The nose has several important functions: respiration, protection of the lower respiratory tract, vocal resonance, olfaction, drainage of secretions, and maintaining eustachian tube function. It filters and conditions air through mechanisms like mucociliary clearance and the nasal cycle. Secretions produced in the nose help fight infections and allergens with lysozymes, immunoglobulins, and interferons. The olfactory epithelium allows for smell detection which is important for functions like regulating food intake and detecting toxins.

2.  Respiration
 Protection of lower respiratory tract
 Vocal resonance
 Olfaction
 Drainage of secretions
 ET function
 Provides beautiful shape to the face

3.  Humans are obligatory nasal breathers – 1st six
months, adults 85% natural nose breathers
 Mouth breathing – pathological/ during exercise
 Nasal airway resistance
 External nasal valve – vestibule – 1/3rd of
resistance
 Internal nasal valve – limen nasi - more than 50%
of resistance
 Ant end of inf and middle turbinate – increase or
decrease in size (erectile tissue) – contribute to
resistance

4.  Low resistance during inspiration, high -
expiration
 Factors affecting nasal resistance – age
(max in infants), posture, drugs
(decongestants and anti hypertensives),
temp of surrounding air (cold air – high
resistance)
 Emotional and psychological problems
regulate the erectile tissues
 Endocrinological disorders – hypothyroidism,
hyperthyroidism, pregnancy

5.  Air flow – between turbinates and septum,
rarely below inf turbinate and above sup
turbinate
 Inspiratory air current
 Pass vertically up the ant nares, at nasal valve
takes a laminar pattern
 Inspiratory air contains allergens and bacteria
 Uncinate process protect the sinus by diverting it
 Expiratory air current
 Turbulent flow, sterile
 Eddies are produced under middle and inf
turbinate so sinuses are ventilated as high
resistance to air flow

7.  Nasal cycle
 Physiological cycle of alternating nasal
congestion and decongestion between two
nasal cavities
 Duration of cycle – 2-12 hrs
 Under control of ANS
 Affected by allergy, infection, emotion,
exercise, hormones – pregnancy and puberty,
drugs, sexual activity

8.  Filtration
 Vibrissae prevents large particles from passing in
(upto 3 micro m)
 Mucus filters finer particles like dust, pollen,
bacteria (0.5 – 3 micro m)
 Less than 0.5 micro m can enter lower airway
 Air conditioning of inspired air
 Counter current mechanism – blood flows in
opposite direction to inspired air – regulates
temperature of inspired air to near body temp
(37 c) – ANS
 Regulates humidity – adjusts around 80%

9.  Muco ciliary clearance
 Resp mucosa coated by thin layer of
secretions called mucous blanket
 This mucous blanket entraps fine particles
during inspiratory phase – takes them to
pharynx – stomach – digested
 Layers of mucous blanket
 Superficial thick mucous layer – viscous - gel
 Deep thin serous layer – watery – sol
 Mucous secreted by nasal glands and goblet
cells

11.  Cilia
 Outer gel layer moves by beating of cilia
 Cilia propels the mucous blanket towards
nasopharynx within 10-20 min
 Cilia beats at 10-20 times per sec
 Cilia acts best at ph 7 which is the ph of
nasal secretions
 Factors affecting cilia beating
 Pollution, smoking, viral and bacterial
infection, heat or cold, humidity, drugs like
adrenaline

12.  Mucous secretions
 Rich in lysozyme – enzyme causing bacterial
destruction
 Contains Ig A and Ig E – neutralizes allergies
and bacterial toxins
 Contains interferon – immunity against URTI
 Contains water and ions
 Contains glycoproteins

13.  Nasal reflexes
 Sneezing
 Protective reflex as a response to irritants
and harmful stimuli which are expelled
 Appetite – good smell of food – reflex
secretions of saliva and gastric juice
 Nasopulmonary and nasobronchial relex –
help in lung function
 Cardio pulmonary reflex – breathing
cessation and bradycardia

14.  Mechanism by which smell is perceived
 Function – regulation of food intake and
perception of flavour and palatability
 Protective functions – detection of toxins and
noxious substances
 Theories
 Stereochemical theory
 Electrochemical theory
 Molecular theory
 Vibration theory

15.  Mechanism
 Olfactory pathway
 Olfactory epithelium present above sup
turbinate high up in nasal cavity
 Olfactory epithelium contains olfactory receptor
cells, basal cells and supporting cells
 Olfactory receptor cells sense the odorant
particles in inspired air
 Central process of these receptor cells form
olfactory nerves
 Olfactory nerves pass through cribriform plate of
ethmoid and end in olfactory bulb

16.  Olfactory bulb contains mitral cells – axon of
these cells form olfactory tract
 Olfactory tract carries sensation to cerebrum
 The region in cerebrum is prepyriform cortex
and amygdaloid nucleus
 Vomero nasal organ of jacobson
 Accessory olfactory tissue
 Behind caudal end of septum 3mm above
nasal floor

18.  VOCAL RESONANCE
 Nasal cavities act as resonators of voice, add
nasal tone to voice
 Outlet for secretions
 Secretions from sinuses drain here
 Lacrimal secretions drain here through NLD
 ET function
 Nose permits equalization of pressure
between external atmosphere and middle
ear cavity – maintains middle ear pressure

19.  Air conditioning of inspired air –
humidification and warming
 Vocal resonance
 Protection of brain and orbit from trauma –
by acting as a buffer
 Mucociliary clearance – secretion of mucus
through ostia to keep nasal cavities moist
 Local immunological defence against microbe
 Reduction of skull weight
 Regulates intra nasal pressure

20.  Ventilation of sinus during expiration
 During expiration – positive pressure in nose
 During inspiration – negative pressure
 Sinus emptied of air during inspiration and
filled with air during expiration (reverse of
lungs)
 Ventilation through ostia

21.  Maxillary sinus
 Secretions start from floor of sinus – walls –
reach ostium at uppermost and posterior part
of sinus
 Drain through ostium – ethmoidal
infundibulum – middle meatus – nasopharynx
 Never drain through accessory ostia
 Frontal sinus
 Secretions inward transport through inter
frontal septum – roof – lateral wall – reach
ostium at floor of sinus

22.  Drain through ostium – frontal recess –
ethmoidal infundibulum – middle meatus
/middle meatus – nasopharynx
 Some secretions recycled from frontal recess
back to sinus through ostium
 Ethmoidal sinus
 Anterior – through middle meatus
 Posterior – through superior/supreme meatus
 Sphenoidal sinus – through spheno ethmoidal
recess

24.  Secretions in nasopharynx
 Infra tubal stream
 Secretions from middle meatus drain below and
in front of tubal orifice (inferior and anterior)
 Supra tubal stream
 Secretions from superior/ supreme meaus and
sphenoethmoidal recess drain drain above and
behind the tubal orifice (superior and inferior)
 During infection can overflow ET orifice
 Finally drain through oropharynx into stomach
and digested