Seals are carnivorous, semi-aquatic, and primarily marine mammals. Seals store oxygen in their lungs, blood, and muscles. They have a large blood volume, which allows them to store large amounts of oxygen for use during diving.
Figure 1: An image from cardio-respiratory simulation from Labster. It is available for High School and University/College courses.
Seals have larger lungs than humans because they are also larger animals, but there is more oxygen in the blood than in the lungs.
Figure 2: oxygen stores comparison between humans and seals
Read on for some thoughts on why this can be a tough topic for teachers and students, five suggestions for changing the situation, and the benefits of using a virtual lab.
There are three reasons why understanding cardio-respiratory physiology can be difficult for even the most active student.
The mechanism of breathing occurs at a cellular level. You cannot see or feel it. Not being able to imagine how seals efficiently store oxygen within themselves and not understanding its relevance to the real world can frustrate studies and make it difficult for students to stay motivated.
Seals have several cardio-respiratory adaptations that allow them to dive to depths of 600m for long periods. These include relatively smaller lungs than humans, high levels of myoglobin in muscles compared to humans, and high levels of hemoglobin and blood volume in humans.
Figure 3 - Comparison between human and seal lung anatomy
As you can see in the image above, seal airways are reinforced with muscle and/or cartilage, which allows them to compress and avoid bending and in the image below you can see a summary of the main adaptations that seals have that allow them to make deep and long dives.
Figure 4 - Seal adaptations to deep diving
Figure 5: An image from cardio-respiratory simulation from Labster. It is available for High School and University/College courses.
Measurement of blood lactate concentrations in Weddell seals and emperor penguins before and after diving led to the definition of the aerobic dive limit (ADL) as the duration of the dive after which there was an increase in post-dive lactate concentration. For all other species where there were no pre- and post-dive lactate measurements, the dive aerobic limit was calculated by dividing usable oxygen stores by the estimated level of oxygen consumption during the dive. Using both approaches because Weddell seals can dive at least 2-3 times longer than their ADL. This means that the ADL still has usable oxygen in storage. The following are the equations used to calculate oxygen stores and the limits for aerobic diving from reserves. For calculating the oxygen stored in the lungs
VO2 in lungs (mL) = lung volume (L) x O2 in lung(mL/L)
Calculate oxygen stored in the blood
VO2 in blood (mL) = O2 in hemoglobin(mL/g) x hemoglobin(g/kg) x blood mass (kg)
Calculate oxygen stored in the muscle
VO2 in muscle (mL) = O2 in myoglobin(mL/g) x myoglobin(g/kg) x blood mass (kg)
The total stored O2 can then be calculated by adding up the O2 in all compartments. Further dividing this value by total body mass (kg) gives a relative and more comparable measure (in ml/kg). Once we know the total oxygen and estimate the factorial increase in O2 consumption during the dive, we can calculate the O2 consumption during the dive:
Diving O2 consumption = factorial increase x resting O2 consumption (mL/min) And then, finally, the aerobic dive limit:
ADL (min) = total O2 in stores (mL) / rate of O2 consumption during diving (mL/min)
Now that the discussion of student challenges has ended on this topic, here are five things you can incorporate into a cardio-respiratory physiology class to make it more engaging, accessible, and fun for you and your students.
The Weddell seal was discovered and named in the 1820s during an expedition led by British seal captain James Weddell in the region of the Southern Ocean now referred to as the Weddell Sea.
The electrocardiogram (ECG) cycle consists of 5 waves: PQRST.
The P wave corresponds to atrial depolarization and the subsequent pumping of blood from the atria to the ventricles. The QRS complex is associated with ventricular depolarization and subsequent pumping of blood to the body and lungs. The T wave is associated with ventricular repolarization and its recovery for the next cycle.
Heart rate is based on the frequency of ventricular contractions. A special adaptation that seals has for long dives is their ability to lower their heart rate, which reduces oxygen consumption and metabolism, and conserves energy. Seal oxygen consumption. The resting oxygen consumption rate can be calculated as follows:
VO2 (rest) = F x (FIO2 - FEO2) / [m x (1 - FIO2)], note that
F is the flow rate (mL/min), FIO2 is the oxygen entering the dome, FEO2 is the oxygen exiting and m is the seal mass (kg). To calculate the rate of oxygen consumption during a dive, time is also added to the equation:
VO2 (dive) = F x (FIO2 - FEO2) / [m x (1 - FIO2)], note that
F is the flow rate (ml/min), FIO2 is the oxygen entering the dome, FEO2 is the oxygen leaving the dome, m is the seal mass (kg) and t is the duration of the dive (min). Compared to humans, harbor seals show a markedly reduced increase in oxygen consumption during diving.
If pre- and post-dive blood lactate measurements are not available, the aerobic dive limit (ADL) can be calculated by dividing usable oxygen stores by the estimated level of oxygen consumption during the dive. However, Weddell seals can dive at least 2-3 times longer than the ADL. This means that the ADL still has usable oxygen in storage.
Weddell seals can perform aerobic dives, in which ATP is made from oxygen, as well as partially anaerobic dives, where ATP is made from lactate. It was observed that no lactate was accumulated during the 12-min dive and that 8mmol lactate was accumulated during the 30-min dive. To find out what percentage of ATP is produced by aerobic or anaerobic metabolism, all we have to do is divide the corresponding number by the total and multiply by 100.
Some general terms for all clinical studies, be it anatomy, physiology, or cardio-respiratory physiology. Some examples are:
Cardiology is the study and treatment of diseases of the heart and blood vessels. After explaining the effects of deep diving on the heart, proceed to explain the role of the heart in blood distribution and respiration.
Aerobic and Anaerobic Respiration: Aerobic respiration occurs in the presence of oxygen; while anaerobic respiration occurs in the absence of oxygen. Carbon dioxide and water are the end products of aerobic respiration whereas alcohol is the end product of anaerobic respiration. Aerobic respiration releases more energy than anaerobic respiration. Take a moment to explain what happens when the respiratory and cardiovascular systems cannot transport oxygen to muscle cells quickly enough to support aerobic respiration. Muscle cells use lactic acid fermentation to activate the continuous production of some ATP.
As students often find it difficult to begin their science journey with so many new terms and concepts being presented, there is a need to make teaching this topic more interactive. One way to achieve more excitement and active student participation is to use Labster's cardio-respiratory physiology simulation, which is designed to help students learn about oxygen reserves, aerobic diving pathways, aerobic and anaerobic ATP production, and specific cardio-respiratory adaptations that allow seals to make deep, long dives that are impossible for humans to do without diving equipment.
Labster's virtual laboratory simulation provides many benefits, such as appreciating interactive diving with seals, where you can watch a summary of their basic cardio-respiratory adaptations for diving.
You can learn more from cardio-respiratory physiology simulation from Labster here, or contact us to find out how virtual labs can be used with your students.
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