Nose and nasal cavity, sinuses, pharynx, larynx, trachea, lungs, bronchi,alevoli

The Nose and Nasal Cavity

The mouth is located above the nose. The interior nasal cavity and the external nose are the two sections that make it up. The external nose is made up of two nasal bones and hyaline cartilage, and it is lined and coated by vascular columnar epithelium. The external nares, often known as the nostrils, are two holes on the underside of the external nose. Through the nostrils, air enters the body for the first time.

The two sizable areas known as the nasal cavities are located immediately inside the nostrils. Between the roof of the mouth and the cranium, there are two irregular cavities that are divided from one another by the nasal septum. Hyaline cartilage forms the septum's anterior portion, and an ethmoid bone and vomer perpendicular plate forms the septum's posterior portion.The septum, the maxilla, the ethmoid bone, the conchae, and the back wall of the pharynx make form the walls of the nasal cavity. A piece of the frontal bone, the ethmoid bone, the sphenoid bone, and the nasal bones combine to create the roof. The rough and soft palates together create the floor. The three mucosa-covered protrusions (superior, middle, and inferior) from each nasal cavity's lateral wall are known as conchae. The internal nares is another name for them. They significantly increase the area that air must pass through when it passes through the nasal cavities. Located between these conchae is the nasal meatus (superior, middle and inferior). While the inferior conchae is an independent bone, the superior and inferior conchae are projections of the ethmoid bone.

The nasal cavity contains two types of epithelium: the olfactory mucosa, and the respiratory mucosa. The olfactory mucosa contains the sensory receptors for smell due to which the nose serve as the organ of smell. The respiratory mucosa contains pseudo-stratified ciliated columnar epithelium with many goblet cells, other glands and the blood vessels. The goblet cells secret a sticky mucus containing lysozyme, an antibacterial enzyme. The anterior portion of the nasal cavity is lined with sebaceous and sweat glands, and numerous hair follicles. The hairs trap larger particles. Smaller particles such as dust, pollen, microbes, and other materials adhere to the mucus, secreted by sebaceous glands, which were not trapped by nasal hairs. The cilia move the contaminated mucus and trapped materials towards the throat (pharynx) where it is spit out, or swallowed.

Blood Supply

The greater palatine artery, spheno-palatine artery, ethmoidal artery, and facial artery all provide abundant blood flow to the nasal cavity. The Keisselbach's area or Little's area, where these vessels form anastomoses at the nasal septum, is a common location for nasal bleeding, or "epistaxis." The venous plexus receives the drainage of venous blood.

Nerve Supply

Sympathetic and parasympathetic nerves supply the nasal cavity.

Functions of the Nose

• It serves as the opening via which air enters the body. By the hair, it purifies and filters entering air.
• Blood in the mucosal capillaries heats the air.
• As it passes across the wet mucosa, it moistens the air.
• It functions as an olfactory organ.
• The nasal cillia blocks the respiratory tract from being affected by the polluted mucus.
• The nose contributes to taste perception.
• The sound of your voice is impacted by nasal air resonance.

Openings and Sinuses

Except external and internal nares, there are several other openings into the nasal cavity known as paranasal sinuses. They are small cavities containing the air in the bones surrounding the nasal cavity. They communicate with the nasal cavities. The main paranasal sinuses are:

• The frontal sinuses (2) and the sphenoidal sinuses (2) lie in the roof. Frontal sinuses drain into middle meatus of lateral wall of nose through frontonasal duct. Sphenoidal sinuses drains into spheno-ethmoidal recess above the superior conchae.
• The ethmoid sinuses (3 ethmoidal cells) lie in the upper part of the lateral walls. Anterior and middle ethmoidal cells drain into middle meatus and posterior ethmoidal cell drains into superior meatus.
• The maxillary sinuses (2) lie in the lateral walls. It is the largest paranasal sinus that opens into middle meatus.

Functions of the Paranasal Sinuses

• They warm and moisten the air.
• They act as resonance chambers for speech.
• They serve to lighten the skull.

The Pharynx

The pharynx is a funnel shaped passageway about 12-14 cm long that extends from the conchae to the larynx and esophagus (base of skull to C7). It consists of a tube of skeletal muscle lined with the mucous membrane which is continuous with the lining of the mouth, nasal cavity, larynx, and esophagus. It serves as a common pathway for food and air and provides a resonating chamber for speech sounds.

Organs Associated with the Pharynx

• Superiorly: The inferior surface of the base of the skull.
• Inferiorly: It is the continuous with the esophagus.
• Anteriorly: The wall is incomplete and opens into the nasal cavity, mouth and larynx.
• Posteriorly: It is separated by loose areolar tissue, involuntary muscle and the bodies of the six cervical vertebrae.

Parts of the Pharynx

The pharynx is divided into three areas: the nasopharynx, oropharynx, and laryngopharynx.

• Nasopharynx: The upper portion located immediately behind the nasal cavity is called the nasopharynx. The posterior apertures (choanae) of the nasal cavities open into nasopharynx. It serves only as an air passageway because it lies just above the point of food entry into the body. It is connected to each middle ear by the auditory (pharyngotympanic) tubes. Its posterior wall contains a lymphoid tissue called the pharyngeal tonsils which trap and destroy airborne pathogens entering the nasopharynx. The nasopharynx is lined with pseudo stratified ciliated columnar epithelium.
• Oropharynx: The oropharynx lies posterior to the oral cavity and extends inferiorly from the soft palate to the epiglottis. The posterior opening of the oral cavity (oropharyngeal isthmus) opens into the oropharynx. The oropharynx is a common passageway for both the respiratory and digestive tracts as it provides air to larynx and the food to the esophagus. It is lined with stratified squamous epithelium to resist friction of the food passage. Its lateral wall contains two pairs of lymphoid tissue called the palatine and lingual tonsils.
•  Laryngopharynx: The laryngopharynx is the most inferior portion of the pharynx. The superior aperture of the larynx (laryngeal inlet) opens into the laryngopharynx. It extends to the larynx anteriorly and to the esophagus posteriorly. It serves as a passageway for both the respiratory and digestive system. It is lined with a stratified squamous epithelium.

Blood Supply

The pharynx receives blood supply from the branches of the facial artery and the venous blood returns through the facial and the internal jugular vein.

Nerve Supply

The pharynx receives the nerve supply from the pharyngeal plexus.

Functions of the Pharynx

• The air coming via the nose is warmed and moistened.
• It acts as a connection between the digestive and breathing systems.
• Through the auditory tubes, it is possible to balance the middle ear pressure with the surrounding air pressure.
• It improves speech by serving as a resonating chamber.
• The pharyngeal and palatine tonsils contribute to the body's defense against the invasion of microbes.