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

Action Potentials and Ion Channels

• Falling Phase: In this phase, sodium channels are blocked and inactive.

  • Sodium permeability significantly decreases while potassium permeability is high (illustrated by a double arrow on slides).

  • The only ion moving during this phase is potassium (K+).

Blood Circulation in Air-Breathing Organs

• Circulation Pathway: Blood moves from the heart to the mouth before reaching the gills.

  • Example Pathway: Heart (1) ➔ Mouth (4) - bypassing gills.

  • Consider various blood flow pathways and their implications on oxygenation.

Total Cross Sectional Area and Blood Flow

• Cross-Sectional Area: The total cross-sectional area of capillaries increases as distance from the heart increases.

  • Inverse relationship exists between total surface area and mean blood velocity: as surface area increases, velocity decreases.

Ion Roles in Cardiac Action Potentials

• Prolonged Plateau Phase:

  • Importance of sodium (Na+) and calcium (Ca2+) in sustaining the plateau phase.

  • Sodium permeability initially increases but drops to zero during plateau phase (plays no role).

  • Calcium helps maintain cell depolarization during the plateau phase.

  • Potassium's role: It builds up inside the cell due to low permeability, contributing to the plateau.

Importance of Email Communication

• Open invitation for questions via email about content or exam-specific doubts. Instructor encourages outreach for clarification.

Circulatory Plan and Independent Modulation

• Key Question: Which circulatory plan allows for independent modulation of blood flow to lungs versus the rest of the body?

  • Solid lines indicate separation between deoxygenated and oxygenated blood allowing for pressure modulation.

  • Example 2 shows a completely separate pathway for deoxygenated blood to lungs.

Insects and Tracheal Systems

• Tracheal System in Insects:

  • Composed of air-filled tubes (trachea) and spiracles for gas exchange.

  • Spiracles open to let air in based on partial pressure gradients, similar to human breathing.

  • Avoids reliance on a circulatory system for oxygen transport.

Limitations on Insect Size

• Size Constraints of Insects:

  • Maximum size of insects is capped due to the inefficiency of the tracheal system over large volumes.

  • Historical context: Higher atmospheric oxygen levels (up to 34%) allowed larger insects in the past.

• Surface Area to Volume Ratio: Larger size would require exponentially more trachea for adequate aeration.

Metabolic Rates and Oxygen Delivery

• Oxygen Delivery Efficiency: Tracheal systems allow for 200 times faster oxygen delivery than mammals.

  • Gases move through air (trachea) significantly faster than in liquids (blood).

• Cell Proximity to Oxygen Sources: Cells must be within a millimeter distance from oxygen sources (trachea or capillaries) for efficient oxygen diffusion.