Embryology Of The Nose

Origin Of Nasal Structures
- Begins around 4th week of intrauterine life
- Arises from frontonasal prominence
- Nasal placodes develop on lateral aspects of frontonasal prominence
Nasal Placode Development
- Invaginates to form nasal pits
- Nasal pits deepen → become nasal sacs
- Nasal sacs eventually form primitive nasal cavity
Medial And Lateral Nasal Processes
- Medial nasal processes fuse → form:
  - Nasal septum
  - Philtrum
  - Intermaxillary segment
- Lateral nasal process → lateral nasal wall structures
Formation Of Primary Palate
- Fusion of medial nasal process + maxillary process
Formation Of Secondary Palate
- Critical for separation of nasal and oral cavities
- Failure results in cleft palate
Congenital Anomalies Linked To Embryology
- Choanal atresia → failure of bucconasal membrane to rupture
- Encephaloceles → neural tube closure defects at skull base
- Proboscis / single nostril → forebrain arrest sequences

External Nose – Detailed Structural Anatomy

Framework Composition
- Upper one-third bony, lower two-thirds cartilaginous
- External shape determines airflow, aesthetics, and function
Bones Forming External Nose
- Nasal bones
  - Create the upper dorsum
  - Thick superiorly, thin inferiorly (fracture-prone)
- Frontal bone (nasal part)
- Maxillary frontal process
Cartilaginous Framework
- Septal cartilage
- Upper lateral cartilages
- Lower lateral cartilages
  - Medial crus
  - Middle crus
  - Lateral crus
- Lesser accessory alar cartilages
Soft Tissue Layers
- Skin → thick sebaceous dorsally, thin at tip
- SMAS (superficial musculoaponeurotic system)
- Nasal muscles contribute to:
  - External valve patency
  - Expression
  - Speech modulation
Nasal Apertures
- Anterior nares → lined by skin
- Posterior choanae → open into nasopharynx

Nasal Cavity – Regional Anatomy

Extends from anterior nares to choanae
Divided by septum into two passages
Contains multiple functional areas:
- Vestibule
- Respiratory region
- Olfactory region
- Meatuses
- Turbinates

Vestibule

Lined by keratinizing stratified squamous epithelium
Contains
- Vibrissae (filtering)
- Sebaceous glands
- Sweat glands
Clinical Notes
- Site of folliculitis
- Nasal vestibulitis
- Furuncles → may spread to cavernous sinus

Nasal Septum – Expanded Anatomy

Bony Part
- Vomer
- Perpendicular plate of ethmoid
Cartilaginous Part
- Quadrangular cartilage
Membranous Part
- Between columella and cartilage
Cutaneous Part
- External component
Septum functions:
- Structural support
- Airflow regulation
- Direction of laminar airflow
Clinical Correlations
- Deviated nasal septum → obstruction, sinusitis
- Septal spur → headache
- Septal hematoma → necrosis → saddle nose
- Septal perforation → crusting, whistling

Written And Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 7 Distinctions And 11 World Records For Educate A Change MBBS 4th Year (Fourth Professional) Otorhinolaryngology (ENT) Free Material

Boundaries Of Nasal Cavity – Ultra Detailed

Roof

Anteriorly → nasal bone
Middle → cribriform plate
- Olfactory nerve passage
- Weakest area of skull base
Posteriorly → body of sphenoid
Clinical Significance
- Cribriform plate fractures → anosmia, CSF leak
- Meningitis risk due to direct communication

Floor

Hard palate
- Maxilla (palatine process)
- Palatine bone (horizontal plate)
Palatal defects lead to:
- Hypernasal speech
- Nasal regurgitation in infants

Medial Wall

Formed entirely by nasal septum
Smooth surface
Contributes to airflow stabilization

Lateral Wall – Deep Anatomy

Contains critical structures:

Superior concha
Middle concha
Inferior concha
Ostiomeatal complex
Hiatus semilunaris
Ethmoid bulla

Turbinates (Conchae)

