Physiology of nose

Physiology of NOSE

1. PHYSIOLOGY OF NOSE Dr. Ankit Choudhary

2. The nose contains organ of smell and respiration It warms, cleans and humidifies the inspired air, cools and remove the water from the expired air It adds quality to speech production ENT surgeons should distinguish normal nasal fuction from pathological symptoms to prevent unnecessary surgery Although the nose is a paired structure divided coronally into two chambers, it act as a functional unit

3. Physiological functions of Nose Respiration. Air conditioning. Protection of lower airway. Ventilation and Drainage of PNS. Vocal resonance. Olfaction.

4. Respiration Nose is the natural pathway for breathing. Mouth breathing is acquired through learning Nose permits breathing and eating to go on simultaneously Air passage through Nose during respiration allows for Humidification, Heat transfer and Filtration of it

5. Expiration lasts longer than inspiration and is more turbulent Friction offered at limen nasi converts it into eddies under cover of inferior and middle turbinates and this ventilates the sinuses through the ostia Airflow is directed upwards and backwards from the nasal valve initially, mainly over the anterior part of the inferior turbinate It then splits into two, below and over the middle turbinate, rejoining into posterior choana

6. Nasal Cycle Under control of autonomic nervous system Nasal mucosa undergoes rhythmic cyclical congestion and decongestion, thus controlling the air flow through nasal chambers. When one nasal chamber is working, total nasal respiration, equal to that of both nasal chambers, is carried out by it. Cycle changes 4-12 hours. Antihistamine has Anticholinergic effects  block the parasympathetic activity  increase the sympathetic tone  improve airway

7. Air Conditioning Nose adjusts temperature and humidity of inspired air before it passes it on to the lungs. Air in post nasal space is approximately at 31 o C and is 95% saturated. Heat Exchange:   Temperature control of the inspired air is by large surface of nasal mucosa, particularly in the region of middle and inferior turbinates and adjacent parts of the septum ( highly vascular with cavernous venous spaces) Time taken is almost one fourth of a sec.

8. Humidification 10% of body heat loss occurs through the nose in humans Energy is required for: Raising the temperature of inspired air (1/5) Latent heat of evaporation (4/5) Humidification of Inspired air done by nasal mucosa is due to Secretions by the serous glands. One third of water comes from Expired air which is saturated and condenses onto the mucosa. Additionally water comes from Nasolacrimal duct and Oral cavity.

9. Protection of lower airway Mechanical The nose protects the lower airway by removing particles down to approximately 30 μ m, including the most pollens from the inspired air. The shape and roughness of smaller particles may cause them to be deposited in the nose. Inspired air travels through 180 o and velocity drops markedly just after the nasal valve. Turbulence increases deposition of particles. Vibrissae will stop the larger particles.

10. Chemical Nasal secretions Composed of two elements – mucus and water Water and ions – produced mainly from the serous glands Mucus composed of Glycoprotein: Sialomucins , fucomucins , sulphomucins Enzymes: Lactoferrin , Lysozymes , α - antirypsin , α 1 -antichemotrypsin, α 2 -antimicroglobulin Circulatory proteins: complement, α 2 -macroglobulin, C reactive protein Immunoglobulins : IgA , IgE , IgG , IgM , IgD Cells: surface epithelium, basophils , eosinophils , leukocytes

11. Mucociliary Clearance Cilia is found on the surface of cells in the respiratory tract Function is to propel mucus backwards in the nose towards the nasopharynx . Nasal cilia are relatively short(5 μ m), with up to 200 per cell. Nasal mucus film is in two layers, one upper more viscous layer and a lower more watery layer in which cilia can move freely. Metachronous movement of cilia consists of a rapid propulsive stroke and a slow recovery phase.

12. Immunological Nasal Immune System Surface properties Mechanical Physical characteristics of mucus Innate immunity Bacteriocidal activity in the mucus Proteins: lactoferrins , lysozymes α 2 macroglobulins , C reactive protein, complement system Cellular: polymorphs and macrophages Acquired immunity Surface IgA , IgM , IgE and IgG Primed macrophages Submucosa macrophage IgM , IgG , T and B Lymphocytes: mucosal associated lymphoid tissue Distant sites Adenoids, lymph nodes and spleen

13. Sneezing Protective reflex. Foreign particles which irritate nasal mucosa are expelled by sneezing Copious flow of nasal secretions that follows irritation by noxious substance helps to wash them out.

14. Ventilation and Drainage 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 . Eddies formed during expiration and Uncinate process aids in ventilation of PNS. Mucociliary action helps in drainage of PNS through their respective ostia .

15. Vocal resonance Nose form resonating chamber for certain consonants in speech Phonating nasal consonants (M/N/NG) – sound passes through the nasopharyngeal isthmus and is emitted through the nose When nasopharynx is blocked, speech becomes denasal , i.e. M/N/NG are uttered as B/D/G respectively Rhinolalia clausa – too little air escapes from nose Rhinolalia aperta – too much air escapes from nose The sinuses have no effect on modifying voice

16. Olfaction Olfactory solute in mucus needs high water and lipid solubility. Olfactory area is 200-400mm 2 with a density of approximately 5x10 4 receptor cells/mm 2 Odours  react with lipid bilayer of the receptor cells at specific sites  causes outflow of K+ and Cl -  Cell depolarization . It is a G-protein coupled receptors which interact with a specific adenyl cyclase within neuroepithelium . Adrenergic and muscarinic antagonists – blocks some odour .

17. Threshold of olfaction depends on :- The chemical nature of the stimuli. Level of inhibitory activity generated by higher centre. Changes in nasal mucus and its pH. Age – decreases the threshold . Hormones (sex hormones) – increases the threshold. Adaptation :- Olfactory response shows marked adaptation and thresholds increase with exposure. Adaptation is both peripheral and central phenomenon. Cross adaptation occurs between odours at high concentration. Olfaction has role in – Food recognition, initiate digestion- lat & ventromedial hypothalamus, ↑ salivation & output of enzymes - Reproduction - Communication

18. Olfactory pathways Smell is perceived in the olfactory region (high up in nasal cavity) Peripheral process of each olfactory cells reaches the mucosal surface with several cilia on it Central process are grouped into olfactory nerves which pass through the cribriform plate of ethmoid and end in the mitral cells of the olfactory bulb Axons of mitral cells forms olfactory tract  Olfactory trigone  Olfactory Striae  Prepyriform cortex, amygdaloid nucleus, hypothalamus, hippocampus

19. Disorders of smell Anosmia: Total loss of sensation of smell Hyposmia: Partial loss of sensation of smell Parosmia : Perversion of smell i.e , interprets the odour incorrectly Seen in recovery phase of post influenzal anosmia, intracranial tumour Cachosmia : Perception of pleasant odour as unpleasant Phantosmia : Perception of odour in absence of olfactory stimulus Olfactory agnosia : Unable to identify previously known odour

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