Physiology of the nose

1. Fuad Ridha Mahabot
1

2. Introduction
• 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 also adds quality to speech production
• The ENT surgeon 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
2

3. Function Mechanism
Respiration
Heat exchange
Direction of blood flow
Latent heat of evaporation
Thermoregulation
Humidification
Anterior serous glands
Mixed serous and mucus glands
Capillary permaebility
Other body fluids; e.g. tears
Filtration Airflow pattern: laminar/turbulent
Nasal resistance
Anatomical, fixed
Neurovascular, variable
Nasal fluids and ciliary
fuction
Mucus, mucins
Protein including immunoglobulins
Ciliary structure and function
Nasal neurovascular
reflexes
Parasympathetic
Sympathetic
Sensory: axon reflexes
Sneezing
Central: pulmonary reflexes
Nasal cycle
Voice modification Nasal escape 3

4. Olfaction
Stimulus
Threshold and suprathreshold
Adaptation, discrimination and classification
Pathways Neurones in contact with the external environment
Two neurone
peripheral pathway
Higher centres
Perceived smell
Trigeminal input Pain
Olfaction and
behaviour
Pheromones
4

5. Respiration
• The nose acts as an air conditioning unit
• Performs: humidification, heat transfer and filtration
• The functions of nose are bypasses during exercise
• The nose may be more important in temperature regulation
than in respiration because of its ability to transfer the heat
• Inspired gases contain pollutants, domestic dust particles and
pollen, industrial products, bacteria, viruses and tobacco
smoke
5

6. I. Heat Exchange
• Temperature of the inspired air can vary from -50 to 50oc
Conduction, convection and radiation
• Conduction occurs without flow when heat is transferred by
increased molecular movement
• A temperature gradient leads to convection of currents 
affect airflow in the nose  turbulence
• Flow results in forced convection
FH = h(Twall – Tf)
FH = heat flux in J/m per s; Tf = bulk temperature; h = heat transfer coefficient
in J/m per s per oC
6

7. • Prandtl number, the heat transfer coefficient
Pr = (CPƞ)KH
CP = heat capacity of gas in J/g per oC; ƞ = viscosity; KH = thermal
conductivity in J/m per oC
7

8. II. Humidification
• Vaporization cools the surface and 10 percent of the body
heat is lost in this way
Inspiration
• Saturation follows the temperature rise rapidly
• Energy required for:
 raising the temperature of inspired air (1/5)
 latent heat of evaporation (4/5)1
• The amount of energy is dependent on ambient temperature
and relative humidity of an inspired air
• 10% of body heat loss occurs through the nose in humans
• Air in post nasal space is approximately 31oC and is 95%
saturated2
8

9. Expiration
• The temperature of the expired air at the back of the nose is
slightly below body core temperature and is saturated
• Some water condenses into the mucosa as the temperature
drops along the nose
• The temperature in the anterior nose at the end of the
expiration is 32oC and approximately 30oC at the end of
inspiration
• Approximately 1/3rd of the water required to humidify the
inspired air is recovered in this way
• People who breathe in through the nose and out through the
mouth will dry the mucosa
9

10. Water production
• Water comes from the serous gland, which are extensive
throughout the nose
• During nasal cycle, secretions are lower on the more
obstructed side
• Additional water comes from the expired air, the nasolacrimal
duct and the oral cavity
• Humidification is reduced by atropine probably acting on the
gland rather than the vasculature3
10

11. III. Airflow
• The airflow and the sensation of it are very different
• Cold receptors sense airflow
• Most of the work of heat and mass transport has been
performed on simple structures with constant cross sections.2
• The flow is turbulent, but is considered laminar at rest
• The equations below describe flow, two for laminar and one
for the transition to turbulent flow
Airflow : VA = constant
Bernoulli’s equation : P + ½ ρV2 = constant
Reynolds number : Re =
ρ = density (g m-1); V = velocity (m sec-1); A = cross-sectional area (m2); P =
pressure (N m-2); d = diameter (m); ƞ = viscosity (g sec-1 m-1)
dVρ
ƞ
11

