General Anatomy/Respiratory System

The respiratory system serves three principal purposes in the human body: gaseous exchange; sound production; and assistance in compression of the abdomen. It can be divided into two structural divisions, upper and lower, as well as two functional divisions, conducting and respiratory.

Respiration involves three separate yet inter-related functions: Ventilation and gaseous exchange at the air blood interface are collectively known as external respiration whereas gaseous exchange between the blood and tissues is known as internal respiration.
 * Ventilation (breathing)
 * Gaseous Exchange
 * Oxygen Utilization

Respiration, both internal and external, is fundamental to homeostasis as without oxygen (O2) the body's tissues can not produce sufficient amounts of ATP, and an accumulation of carbon dioxide (CO2) and other waste products would poison the tissues.

Structure of The Respiratory System
The respiratory system is composed of the nasal cavity, pharynx, larynx, and trachea and the bronchi, bronchioles, and pulmonary alveoli in the lungs.diaphragm

The nose and pharynx make up the upper respiratory system, while the lower respiratory system is comprised of the larynx, trachea, bronchial tree, alveoli and the lungs. Another equally common classification system divides the structures according to function i.e. those that transport gases between the environment and the alveoli - conducting system, and the pulmonary alveoli themselves - the respiratory division where gaseous exchange takes place between the atmosphere and the blood.

The Conducting System
The functions of the conducting system are to transport, warm, humidify, and filter the air. These functions are facilitated by the various epithelia lining the passageways of the respiratory system.

The Nose
The nose is found on the anterior aspect of the face and includes both an external protuberance and the internal nasal cavity. It is situated above the hard palate and is the organ of smell. The nasal cavity is divided into right and left cavities by the nasal septum. The functions of the nose are olfaction (smelling) and respiration (breathing) and each nasal cavity can be divided into olfactory and respiratory regions accordingly. Other functions include the filtration of foreign particles from inspired air and humidifying the air.

External Nose
The external nose is a protuberance on the face, it varies greatly in size and shape from one individual to another. The superior aspect of the nose extends from its root to the apex, while the inferior aspect extends from the superior lip to the apex of the nose. The inferior surface contains two piriform openings, the nostrils (also nares) which are separated by the skin overlying the nasal septum and which are bound on either side by the nasal alae. The external nose is covered in skin which continues into the nostrils where it becomes continuous with the internal mucous membrane. Before the junction with the mucous membrane but inside the nostrils the skin is covered in stiff hairs (also vibrissae).

Bony Structure of the External Nose
The bones of the nose are the: nasal bones, the nasal part of the frontal bone and its nasal spine, and the frontal processes of the maxillae. The nose is also comprised of various softer cartilaginous structures namely: two lateral cartilages, two alar cartilages and the septal cartilage. The alar cartilages are motile and control the degree to which the external nares are open or closed (nasal flairing)

Nasal Septum
The bony components of the nasal septum are the: Vomer, and the perpendicular plate of the ethmoid bone. The septal cartilage makes up the rest. The perpendicular plate of the ethmoid bone forms the superior part of the septum while the vomer forms the postero-inferior section of theseptum along with the nasal crests of the maxillary and palatine bones. The septal cartilage forms the antero-inferior part of the nasal septum and articulates with the bony components of the septum.

Nasal Cavities
The nasal cavity and its contents serve three main functions: ====Boundaries of the Nasal Cavity the floor is the widest than the roof.
 * Warm, moisten and purify inspired air
 * Olfaction
 * Resonance, i.e. changes quality of voice
 * Palatine process of maxilla and horizontal plate of palatine bone.
 * Roof which is the narrowest: The roof is narrower than the floor and curved.
 * Anteriorly: Cribriform plate, nasal spine of frontal bone, nasal bone.
 * Posteriorly: Anterior surface of body of sphenoid bone.
 * Walls:
 * Medial Wall: Nasal septum
 * Lateral Wall: Nasal and lacrimal bones, nasal surface maxilla, alar and lateral cartilages (anteriorly), and the superior, middle, and inferior nasal conchae (see below).