PHYSIOLOGY of NOSE,OLFACTION and

PATHWAY

Dr. Anunya ReddyDept of E.N.T

Nose 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.

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

INTRODUCTION

Breathing Air conditioning of inspired air Protection of lower airway Ventilation and drainage of p.n.s Olfaction Nasal resistance Vocal resonance Nasal reflexes

FUNCTIONS OF NOSE

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

1.BREATHING

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.

Under 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.

Nasal cycle

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.

Nose 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 20ºC or 0º C or even at subzero temperature is heated to near body temperature in one fourth of seconds.

2.Air conditioning

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 Production Water 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.

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

Particles <0.5 μm seem to pass through nose into lower airways without difficulty.

Mucociliary blanket traps pathogens in inspired air >0.5μm 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.

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.

Composition of mucus

ULTRA STRUCTURE Found 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 5μm ,with up to 200 per cell.

A cilium has a surface membrane.

cilia

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 kartagener’s 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 nasopharynx

It consist of Superficial mucus or gel layer Deep serous and sol layer

Beat frequency is between 7 and 16Hz at body temperature,it remain constant between 32 and 40º 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.

Ciliary action

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

Dry atmosphere(absence of humidity) Smoking Air pollutants and nasal irritants Infections Excessive summer above 45˚c and

excessive cold below 10˚c Hypoxia Solutions above 5% and below 0.2% Drugs

Factors compromising the mucociliary function

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.

4.Ventilation of PNS

5.Nasal resistance

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.

6.Vocal resonance

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.

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.

7.Olfaction

OLFACTORY AREA Olfactory mucosa is located in roof of nasal

cavity and adjacent area of superior turbinate and upper part of septum.

Area :200-400mm² with a dencity of approx 5×10 receptor cells/mm² 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.

STIMULUS Odours→react with lipid bi layer of receptor

cells at specific sites→causes outflow of k+ and cl-→causes depolarization of cells.

RECEPTORS Olfaction 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 ADAPTAION Olfactory 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).

ADAPTATION Olfactory 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.

DISCRIMINATION Man 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.

QUALITATIVE OLFACTOMETRY: Olfactory sense is assessed by taking a

solution or extract before the patients nose. Following primary odours are usually tested.

1. Etherial –ether2. Camphoraceous-camphor3. Flora(l)-salicyldehyde4. Musky-phenyl acetic acid5. Minty-mint6. Pungent-formalin7. Putrid-thiophenol

Olfactometry(odour measurement)

QUANTITATIVE OLFACTOMERY Measurement 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

1. The extent of the field of smell.2. Gives an idea about pts acuity of smell.3. 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.

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.

Olfactory pathway

Olfactory mucosa is lined by olfactory mucus with olfactory receptor neurones with in it, which has” cilia” finger like projections extents down to mucus where smell molecules binds

Olfactory tract extends in to higher center of brain to give individual sense of smell.

Cilia and mucus layer

Bowmens glandSupporting

epith.cells

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

THANKS…HAVE A GOOD SMELL