Thin bony projections
Covered by vascular mucosa
Functions:
- Increase surface area
- Warm air
- Humidify air
- Regulate resistance
Inferior turbinate hypertrophy → common obstruction cause

Meatuses

Superior Meatus
- Receives posterior ethmoid sinus drainage
Middle Meatus
- Most important clinically
- Drains:
  - Frontal sinus
  - Maxillary sinus
  - Anterior ethmoid sinus
Inferior Meatus
- Opening of nasolacrimal duct

Ostiomeatal Complex (OMC)

Functional area regulating sinus aeration
Blockage leads to chronic sinusitis
Diseases associated with OMC obstruction:
- Polyposis
- DNS
- Allergic rhinitis
- Concha bullosa

Paranasal Sinuses – Expanded Anatomy

Air-filled cavities
Lined by respiratory mucosa
Communicate with nasal cavity
Act as resonance chambers

Maxillary Sinus

Largest sinus
Pyramidal shape
Drainage into middle meatus
Clinical correlation:
- Most commonly infected
- Ostium located superiorly (poor drainage by gravity)

Ethmoid Sinuses

Multiple air cells
Divided into anterior and posterior groups
Located between orbit and nasal cavity
Infection may spread → orbital cellulitis

Frontal Sinus

Drains into frontal recess → middle meatus
Hypoplasia common

Sphenoid Sinus

Deepest sinus
Near important structures:
- Optic nerve
- Pituitary gland
- Internal carotid arteries

Blood Supply – Expanded Clinical Anatomy

Nose is highly vascular
Supplies heating and humidification functions

Arterial Supply

Internal Carotid:
- Anterior ethmoidal artery
- Posterior ethmoidal artery
External Carotid:
- Sphenopalatine artery
- Greater palatine artery
- Superior labial artery

Kiesselbach’s Plexus (Anterior Epistaxis)

Major anastomotic site
Common bleeding site due to:

Trauma
Nose picking
Hypertension
Inflammation

Woodruff’s Plexus (Posterior Epistaxis)

Located in posterior inferior meatus
Bleeds are profuse, dangerous

Venous Drainage

Facial vein
Pterygoid plexus
Ophthalmic veins
Communication with cavernous sinus
Clinical Concern:
- Retrograde infection → cavernous sinus thrombosis

Lymphatic Drainage

Extremely important for metastasis mapping.

Anterior region → submandibular nodes
Posterior region → retropharyngeal nodes + deep cervical nodes
Important in:
- Nasopharyngeal carcinoma
- Chronic infections

Nerve Supply – Expanded

Sensory

CN V1 (anterior-superior)
CN V2 (posterior-inferior)

Autonomic

Parasympathetic → increases secretion
Sympathetic → vasoconstriction

Olfactory Nerve

Responsible for smell
Damage → anosmia

Histology Of Nasal Cavity – Deep Microanatomy

Respiratory Epithelium

Pseudostratified ciliated columnar epithelium
Goblet cells produce mucus
Basal cells regenerate epithelium

Submucosal Layer

Serous glands
Venous sinusoids
Erectile tissue → important in nasal cycle

Olfactory Epithelium

Tall pseudostratified columnar
Contains:
- Olfactory receptor cells
- Supporting cells
- Basal cells
- Bowman’s glands

1. Air Conditioning Function Of The Nose

The nasal cavity conditions inspired air through warming, humidification, and filtration, ensuring the lower respiratory tract receives clean, moist, body-temperature air.

Warming Mechanism

Turbinates create large mucosal surface area for heat exchange.
Venous sinusoids located beneath mucosa act as radiators.
Blood flow increases in cold weather due to sympathetic down-regulation.
Nasal mucosa can raise inhaled air temperature from 0°C to over 30°C before it reaches the pharynx.
Clinical correlation:
- Patients with turbinate atrophy show dryness, crusting, and altered airflow.
- Total turbinectomy leads to “empty nose syndrome,” with paradoxical obstruction.

