Final answer:
The 'Doorways' leading from the nasal cavity into the pharynx are the internal nares. The hard palate and soft palate form the floor of the nasal cavity, while various bones and cartilage make up the roof. The nasal cavity includes features like the nasal septum and conchae which aid in air filtration and moisture retention.
Step-by-step explanation:
The internal nares, also known as choanae, are what you might refer to as the 'Doorways' that lead from the nasal cavity into the pharynx. The nasal cavity itself plays a significant role in the inhalation process, warming, humidifying, and filtering the air we breathe.
The anterior portion of the nasal cavity is based on the hard palate, which is a bony structure formed by the palatine process of the maxillary bones and the horizontal plate of the palatine bones. Behind it lies the soft palate, composed of muscle tissue, which separates the nasopharynx from the oropharynx during swallowing and contributes to respiration and digestion. It is the hard and soft palates that create the floor of the nasal cavity, while the roof is a complex structure composed of several bones: nasal, frontal, ethmoid, and sphenoid bones, along with a portion of cartilage.
The nasal cavity also includes important structures such as the nasal septum, which divides the cavity into left and right sections and is composed of septal cartilage, ethmoid bone, and vomer bone. Lateral to the septum, each side of the nasal cavity features the superior, middle, and inferior nasal conchae that increase surface area for air filtration and moisture retention. Additionally, several bones that form the walls of the nasal cavity contain air-filled spaces known as paranasal sinuses, which include the frontal, maxillary, sphenoidal, and ethmoidal sinuses, all serving to further warm and humidify incoming air.