Recording-2025-03-13T21:04:46.004Z

Aquatic Invertebrates and Buoyancy

• Water Beetles and Backswimmers

  • Water beetles can extract oxygen from water, maintaining a positive buoyancy.

  • Backswimmers utilize hemoglobin to maintain neutral buoyancy by minimizing gas exchange with water.

  • They initially rely on gas in their trachea for buoyancy, utilizing oxygen when needed to achieve neutral buoyancy, which conserves metabolic energy.

Respiratory Systems Explained

• Fick's Law of Diffusion

  • J (diffusion rate) can be increased by increasing surface area, essential for larger organisms.

  • Air contains ample oxygen (21%) allowing for thicker membranes for gas exchange compared to aquatic environments.

• Surface Area in Human Lungs

  • Each lung contains approximately 300 million alveoli, creating a surface area around 75 square meters (roughly the size of a tennis court).

Mechanism of Breathing

• Thoracic Cavity Dynamics

  • Inhalation involves contraction of external intercostal muscles, increasing thoracic cavity volume and decreasing pressure, causing air to rush in.

  • Exhalation involves relaxation of the external intercostals and contraction of internal intercostals to compress the thoracic cavity and increase pressure, expelling air.

• Air Flow Dynamics

  • Humans exhibit tidal flow of air, where air enters and exits through the same opening, leading to mixing of fresh and stale air, creating dead air space.

  • The inclusion of dead air makes breathing less efficient, as not all inhaled air is fresh.

Vital Capacity and Lung Volumes

• Lung Volume Definitions

  • Inspiratory Reserve Volume: Air volume beyond normal inhalation.

  • Expiratory Reserve Volume: Air volume beyond normal exhalation.

  • Vital Capacity: The total amount of air moved in and out, excluding residual air that remains in the lungs.

  • Residual Volume: Air that never gets expelled, contributing to dead air space.

Tidal Gas Exchange Sequencing

• Gas Exchange Efficiency

  • During tidal breathing, oxygen partial pressure drops from 100 mmHg to 60 mmHg when traveling to the capillaries due to dead air space, reducing efficiency.

  • The actual difference between inhaled air and the blood reaching the lungs represents the usability of oxygen in the body.

Unidirectional Flow in Other Organisms

• Comparison of Breathing Mechanisms

  • Birds and Fish: Exhibit unidirectional flow of air or water, enhancing gas exchange efficiency compared to tidal flow.

  • Concurrent Exchange: Blood and media flow in the same direction; maximal exchange is only 50% due to the gradient diminishing quickly.

  • Countercurrent Exchange: Blood flows against the media, maintaining a continuous gradient for gas diffusion.

  • Cross-current Exchange: Blood encounters medium with oxygen at varying concentrations across the branches, achieving better efficiency than concurrent but lesser than countercurrent.

Summary of Flow Types

• Exchanging Mechanisms

  • Concurrent Flow: Limited to 50% exchange efficiency.

  • Countercurrent Flow: Maximizes exchange efficiency sustaining the gradient.

  • Cross-current Flow: Intermediate efficiency, as blood always initially contacts low oxygen media before moving along.