Page 542 - Anatomy and Physiology of Farm Animals, 8th Edition

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birds, only the left oviduct persists in
development, and this oviduct opens lateral
VetBooks.ir to the left ureter. Unlike for mammals, A3 A2 A1

oviduct refers to the entire tubular portion
of the female reproductive tract in birds. B
The last portion of the cloaca is the
proctodeum. The unpaired bursa of
Fabricius (cloacal bursa) opens into the A
dorsal aspect of the proctodeum. This
bursa (for which the B‐cells of the immune
system are named) is lined by lymphore-
ticular tissue and is largest in the juvenile
animal, gradually becoming smaller as the
bird ages. In Anseriformes, the proctodeum C
also houses the male copulatory organ.
Absorption of water and electrolytes in E D
the ceca, rectum, and coprodeum contrib-
ute to overall fluid and electrolyte balance.
As discussed in the “Urinary System” sec-
tion, birds have a limited ability to form
hypertonic urine, so conservation of water
and electrolytes may include absorption
from the relatively dilute urine after it
enters the gastrointestinal tract. Urine Figure 30-7. Schematic of one side of the avian
from the urodeum is moved through the respiratory system. The trachea (unlabeled) ends at
tract to the ceca by reverse peristalsis. the syrinx. The clavicular sac (A) has a lateral diver-
Water absorption appears to be secondary ticulum (A1), a subscapular diverticulum (A2), and
to the absorption of sodium, and sodium axillary diverticulum (A3). The primary bronchus
absorption is promoted by aldosterone. passes through the lung where it gives rise to
The anus of the bird is often referred to numerous secondary bronchi which are continuous
as the vent. It presents as a horizontally with the cervical (B), cranial thoracic (C), caudal
oriented slit on the exterior of the body. thoracic (D), and abdominal (E) air sacs.
opening into the nasal cavity. With such a
Respiratory System high intake of sodium chloride in their
diet, the nasal gland aids the kidney in
The avian respiratory system is dramati- osmoregulation by secreting a highly con-
cally different from the mammalian coun- centrated solution of sodium chloride. The
terpart in that the lungs are part of a avian nasal cavity is widely open to the oral
unidirectional circuit that includes a series cavity via the choanal cleft, but is other-
of nonrespiratory (that is, lacking gas wise not functionally different from the
exchange surfaces) air sacs (Fig. 30‐7), and mammalian nose. Epithelium‐lined nasal
airflow is created by movements of the ster- turbinates aid in warming and moistening
num rather than through contraction of a air entering the respiratory system, and
muscular diaphragm. The arrangement is an also function to conserve water by dehu-
especially efficient way of extracting oxy- midifying exhaled air. The oral end of the
gen from air, in keeping with the extreme trachea is guarded by the larynx, which in
respiratory demands created by flight. birds comprises only cricoid and arytenoid
In ducks and other marine birds feeding cartilages. The opening into the larynx is
in lakes with high salt content, a nasal or situated in a prominence caudal to the
salt gland can be found exterior to but tongue called the laryngeal mound. The