Respiratory System Study Guide

• A study guide on the Respiratory System.

Learning Objectives

• Identify the upper respiratory tract components, describing their structure and functions.
• Discuss the prevalent issues in animals affected by brachycephalic obstructive airway syndrome.
• Recognize the lower respiratory tract components, detailing their structure and functions.
• Explain the structure and function of the avian respiratory system.
• Describe the processes of inspiration and expiration.
• List the muscles utilized during inspiration and expiration.
• Define tidal volume, minute volume, and residual volume.
• Describe oxygen and carbon dioxide exchange between alveoli and blood.

Upper Respiratory Tract

• Includes the frontal sinus, nasal cavity, turbinates, hard palate, pharynx, tongue, soft palate, epiglottis, larynx, trachea, and esophagus.
• The guttural pouch's lining contains respiratory epithelium and is found in odd-toed mammals and bats.
• Parotid and mandibular salivary glands surround the guttural pouch.
• The Ramus of the mandible is rostral relative to the Viborg's Triangle
• The sternomandibularis muscle and linguofacial vein are important features of Viborg's Triangle.
• Being familiar with Viborg's Triangle is helpful to gain surgical access to the Guttural pouch.

Clinical Issues with Upper Respiratory Tract

• Bacteria and viruses are a frequent issue.
• Tumors and foreign bodies in the upper respiratory tract can cause clinical issues.
• Parasites and anatomy of the upper respiratory tract can also pose clinical issues.
• Rhinitis or rhinotracheitis can become clinical concerns.
• Chronic rhinitis in a rabbit caused by Pasteurella multocida.
• Nasal turbinate tumors can develop in dogs.
• Epistaxis is another clinical manifestation.

Brachycephalic Obstructive Airway Syndrome (BOAS)

• An elongated soft palate and stenotic nares (abnormally small nostrils) can cause BOAS.
• BOAS can also result in hvpoplastic trachea.
• Stenotic nares can require surgery to create wider nostrils.
• Enlarged alar folds that fall medially onto the nasal septum are observed in BOAS.
• Caudal aberrant turbinate tissues that protrude into the nasopharynx relate to BOAS.
• Oversized tongues which displace or obstruct the nasopharynx are seen in BOAS.
• Elongated and thickened soft palates can cause pharyngeal and nasopharyngeal obstructions.
• Hypoplastic larynx, everted laryngeal saccules, and collapse of the laryngeal cartilages contribute to the syndrome.

Larynx

• It is important to know the arytenoid cartilage/fold, vocal fold (cord), epiglottis, and glottis.
• Laryngeal paralysis can occur.
• Laryngeal paralysis can cause laryngeal folds.
• Intubation, particularly in cats, often includes lidocaine spray to prevent laryngeal spasms.

Trachea

• Includes the trachealis muscle, mucosa, cartilaginous ring, and adventitia and serosa.
• Tracheal collapse can occur leading to the need for a tracheoscopy.

Bronchial Tree (Lower Respiratory Tract)

• Includes the trachea, larynx, root of the right and left lung, primary and secondary bronchi, lung tissue, tracheal cartilages, and location of carina.
• Components of the Bronchial tree also include the left primary bronchus, root of the lung, visceral pleura, secondary and tertiary bronchi, smaller bronchi, and bronchioles.
• Alveoli sit in a pulmonary lobule.
• Bronchitis occurs in the lower airway
• Pneumonia is an alveolar disease.
• 1 alveolus is the singular form of 2 alveoli.

Pneumonia

• Specifically an alveolar disease.
• In foals, it typically stems from a bacteria spread through the blood stream.
• Bacterial pneumonia in a pig is frequently acquired through the air breathed in.

Feline Asthma

• Related to airway health.
• Use chambers and puffers to administer cat asthma medication.
• Aspiration pneumonia can occur if foreign material is breathed in.
• Giving oral liquid medications with care and ensuring the ability to swallow prior to endotracheal tube (ETT) removal are key to preventing aspiration pneumonia.
• Mammalian lungs typically have specific lobe arrangements.
• Domestic animals have 2 lobes typically on the left, and 4 on the right.
• Horses typically have 2 lobes on each side: left and right total.

Canine Lungs

• Organized into cranial and caudal lobes, accessory lobe, and middle lobe.

Avian Respiratory System

• Major differences include; presence of air sacs (5 cranial, 4 caudal) plus lungs, and a one-way airflow.
• Other components are the lung tissue (parabronchi), paranasal sinus, humoral diverticulum over the clavicular air sac, paratympanic sinus, trachea, cervical and clavicular air sacs, and anterior and posterior thoracic air sacs, and abdominal air sac.
• There is no soft palate.
• The Choana closes when swallowing.
• A bird lacks an epiglottis, and vocal cords.
• Possesses a Syrinx to compensate for the vocal cords.
• Tracheal cartilages are complete rings.
• Also, birds do not have a diaphragm.

Syrinx

• There is an enlargement of the trachea where it bifurcates.
• Vibration of the Syrinx’s walls produce sounds
• Each side vibrates independently to create 2 toned calls.

Inspiration & Expiration

• Inspiration is aka inhalation.
• During inspiration, the Diaphragm contracts going from dome to flat.
• The External intercostal muscles also contract lifting.
• Expiration is aka exhalation.
• During expiration, The Diaphragm relaxes.
• The internal intercostal muscles contract, rotating the ribs back and down.
• Additionally, abdominal muscles contract, if needed.

Control of Breathing

• The pons (part of brainstem) - provides centre point to control breathing rate.
• The medulla houses separate centers for insp, exp, and breath holding.
• Efferent messages are delivered by the subconscious to the respiratory muscles.
• Conscious mind can override breath control.

Mechanical Control

• Stretch receptors, Normal breathing pattern, and Preset points.

Chemical Control

• Homeostasis: Monitors CO2, pH, O2 in arterial blood.
• Chemoreceptors in the heart, medulla, carotid arteries and aorta monitor for breathing abnormalities.