12. • Gases flow faster through the choana4
• The characteristic of air flow were similar in different noses
regardless of variety of nasal shape
• The cross-sectional flow is maximal at the centre and is zero at
the edge
• Bernoulli equation is not strictly applicable since the energy
overcoming the viscosity results in an irreversible drop in
pressure
• The nose has variable cross section – the pressure and
velocity will alter continuously within the system
• Because of the flow is turbulent in an irregular tube, the
resistance is inversely proportional to the square of the flow
rate5
12

13. Inspiration
• 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
• Air reaches the other parts of the nose to a lesser degree
• The velocity at the anterior valve is 12 - 18 m per sec during
quiet respiration
13

14. 14

15. Expiration
• Expiration lasts longer than inspiration and is more turbulent
• Extrapulmonary airflow is turbulent because of the direction
changes, the calibre varies markedly and walls are not
smooth. The surface area is enlarged by the turbinates and
the microanatomy of the epithelium
15

16. Nasal resistance
• Differs between races
• Negroes and Caucasians are similar, but it is difficult to obtain
the sampling pressure for rhinometry in Japanese6,7
• The nose accounts for up to half of the total airway resistance
• Produced by two resistors in parallel and each cavity has a
variable value produced by the nasal cycle
 fixed: bone, cartilage and muscle
 variable: mucosa
• High in infants (obligatory nose breathers)
• Adult breath preferentially through the nose at rest even
though there is a significant resistance
16

17. • During expiration, the positive pressure is transmitted to the
alveoli
• Removal of this resistance by tracheostomy reduces dead
space but results in a degree of alveolar collapse
• Reduced alveolar ventilation gives a degree of right to left
shunting of the pulmonary blood
17

18. The anterior nasal valve
• Narrowest part of the nose and less well defined physilogically
then anatomically
• Greatest resistor – produces the most turbulent airflow8
• Formed by the lower edge of the upper lateral cartilages, the
anterior end of inferior turbinate, the adjacent nasal septum
and with the surrounding soft tissues
• EMG – shows contraction of the dilator naris alone during
inspiration9 which increases during exercise and can be
mimicked by voluntary dilatation10
• Alar collapse occurs after denervation, even in quiet
respiration
18

19. Nasal cycle
• Consists of alternate nasal blockage between passages
• First physiological description by Kayser in 189511
• The changes are produced by vascular activity particularly the
volume of blood on the venous sinusoids (capasitance vessels)
• Cyclical changes occurs between 4 to 12 hours, they are
constant for each person
• Can be demonstrated in over 80% of adults
• Difficult to demonstrate in children and it is present in early
childhood12
• Nasal secretions are also cyclical with an increase in
secretions in the side with the greatest airflow3
19

20. • Factors modify the nasal cycle: allergy, infection, exercise,
hormones, pregnancy, fear and emotions, sexual activity
• Vagal overactivity may cause nasal congestion
• High levels of CO2 in the inspired air produced by rebreathing
may also reduce the nasal resistance – this reverses following
hyperventilation
• Drugs which block the action of noradrenaline cause nasal
congestion
• Antihistamine has anticholinergic effects  block the
parasympathetic activity  increase the sympathetic tone 
improve airway
• Puberty and pregnancy – affect nasal mucosa – mediated
directly on the blood vessels
20

21. IV. Protection of Lower Airway:
Mechanical and Chemical
• The nose protects the lower airway by removing particles
down to approximately 30 μm, 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 180o and velocity drops markedly
just after the nasal valve
• Turbulence increases deposition of particles
• Particles in motion will tend to carry on in the same direction
• Resistance to change in velocity is greater in irregular particles
because of larger surface area and the number of facets
• Vibrissae will only stop the largest particles
21

