Nose

The nose is a prominent structure on the face that serves as the entryway to the respiratory system and houses the olfactory receptors for the sense of smell. It is composed of a combination of bone, cartilage, and soft tissues, providing it with structure and flexibility. The nose includes the external nose (visible portion) and the nasal cavity (internal space) that leads to the pharynx.

Location

The nose is located in the central region of the face, between the eyes and above the mouth. It extends from the nasal bridge (at the upper part, between the eyes) to the nostrils at the lower end. Internally, it connects with the nasal cavity, which opens into the pharynx at the back.

Anatomy

The nose is a complex anatomical structure composed of external and internal components. It serves as the external opening for the respiratory system and houses the sensory structures for smell. The nose is made up of bone, cartilage, soft tissue, and mucous membranes that together support its structural integrity and functionality. Below is a detailed description of the nose’s anatomy:

External Nose

The external nose is the visible portion projecting from the face. It consists of bone, cartilage, and soft tissue that give it shape and support.

Bony Framework

The upper third of the external nose is formed by bony structures:

• Nasal Bones: Two small, paired bones that form the bridge of the nose.
• Frontal Processes of the Maxilla: Extend upward from the maxillary bones to support the lateral aspect of the nose.
• Nasal Part of the Frontal Bone: Forms the superior border of the nose, where it articulates with the nasal bones.

Cartilaginous Framework

The lower two-thirds of the external nose are supported by hyaline cartilage, which provides flexibility and shape:

• Upper Lateral Cartilages: Located beneath the nasal bones, they support the midsection of the nose.
• Lower Lateral Cartilages (Alar Cartilages): Paired cartilages that form the nostrils and the tip of the nose, providing flexibility.
• Septal Cartilage: A single, flat cartilage that forms the anterior part of the nasal septum, separating the two nostrils.
• Accessory Cartilages: Small cartilaginous components located near the lower lateral cartilages.

Soft Tissues and Skin

• The skin overlying the nasal framework is thin near the bridge but thicker and more sebaceous near the tip.
• The nostrils (nares) are the two external openings that lead into the nasal cavity. They are surrounded by soft tissue and lined with fine hairs (vibrissae) that filter larger particles from the air.

Nasal Cavity

The nasal cavity is the internal space of the nose, extending from the nostrils to the choanae (posterior openings leading to the pharynx). It is divided into two halves by the nasal septum and lined with mucous membranes.

Boundaries of the Nasal Cavity

• Roof: Formed by:
  • Cribriform plate of the ethmoid bone (perforated for passage of olfactory nerves).
  • Nasal part of the frontal bone and sphenoid bone.
• Floor:
  • Formed by the palatine process of the maxilla (anterior) and the horizontal plate of the palatine bone (posterior).
  • Separates the nasal cavity from the oral cavity.
• Medial Wall (Nasal Septum):
  • Formed by the vomer (posterior), perpendicular plate of the ethmoid bone (superior), and the septal cartilage (anterior).
  • Divides the nasal cavity into left and right halves.
• Lateral Walls:
  • Formed by the maxilla, ethmoid bone, palatine bone, and inferior nasal conchae.
  • The lateral walls contain bony projections called nasal conchae (turbinates):
    • Superior Concha (part of ethmoid bone).
    • Middle Concha (part of ethmoid bone).
    • Inferior Concha (a separate bone).
  • The conchae increase the surface area of the nasal cavity and create airflow turbulence to warm and filter air.

Nasal Meatuses

Beneath each nasal concha is a corresponding meatus (passageway) that allows drainage of sinuses and tear ducts:

• Superior Meatus: Drains the posterior ethmoidal sinuses.
• Middle Meatus: Drains the frontal sinus, maxillary sinus, and anterior ethmoidal sinuses.
• Inferior Meatus: Receives drainage from the nasolacrimal duct (tears from the eyes).

