Lecture Notes: The Respiratory and Circulatory Systems

Key Points

• Oxygen & Cellular Respiration
  • All members of the kingdom Animalia require oxygen for energy.
  • Carbon dioxide (CO2) is a byproduct of cellular respiration and must be expelled.

Oxygen Intake Process

• Respiratory System
  • Takes in oxygen using lungs (in most animals).
  • Circulatory system distributes oxygen to cells and collects CO2 for expulsion through lungs.

Unique Respiratory Mechanisms

• Simple Diffusion
  • Some animals can absorb oxygen through wet membranes.
  • Examples:
    • Arthropods: Utilize pores for oxygen intake.
    • Amphibians: Can take in oxygen through moist skin.
    • Fish: Absorb dissolved oxygen through gills.
    • Lungfish: Have lungs and are an example where lungs first appeared in the animal kingdom.

Lungs and Their Functionality

• Structure and Surface Area
  • Lungs contain large surface area (approx. 75 square meters of oxygen-dissolving membrane).
  • Oxygen enters through the nose/mouth, travels through larynx, trachea, bronchi, and bronchioles to alveoli.

Alveoli

• Gas Exchange
  • Tiny sacs where oxygen is exchanged for CO2.
  • Each alveolus is covered with capillaries where oxygen dissolves and enters the bloodstream.
  • CO2 is collected from the bloodstream and expelled.

Mechanics of Breathing

• Diaphragm Role
  • The diaphragm contracts (flattens) during inhalation, increasing lung volume.
  • Air flows in due to decreased pressure in lungs.
  • During exhalation, the diaphragm relaxes, increasing pressure and pushing air out.

Circulatory System Overview

• Heart Function
  • The heart pumps oxygenated blood to the body and brings deoxygenated blood back to the lungs.
  • The circulatory circuit resembles a figure eight:
    • Oxygenated blood is pumped from the heart to the body.
    • Deoxygenated blood returns to the heart, then to lungs for oxygenation.

Blood Flow Dynamics

• High Pressure in Arteries
  • Blood travels from the left ventricle through the aorta and arteries.
  • Arteries have thick walls to maintain high pressure.
  • Blood picks up CO2 and flows back through veins to the heart.

Major Veins

• Inferior and Superior Vena Cava
  • Collect deoxygenated blood from the body and return it to the right atrium of the heart.

Heart and Circulatory Efficiency

• Four-Chambered Heart
  • Allows efficient transport of oxygenated and deoxygenated blood.
  • Essential for endotherms (warm-blooded animals) to maintain high metabolism and stable body temperature.

Comparison with Ectotherms

• Ectotherms (cold-blooded animals)
  • Have slower metabolism and need less oxygen.
  • Their circulatory systems can be less efficient.

Evolution of Heart Complexity

• Heart Structures in Different Animals
  • Fish: Two-chambered hearts.
  • Reptiles & Amphibians: Three-chambered hearts (less efficient oxygenation).

Upcoming Topics

• Source of Energy for Diaphragm and Heart
  • Discussion on the digestive system and how it powers these functions will follow in the next lecture.

Conclusion

• Understanding respiratory and circulatory systems is crucial to grasp how oxygen is delivered and CO2 expelled in animals.