D

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).