Animal Anatomy II - The Respiratory System

Overview

• The respiratory system's primary function is to bring oxygen into the body and facilitate the exchange of oxygen and carbon dioxide between the atmosphere and the body cells.
• Ventilation, also known as breathing, involves the intake of fresh air.

Components of the Respiratory System

Upper Airways

• Includes external nares, nasal cavity, nasopharynx, oropharynx, laryngopharynx, and larynx.

Conducting Zone

• Composed of trachea, bronchi, bronchioles, and terminal bronchioles.

Respiratory Zone

• Includes bronchi, bronchioles, alveolar ducts, and alveoli.

Detailed Anatomy

The Larynx

• A protective cartilaginous structure surrounding the glottis.
• Made up of thyroid cartilage, cricoid cartilage, arytenoid cartilage, and epiglottis.
• Contains vestibular folds and vocal folds, which produce sound by vibrating air passing through the glottis.

The Trachea

• Extends from the larynx to the primary bronchi.
• Located ventral to the esophagus.
• Supported by incomplete C-shaped cartilages (except in birds).

The Bronchial Tree

• The trachea divides into two primary bronchi, each further branching into secondary and tertiary bronchi, terminal bronchioles, and respiratory bronchioles.
• Lined by pleura, a serous membrane, encompassing the lungs.

The Lung

• Elastic, air-filled organs with lobes; differences in lobation exist among species:
  • Canine: Right lung larger, divided into four lobes; left lung has two lobes.
  • Bovine: Right lung significantly larger, left divided into cranial and caudal lobes.
  • Equine: More equal in size, with minimal external lobation.
  • Camel: Each lung has a cranial and caudal lobe, with an accessory lobe on the right.
• The diaphragm aids in respiration by contracting to increase thoracic cavity volume during inspiration.

Avian Respiratory Tract

• Differences include:
  • No diaphragm.
  • Stiff lungs with continuous unidirectional airflow.
  • Air sacs acting as bellows to store air.
  • Syrinx located at trachea bifurcation for sound production.

Blood Supply and Pleura

• Blood supply carried by pulmonary arteries into the lungs, with capillaries surrounding alveoli for gas exchange.
• Oxygenated blood exits via pulmonary veins to the left atrium.
• Each lung is covered by visceral pleura, and the thoracic cavity lining is the parietal pleura, enclosing the pleural cavity.

Muscles and Diaphragm

• Intercostal muscles assist in breathing:
  • External: Run caudoventrally, responsible for inspiration.
  • Internal: Run caudodorsally, divided into interosseus and interchondral components.
• The diaphragm separates thoracic and abdominal cavities, with muscular and tendinous parts.
• Supplied by the phrenic nerve, contracts to facilitate inspiration.

Additional Structures

• Lymph Nodes: Various nodes located in the head and neck, with specific drainage routes.
• Cervical and Thoracic Thymus: Present in newborn calves, located in both cervical and thoracic regions.

Notable Anatomical Features

• Tracheal bronchus in pigs and ruminants.
• Extensive interlobular connective tissues in certain species.
• Cardiac notch and line of pleural reflection relevant to lung anatomy and procedures such as auscultation and surgery.

Special Considerations

• Audible lung fields delineated by anatomical landmarks for clinical assessments.
• Puncta maxima used for identifying heart valve auscultation points.
• Specific adaptations in species like camels and horses highlight diversity in respiratory anatomy.

This detailed overview serves as an excellent reference for understanding the complex anatomy and physiology of the respiratory system across different animal species.