22. Nasal secretions
• Composed of two elements – mucus and water
• Glycoprotein – produced by mucus glands
• Water and ions – produced mainly from the serous glands and
indirectly from transudation from the capillary network
• 2 secretory cell types – mucus and serous cells
• Glycoprotein found in mucous are produced in goblet cells
(within the epithelium) and the glandular mucus cells
• Submucosal glands are mixed and are arranged around ducts
• The anterior part of the nose contains serous glands only in
the vestibular region – produce a copious watery secretion
when stimulated
• Sinuses has fewer goblet cells and mixed glands 22

23. 23

24. Composition of mucus
• Water and ions from transudation
• Glycoprotein: sialomucins, fucomucins, sulphomucins
• Enzymes: lactoferrin, lysozymes
• Circulatory proteins: complement, α2-macroglobulin, C
reactive protein
• Immunoglobulins: IgA, IgE, IgG, IgM, IgD
• Cells: surface epithelium, basophils, eosinophils, leukocytes
24

25. Rheology of mucus
• Glycoproteins give mucus viscosity and elasticity
• Viscosity is lowered by reducing the ionic content
• The temperature of nasal cavity is relatively constant and is
lower than tracheobronchial tree
• Movement of the cilia produce shearing effects that the
elasticity counteracts - if it is the right consistency – viscosity
and elasticity complement each other and mucus moves
• Techniques to measure the rheology: microspherometry and
controlled stress technique
• Mucus viscosity can be measured by drawing up mucus into a
capillary tube under negative pressure and measuring the
flow relative to the pressure
25

26. Proteins in nasal secretion
1. Lactoferrin
 Produced by glandular epithelium, mainly the serous gland
 Its action is to bind divalent metal ions – like transferrin in the
circulation
 Lactoferrin and transferrin both bind two divalent metal ions,
particularly irons  prevent growth of certain bacteria, particularly
staphylococcus and pseudomonas
2. Lysozymes
 Comes from serous glands and tears
 Also produced from leukocytes and microphages found in nasal
secretion and mucosa
 Act only on non capsulated bacteria
26

27. 3. Antiproteases
 Produced by leukocytes
 Increase with infection
 Example: α-antirypsin, α1-antichemotrypsin, α2-antimicroglobulin,
etc.
4. Complement
 C3 – produced by liver and locally by macrophages
 Functions: lysis of microorganism, enhancing neutrophil function
(leukotaxis)
5. Lipids
27

28. 6. Ions and Water
 Na+ and Cl- are hyperosmolar in mucus
 Hyperosmolarity caused by evaporation and active ion transport
 This mainly occurs within serous gland which produce the major
proportion of the fluids in nasal secretion
7. Immunoglobulins
 All classes of immunoglobulins heve been found in nasal secretions
 IgA2 and IgE involved in mucosal defense and present in greater
quantities than serum (IgA = 50% of the total protein content)
28

29. Cilia
ULTRASTRUCTURE
• 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 5 μm, with up to 200 per cell
• A cilium has a surface membrane
• 9 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
29

30. • Outer pair also have inner and outer dynein arms, which
consists of an ATPase, which is 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 a lower more watery layer in which cilia can move
freely
• There are small hooks at the tips of the cilia where they enter
the viscous layer to remove it
30

31. 31

32. CILIARY ACTION
• Best frequency is between 7 and 16 Hz at body temperature13
• Beat frequency remains constant between 32 and 40oC
• Beat consists of a rapid propulsive stroke and a slow recovery
phase
• Propulsive phase: the cilium is straight and the tip points into
the viscous layer of the mucous blanket
• Recovery phase: the cilium is bent over in the aqueous layer
• Energy is produced by conversion of ATP to ADP by ATPase of
the dynein arms – dependent of Mg2+ ions
• Motions is produced by the pair of outer microtubules sliding
with respect to each other
32

33. • ATP is generated by the mitochondria near the cell surface
next to the basal bodies of the cilia
• The mucus blanket is propelled backwards by metachronous
movement of cilia – only those at 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 –
most going through middle meatus  pass around the
Eustachian orifice  swallowed
33

34. FACTORS AFFECTING CILIARY ACTION
• Drying stops the cilia
• Temperature below 10oC and above 45oC
• Solutions above 5 % and below 0.2%
• pH below 6.4 and above 8.5
• Upper respiratory tract infection – damage the epithelium
• Ageing
34