Humidification Mechanism

650–1000 ml of water is added daily to inspired air.
Mucous glands, goblet cells, and transudation from capillaries contribute moisture.
Warmer air holds more moisture, so the nose adjusts accordingly.
Nasal cycle redistributes mucosal workload to prevent desiccation.

Filtration Mechanism

Air entering the nostrils undergoes multi-stage filtering:

Stage 1 (Coarse filtration):
- Vibrissae capture particles >10 microns.
Stage 2 (Mucosal filtration):
- Mucus traps bacteria, viruses, pollutants, allergens.
Stage 3 (Mucociliary transport):
- Cilia beat at 700–900 times/min to push mucus toward nasopharynx.

Clinical associations:

Smokers → paralyzed cilia → chronic rhinosinusitis.
Primary ciliary dyskinesia → recurrent infections, situs inversus (Kartagener triad).
Viral infections ↓ ciliary beat frequency → congestion.

2. Mucociliary Clearance (Ultra-Expanded)

The mucociliary escalator is fundamental for respiratory defense.

Structure

Sol layer (periciliary fluid): thin, watery layer allowing ciliary beating.
Gel layer: thick mucus layer above sol, trapping particles.

Ciliary Movement

Each cilium 5–7 μm long.
Cilia move in coordinated metachronal waves.
Push mucus backward toward the pharynx at 3–25 mm/min.

Factors Affecting Mucociliary Function

Temperature (cold air slows cilia)
Humidity (dry air thickens mucus)
Smoking and pollution
Viral infections
Genetic disorders (immotile cilia syndromes)

Clinical Correlation

Chronic sinusitis is often due to impaired mucociliary clearance.
Post-nasal drip results from excessive mucus production or slowed transport.

3. Olfactory Physiology (Deep Clinical Detail)

Olfactory Epithelium Structure

Occupies 2–3 cm² of superior nasal cavity.
Contains:
- Olfactory receptor neurons (bipolar)
- Supporting cells
- Basal stem cells
- Bowman’s glands (produce serous fluid)

Mechanism Of Smell Perception

Odor molecules dissolve in mucus.
Bind to G-protein coupled receptors on olfactory neurons.
Generate action potentials.
Pass through cribriform plate to olfactory bulb.
Relay to olfactory cortex → amygdala → limbic system.

Factors Affecting Olfaction

Age → sense declines with age.
Upper respiratory infections → temporary loss.
Nasal polyps → obstruct odorant access.
Head trauma → avulsion of olfactory filaments.
Neurodegenerative diseases → early anosmia (Parkinson’s, Alzheimer’s).

Clinical Correlations

Anosmia (complete loss)
- COVID-19
- Trauma
- Cribriform plate fracture
- Meningiomas
Hyposmia (partial loss)
- Allergies
- DNS
- Sinus disease
Parosmia
- Misinterpretation of odors
Phantosmia
- Smelling odors that aren’t present (often neurological)

4. Nasal Cycle – Autonomic Regulation

Nature Of Nasal Cycle

Alternating partial congestion/decongestion of nasal chambers every 2–7 hours.
One side congests → the other decongests.
Mediated by sympathetic (vasoconstriction) and parasympathetic (vasodilation) control.

Functional Purpose

Prevents mucosal overuse/fatigue.
Maintains humidity.
Optimizes sense of smell.
Ensures airflow distribution.

Clinical Notes

More noticeable during URTI or allergic rhinitis.
Deviated septum → exaggerates nasal cycle → obstruction.

5. Immunological Defense Of The Nose

Innate Immunity

Mucus contains:
- IgA
- Lysozyme
- Lactoferrin
- Defensins
Cilia physically remove pathogens.

Adaptive Immunity

MALT (Mucosa Associated Lymphoid Tissue) present.
Dendritic cells sample antigens.
Plasma cells secrete IgA.

Clinical Correlation

Immunocompromised patients → nasal fungal infections (Mucormycosis).
Allergic rhinitis → IgE on mast cells → histamine release.

