1. What Signals Your Body When You Hold Your Breath?
The speed of your breathing is controlled by the respiratory center in the medulla, which is located at the base of the brain. This center receives signals about the state of your blood and adjusts your breathing rate accordingly. [3]
Among these signals, the strongest one is the increase in carbon dioxide in your arterial blood. The next strongest signal is a slight increase in blood acidity (a drop in pH). Other factors like rising body temperature, exercise, and even low oxygen levels also stimulate faster breathing. [2]
This means the main trigger for breathing faster is high carbon dioxide, not low oxygen. However, the feeling of breathlessness is complex and still debated. Think of it like a warning light that glows when trash piles up. While the carbon dioxide sensor is primary, there is a separate sensor specifically for low oxygen.
2. The Two Sensors That Watch Your Oxygen and Carbon Dioxide
The sensors that send signals to the respiratory center are called chemoreceptors. Central chemoreceptors in the medulla mainly react to increased carbon dioxide. On the other hand, peripheral chemoreceptors, found in places like the carotid bodies in the neck, are thought to react strongly to a drop in oxygen partial pressure. [3]
So, your body has separate sensors for watching carbon dioxide and watching oxygen. The exact way we feel breathlessness is still a topic of discussion. [4]
Interestingly, the air you exhale still contains oxygen. The air you breathe in is about 21% oxygen, and a significant amount of oxygen remains in the air in your exhaled breath. If you are only using a small part of the oxygen you inhale, why must you keep breathing without rest?
3. Oxygen Is Used at the Very Last Step Inside Cells
The real reason we breathe is not in the lungs, but inside the cells that make up our bodies. We distinguish between external respiration, which is the exchange of gases between air and blood in the lungs, and cellular respiration, which is the process of extracting energy (ATP) from nutrients using oxygen inside the cells. [1]
When glucose (sugar) is broken down, the first stage happens in the cytoplasm and does not use oxygen. The subsequent reactions take place in tiny parts of the cell called mitochondria. In the final stage, known as the electron transport chain, oxygen acts as the final receiver of electrons, forming water. [1]
You can think of it like an electron relay race. Oxygen is the last runner who must catch the baton. If the final receiver is missing, the relay gets stuck. However, oxygen itself does not become energy. [1]
In the past, textbooks said that 1 molecule of glucose produces 38 ATP molecules. Recent estimates suggest this number varies depending on conditions, with about 30 ATP molecules or so, depending on conditions. [1]
4. Cells Themselves Sense the Amount of Oxygen
It is not just the sensors in your neck that detect oxygen levels. The 2019 Nobel Prize in Physiology or Medicine was awarded to Kaelin, Ratcliffe, and Semenza for discovering the mechanism of the cellular response to low oxygen. [5]
Inside cells, there is a protein called HIF. When oxygen is plentiful, HIF is marked and quickly destroyed. The enzyme that applies this mark cannot work without oxygen. Therefore, when oxygen levels drop, the mark is not applied, and HIF levels increase. [6]
When HIF increases, genes for hormones like erythropoietin, which increases red blood cells, begin to work. This is described as the entry point for the body to adapt to low-oxygen environments. [6] Note that these details come from explanatory articles.
5. How Insects, Fish, and Squid Take in Oxygen
The way animals take in oxygen varies greatly. Insects take in air through openings on their body surface called spiracles. Oxygen is sent to various parts of the body through branching tubes called tracheae. Valves just behind the spiracles can open and close. [7]
Some insects close their spiracles for several hours or even days, breathing intermittently. One theory suggests this prevents water evaporation. Another theory, proposed in 2005, suggests it helps avoid oxygen toxicity (reactive oxygen species). It is not settled which reason is the main one. [8]
Fish gills are fold-like with a large surface area. They take in oxygen efficiently because the water flow and blood flow move in opposite directions. [9] Squid, octopus, shrimp, and crabs carry oxygen using hemocyanin, which contains copper instead of iron. Hemocyanin turns blue when it binds with oxygen. [10]
Even though the tools are different, it is thought that the purpose is the same: to use oxygen as the final receiver inside the cells.
6. Count Your Breaths to See Your Body’s Signals
Try counting your breaths for 1 minute while sitting at home. Count one breath as one inhale and one exhale. It is easier if a family member helps you watch the clock.
Next, march in place for about 30 seconds, then immediately count your breaths for 1 minute again. Did your breathing rate increase after exercise? Exercise is considered one of the stimuli that speeds up breathing. [2]
Do not force yourself to hold your breath for a long time. If you feel unwell, stop immediately.
A science portal article from the Japan Science and Technology Agency summarizes how cells sense oxygen. [5] The answer to what your breathing rate is reporting lies partly in the signals from the medulla and partly in the HIF inside your cells.