Americas Pavilion: Respiratory and Circulatory Systems

Comparative Analysis of Single and Double Circulatory Systems

• Single Circulation System (Fish):

  • Found in species such as the Round Goby ($Neogobius \, melanostomus$) and the Blind Cave Characin ($Astyanax \, jordani$).

  • Fish possess a single circuit for blood flow because they lack lungs.

  • The path of blood flow is: Heart $\rightarrow$ Gills $\rightarrow$ Body $\rightarrow$ Heart.

  • The heart consists of one Atrium ($A$) and one Ventricle ($V$).

• Double Circulation System (Mammals and Land Vertebrates):

  • This system involves two distinct circuits: the Pulmonary circuit and the Systemic circuit.

  • Pulmonary Circuit: Blood flows from the heart to the lungs and back to the heart.

  • Systemic Circuit: Blood flows from the heart to the rest of the body and back to the heart.

  • Blood must pass through the heart twice before completing a full cycle to oxygenate the body.

Mammalian Adaptations for Semi-Aquatic Life: The River Otter and Beaver

• North American River Otter ($Lontra \, canadensis$):

  • Physical Adaptations:

    • Thick protective fur for warmth in cold water.

    • Short legs and webbed feet for propulsion.

    • Long, narrow body with a flattened head for streamlined movement.

  • The Diving Reflex:

    • Triggered by nerve endings in the mouth and nose upon contact with water.

    • Vasoconstriction: The narrowing of blood vessels to slow circulation to extremities.

    • Bradycardia: A significant slowing of the heart rate to conserve oxygen.

    • Organ Prioritization: Blood is rushed to the brain and heart to prevent damage from oxygen shortage.

  • Oxygen Storage: Otters have large lungs and a large liver that stores oxidized blood, enabling submersion for several minutes (up to $8 \, \text{minutes}$).

  • Recovery: Post-dive, the heart rate increases to "pay off" the oxygen debt.

• North American Beaver ($Castor \, canadensis$):

  • Submersion Capabilities: Can stay underwater for up to $15 \, \text{minutes}$.

  • Anatomical Seals: Valves in the nose and ears close automatically. The mouth can close behind the incisors so the beaver can carry sticks without swallowing water.

  • Respiratory Efficiency: Beavers can exchange up to $75 \, \text{percent}$ of the air in their lungs per breath. In comparison, humans only exchange approximately $15 \, \text{percent}$.

  • Physiological Similarities to Otters: Shares the diving reflex (bradycardia and vasoconstriction) and uses the liver to store oxidized blood.

Respiratory and Circulatory Systems in Invertebrates

• Florida Lubber Grasshopper ($Romalea \, microptera$):

  • Tracheal System: Respiration occurs without lungs. A network of internal tubes called tracheae and sacs deliver oxygen directly to tissues.

  • Spiracles: Holes along the body where oxygen and carbon dioxide are exchanged.

  • Open Circulatory System: Because oxygen is delivered directly by tubes, the circulatory system is reduced and lacks closed vessels (no veins or arteries).

  • Mechanism: Consists of a single tube that pulses peristaltically to circulate hemolymph (body fluid).

  • Pigmentation: The "blood" is green because it does not need to carry oxygen.

• American Lobster ($Homarus \, americanus$):

  • Open System Components:

    1. A muscular heart.

    2. Thin-walled arteries that branch into smaller vessels.

    3. Irregular channels called venous sinuses that return blood to the heart via the gills.

  • Blood Chemistry (Hemocyanin): Oxygen is carried by hemocyanin, which contains copper.

    • Blood is transparent when deoxygenated.

    • Blood turns light blue when oxygenated.

  • Efficiency: Hemocyanin is only about $0.25 \times$ as effective at carrying oxygen as human hemoglobin. This explains why lobsters can perform sudden jetting motions but cannot sustain high-speed movement.

• Leather Sea Star:

  • Water Vascular System: Sea stars do not pump blood. Instead, they circulate seawater through a complex vascular system.

  • Tube Feet: Hundreds of feet on the underside are used for both movement and circulation.

  • Diffusion-Based Respiration: They lack lungs and gills. Oxygen is taken up via diffusion over the tube feet and papulae (skin gills), which are small projections near the base of spines on the topside.

Specialized Respiratory Mechanics in Reptiles and Amphibians

• Eyelash Viper ($Bothriechis \, schlegelii$):

  • Lung Structure: Most snakes possess only one functional lung; the second is often a small, unused vestigial organ.

  • Feeding Adaptation: To breathe while swallowing large prey, the tip of the trachea is pushed forward in front of the prey.

  • Hypotensive Shock: Human bodies contain approximately $96,000 \, km$ of capillaries, which cannot all be full of blood simultaneously. Snake venom can trigger a massive opening of vessels, causing blood pressure to drop and circulation to fail (hypotensive shock).

• San Esteban Island Chuckwalla:

  • Ventilation: Lacks a diaphragm. Respiration is driven by the expansion and compression of the rib cage via muscles.

  • Faveoli: Instead of complex bronchioles, the internal lining of the lung consists of faveoli—honeycomb-shaped structures that increase surface area for gas exchange with lining capillaries.

• Blue Poison Dart Frog:

  • Cutaneous Respiration: Amphibians can breathe through their skin in both air and water.

  • Efficiency: Frogs eliminate carbon dioxide ($CO_2$) approximately $2.5 \times$ faster through their skin than through their lungs.

• Axolotl ($Ambystoma \, mexicanum$):

  • External Gills: Used for extracting oxygen underwater.

  • Secondary Respiration: Large individuals may gulp air at the surface to fill their lungs as a supplement to gill respiration.

The Cephalopod System: Giant Pacific Octopus ($Enteroctopus \, dofleini$)

• The Three-Heart System:

  1. Gill Hearts (2): Located near the gills; they pump deoxygenated blood into the gills to dump waste and load oxygen.

  2. Systemic Heart (1): Receives oxygen-rich blood and pumps it throughout the rest of the body.

• Anatomy: The mantle houses the organs and the siphon (used to expel water). Water is drawn into the mantle cavity to provide oxygen to the gills.

• Closed Circulatory System: Unlike lobsters or insects, octopuses have a closed system where blood travels exclusively through vessels.

• Blood Characteristics:

  • Volume: Blood makes up approximately $5 \, \text{percent}$ of body volume, similar to humans.

  • Hemocyanin: Like lobsters, they use blue copper-based hemocyanin.

  • Performance: The limited oxygen-carrying capacity of hemocyanin ($0.25 \times$ that of hemoglobin) limits the octopus's ability to maintain sustained fast movement, though it can perform quick bursts.