Paranasal Sinuses

The nasal cavity is surrounded by paranasal sinuses, which are air-filled cavities within the skull bones. These sinuses communicate with the nasal cavity and are lined with mucosa:

• Frontal Sinuses: Located in the frontal bone above the eyes.
• Ethmoidal Sinuses: A group of small air cells located in the ethmoid bone between the eyes.
• Maxillary Sinuses: The largest sinuses, located in the maxilla (cheekbones).
• Sphenoidal Sinuses: Located in the body of the sphenoid bone at the base of the skull.

These sinuses reduce skull weight, humidify air, and enhance vocal resonance.

Blood Supply of the Nose

The nose has a rich blood supply derived from branches of both the internal carotid artery and external carotid artery:

• Kiesselbach’s Plexus: A vascular network in the anterior septum prone to nosebleeds (epistaxis).
• Arteries:
  • Sphenopalatine Artery (from the maxillary artery).
  • Ethmoidal Arteries (from the ophthalmic artery).
  • Facial Artery: Supplies the external nose.

Venous drainage occurs via:

• The facial vein and pterygoid venous plexus.

Nerve Supply of the Nose

The nerve supply of the nose includes sensory, motor, and special sensory innervation:

• Olfactory Nerve (CN I):
  • Provides the sense of smell via the olfactory epithelium located on the roof of the nasal cavity.
• Trigeminal Nerve (CN V):
  • Ophthalmic Division (V1): Innervates the upper nose and nasal cavity.
  • Maxillary Division (V2): Supplies the lower nasal cavity and lateral walls.
• Facial Nerve (CN VII):
  • Controls secretions from nasal glands (parasympathetic innervation).

Lymphatic Drainage

The lymph from the nose drains into regional lymph nodes:

• Submandibular Lymph Nodes: Drain the external nose.
• Deep Cervical Lymph Nodes: Drain the internal nasal cavity.

External Openings (Nostrils)

The nostrils (nares) are the anterior openings of the nose, bordered by:

• Alae: The soft, lateral wings of the nostrils.
• Columella: The tissue separating the two nostrils.

The nostrils lead directly into the nasal vestibule, the anterior portion of the nasal cavity lined with vibrissae (coarse hairs) for filtering particles.

Function

The nose serves as a multifunctional organ vital for respiration, filtration, humidification, olfaction (sense of smell), and vocal resonance. Its intricate anatomy, including the external nose, nasal cavity, and paranasal sinuses, enables it to efficiently perform these tasks. Below is a detailed explanation of the functions of the nose:

Respiration (Air Passageway)

The nose serves as the primary entry point for air into the respiratory system:

• Air Entry: Air enters through the nostrils (nares) and flows into the nasal cavity.
• Nasal Cavity: The nasal cavity directs the air toward the pharynx, where it enters the lower respiratory tract (trachea, bronchi, and lungs).
• The conchae (turbinates) create airflow turbulence, ensuring better conditioning of the air as it moves through the nasal passages.

The nose provides a direct route for oxygen intake while minimizing resistance, making it essential for effective breathing.

Filtration of Air

The nose filters dust, allergens, microorganisms, and other particles from the air:

• Nasal Hairs (Vibrissae): Located in the nasal vestibule, these coarse hairs trap larger particles present in inhaled air.
• Mucous Membrane: The nasal cavity is lined with a mucous membrane that secretes mucus, which traps smaller particles like dust, pollen, and pathogens.
• Cilia: Tiny hair-like structures on the mucosa (ciliated epithelium) sweep trapped particles backward toward the throat, where they are swallowed or expelled.

This filtration system protects the lower respiratory tract from inhaled pollutants and microorganisms.

Humidification and Warming of Air

The nose conditions incoming air to make it suitable for the lungs:

• Humidification:The mucous membranes of the nasal cavity secrete moisture to humidify dry air, ensuring that it reaches the lungs at an appropriate humidity level.
• Warming:The extensive network of blood vessels in the nasal cavity transfers heat to the inhaled air, warming it to body temperature.
• Turbinates: The nasal conchae increase the surface area of the nasal cavity, allowing more contact between the air and mucosa for efficient warming and humidification.

By the time air reaches the lungs, it is moist, clean, and at an ideal temperature.

