RESPIRATORY SYSTEM
The respiratory system is the system of organs in the body responsible for the intake of oxygen and expiration
of carbon dioxide. Oxygen is a vital requirement of animals. An animal may survive for days without water or
for weeks without food, but life without oxygen is measured in minutes. Delivering oxygen and removing
carbon dioxide (the product of cellular respiration) are the two major functions of the respiratory system. The
processes involved with these functions related to gases include ventilation (movement of air in and out of the
lungs), gas exchange between air and blood in the lungs, gas transport in blood, and gas exchange between
blood and cells at the level of the tissues.
Secondary functions of the respiratory system include assistance in the regulation of the pH of the body fluids,
assistance in temperature control, Olfaction and phonation (voice production caused by movement of air
across the vocal folds, caused them to vibrate). The role of the respiratory system in the regulation of the pH
of blood and other body fluids is closely associated with the ability of the respiratory system to remove carbon
dioxide. If carbon dioxide accumulates in the blood because the respiratory system cannot remove it, blood
pH falls; this is respiratory acidosis. Blood pH rises if the respiratory system removes more carbon dioxide
than is appropriate and blood levels of carbon dioxide are lower than normal; this is respiratory alkalosis.
ELEMENTS OF THE RESPIRATORY SYSTEM
The respiratory system consists essentially of the lungs and the passages that conduct air into and out of the
lungs. These passages include the nostrils, nasal cavity, nasopharynx, larynx, trachea, and bronchi and lungs.
Respiratory organs, which are located within the head (nose, paranasal sinuses, nasopharynx) are termed the
"upper respiratory tract", whereas the "lower respiratory tract" consists of the larynx, the trachea and the
lungs.
Sites of gaseous exchange within the lungs are:
⚫ Respiratory bronchioli (bronchioli respiratorii),
⚫ Alveolar ducts (ductus alveolares)
⚫ Alveolar sacs (sacculi alveolares)
⚫ Alveoli (alveoli pulmonis)
Nose
External opening is known as the nostril also referred to as the nares. Outer walls are made of nasal cartilage
which are variable in form, size and number depending on the species, and are largely dictated by the nasal
cartilages that form this most rostral end of the respiratory tract. Lateral wall referred to as nasal alae (wing).
External groove between the nares is referred to as nasal philtrum and flat area between nostrils is the nasal
planum. In addition to these hyaline cartilages, the pig also possesses a rostral bone in the tip of its flat,
disklike nose. This is presumably an adaptation to the rooting habits of the pig.
The lateral dorsal cartilage determine the form of the opening of the nostril. Depending on the species several
accessory nasal cartilages may arise from the lateral nasal cartilages. The alar cartilages account for the
characteristic comma shape, which divides the nostril into the ventral, so-called true nostril leading to the nasal
cavity, and the dorsal or false nostril leading to a skin-lined diverticulum (diverticulum nasi) occupying the
UILDVA/ESK/VAN215/2024_2025 Lecture Notes Page 1
, naso-incisive notch (incisura nasoincisiva). Therefore, it is essential when passing a nasogastric tube to guide it
ventrally.
Boundaries of the nose are the nasal
bones dorsally, the maxillae laterally
and the palatine processes of the
incisive bones, the maxillae and the
palatine bones ventrally. Caudally it is
limited by the cribriform plate of the
ethmoid bone. Ventrally it is
continuous with the nasopharynx.
The lateral aspect of the nose is
covered with typical hairy skin, which
contains both sebaceous and sweat
glands. The hairless region of the
most rostral parts of the nose in
species other than the horse contains
no sebaceous glands but does have
numerous sweat glands, which keep
the region around the nostrils moist.
This area is the planum nasale in the sheep and goat, planum rostrale in the pig, and planum nasolabiale in the
cow. The grooves and bumps in the plana are distinctive enough to allow nose prints to be used for positive
individual identification.
The equine nose lacks a planum, being instead covered with short, fine hairs. The lateral wall of the external
naris is flexible, allowing for an enormous range of diameters. During exertion, the lateral wall is dilated,
creating a wider, lower-resistance passageway for the movement of air. In this, the nostril is aided by the
presence of a short blind-ended diverticulum lateral to the true nasal cavity. This “false nostril” (nasal
diverticulum) is probably a construct that aids in passive dilation of the nostrils during vigorous ventilation.
The nasal cavity is separated from the mouth
by the hard and soft palates and separated into
two isolated halves by a median nasal septum.
The rostral part of the septum is cartilaginous,
whereas the most caudal part is created in part
by a plate of bone. Each half of the nasal cavity
communicates with the nostril of the same side
rostrally and with the pharynx caudally by way
of the choanae (caudal nares).
