Page 365 - Anatomy and Physiology of Farm Animals, 8th Edition

350 / Anatomy and Physiology of Farm Animals

xygen is a vital requirement of animals. respiratory tract (Fig. 19‐1). Their size and
shape, highly variable among domestic
OAn animal may survive for days with-
VetBooks.ir out water or for weeks without food, but farm animals, are largely dictated by the
life without oxygen is measured in minutes.
nasal cartilages that form this most ros-
Delivering oxygen and removing carbon tral end of the respiratory tract. In addition
dioxide (the product of cellular respira- to these hyaline cartilages, the pig also pos-
tion) are the two major functions of the sesses a rostral bone in the tip of its flat,
respiratory system. The processes involved disk‐like nose. This is presumably an adap-
with these functions related to gases tation to the rooting habits of the pig.
include ventilation (movement of air in The lateral aspect of the nose is covered
and out of the lungs), gas exchange between with typical hairy skin, which contains
air and blood in the lungs, gas transport in both sebaceous and sweat glands. The
blood, and gas exchange between blood hairless region of the most rostral parts of
and cells at the level of the tissues. the nose in species other than the horse
Secondary functions of the respiratory sys- contains no sebaceous glands but does
tem include assistance in the regulation of have numerous sweat glands, which help
the pH of the body fluids, assistance in keep the region around the nostrils moist.
temperature control, and phonation (voice This area is the planum nasale in the
production). sheep and goat, planum rostrale in the
The role of the respiratory system in the pig, and planum nasolabiale in the cow.
regulation of the pH of blood and other The grooves and bumps in the plana are
body fluids is closely associated with the distinctive enough to allow nose prints to
ability of the respiratory system to remove be used for positive individual identifica-
carbon dioxide (CO ). The changes in CO tion, much like human fingerprints.
2
2
and pH are closely linked because of the The equine nose lacks a planum, being
chemical reaction shown in the equation instead covered with short, fine hairs. The
below. The hydrogen ions (H ) generated lateral wall of the equine external naris is
+
by the combination of CO and water help flexible, allowing for an enormous range
2
determine the acidity (and therefore pH) of of diameters. During exertion, the lateral
blood. wall is dilated, creating a wider, lower‐
resistance passageway for the movement
2
HO CO 2 H HCO 3 of air. In this, the nostril is aided by the
presence of a short blind‐ended diverticu-
If carbon dioxide accumulates in the lum lateral to the true nasal cavity. This
blood because the respiratory system can- “false nostril” (nasal diverticulum) is
not remove it, blood pH falls; this is res- probably a construct that aids in passive
piratory acidosis. Blood pH rises if the dilation of the nostrils during vigorous
respiratory system removes more carbon ventilation.
dioxide than is appropriate and blood The nasal cavity is separated from the
levels of carbon dioxide are lower than mouth by the hard and soft palates and
normal; this is respiratory alkalosis. separated into two isolated halves by a
median nasal septum. The rostral part of
the septum is cartilaginous, whereas the
Upper Respiratory Tract most caudal part is created in part by a
plate of bone. Each half of the nasal cavity
Nose communicates with the nostril of the same
side rostrally and with the pharynx cau-
The nose of domestic animals comprises dally by way of bony openings, the choa-
the parts of the face rostral to the eyes and nae (caudal nares).
dorsal to the mouth. The external nares The nasal cavity is lined with mucous
(nostrils) are the external openings of the membrane that covers a number of