The Respiratory System


The nasal passages of humans extend from the external nares (nostril openings) to the internal nares. Posterior to the internal nares the passages open into the nasopharynx.

Stuctures of the nasal passages include the external nares, nasal vestibule, nasal cavities, nasal septum, olfactory epithelium, nasal conchae, and nasal sinuses.

The external nares, or nostril openings, lead into the nasal vestibule, a short passage that leads into the main nasal cavities.

The nasal sinuses connect to the nasal cavities via small ducts. There are four sets of nasal sinuses. The frontal sinuses are locaed in the frontal bone near the median brow line. The ethmoidal sinuses are just above the roof of the nasal cavities. The sphenoidal sinus is centrally located in the sphenoid bone beneath the pituitary and above the nasopharynx. The maxillary sinuses are large cavities in each maxilla, above the molar teeth.

The nasal septum consists of the bone and overlying tissues which separate the left nasal cavity from the right. The nasal conchae are thin curved plates of bone and overlying mucosal lining tissues that extend from the roof and side of the nasal cavities and serve to warm, filter, and moisten the air that passes through. There are three in each nostril, a superior nasal concha, middle nasal concha, and inferior nasal concha.

A special olfactory epithelium lines the roof of the nasal cavities. Cells of the olfactory epithelium have receptors for hundreds of different odor molecules. These cells act as neurons and send signals for the olfactory sense through neuronal fibers to the brain.




























Overview of Respiratory System

Human Nasal Passages

Human Pharynx Regions

Human Larynx and Trachea

Human Bronchi and Lungs

Muscles of Human Respiration

Lower Respiratory Development

Fish Lungs/Air Bladders

Tetrapod Lungs

Lung Ventilation Systems

Gills of Vertebrate Animals

Things I Should Know