The nasal cavity is lined with mucous
membrane that covers a number of scroll-like
conchae (turbinate bones) arising from the
UILDVA/ESK/VAN215/2024_2025 Lecture Notes Page 2
The respiratory system is the system of organs in the body responsible for the intake of oxygen and expiration
of carbon dioxide. Oxygen is a vital requirement of animals. An animal may survive for days without water or
for weeks without food, but life without oxygen is measured in minutes. Delivering oxygen and removing
carbon dioxide (the product of cellular respiration) are the two major functions of the respiratory system. The
processes involved with these functions related to gases include ventilation (movement of air in and out of the
lungs), gas exchange between air and blood in the lungs, gas transport in blood, and gas exchange between
blood and cells at the level of the tissues.
Secondary functions of the respiratory system include assistance in the regulation of the pH of the body fluids,
assistance in temperature control, Olfaction and phonation (voice production caused by movement of air
across the vocal folds, caused them to vibrate). The role of the respiratory system in the regulation of the pH
of blood and other body fluids is closely associated with the ability of the respiratory system to remove carbon
dioxide. If carbon dioxide accumulates in the blood because the respiratory system cannot remove it, blood
pH falls; this is respiratory acidosis. Blood pH rises if the respiratory system removes more carbon dioxide
than is appropriate and blood levels of carbon dioxide are lower than normal; this is respiratory alkalosis.
ELEMENTS OF THE RESPIRATORY SYSTEM
The respiratory system consists essentially of the lungs and the passages that conduct air into and out of the
lungs. These passages include the nostrils, nasal cavity, nasopharynx, larynx, trachea, and bronchi and lungs.
Respiratory organs, which are located within the head (nose, paranasal sinuses, nasopharynx) are termed the
"upper respiratory tract", whereas the "lower respiratory tract" consists of the larynx, the trachea and the
lungs.
Sites of gaseous exchange within the lungs are:
⚫ Respiratory bronchioli (bronchioli respiratorii),
⚫ Alveolar ducts (ductus alveolares)
⚫ Alveolar sacs (sacculi alveolares)
⚫ Alveoli (alveoli pulmonis)
Nose
External opening is known as the nostril also referred to as the nares. Outer walls are made of nasal cartilage
which are variable in form, size and number depending on the species, and are largely dictated by the nasal
cartilages that form this most rostral end of the respiratory tract. Lateral wall referred to as nasal alae (wing).
External groove between the nares is referred to as nasal philtrum and flat area between nostrils is the nasal
planum. In addition to these hyaline cartilages, the pig also possesses a rostral bone in the tip of its flat,
disklike nose. This is presumably an adaptation to the rooting habits of the pig.
The lateral dorsal cartilage determine the form of the opening of the nostril. Depending on the species several
accessory nasal cartilages may arise from the lateral nasal cartilages. The alar cartilages account for the
characteristic comma shape, which divides the nostril into the ventral, so-called true nostril leading to the nasal
cavity, and the dorsal or false nostril leading to a skin-lined diverticulum (diverticulum nasi) occupying the
UILDVA/ESK/VAN215/2024_2025 Lecture Notes Page 1
, naso-incisive notch (incisura nasoincisiva). Therefore, it is essential when passing a nasogastric tube to guide it
ventrally.
Boundaries of the nose are the nasal
bones dorsally, the maxillae laterally
and the palatine processes of the
incisive bones, the maxillae and the
palatine bones ventrally. Caudally it is
limited by the cribriform plate of the
ethmoid bone. Ventrally it is
continuous with the nasopharynx.
The lateral aspect of the nose is
covered with typical hairy skin, which
contains both sebaceous and sweat
glands. The hairless region of the
most rostral parts of the nose in
species other than the horse contains
no sebaceous glands but does have
numerous sweat glands, which keep
the region around the nostrils moist.
This area is the planum nasale in the sheep and goat, planum rostrale in the pig, and planum nasolabiale in the
cow. The grooves and bumps in the plana are distinctive enough to allow nose prints to be used for positive
individual identification.
The equine nose lacks a planum, being instead covered with short, fine hairs. The lateral wall of the external
naris is flexible, allowing for an enormous range of diameters. During exertion, the lateral wall is dilated,
creating a wider, lower-resistance passageway for the movement of air. In this, the nostril is aided by the
presence of a short blind-ended diverticulum lateral to the true nasal cavity. This “false nostril” (nasal
diverticulum) is probably a construct that aids in passive dilation of the nostrils during vigorous ventilation.
The nasal cavity is separated from the mouth
by the hard and soft palates and separated into
two isolated halves by a median nasal septum.
The rostral part of the septum is cartilaginous,
whereas the most caudal part is created in part
by a plate of bone. Each half of the nasal cavity
communicates with the nostril of the same side
rostrally and with the pharynx caudally by way
of the choanae (caudal nares).
The nasal cavity is lined with mucous
membrane that covers a number of scroll-like
conchae (turbinate bones) arising from the
UILDVA/ESK/VAN215/2024_2025 Lecture Notes Page 2