6. Radiological Anatomy Of The Nose

X-Ray Views

Water’s View
- Maxillary sinuses
- Orbital rims
Caldwell’s View
- Frontal and ethmoid sinuses
Lateral View
- Nasopharynx
- Adenoid hypertrophy

CT Scan (Gold Standard)

Essential for sinus anatomy before FESS.
Defines:
- Ostiomeatal complex
- Septal deviation
- Concha bullosa
- Polyps
- Mucosal thickening
Shows dangerous proximity of skull base during surgery.

MRI

Used for soft tissue tumors
Evaluates olfactory groove lesions
Differentiates fungal vs. bacterial sinusitis

7. Anatomical Variations (Ultra Important For Surgery & Exams)

Concha Bullosa

Pneumatization of middle turbinate
May obstruct OMC → sinusitis
Common exam question

Haller Cells

Ethmoid cells projecting into maxillary roof
Cause narrowing of infundibulum

Agger Nasi Cells

Most anterior ethmoid cells
Important in frontal sinus drainage

Septal Deviation Types

C-shaped
S-shaped
Spur formation
High deviation impacting airflow

Paradoxical Middle Turbinate

Curved reverse to normal
May obstruct airflow

Onodi Cells

Posterior ethmoid cells close to optic nerve

8. Surgical Anatomy Relevance

Septoplasty Surgical Notes

Septal cartilage harvested preserving L-shaped strut
Danger zones:
- Cribriform plate
- Upper lateral cartilage attachments
- Sphenopalatine artery branches

Turbinate Surgery

Over-resection → empty nose syndrome
Submucosal resection preferred

Functional Endoscopic Sinus Surgery (FESS)

Essential landmarks:
- Middle turbinate
- Uncinate process
- Ethmoidal bulla
- Hiatus semilunaris
- Lamina papyracea
Potential complications:
- CSF leak
- Orbital injury
- Bleeding from sphenopalatine artery

9. Pathology-Linked Physiology

Allergic Rhinitis

IgE mediated
Mast cells release histamine
Increases vascular permeability
Causes turbinate swelling
Contributes to sinus obstruction

Atrophic Rhinitis

Mucosal atrophy
Wide nasal cavities
Crusting
Foul smell (ozaena)

Vasomotor Rhinitis

Dysautonomia
Triggered by humidity, temperature changes

Nasal Polyposis

Chronic inflammation
Edematous stroma
Can obstruct OMC

Sinusitis

Obstruction + infection → mucociliary dysfunction
Maxillary sinus most commonly affected

10. Clinical Scenarios (Exam-Style Integration)

Scenario 1: Post-Traumatic CSF Rhinorrhea

A patient presents after head trauma with watery nasal discharge.
Beta-2 transferrin positive → confirms CSF leak
Anatomical site affected: cribriform plate
Risk: ascending meningitis

Scenario 2: Chronic Mouth Breathing

Due to hypertrophied inferior turbinates or severe DNS
Causes:
- Dry mouth
- Sleep disturbance
- Orthodontic abnormalities in children

Scenario 3: Unilateral Foul-Smelling Nasal Discharge

Suggestive of nasal foreign body in children
Related anatomy: inferior meatus

Scenario 4: Allergic Rhinitis With Sinusitis

OMC obstruction
Turbinate hypertrophy
Mucociliary dysfunction
Thick mucus leads to maxillary sinus infection

11. Contribution Of Nose To Speech Physiology

Acts as a resonator
Nasal obstruction leads to hyponasality
Palatal defects cause hypernasality
Proper nasal patency essential in phonation

12. Taste And Smell Integration

70% of taste is smell-dependent
Olfactory nerve dysfunction causes:
- Loss of flavor perception
- Poor appetite

13. Detailed Functional Integration With Respiratory System

Nose regulates resistance (up to 50% of total airway resistance)
Warmed, humidified air protects lower airways
Prevents bronchoconstriction
Filters pathogens before entry