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Dr. Hirabe

The main functions of the respiratory system are
the exchange of oxygen and carbon-dioxide
between
the
blood
or
body
tissue
and
Environmental air.

As such to the satisfactorily discharge this
function, respiratory system depends on the work
of the heart.

STRUCTURE AND FUNCTION

Respiratory
system
divides
into
conducting,
transitional, and gas exchange systems:

The conducting system includes nasal cavity. paranasal
sinuses, pharynx, larynx, trachea, and extrapulmonary
and intrapulmonary bronchi, all of which are largely
lined by pseudostratilled, ciliated columnar cells plus a
variable proportion of secretory goblet (mucous) and
serous cells

The transitional system of the respiratory tract is composed of
bronchioles, which serve as a transition zone between the conducting
system (ciliated) and the gas exchange (alveolar) system

The gas exchange system of the respiratory tract in all mammals is
formed by alveolar ducts and millions of alveoli.

Alveoli are superficially lined by two distinct types of epithelial cells
known as type I pneumonocytes (membranous) and type II
pneumonocytes (granular)

All three-the conducting, transitional and
exchange systems of the respiratory system-
are vulnerable to injury because of constant
exposure to a myriad of microbes, particles
and fibers, and toxic gases and vapors present
in the air.




Vulnerability of the respiratory system to aerogenous
(airbome) injury is primarily because of
1) The extensive area of the alveoli, which are the
interface between the respiratory system and inspired
air
(2) The large volume of air passing continuously into
the lungs; and
(3) The high concentration of noxious elements that can
be present in the air
Common Pathogens, Allergens, and Toxic Substances Present in
Inhaled Air
Microbes
Viruses, Chlamydophila ,bacteria, fungi, protozoa
Plant dust
Grain, flour, cotton, wood
Animal
feathers, mites, insect chitin
products
Ammonia
Toxic gases
nitrogen
(NH3),
hydrogen
dioxide
sulfide
(NO2),
dioxide (S02), chlorine
Chemicals
Organic and inorganic solvents, herbicides, lead
(H2S),
sulfur
Main Defense Mechanisms of the Respiratory System
Conducting system (nose, trachea
and bronchi)
Mucociliary clearance, antibodies,
lysozyme, mucus
Clara cells, antioxidants, lysozyme,
Transitional system (bronchioles)
antibodies
Alveolar
macrophages
(inhaled
pathogens),intravascular
Exchange system (alveoli)
macrophages
(circulating
pathogens), opsonizing antibodies,
surfactant, antioxidants
Portals of Entry into the Respiratory System
Aerogenous(air)
Virus,
bacteria,
fungi,
toxic
Chlamydophila,
gases,
and
and
pneumotoxicants
Hematogenous (blood)
Virus, bacteria, fungi, parasites,
toxins, and pneumotoxicants
Direct extension
Penetrating
awns,
wounds,
bites,
and
esophagus or perforate
migrating
ruptured
Pathology of respiratory system can be divided:
1.Upper
respiratory system
2.Lower
respiratory system

In general diseases of respiratory system are
often accompanied by some abnormalities of
the nasal cavity of the upper respiratory
systems.

The abnormality of the upper respiratory tract
may be congenital or acquired.

Congenital localized anomalies of the nasal cavity
in domestic animals are often merely part of a
more deformity or component of generalized
malformation.

Common Congenital and acquired anomalies
involving the nasal cavity and sinuses includes
the following:
Cleft palate or palatoschisis is a fairly
common congenital effect seen in the new –
born or neonatal animals.
 In this condition there is an abnormal
connection between the nasal cavity and the
mouth and hence milk passes in to the lungs.
 So the animal does not survive long dying of
pneumonia and starvation.


1.
Nose
congestion:
Occurs
when
ever
animals are exposed to cold air. The blood
vessels in the nasal passage dilate so that the
air breathed in may be sufficient warmed.
Secondary
bacterial
infection
inflammation and edema.
may
result

2. Epistaxis: Is a hemorrhage from the nasal cavity.
Unlike blood in the digestive tract, where approximate
anatomic location of the bleeding can be estimated by
the color the blood imparts to fecal materials, blood in
the respiratory tract always is red.

This fact is due to the rapid transport out of the
respiratory tract by the mucociliary blanket.
Causes of Epistaxis can be:
1.
2.
Trauma
2. Convulsive expiration
3.
3. Parasites –Oestrus ovis in sheep.
4.
4. Erosion of the vessels by pathological processes in
the nasal cavities –Neoplasm.
5.
5. during certain infectious diseases example: Anthrax,
infectious bovine rhino-tracheitis, malignant catarrhal
fever, septic Metritis.
3. Hemoptysis is the coughing up of blood,
Causes:
 Rupture of pulmonary aneurysms (Sac formed
by localized dilatation of the of an artery, vein)
in the lungs of cattle with chronic lung
abscesses.
 From polyps
 Neoplasm and
 Trauma.



