PHYSIOLOGY OF NOSE AND PNS Functions of the

PHYSIOLOGY OF NOSE AND PNS

Functions of the nose Respiration Air conditioning of the inspired air Protection of the lower airway Vocal resonance Nasal reflex function Olfaction

Respiration Natural pathway for breathing Inspiratory air passes across the middle part of the nose between the septum and the middle turbinate – laminar flow – required for cleaning & conditioning the air Expired air eddies under the inferior and middle turbinates and ventilates the sinuses through the ostia – Turbulant flow Nasal valve area accounts for 40 -70% of total airway resistance which can also be influenced by age, turbinate size, exercise, position, alcohol, smoke, dust, emotional stimuli and nasal cycle.

Respiration In 80% of healthy individuals, each side of the nose alternatively congests and decongests every 3 -7 hours leading to exchange of respiration and humidification function between the nostrils. Proposed by Kayser in 1895 Sensation of nasal airflow could also depend on thermal and sensitive stimulation of inhaled air. Uncinate process protects the sinuses by diverting the inspired air which is rich in allergens & bacteria

Air conditioning Nose filters and purifies the inspired air and adjusts its temperature and humidity before it reaches the lungs Filtration & purification: Nasal vibrissae can filter particles up to 3µm Nasal mucus traps particles from 0. 5 -3µm

Air conditioning Temperature control: Mucous membrane over the inferior and middle turbinates and adjacent septum is highly vascular with cavernous venous sinusoids which control the blood flow. The direction of blood flow in nasal cavity is opposite to that of inspiratory air currents. This radiator mechanism brings the temperature of the inspired air to around body temperature in one fourth of a second. AV shunts within the nasal mucosa and supplementation of the inspired air with NO synthesized in the PNS contributes to improved oxygenation and perfusion.

Air conditioning Humidification: Occurs simultaneously with temperature control Relative humidity of the inspired air is adjusted to around 80% Water, to saturate the inspired air is provided by nasal mucous membrane Humidification is required for proper mucociliary clearance and effective gas exchange at the lungs.

Protection of the lower airway – Mucociliary mechanism Mucous blanket spread over the nasal mucosa has a superficial mucous layer(gel) and a deep serous layer(sol), floating on the top of cilia which are constantly beating to carry it like a conveyer belt towards the nasopharynx. Cilia move at 5 -10 mm/min. & mucous gets cleared into nasopharynx every 10 -20 min. Inspired bacteria, dust and other particles are entrapped in the viscous layer and are swallowed. Presence of turbinates doubles the surface area to perform this function

Protection of the lower airway – Mucociliary mechanism Cilia beat 10 -20 times/sec Nine doublets of pheripheral microtubules and two central microtubules with 2 dynein arms at the pheriphery containing ATPase Rapid effective stroke reaching mucous layer and a slow recovery stroke in the serous layer in the reverse direction, thus moving the mucous blanket in only one direction. Ciliary movements are affected by drugs, diseases, dust, drying etc

Microscopic Anatomy 14

Protection of the lower airway – Enzymes and immunoglobulins Lysozyme – muramidase kills viruses and bacteria Ig. A, Ig. E & Interferons provide immunity against infections p. H of the nasal secretions is maintained at 7 at which cilia and lysozyme act best.

Protection of the lower airway – Sneezing Protective reflex Foreign particles causing irritation are expelled by sneezing. Copious nasal secretions following sneezing helps to wash the foreign material out

Vocal resonance Nose forms resonating chambers for certain consonants like M, N, NG etc When nose is blocked, speech becomes denasal. Reverse is true in velopharyngeal insufficiency

Nasal reflexes Smell of a palatable food causes reflex secretion of saliva and gastric juice. Irritation causes sneezing Nasobronchial and nasopulmonary reflexes regulate pulmonary functions S I N

Olfaction Less developed in man compared to lower animals. Required for enjoying the taste of food, protective function in the detection of toxic substances and regulation of reproductive behaviour in lower animals Smell is perceived in the olfactory region of the nose situated high up in the nasal cavity Humans can detect >10000 odours and discriminate between 5000 of them, sniffing increases the amount of inspired air available for olfaction Age related worsening is seen after 70 years Women can smell better than men L R S H A W

Olfaction Pheripheral process of olfactory cell reaches the mucosal surface of a olfactory receptor neuron with 8 -20 cilia on it. Central processes are grouped into olfactory nerves which pass through the cribriform plate of the ethmoid and end in the mitral cells of olfactory bulb. Axons of the mitral cells form the olfactory tract and carry smell to the prepyriform cortex and amygdaloid nucleus where it reaches consciousness Also associated with autonomic system at hypothalamic level P C A A

Olfaction Hydrophilic odorants are dissolved in the mucus, while hydrophobic molecules are bound and solubilised by odorant binding proteins Transformation of mechanical stimulation into electrical activity excites an ionic channel in the cilia which depolarises olfactry neuron. H T

Olfaction Mechanism of smell discrimination: M Specific odorants stimulating specific receptors – lock & key concept of chemical recognition Differing solubilities of odorants – lipid solubility will enhance the interaction with the plasma membrane Response to molecule's vibration spectra. Olfactory disorders Transport disorders/sensory or neural O

Physiology of PNS Ventilation of the sinuses occurs during expiration through the ostia because of the eddying set up at the level of nasal valve and inferior and middle turbinates Emptied of air during inspiration and filled with air during expiration NO synthesised in PNS gets added to the inspiratory air helping in better oxygenation and perfusion, Toxic to bacteria & viruses and increases ciliary motility V E N

Mucus Drainage of Sinuses Mucus secreted in the sinus spreads to the ostium in a spiral manner Propelled by the cilia towards the meatus and subsequently to nasopharynx, essential to replace the contaminated nasal secretions M P E

Mucociliary Transport 29

Functions 1. Air conditioning of the inspired air by providing large surface area over which air is humidified and warmed and increases surface area for olfaction. 2. Mucociliary Clearance: Helps to replace contaminated nasal secretions 3. Vocal resonance 4. Thermal insulators to protect delicate structures in the orbit and the cranium from variations in the intra nasal temperature 5. To lighten the skull bones 6. Contributes to facial growth