Changes

*One '''Primary Bronchi''' from the [[Trachea - Anatomy & Physiology|trachea]] enters each lung, narrowing as it travels through, and communicates with the '''Abdominal Air Sac'''. This bronchi gives off branches as it travels through the lung, known as '''Secondary Bronchi'''. Each of these gives off a further 400-500 '''Parabronchi''' in the walls of which, [[Gas Exchange - Anatomy & Physiology|gaseous exchange]] takes place.

*One '''Primary Bronchi''' from the [[Trachea - Anatomy & Physiology|trachea]] enters each lung, narrowing as it travels through, and communicates with the '''Abdominal Air Sac'''. This bronchi gives off branches as it travels through the lung, known as '''Secondary Bronchi'''. Each of these gives off a further 400-500 '''Parabronchi''' in the walls of which, [[Gas Exchange - Anatomy & Physiology|gaseous exchange]] takes place.

*Avian Gas exchange takes place not in alveoli, as in mammals, but within '''Air Capillaries''' which are extensions of the parabronchial lumen. They are an interconnecting network of loops, and closely intertwine with Blood Capillaries.

*Avian Gas exchange takes place not in alveoli, as in mammals, but within '''Air Capillaries''' which are extensions of the parabronchial lumen. They are an interconnecting network of loops, and closely intertwine with Blood Capillaries.

*The Air Capillaries and Blood Capillaries are arranged so that flow is ''crosscurrent''. This makes the gaseous exchange which occurs from one to the other extremely efficient.

*The Air Capillaries and Blood Capillaries are arranged so that flow is ''crosscurrent''. This makes the [[Gas Exchange - Anatomy & Physiology|gaseous exchange]] which occurs from one to the other extremely efficient.

==Links==

==Links==