Biology and Chemistry

Lungs and pipes

We all own a clever air pump, which sucks air in and out of the body. The air pump consists of two balloons which are inflated and deflated by muscle power. These are the two lungs we have, and they are not symmetric. The right lung is divided into three parts  (lobes), and the left into two. So, the left lung is slightly smaller, leaving space for the heart to fit snugly in the space left.

Our nose and mouth are connected to an upright Y-shaped splitter. The splitter connects to our windpipe, which passes down the throat. At the bottom of the windpipe is another upside-down Y-shaped splitter to which both lungs are connected.

The movement of the air in the human lungs is bidirectional. First, the lungs are filled and then emptied by pushing the air in a reverse route. Birds and some reptiles have a circular breathing system where the air moves in one direction. A circular breathing system has efficiency advantages.

Air mixture

Fresh air is a gas mixture consisting of roughly:

80% Nitrogen + 20% Oxygen

Once fresh air is inhaled, it fills the lungs, and there is an exchange process. About 4% of the inhaled Oxygen is exchanged with 4% Carbon-diOxide, which is carried to the lungs by the bloodstream.

The air that we exhale consists of roughly:

80% Nitrogen + 16% Oxygen + 4% Carbon-diOxide.

We can keep holding the air in our lungs for a looooooong time, and even though there is still plenty of Oxygen left in the lungs, no exchange will occur. That is because a minimum of 16% Oxygen concentration is required in the lungs for Oxygen to exchange with Carbon-diOxide.

If you ask me, this doesn’t seem to be a very efficient process. Making the effort of pumping all this air into the lungs, and only 4% is exchanged? Couldn’t evolution do better than that? It’s most unfortunate that I wasn’t around at the time of creation; I could have pointed out this inefficiency in advance.

Bloodstream and cells

My heart is the pump that circulates blood in a network of pipes in my body. Blood vessel pipes carry different gasses, food fuels, moody hormones, and other substances. My bloodstream delivers burning fuels and clears waste from every living cell in my body.

Body cells are miniature power plants that generate energy, powering my muscles and keeping me warm. The cells facilitate the release of energy from the food I eat in the presence of Oxygen. Cells in my body can burn different food fuels like Sugar, Fat, or Protein. All these food fuels have one thing in common; they contain Hydrogen and  Carbon, which hold energy in their bonds. The two gases readily react with Oxygen in the cells, which allows the release of the energy they hold. Carbon-diOxide and water discharge following the reaction.

Gas exchange and delivery

The inside of my lungs is fascinating. I have hundreds of millions of tiny bubbles with a total surface area of about the size of a tennis court. The millions of bubbles have a bidirectional membrane allowing gas exchange. When Oxygen and Carbon-diOxide are at the proper concentrations on either side of the bubbles, they exchange places spontaneously.

These bubbles are covered on the inside with blood vessels rich in Carbon-diOxide from the bloodstream. On the outer side of the bubbles, inhaled air with Oxygen awaits.

All gasses in nature have some sort of characteristic pressure. If the difference in the pressure between two gasses is high enough, they exchange places on opposite sides of the bubbles, and the pressure equalizes. Nitrogen, makes up most of the air we breathe, but it doesn’t create a pressure difference with Carbon-diOxide, and therefore is not exchanged into the bloodstream. However, Oxygen and many other gases have a pressure difference with Carbon-diOxide, and as a result, they swap.

Once Oxygen exchanges with Carbon-diOxide, the Oxygen is ‘captured’ in the bloodstream by my red blood cells, which function as a gas-transporting agent. To be precise, a protein called Hemoglobin in the red blood cells binds with Oxygen. Hemoglobin attracts Oxygen like a magnet and holds tightly onto the Oxygen as it circulates in my bloodstream.

At the beginning of the 20th century, a Danish scientist named Christian Bohr researched the relationship between bloodstream gases and how they impact Oxygen delivery to our body cells. He and his team discovered that the strength of the bond between the Hemoglobin carrier and the Oxygen it carries depends on the level of Carbon-diOxide, surrounding it. The more Carbon-diOxide, the weaker the Oxygen is bound to its carrier. This association between Carbon-diOxide,  Oxygen, and Hemoglobin was named the Bhor effect. It explains important breathing phenomena.

The Hemoglobin’s ability to ‘let go’ of its Oxygen cargo depends on the ambient Carbon-diOxide level. Our blood-vessels branch again and again into smaller tubes until they reach their final destinations, the cells. More active cells produce more Carbon-diOxide, and as a result, these cells need more Oxygen. Hemoglobin traveling with its Oxygen cargo ‘senses’ where there is a high concentration of Carbon-diOxide, and releases its Oxygen cargo. Only then Hemoglobin picks up a new Carbon-diOxide load. Finally, Hemoglobin travels back to the lungs with its new cargo of Carbon-diOxide, and another exchange cycle occurs.

That is how our body regulates where and what amount of Oxygen, is delivered to the body cells.

Outer breathing is when we bring air in and out of our lungs. In the lungs, Oxygen is absorbed from the air and sent into the bloodstream.

Inner breathing is when the cells ‘inhale’ Oxygen transported by Hemoglobin. A byproduct of the burning in the cells is Carbon-diOxide, which is then ‘exhaled’ by the cells into the bloodstream.

A healthy person’s bloodstream is saturated with Oxygen, and the concentration of Carbon-diOxide secures that Oxygen is released only around cells that need Oxygen.

The importance of carbon dioxide

Our body runs on food fuel and Oxygen, but what regulates many body processes is the concentration of Carbon-diOxide in the bloodstream. If breathing is the vehicle that propels life, Carbon-diOxide is the driver. We have no Oxygen sensors in our bloodstream, and our ‘breathing app’ is ‘indifferent’ to Oxygen. Instead, it’s Carbon-diOxide that is closely monitored. Sensors in the bloodstream send information on the concentration level of Carbon-diOxide, and our ‘breathing app’ is constantly updated. We feel the urge to breathe when levels of Carbon-diOxide in our bloodstream rise.

Important: What triggers our breathing muscles is high levels of Carbon-diOxide in the bloodstream, not low levels of Oxygen. As long as Carbon-diOxide in the bloodstream is below our personal triggering level, we don’t feel the urge to breathe.

Contrary to the belief of many, Carbon-diOxide is not a waste product that should be disposed of; it’s an essential blood gas with many important bodily functions.

Carbon-diOxide is a:

  • Tranquilizer to my nerves.
  • Dilator of my blood vessels.
  • Relaxing agent for my muscles.
  • Opener of air passages to and inside my lungs.
  • Regulator of my blood-gas balance.

Carbon-diOxide is needed for many chemical reactions in the body, like converting vitamins so that our body can absorb them.

Protective oxygen

Trees ‘inhale’ the Carbon-diOxide that we and other breathing beings exhale. They separate the pairs of Oxygen from the Carbon and release these pairs into the atmosphere.

Oxygen also comes in nature as a combination of three atoms which is called Ozone. These Oxygen triplets in the earth’s atmosphere shield us from the harmful radiation coming from the sun. It filters sunlight, and without it, our skin would get sunburns.

As we go up to higher altitudes, there is a change in the concentration of the Oxygen we breathe. The higher we climb, the lower the Oxygen concentration. Therefore, it’s more difficult for us to breathe at high altitudes. In addition, we have less protection from sun radiation as we climb higher up.