

Parosmia(dysosmia/cacosmia):It is a qualitative change.Occurs an unpleasent change in sense of smell.Causes are:Skull fracturesInjury to uncus of temporal bone.Recovery state of post influenzal anosmia.Intracranial tumour.Following administration of streptomysin or thyrothiricin.

Phantosmia: sense of imaginaryn odour(phantom smell)Also known as olfactory hallucination.Seen inNeurological and psychological disorders such as schizophrenia,mood disorders,prkinsons disease, epilepsy,neuroblastoma and frequent migrains.Heterosmia :all odours smell the same.Osmophobia:dislike or fear of certain smell.Presbyosmia:decline in smell sense with age.

Conditions associated with change in olfaction

Olfactory pathway

Air enters through the nostrils.As air passes through the nasal cavity ,it passes by the olfactory mucosa that lines the superior aspect of the cavity.

This is where smell begins.

small molecules of smell olfactory ligands stick to olfactory mucosa and diffuse across and triggering the cascade of events eventually ends with sensation of smell.

Cilia and mucus layerBowmens glandSupporting epith.cells

Guess !!!!what is this?????

CONCLUSIONAn understanding of the physiology of the nose is required to:

Evaluate nasal symptoms.Know its protective role in health and disease.Determine the role of investigations in the assessment of airway function and mucociliary clearance.Understand the action of drugs on the nasal mucosa.Assess smell and taste.

THANKSHAVE A GOOD SMELL