Respiratory system of the horse
Encyclopedia
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
, the respiratory system of the horse is the means by which a horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
circulates air around its internal organs.
Anatomy
The respiratory system begins with the nares, commonly known as the nostrils, which can expand greatly during intense exercise. The nostrils have an outer ring made of cartilage (the alar cartilageGreater alar cartilage
The greater alar cartilage is a thin, flexible plate, situated immediately below the lateral nasal cartilage, and bent upon itself in such a manner as to form the medial wall and lateral wall of the naris of its own side....
), which serves to hold them open during inhalation
Inhalation
Inhalation is the movement of air from the external environment, through the air ways, and into the alveoli....
. Additionally, a small pocket within them, called the nasal diverticulum, filters debris with the help of the hairs lining the inner nostril. The nasal cavity contains the nasolacrimal duct
Nasolacrimal duct
The nasolacrimal duct carries tears from the lacrimal sac into the nasal cavity. Excess tears flow through nasolacrimal duct which drains into the inferior nasal meatus...
, which drains tears from the eyes and out the nose.
The nasal passages contain two conchae
Turbinate
In anatomy, a nasal concha is a long, narrow and curled bone shelf that protrudes into the breathing passage of the nose...
on either side, which help to increase the surface area to which the air is exposed. Additionally, the sinuses within the skull are able to drain through the nasal passage. The nasal passage join to the larynx
Larynx
The larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...
via the pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
. The pharynx is about 15 cm long in an adult, and includes the naspharynx, which protect the entrance to the auditory tubes, the oropharynx, which contains tonsillar tissue, and the laryngopharynx.
- Frontal sinusFrontal sinusSinuses are mucosa-lined airspaces within the bones of the face and skull. The frontal sinuses, situated behind the superciliary arches, are absent at birth, but are generally fairly well developed between the seventh and eighth years, only reaching their full size after puberty...
es: Occupy the dorsal (top) part of the skull, between the eyes. There are two, one on each side, divided by a bony septum. These communicates with the inside of the conchae, forming the concho-frontal sinuses. Drainage into the nasal passages is via the caudal maxillary sinus. - Maxillary sinusMaxillary sinusThe pyramid shaped maxillary sinus is the largest of the paranasal sinuses, and drains into the nose. It is present at birth as rudimentary air cells, and develops throughout childhood.-General characteristics:...
es: Within the maxilla, above the tooth rootsHorse teethHorses' teeth are often used to estimate the animal's age, hence the sayings "long in the tooth", "straight from the horse's mouth" and "Don't look a gift horse in the mouth".- Types of teeth :At five years of age a horse has between 36 and 44 teeth...
. Each is divided into two components, the Rostral maxillary sinus in front and the Caudal maxillary sinus behind. They do not communicate. In addition, each of these is subdivided into a medial (inside) and lateral (outside) component, by an incomplete bone wall that carries the infraorbital canalInfraorbital canalNot to be confused with the infraorbital groove and infraorbital foramen, which are on opposite ends of the canal.One of the canals of the orbital surface of the maxilla, the infraorbital canal, opens just below the margin of the orbit...
containing nerves and blood vessels. The close proximity to the tooth roots mean that as the teeth erupt with age, the maxillary sinuses become larger. - Sphenopalatine sinuses: Small pouches medial (inside) to the Caudal maxillary sinus.
Pant
Pant may refer to:* Pants, an article of clothing* To breathe quickly, spasmodically, or in a labored manner** Panting is used by many furry animals as a means of thermoregulation* Pant , a North Indian and Nepalese surnamePlaces...
as a method of thermoregulation
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
.
The genus Equus
Equus (genus)
Equus is a genus of animals in the family Equidae that includes horses, donkeys, and zebras. Within Equidae, Equus is the only extant genus. Like Equidae more broadly, Equus has numerous extinct species known only from fossils. This article deals primarily with the extant species.The term equine...
has a unique part of the respiratory system called the guttural pouch
Guttural pouch
In the equids and some rodent-like species such as the desert hyrax, the guttural pouch is a pair of air chambers in the neck just behind the skull and below the ears...
, which is thought to equalize air pressure on the tympanic membrane. These (left and right, separated by a narrow septum) is located in "Vyborg's triangle", between the mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
s but below the occiput
Occiput
The occiput is the anatomical term for the posterior portion of the head, in insects the posterior part of those head capsule.-Clinical significance:Trauma to the occiput can cause a basilar skull fracture....
. With a capacity of 300 to 500 ml, it fills with air when the horse swallows or exhales.
The larynx lies between the pharynx and the trachea
Vertebrate trachea
In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...
, and is made up of 5 pieces of cartilage which serve to open the glottis
Glottis
The glottis is defined as the combination of the vocal folds and the space in between the folds .-Function:...
. The larynx not only allows the horse to vocalize, but also prevents aspiration of food and helps to control the volume of air inhaled. The trachea is the tube which carries air from the oral cavity and into the lungs, and is about 75-80 cm in length in the adult. It is held permanently open by 50-60 "C"-shaped rings of cartilage, 5-6 cm in diameter .
At the bifurcation of the trachea, there are two bronchi, the right of which is slightly larger in size. The bronchi then branch into smaller bronchioles, which in turn branch off into smaller bronchioles until they reach the alveoli (which absorb oxygen from the air and releases the carbon dioxide waste). The bronchi and bronchioles are all held within the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s of the horse, which is located in the animal's thoracic cavity. The lung is made up of a spongy, but very stretchy, material which has 2 lobes on the right and left side (a smaller, apical lobe and a large, caudal lobe) in addition to the accessory lobe. Blood is carried into the lungs via the pulmonary artery, where it is oxygenated at the alveoli and then returned to the heart by the pulmonary veins.