Olfaction (Sense of Smell)

The nose is the primary organ for olfaction, the sense of smell:

• The olfactory epithelium is located in the roof of the nasal cavity, beneath the cribriform plate of the ethmoid bone.
• It contains specialized olfactory receptor cells that detect airborne odor molecules.
• When inhaled air passes over the olfactory epithelium, these receptors transmit signals via the olfactory nerve (Cranial Nerve I) to the olfactory bulb in the brain.
• The brain interprets these signals as smells.

This function is essential for detecting pleasant and unpleasant odors, identifying food, and recognizing potential dangers like smoke or gas.

Vocal Resonance

The nose contributes to speech and vocal resonance by acting as a resonating chamber:

• Air passing through the nasal cavity enhances the quality and tone of the voice.
• The paranasal sinuses amplify and modulate sound produced in the larynx.
• Blockage or abnormalities (e.g., nasal congestion) can alter vocal resonance, producing a nasal voice or muffled speech.

This function is vital for clear and natural-sounding speech.

Smell and Taste Connection

The nose is intricately connected to the sense of taste:

• The perception of taste is enhanced by the ability to smell, as flavor depends on both taste receptors in the mouth and olfactory receptors in the nose.
• During chewing, volatile chemicals from food travel to the olfactory epithelium via the nasopharynx, contributing to the overall flavor experience.
• When nasal passages are blocked (e.g., due to a cold), the sense of taste is significantly diminished.

Defense Mechanisms

The nose plays a critical role in defending the respiratory tract from harmful particles and pathogens:

• Sneezing: A protective reflex triggered by irritation of the nasal mucosa (e.g., dust, allergens). It forcefully expels irritants from the nose.
• Mucus Production: Mucus traps pathogens and particles, preventing their entry into the lungs.
• Immune Defense: The nasal mucosa contains immune cells (e.g., lymphocytes and macrophages) that help neutralize pathogens.

These mechanisms ensure that the respiratory tract remains clear and protected.

Regulation of Airflow

The nose helps regulate airflow during breathing:

• The nasal cycle alternates airflow between the two nostrils by swelling and de-swelling of the nasal turbinates. This allows the nasal mucosa to rest and recover.
• The pupil-like dilation or constriction of the nostrils further modulates airflow during activities such as deep breathing or exercise.

This regulation optimizes the efficiency of air intake and minimizes strain on the respiratory system.

Temperature Regulation

The nose helps regulate body temperature:

• By warming cold air during inhalation, the nose prevents a drop in body temperature.
• During hot conditions, the nose also allows for heat loss through evaporation of moisture in exhaled air.

This ensures a balance in maintaining core body temperature.

Facial Aesthetics

The nose serves an important role in facial appearance and symmetry:

• It is a central and prominent feature of the face that significantly influences an individual’s appearance.
• Variations in size, shape, and structure contribute to facial identity and aesthetics.

While not functional in the physiological sense, its role in facial harmony and communication (via expressions) is noteworthy.

Clinical Significance

The nose is critical for respiration, filtration, and olfaction, making it prone to various clinical conditions and injuries that affect its functions.

Respiratory Conditions

• Nasal Congestion: Caused by colds, sinusitis, allergies, or nasal polyps, leading to difficulty in breathing.
• Sinusitis: Inflammation of the paranasal sinuses due to infection or allergies, causing pain and pressure.

Trauma and Deformities

• Nasal Fractures: Common in facial injuries, resulting in deformities and airway obstruction.
• Deviated Nasal Septum: A misalignment of the nasal septum, leading to breathing difficulties and frequent infections.

Olfactory Disorders

Anosmia (loss of smell) and hyposmia (reduced sense of smell) occur due to infections, trauma, or neurological conditions.

Epistaxis (Nosebleeds)

Often caused by trauma, dry air, infections, or hypertension, with Kiesselbach’s plexus being the most common site of bleeding.

Obstructive Conditions

• Nasal Polyps: Benign growths that block airflow.
• Hypertrophy of Turbinates: Enlargement of nasal turbinates leading to nasal obstruction.

Infections

• Rhinitis: Inflammation of the nasal mucosa (infectious or allergic).
• Fungal or bacterial infections in immunocompromised individuals can affect the nasal cavity and sinuses.