4. Mucocele is referred the accumulation of
seromucinous or mucus secretions in sinuses
5. Empyema is the accumulation of purulent
exudates of the sinuses.
Remember, Suppurative infection of the sinuses is of
more significance than those in the nose because of
the close relationship of these structures to the cranial
vault.


6. Tumors in the nasal cavity the one interesting Tumor
is the Adencarcinoma Horses and cattle are affected.
The tumor are highly malignant and destructive and
metastasis rapidly.
7. Nasal polyps: Nasal polyps are inflammatory new
growths which resemble true Neoplasm. They represent
focal accumulations of edematous fluid accompanied
by hyperplasia of submucosal connective tissue and
inflammatory cells (neutrophils, lymphocytes, plasma
cells). Older polyps may contain considerable fibrous
connective tissue. .



In addition the functional efficiency of the respiratory
system depends on its ability to oxygenate and to
remove carbon-dioxide from the blood as it passes
through in the respiratory circulation.
Interference with functions can occur in a number of
ways, but the underlying defecting in all instances is
lack of adequate oxygen supply to tissues.
The anoxia (or more correctly hypoxia) of respiratory
insufficiency is responsible for most pathological signs
of the respiratory diseases and for respiratory failure,
the terminal event of fatal cases.



Thus understanding anoxia and respiratory problem and
disorders is essential to the study of the pathological
changes of the upper respiratory systems.
Hypoxia (lowered oxygenation, often termed anoxia)
and can be in general resulted or caused from the
following.
General causes of anoxia: The general causes of Anoxia
are 4 factors that are presented as below:




1) Reduced oxygen - The oxygen carrying capacity
of the blood as example of anemic anoxia, caused by
carbon monoxide or nitrite poisoning, or true
anemia.
The anemic anoxia occurs when there is a deficiency
of hemoglobin in the blood and the oxygen carrying
capacity of the blood is reduced.
Mechanism of development of anemic Anoxia :
In poisoning caused by nitrite, the hemoglobin is
converted to methemoglobin and that due to carbon
monoxide, when the hemoglobin is converted to
carboxyhemoglobin there is anemic anoxia.


2) Reduced blood follow: As example of stagnant
anoxia caused or resulted by congestion heart failure
or shock.
Stagnant anoxia
is the state in which the rate
follow of blood through the capillaries is reduced and
/or the rate of oxygen change is reduced, resulting a
relative anoxia of tissues (stagnant anoxia the basic
defect caused
by
congestive heart failure ,
peripheral circulatory failure and local venous
obstructions.

Laryngeal and tracheal Hemorrhages :
Laryngeal and tracheal hemorrhages may
occur as a result of infection, trauma, violent
coughing, etc. Laryngeal hemorrhages occur in
many septicemic diseases (salmonellosis, etc.).
In the trachea, agonal hemorrhages are often
times associated with severe dyspnea and
hypoxia. Such hemorrhages are produced by
small extravasations in the submucosal lymph
follicles and tend to spread in a linear fashion.
3) Insufficient alveolar ventilation or
diffusion impairment (anoxic anoxia,
example as pneumonia, pulmonary edema,
Pneumothorax and paralysis of respiratory
muscles).
 Anoxia anoxia may occur or is when the
oxygen tension in the inspired air is too low
to oxygenate the pulmonary blood efficiency.


Anoxia anoxia is also the basic defects of the heart
failure and large blood vessels when mixing of arterial
and venous blood occurs through shunts of between the
two circulations.

Anoxia anoxia occurs also when there is paralysis of
the respiratory muscles in tick paralysis, botulism,
tetanus and strychnine poisoning


Cause of anoxic anoxia: The common causes in animal
diseases are lesions or dysfunctions of the respiratory tract
which reduce the supply of alveolar air that includes:
 Abnormalities of the alveolar epithelium such as
occur in pneumonia,
 Decreased vital capacity as it occurs in atelectasis,
pneumonia, Pneumothorax
 Pulmonary edema and congestion
 Decreased movements of the chest due to pain of
the chest wall all reduce the oxygen tension of the
blood leaving the lungs
4) Inability of tissues to use oxygen


Edema of the larynx is usually inflammatory and part
of the picture of acute respiratory infection. Also,
laryngeal edema may be associated (caused) with
allergic reactions, inhalation of irritants, insertion of
tracheal tubes, etc.
In the tracheal lumen, foamy fluid is commonly
observed. Such foamy fluid is associated with severe
pulmonary edema. The foams are actually formed in
the alveoli.



