The Respiratory System Structure

The upper respiratory tract is made up of the tubes that connect the lungs with the outside world. From the outside in they are:

Nostrils

 

Nasal passages - warm, moisten, and filter the inhaled air. Smell receptors are located in the nasal passages and the sinuses are outpouchings.

	Nasal Passage Histology
	Gross Anatomy of Nasal Passage Sheep
	Frontal Sinus Cat skull radiograph
	Turbinates Deer

 

Pharynx - the throat. It is a passageway shared by the respiratory and digestive systems.

 

Larynx - the voice box. It controls airflow to and from the lungs and helps produce vocal sounds. The epiglottis is a cartilagenous trap door that covers the opening of the larynx during swallowing.

 

Trachea - the windpipe. Held open by rings of hyaline cartilage. Branches into the left and right bronchi at its caudal end. The bronchi enter the lungs.

	trachea histology
	sheep pluck 1
	sheep pluck 2

 

The lower respiratory tract is made up of the structures of the lungs. Each lung is roughly cone-shaped with its base lying against the diaphragm and its apex in the cranial part of the thorax.

Thorax Dog lateral ragiograph
Lungs, lateral view	Lungs, dorsal view	Lungs, ventral view

 

Bronchi enter each lung and branch into smaller air passageways.

Bronchioles are tiny air passageways that lead to alveolar ducts and alveoli.

Alveoli are tiny sacs surrounded by networks of elastic fibers and capillaries. They are like clusters of grapes and are the sites of gas exchange between the blood and the air.