35. DRUGS
• Acetylcholine - increases the rate
• Adrenaline - reduces the rate
• Propanolol – reduces the rate
• Cocaine hydrochloride (>10%) – causes immediate paralysis
• Corticosteroids – reduces the rate
35

36. V. Protection of Lower Airway:
Immunological
• IgA and IgE are mainly present on the surface of the mucosa
• IgM and IgG act if the mucosa if breached
• Certain bacterial allergens are neutralized but several bacteria
and viruses require the activation of the cell-mediated
immune response
• The T and some B cells interact with microphages, which have
specific and non specific immunological properties
• Dendritic cells are important in the allergic response
• 2 groups of cytokines act on CD4+ T cells and give rise to two
main responses – the Th1 and Th2
• Local lymphatic system:
 mucosal-associated lymhoid tissue (MALT) – tonsils, adenoid
 lymph nodes
36

37. Nasal Immune System
Surface properties
Mechanical
Physical characteristics of mucus
Innate immunity
Bacteriocidal activity in the mucus
Proteins: lactoferrins, lysozymes
α2 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
37

38. Non specific immunity
• Lactoferrin, lysozymes, complement, antiproteases
Acquired immunity
• IgA
 Divided into IgA1 and IgA2
• IgA1 – more frequent in the serum; monomer
• IgA2 – more frequent in the nasal secretion; dimer
 Accounts for up to 70% of the total protein in nasal secretion
 Transferred passively through interstitial fluid  actively taken up by
seromucinous glands and surface epithelium
• Forms insoluble complex when reacts with antigen  swallowed
and destroyed by stomach acid
38

39. • IgE
 main Ig involved in allergic reaction
 Produced mainly in lymphoid aggregates such as tonsils and adenoids
and within the mucosa
39

40. VI. 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
• Many nasal condition affect the quality of voice by blocking
the passage of air in expiration
• 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 the nose
• Rhinolalia aperta – too much air escapes
• The sinuses have no effect on modifying voice
• The most affective resonance occurs at lower laryngeal
frequencies 40

41. VII. Olfaction
• Olfactory compound need high water and lipid solubility
• The solute in the mucus is presented to the sensory mucosa
Olfactory area
• Area: 200-400mm2 with a density of approximately 5x104
receptor cells/mm2
• Receptor cells have modified cilia, which increase surface area
and project like normal cilia into the mucus
Stimulus
• Odours  react with lipid bilayer of the receptor cells at
specific sites  causes outflow of K+ and Cl-  Cells
depolarization14
41

42. Receptors
• Olfaction is mediated by G-protein coupled receptors in the
cells which interact with a specific adenyl cyclase within
neuroepithelium15
• Adrenergic and muscarinic antagonists – blocks some odour
Threshold
• Threshold concentrations can vary by 1010 depending on the
chemical nature of the stimuli
• Thresholds depend on levels of inhibitory activity which
generated by higher centres
42

43. Adaptation
• Olfactoy responses show marked adaptation and thresholds
increase with exposure
• Adaptation is a peripheral and central phenomenon
• Cross adaptations are present between odours at high
concentrations
• Other factors affecting threshold:
 changes in nasal mucus and its pH
 Age – decreases the threshold
 Hormones (sex hormones) – increases the threshold
43

44. Olfactory pathways
• Smell is perceived in the olfactory region (high up in nasal
cavity)
• Peripheral process of each olfactory cells reaches the mucosal
surface and is expended into a ventricle 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 from olfactory tract and carry smell to
the prepyriform cortex and amygdaloid nucleus where it
reaches consciousness
44

45. 45

46. Disorders of smell
• Anosmia: total loss of smell
• Hyposmia: partial loss
• Parosmia: Perversion of smell – the person interprets the
odour incorrectly
 seen in recovery phase of post influenzal anosmia, intracranial tumour
46

47. Conclusion
• An 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 clearence
 Understand the action of drugs on the nasal mucosa
 Assess the smell and taste
47

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