Agriculture Reference
In-Depth Information
The Cardiovascular and Respiratory Systems
As in the human cardiovascular system, the blood in poultry serves the primary purpose
of carrying oxygen to the cells and removing carbon dioxide. The blood also brings hor-
mones, antibodies, and nutrients to the tissues and removes waste products, conveying
them to the kidneys. Unlike the red blood cells of humans, poultry red blood cells con-
tain a nucleus. Poultry hearts beat at a much higher rate than the human average of 60 to
68 beats per minute; the birds' rates average between 280 and 340 beats per minute.
Respiration is different in poultry as, along with lungs, birds have
air sacs
and hollow
bones. The avian lung is a rigid system of blood capillaries and air in close contact. The
lung does not expand as it does in mammals; it is more like a flow-through system with
a small capacity that does not expand to accept the tidal gas volume. The air sacs func-
tion similarly to bellows. They are divided into pairs: one in the abdomen, one in the
cervical
(neck) area, and two pairs in the thorax. Additionally, there is one interclavicu-
lar air sac.
Poultry do not possess a
diaphragm,
the muscular membrane in humans that con-
tracts and relaxes to move air. In birds, breathing occurs when the abdominal muscles
relax, the inspiratory muscles contract, and the body cavity expands. This creates neg-
ative pressure in the air sacs throughout the body, drawing air through the lungs and
over tiny honeycombed passageways called
parabronchi
. Upon expiration, the expirat-
ory muscles contract and force air back over the lungs and out the mouth and nostrils.
THE RESPIRATORY SYSTEM
The connection of the air sacs, lungs, and hollow bones give the bird the advantage of
an almost constant supply of air during movement and flight.
