Why Respire?

To Generate Energy

As we have seen aerobic respiration and chemiosmosis are the most efficient ways our cells have of making energy. However, the electron transport chain and thus cells must have oxygen to function properly. Most of our cells don’t have direct access to the oxygen in the air though. Instead, they rely on the lungs to gather oxygen and then the circulatory system to transport the oxygen to them. Making the respiratory system a key player in our ability to generate enough energy in the form of ATP.

To Get Rid of Waste

Additionally, our metabolic process produces a variety of waste products that are dangerous in high quantities. Our respiratory system provides one outlet to help eliminate this waste and maintain homeostasis. Specifically, our lungs help us eliminate the massive amount of CO2 produced in the citric acid cycle.

pH Regulation

As a result, our respiratory system in conjunction with the bicarbonate buffering system offers a fast and effective way to help regulate and maintain physiological pH values. This is why when people have diabetic ketoacidosis, a build-up of acid in the blood due to an insulin deficiency, they start to breathe more quickly and heavily in order to “blow-off” CO2. Lowered CO2 levels shift the bicarbonate buffering system to the right and away from H+ ions helping increase pH to a physiologically favorable level.


\[ H_2O + CO_2 \to H_2CO_3 \to HCO_3^- + H^+\]

Regulate Temperature

Although not typically seen as a waste product our metabolism produces a lot of heat. Our respiratory system is an oft-overlooked way of eliminating heat since we can sweat and change clothes. However, for other animals such as dogs who can’t sweat they predominately regulate their temperature by panting. In doing so they expel hot air and hopefully take in colder ambient air to help cool themselves down. We do the same except it isn’t as efficient as sweating so it only accounts for a small portion of our ability to thermoregulate.

Problems: Invaders

Anytime we open up a hole in our body to the environment we open up ourselves to attack by pathogens, harmful chemicals, or damaging particulates. Our respiratory system has an arsenal of defense mechanisms at its disposal from cilia and mucus to resident immune cells.

Problems: Fluids Loss

Additionally, we lose a decent amount of water (400mL/day in adults) in the form of gas through breathing. This is important in an ICU setting where patients can’t eat or drink and instead must have all of their fluid provided intravenously. While it is easy to measure how much water is excreted in urine insensible water loss from respiration and sweating is much harder to calculate. One way physicians combat respiration associated water loss is through providing humidified air. However, patients still lose water via respiration so the amount of IV fluids a patient receives needs to account for respiratory water losses too.

Concept Check: Why Respire?