Respiratory System: Adaptations and Behaviours

Whilst it is widely understood that mammalian respiration is a process of inhalation of oxygen and exhalation of carbon dioxide, the complexities of the variations of respiration methods amongst various mammals are a result of evolutionary adaptations borne from the necessities of habitat and environmental conditions. Due to this, land-based and aquatic mammals possess notable variations to their respiratory systems, including the processes of gas exchange and resistance to the absence of oxygen for extended periods.

Humans cannot exist underwater for extended periods due to their inability to effectively function when oxygen is lacking. The human respiratory system is not evolutionarily adapted to withstand the requirement of oxygen for long periods due to the relatively low oxygen holding capacity of the lungs, muscles and blood. Furthermore, whilst humans have the ability to perform anaerobic respiration, this cannot be maintained for long periods due to the amassing of lactic acid in the muscles. Also, within the human body oxygen is required frequently and is rapidly used, also resulting in the production of the respiratory waste product carbon dioxide. The high rate at which oxygen is expended and carbon dioxide is produced necessitates a continual input of oxygen and equally constant removal of carbon dioxide, lest oxygen content depletes to a level of inefficient bodily function and carbon dioxide content accumulates excessively, resulting in the increased production of carbonic acid within the blood.

In order to combat the problem posed by the absence of air or breathable oxygen in water for aquatic mammals, these animals (categorised by their diving habits and extended interludes of underwater habitation) have developed specialised respiratory systems in order to effectively obtain, utilise and retain the necessary oxygen they require. Mammals such as whales, dolphins and seals living in aquatic environments do not need the continual intake of oxygen and expiration of carbon dioxide required by terrestrial mammals to survive.

The human respiratory system relies on the continuous intake of oxygen and the removal of carbon dioxide in order to allow the body to function properly and effectively.

As well as retaining more oxygen than humans, aquatic mammals require less oxygen for their bodily functions. After inhaling, marine mammals shut down non-vital organs to minimise metabolic rate and nonessential oxygen usage. This decreases carbonic acid production. Heart rate decreases, often to as low as two to three beats per minute. The animal then relies on aerobic respiration for energy use in the absence of oxygen inflow. Furthermore, to minimise the effects of increased water pressure, aquatic mammals are able to collapse their rib cage and trachea to force oxygen to dissolve in their blood. Due to these physiological features, marine mammals are able to remain submerged for as long as 60 minutes, and whilst the official record for the longest submersion time for a human is 18 minutes 32.59 seconds, this occurred under extremely controlled conditions.

These are tiny sacs with in the lung tissue that air collects within.

Which then travels down through the pharynx, larynx and trachea (windpipe) toward the lungs.

The adaptive features of aquatic mammals to allow them to extendedly remain underwater begin with the air intake system. Unlike humans, who breathe through the nasal and oral cavities, aquatic mammals breathe through a blowhole situated on the top of their head. This allows for the efficient inhalation of oxygen and exhalation of carbon dioxide, without the need to surface completely in order to breathe. Rather than being an avenue for the intake of both food and air, as in humans, the mouth does not lead to the trachea. The blowhole channels air directly into the trachea, and contains a cartilaginous glottis located within the sporacular channel to prevent any foreign objects being transported into the trachea. Humans also have an epiglottis for the protection of the trachea, but this only comes into effect as a result of the swallowing motion.

Tool Module: The Human

Vocal Apparatus, 2010,

The Cleveland Clinic, 2010

Humans inhale air from the atmosphere through the nose or mouth:

From the trachea, air branches into the bronchi and in turn the bronchioles, ultimately arriving in the alveoli.

Respiration Mindfiesta, 2009

(NYU Medical Center, 2005)

Aquatic mammals must absorb as much oxygen as possible to have a sufficient store to access and use when underwater. To maximise the oxygen intake, aquatic mammalian lungs have more alveoli and the blood has a much higher red blood cell count than humans. This increased number of red blood cells allows for significantly higher levels of the oxygen carrying pigment haemoglobin, which in turn results in more oxygen being fixed and transported to the required organs than would occur through human respiration. The muscles of diving mammals also contain very high levels of myoglobin to retain more oxygen than possible in humans. Also, aquatic mammals have a larger volume of blood relative to body mass than humans, permitting the further increased oxygen retaining capacity.

RESPIRATORY

SYSTEM:

This is the point at which gas exchange occurs. A network of capillaries surrounds the very thin walls of the alveoli, and oxygen and carbon dioxide is transferred into and out of the bloodstream. Oxygen that has entered the blood binds to the iron ions within the blood carrying protein haemoglobin, and is pumped to the required organs by the heart. Carbon dioxide that has been removed from the bloodstream can now be exhaled through the relaxation of the diaphragm.

ADAPTATIONS

and

BEHAVIOURS

Aquatic mammalian respiration

Therefore, whilst humans – and hence the diver – can partially imitate the suspended breathing behaviours of aquatic, diving mammals, they can by no means hold their breath for the same length of time as these animals without suffering from the effects of extended oxygen deprivation, carbon dioxide (and therefore carbonic acid) accumulation, increased water pressure and impaired organ functioning.

The diver who claims to have the ability to hold their breath and remain underwater for extended periods of time rivalling that of which aquatic mammals are able to stay submerged is incorrect. Whilst humans are able to resist breathing for a short time, this cannot be maintained for extended periods and certainly not to the degree capable of aquatic mammals.

Evaluation of diver's claims