Inflammation of the nasal mucosa is called rhinitis
and that of sinuses, larynx, and trachea is called
respectively sinusitis, laryngitis and tracheitis.
Rhinitis and sinusitis are conditions usually occur
together, although mild sinusitis can be undetected:
Rhinitis: The occurrence of infectious rhinitis
presupposes an upset in the balance of the normal
microbial flora of the nasal cavity.
Innocuous bacteria are present normally, protecting
the host through a process called competitive
exclusion; where by the number of potential
pathogens are kept at harmless numbers.

Causes of Rhinitis:

The cause of rhinitis are either primary or secondary
and are the result of direct action of inflammatory
agents, whether infective or non-infective acting on
normal nasal mucosa.

Causes of non-infective primary inflammation
(Rhinitis) include:
Inhaled irritant (dusts, smoke, foreign bodies,
pollen and gases).
Local trauma.
Stress or prolonged antibacterial therapy.
Environment change and
Parasites.
Causes of infective rhinitis may be caused by
great variety of: Bacteria, virus and protozoa.
•Rhinitis as a part of a general infection localizing in the upper air
passages occur in cattle such as
Pasteurellosis, Ma1ignant
catarrhal fever, infectious bovine rhinotracheitis and calf diphtheria
in cattle.
•Based on the nature of exudates, rhinitis can be classified in to:
Serious, catarrhal, purulent, and fibrous.
•Rhinitis is also classified according to the course and age of
lesions as: Acute, sub acute and chronic and as to severity of the
insult as mild, moderate or severe.

Serous rhinitis: is the mildest form of inflammation and

Grossly is characterized by: Hyperemia and increased production of clear fluid locally
produced by serous glands present in the sub-mucosa.

Catarrhal rhinitis

Catarrhal rhinitis is a slightly more severe process and has in addition to serous secretions, in
substantial increase in mucus production by increased activity of goblet cells and mucus
glands.

Grossly: Mucus exudates are a thick, translucent or slightly turbid viscous fluid, sometimes
containing a few leukocytes and cellular debris.

In chronic cases catarrhal rhinitis is characterized microscopically by marked hyperplasia of
goblet cells. As inflammation becomes more severe, the mucus is in filtered with neutrophils
that have a cloudy appearance. This exudate is referred to as muco- purulent.

Purulent rhinitis (Suppurative): This inflammation is characterized
by a neutrophilic exudates (especially neutrophils, which mix with
nasal secretions including mucus) occurs when the nasal mucosa
suffers a more severe injury that generally is accompanied by mucosa
necrosis.

Grossly the exudates in Suppurative rhinitis is thick and opaque , but
can vary from white to green to brown, depending on to the types of
bacteria and type of leukocytes present in the exudates. In severe cases
the nasal passage are completely blocked by the exudates.

Pseudomembrane.

If these Fibrinous exudates can be removed, leaving an intact underling mucosa it is
termed as a croupous or pseudodipthereitic rhinitis.

Conversely if removal of this Pesudomembrane leaves an ulcerated mucosa, it is
referred to as diphtheritic or fibrin necrotic rhinitis .The term diphtheritic was derived
from human diphtheria, which causes a severe and destructive inflammatory process of
the respiratory mucosa.

Chronic granulomatous rhinitis is characterized by the presence of fibrous connective
tissue scarring; the epithelium becomes atrophic, foci of squamous metaplasia may
develop and there is progressive atrophy of the mucous secreting glands.

Sinusitis Inflammation of the paranasal sinuses and is frequently
combined with rhinitis Almost invariably, rhinitis precedes and
leads to infections and inflammations of the paranasal sinuses by
obstructing the drainage orifices of the sinuses.

Sinusitis is common in sheep as a response to the larvae of
Oestrus ovis. Also, it follows penetration of infect ion in
dehorning wounds (frontal sinusitis in cattle), periodontitis
(maxillary sinusitis in horses) and fractures.

Laryngitis is the inflammation of larynx.
Commonly a mild catarrhal
laryngitis is met with which may progress to chronic form if the cause persists.


Causes of laryngitis:
Usually an extension of infection from nasal cavity or pharynx in infectious
diseases Bacteria and viruses, influenza in horses’ infectious larynx-tracheitis.

Irritant vapour, chemical irritant.

Mechanical injury- kicks, bites, injury while passing probing or stomach tube.

Grossly the lesion is a swelling of the mucous membranes of larynx and
trachea, which is hemorrhagic and dry at first, later becoming coated with
mucoid exudates that may turn mucopurulant.

Laryngitis and tracheitis : Inflammation is the most
common and important disorder affecting the larynx
and trachea. Because of their location, these structures
frequently become inflamed as a part of inflammatory
diseases of either the upper or lower parts of the
respiratory tract. Thus, laryngitis and, to a lesser extent,
tracheitis is expected to accompany rhinitis.
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