Diving Physiology in Marine Mammals

The lecture emphasizes features related to diving in marine mammals, including physiological adaptations that allow for efficient swimming and oxygen utilization.
The lecturer highlights that many concepts will reappear in future labs and exams.

Focus on two important proteins: myoglobin and hemoglobin, which bind oxygen—crucial for oxygen transport in diving animals.
These proteins help minimize lung storage and maximize oxygen utilization, as they can store oxygen in tissues and muscles during dives.

Marine mammals exhibit a unique dive response that includes several adaptations:
- Apnea: Period of cessation of breathing to conserve oxygen.
- Bradycardia: Defined as a slowing of the heartbeat, reducing oxygen consumption.
- Peripheral Vasoconstriction: Diverts oxygen-rich blood away from non-vital body parts towards vital organs (like the brain and heart).

Oxygen Limitation: Marine mammals have a finite supply of oxygen, hence they must return to the surface to replenish it.
When oxygen is low, the body may switch to anaerobic respiration to produce energy, leading to a buildup of lactate in the blood and muscles, which increases acidity.
Anaerobic respiration is outlined as:
- Reduced oxygen leads to anaerobic respiration leads to lactate buildup.
- Recovery is necessary after a dive; animals may take time to manage and metabolize excess lactate upon resurfacing.

The Aerobic Dive Limit is characterized as the longest dive that does not cause an increase in blood lactate levels.
Staying within the ADL allows marine mammals repeated dives without lactic acid accumulation, thus avoiding the need for a lengthy recovery period.
Visual representation indicates significant peaks in blood lactate levels correlate with dive duration beyond the ADL.

Bradycardia: Mechanism to conserve oxygen, as it lowers the heart's overall oxygen consumption.
- Heart rate can drop drastically during dives (e.g., from over 100 bpm to 4 bpm within minutes).
Physiological adaptation is essential for long-diving capabilities, resulting in lower metabolic rates.

During dives, peripheral vasoconstriction occurs, whereby oxygen-rich blood is restricted from flowing to limbs, reducing overall body temperature and energy expenditure by concentrating blood flow to vital organs.

Decompression sickness occurs due to nitrogen absorption during dives at depth and can lead to serious issues upon rapid ascent when nitrogen bubbles form in the body.
Marine mammals have adaptations to minimize this risk:
- Compressible Rib Structure: Allows the ribcage to compress and thus prevent lung alveoli from becoming over-pressurized.
- Gradual compression enables safe nitrogen exchange, mitigating decompression risks.
Prevention of The Bends is further reinforced by an evolutionary adaptation where sirenians lack compressible ribs and are less prone to nitrogen absorption during deep dives.

The respiratory anatomy of marine mammals, particularly cetaceans, allows for efficient breathing.
Intercostal Muscles: Marine mammals have poorly developed intercostal muscles, relying on the diaphragm for forced ventilation.
- The diaphragm serves as a hydrostatic barrier and aids in buoyancy control.
Cetacean Larynx Adaptation: The elongated epiglottis (goosby) separates the respiratory tract from the gastrointestinal tract, preventing water entry during feeding and improving respiratory efficiency.