The Respiratory System



The lungs of lunged amphibians are not much different from the air bladders of polypterids and lungfishes. They are simple membranous bags which grow from the laryngotracheal groove.

In many of the reptile species the lung is no longer membranous, but the wall of the bag-like lung is either spongy or modified with low septa to form a number of shallow pits. Some reptile species have accessory air sacs, membranous spaces which are connected to the lungs. In some species these accessory air spaces are inflated in order to make the animal appear larger, as when the animal is assuming a threatening posture. When the chuckwalla lizard feels threatened it will hide in tight rock crevices and then inflate its body to become securely wedged in place.

Mammal lungs consist of a network of branching passages leading to the alveolar ducts and alveoli. The numerous small ducts and alveoli give the lung its spongy appearance.

The respiratory system of birds has a complicated structure. There are several large accessory air sacs, and additional smaller air spaces that work in the process of lung ventilation. Air in the bird respiratory system passes through in two breath cycles. On the initial inhalation air is passed through straight ducts, the bronchi and mesobronchi, to posterior air sacs. The following exhalation moves this air into the parabronchi of the lungs. This is where gas exchange occurs in the bird lung. The parabronchi are small spongy walled tubules. Unlike other vertebrates with bag-like lungs, this one way passage of air through the lung keeps the lung free of residual, and less oxygen rich air. The second inhalation moves this air on into the anterior air sacs. The second exhalation then passes the air through the bronchi and out of the system.

















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