Medical Dictionary Search here

The Respiratory System

This consists of the lungs and the air passages that lead to and form the lungs.

The air passages branch as they enter the lungs to finally form alveoli.

This system has 3 main functions:

1.Air conduction;
2.Air filtration;
3.Gas exchange (respiration).

Also air passing through the larynx gives rise to speech and air passing over the olfactory mucosa leads to our sense of smell.

Air passages consist of a conducting portion and a respiratory portion.

The conducting portion is the air passages that lead to the sites of respiration so gas exchange can occur.

The passages external to the lungs are:
1.Nasal cavities;
2.Nasopharynx and oropharynx;
5.Paired primary bronchi.

Bronchi within the lungs branch extensively to form bronchioles, which are the terminal part of the conducting system.

The respiratory portion is the part of the tract where gas exchange takes place and includes:
Respiratory bronchioles;
Alveolar ducts;
Alveolar sacs;

Capillaries within the lungs come into intimate contact with the alveoli and are the structural basis of gas exchange in the lung.

Conditioning of the air before it reaches the respiratory portion occurs and consists of warming, moistening, and removal of particulate material.

Nasal cavity

It is pyramidal in shape and it is divided in to two halves by a septum
Anterior nasal apertures
Posterior nasal apertures


The nasal cavity has 3 parts
Olfactory Region
Respiratory region


Each half of nasal cavity has a
Lateral wall
Medial wall


Dilated part immediately inside the
anterior nasal opening. It is lined by
skin and has hairs projecting downwards called vibrissae

Olfactory region: located in upper nasal cavity, above superior nasal conchae,contains olfactory cells

Respiratory region

Lower 2/3 of nasal cavity
Thick mucous membrane due to presence of cavernous vascular tissue
its function is to warm, moisten, and clean the inspired air

Lateral wall of nasal cavity

Limen nasi – A line at the Muco cutaneous junction
Sphenoethmoidal recess-Triangular depression
Superior meatus-opening of posterior ethmoidal sinus

sphenoethmoid recess (arrow above 1)
superior concha (1)
superior meatus (tip of arrow)
middle concha (2)
middle meatus (tip of arrow)
inferior concha (3)
inferior meatus (ti of arrow)

Middle meatus

Bulla ethmoidalis- is caused by the bulging of the middle ethmoidal cells which open on or immediately above it

Hiatus semilunaris-Curved cleft below
The bulla

Infundibulum- Anterior funnel shaped expansion of hiatus

Inferior meatus

Naso lacrimal duct- opening in the anterior part of meatus

Kieselbach’s Area

Also called Little’s area, at antero-inferior part of nasal septum.
90% of nasal bleeding occurs.
Supplied by septal branch of facial artery and nasopalatine branch of spheno-palatine artery anastomose & join With Twigs of anterior ethmoidal & greater palatine arteries

1.anterior ethmoidal (ophthalmic)
2.posterior ethmoidal (opththalmic)
3.sphenopalatine (maxillary)
4.greater palatine (maxillary)
5.branch of superior labial (facial