Dissection of the Swine Pluck

Introduction to the Pluck

• Pluck Definition: Refers to the organs from the respiratory and circulatory systems removed together from the thoracic cavity after slaughter.
• Focus for Today's Lab: Examination of the swine pluck, specifically its respiratory system components:
  • Trachea
  • Larynx
  • Bronchi
  • Lungs

Anatomy of the Respiratory System

• Epiglottis:

  • Leaf-shaped elastic cartilage located above the larynx, at the base of the tongue.
  • Function: Covers the glottis to prevent food and fluids from entering the larynx during swallowing.

• Larynx (Voice Box):

  • Contains vocal folds which vibrate to produce sound as air passes through.
  • Connected to arytenoid cartilages that adjust the vocal folds' length and tension to control pitch.
  • Pathologies:
  • Roaring in Horses: Damage to the nerve controlling the arytenoid cartilage can result in laryngeal hemiplegia, causing a characteristic roaring sound during breathing.

• Trachea (Windpipe):

  • Rigid, hollow tube extending from the larynx to the carina, where it bifurcates into the right and left primary bronchi.
  • Supported by C-shaped cartilaginous rings that provide structure while allowing flexibility.
  • In birds, these rings are complete O-rings.

• Histology of the Trachea:

  • Lined with tall, columnar ciliated epithelial cells and contains mucus-producing goblet cells to trap debris.
  • The submucosa contains blood vessels and glands that warm and humidify air.

• Bronchi and Lungs:

  • Trachea branches into two primary bronchi leading to the right and left lungs.
  • Bronchi further divide into smaller bronchioles, terminating in alveoli (sites for gas exchange).
  • Gas Exchange Mechanism: Oxygen diffuses from the alveoli into the bloodstream; carbon dioxide diffuses from the blood to the alveoli.

• Alveoli:

  • Function: Primary site for gas exchange (oxygen and carbon dioxide).
  • Gas exchange is driven by partial pressure differences between the alveoli and blood plasma.

• Lungs:

  • Composed of lobes; most mammals have seven lung lobes: cranial, middle, caudal, and an accessory lobe (on the right side).
  • The left lung is typically narrower due to the heart's position.

Avian Respiratory Adaptations

• Syrinx:
  • Found at the bifurcation of bronchi, serving as the vocalization source in birds.
  • Birds can control vocalizations from both bronchi, allowing complex sound production.
  • Example: Whooping Cranes possess elongated, coiled tracheas to amplify sound.

Dissection Procedure for the Swine Pluck

1. Observation:

   • Identify major structures of the respiratory and circulatory systems (larynx, trachea, bronchi, lungs).
   • Note any missing components as some parts may be separated during processing.

2. Step-by-Step Dissection:

   • Start by locating the epiglottis, then trace down through to the larynx and trachea.
   • Follow the trachea until it bifurcates into the primary bronchi.
   • Note the lobular arrangement of the lungs (may vary in swine).
   • Cut into the trachea to reveal the cartilaginous rings and ciliated epithelium.
   • Remove a section of lung tissue and place it in water:
     • Expected Outcome: Lung tissue should float due to air trapped in the alveoli.
     • Implications: Buoyancy is an indicator of lung function in certain pathological conditions.

Miscellaneous Anatomical Considerations

• Intercostal Muscles:

  • Located between the ribs, these muscles expand the ribcage during inhalation, aiding active inspiration.

• Diaphragm:

  • Primary muscle responsible for creating negative pressure in the thoracic cavity, facilitating lung expansion during inhalation.

• Pleura:

  • Double-layered membrane surrounding the lungs:
  • Parietal pleura: lines the chest wall.
  • Visceral pleura: covers the lungs.
  • A small fluid layer between these pleurae allows for smooth movement of the lungs against the chest wall during breathing.

• Pneumothorax:

  • Condition where a collapsed lung occurs due to air or gas accumulation in the pleural cavity, hindering lung expansion.

Final Exercise

• Float Test for Lungs:
  • Hypothesis: Lung tissue contains air-filled alveoli, causing it to float when submerged in water.
  • Clinical Relevance: This serves as a simple diagnostic method to assess lung function and confirm prior ventilation of lung tissue (useful in forensic cases).