The lungs are expanded with the help of the diaphragm, a muscular sheet of tissue which contracts away from the thoracic cavity, thereby decreasing the pressure and pulling air into the lungs. When fully expanded, the lungs can reach to the 16th rib of the horse.
Respiration rate of the horse
Although respiration rates vary widely between individual horses, the average resting rate of respiration usually falls between 8-12 breaths per minute Heat and humidity can raise the respiration rate considerably, especially if the horse has a dark coat and is in the sun. The respiration will often change if the horse becomes excited or distressed, and can therefore be useful in determining the health of the animal.At the gallop, the horse breathes in rhythm with every stride: as the abdominal muscles pull the hind legs forward in the "suspension phase" of the gallop, the organs within the abdominal cavity are pushed backward from the diaphragm, thereby bringing air into the lungs and causing the horse to inhale. As the neck is lowered during the extended phase of the gallop, the hind legs move backward and the gut contents shift forwards, pushing into the diaphragm and forcing air out of the lungs.
Ability to smell
The horse's olefactory receptors are located in the mucosa of the upper nasal cavity. Due to the length of the nasal cavity, there is a large area of these receptors, and the horse has a better ability to smell than a human. Additionally, the horse also has a vomeronasal organVomeronasal organ
The vomeronasal organ , or Jacobson's organ, is an auxiliary olfactory sense organ that is found in many animals. It was discovered by Frederik Ruysch and later by Ludwig Jacobson in 1813....
, or Jacobson's Organ, which is in the hard palate, and is able to pick up pheromones and other scents when a horse exhibits the flehmen response
Flehmen response
The flehmen response , also called the flehmen position, flehmen reaction, flehming, or flehmening , is a particular type of curling of the upper lip in ungulates, felids, and many other mammals, which facilitates the transfer of pheromones and other scents into the vomeronasal organ, also called the...
. The flehmen response forces air through slits in the nasal cavity and into the vomeronasal organ. Unlike many other animals, the horse's Jacobson's Organ doesn't open into the oral cavity .
Respiratory diseases
- InfluenzaHorse fluEquine influenza is the disease caused by strains of Influenza A that are enzootic in horse species. Equine influenza occurs globally, and is caused by two main strains of virus: equine-1 and equine-2...
- Left Recurrent Laryngeal Hemiplegia ("Roaring")
- Recurrent airway obstructionRecurrent Airway ObstructionRecurrent airway obstruction, also known as broken wind, heaves, or sometimes by the term usually used for humans , is a respiratory disease in horses...
("Heaves"), akin to COPDChronic obstructive pulmonary diseaseChronic obstructive pulmonary disease , also known as chronic obstructive lung disease , chronic obstructive airway disease , chronic airflow limitation and chronic obstructive respiratory disease , is the co-occurrence of chronic bronchitis and emphysema, a pair of commonly co-existing diseases...
or emphysemaEmphysemaEmphysema is a long-term, progressive disease of the lungs that primarily causes shortness of breath. In people with emphysema, the tissues necessary to support the physical shape and function of the lungs are destroyed. It is included in a group of diseases called chronic obstructive pulmonary...
in humans. - StranglesStranglesStrangles is a contagious upper respiratory tract infection of horses and other equines caused by a bacterium, Streptococcus equi var equi...
(Streptococcus Equi infection) - RhinopneumonitisEquine herpesvirus 4Equine herpesvirus 4 is a virus of the family Herpesviridae that cause rhinopneumonitis in horses. It is the most important viral cause of respiratory infection in foals. Like other herpes viruses, EHV-4 causes a lifelong latent infection in affected animals. These horses are usually the source...
- Exercise Induced Pulmonary HemorrhageExercise Induced Pulmonary HemorrhageExercise induced pulmonary hemorrhage , also known as "bleeding" or a "bleeding attack", refers to the presence of blood in the airways of the lung in association with exercise. EIPH is common in horses undertaking intense exercise, but it has also been reported in human athletes, racing camels and...
- Equine nasal cystsEquine nasal cystsEquine nasal cysts are epithelium lined, single or loculated cavities filled with fluid or pus. They normally form in the ventral concha, maxillary sinuses, and can extend down the nasal passages into the frontal sinuses....
- Ethmoid HematomaEthmoid hematomaEthmoid hematoma is a progressive and locally destructive disease of horses. It is indicated by a mass in the paranasal sinuses, that resembles a tumor but is not neoplastic by any means. The origins and causes of the ethmoid hematoma are generally unknown...
- Nasal polyps
- Bacterial Sinusitis (EmpyemaEmpyemaPleural empyema is an accumulation of pus in the pleural cavity. Most pleural empyemas arise from an infection within the lung , often associated with parapneumonic effusions. There are three stages: exudative, fibrinopurulent and organizing. In the exudative stage, the pus accumulates...
) - Bacterial Pleuropnemonia
- Dorsal Displacement of the Soft Palate
- SilicosisSilicosisSilicosis, also known as Potter's rot, is a form of occupational lung disease caused by inhalation of crystalline silica dust, and is marked by inflammation and scarring in forms of nodular lesions in the upper lobes of the lungs...