Breathing and Circulation: A Quick Lesson On These Processes

Breathing is the process of taking air from the atmosphere and inhaling it into the lungs. It occurs all the time without any thought processing, so it is referred to as an automatic process, however, it can also be controlled if desired. The breathing mechanism is initiated when sensors in the brain detect low levels of oxygen and high levels of carbon dioxide in the blood. During times of physical exertion oxygen levels decrease and carbon dioxide levels increase which results in an increase in breathing rate and breathing depth. During times of rest the opposite occurs.

Oxygen is vital for all metabolic processes. As it enters the body it will travel down the trachea (throat), through the bronchioles (tubes leading to the lungs), and into the lungs. In the lungs there are very tiny grape-like-sacs called alveoli. The membrane on these sacks is very thin, and they are surrounded by many tiny capillaries (blood vessels) whose membrane is also very thin. It is here where oxygen from the alveoli enters the capillaries, and carbon dioxide (waste product) from the capillaries enters the alveoli. The oxygen is now carried through the blood to the heart where it is pumped throughout the body, and the carbon dioxide, now in the alveoli, is expelled as the person exhales. In a situation of altitude it is this process that is hindered. Because of the lower pressure of oxygen the oxygen does not enter the capillaries as easily and the body is deprived of oxygen.

With the oxygen now bound to the hemoglobin, the blood will now travel throughout the body supplying organs, muscle, nerves, and all other tissue. Example, at a muscle site the oxygen will pass from small capillaries into the muscle cells. And carbon dioxide will pass from the muscle cells into the small capillaries which will now carry the waste produce back to the lungs to be expelled into the atmosphere.

As blood leaves the lungs it will travel through the pulmonary veins to the heart into the left atrium (top left chamber). The left atrium will pump the blood to the left ventricle (bottom chamber). The Mitral valve separates the left atrium from the left ventricle and prevents back flow. From the left ventricle the blood is pushed through the aortic valve (also preventing back flow) and through the aorta. The aorta is the largest blood vessel in the body and carries oxygenated blood through the body. From the body the blood returns to the heart through the superior and inferior vena cava. It enters the right atrium, then passes through the Tricuspid valve into the right ventricle. From the right ventricle it is pumped through the pulmonary arteries to the lungs, where the cycle begins all over again.

Blood Flow Summary:

  • Oxygenated blood from lungs, through pulmonary veins, to the left atrium.
  • Left ventricle.
  • Aorta through the body.
  • Deoxygenated blood from the body to the right atrium.
  • Right ventricle.
  • Pulmonary arteries to the lungs.

Carotid arteries are the first arteries that branch out of the aorta as it leaves the left ventricle. There is a special mechanism to protect the carotid arteries from the extreme pressure from the heart contraction. The carotid arteries are responsible for carrying oxygenated blood to the heart (cardiac) muscle. Healthy carotid arteries are vital to a healthy heart. With coronary artery disease blood flow is impaired and the heart lacks starves of oxygen. If severe enough this will lead to a heart attack and death.

The mitral, tricuspid, and aortic valves prevent blood from flowing the other way. If these valves are damaged (e.g. they don't close properly) then blood flow is impaired. This is called a murmur. If severe enough medication and surgery may be required. Real valves can be replaced by plastic valves.

Fast Facts

Hemoglobin is a protein molecule that is found in the red blood cells in the blood which is the agent that oxygen will bind to as it enters the capillaries in the alveoli. Hemoglobin is essential in oxygen transportation. It has been shown that people who live at higher altitudes have higher levels of hemoglobin which acts to assist in dealing with the low pressure of oxygen. Some athletes may train at altitude in hopes of increasing their levels of hemoglobin, so when they compete at sea levels they will have better oxygen carrying ability and have an advantage over other athletes.

Blood doping involves removing blood months before a competition. Separating the hemoglobin and storing it. Before the competition, after the body has replaced the removed blood and hemoglobin, the saved hemoglobin is injected into the body. Now, the athlete has higher levels of hemoglobin than normal, which can provide an advantage since more oxygen can now be carried to the muscles. This is a forbidden practice and if an athlete is called they will face severe penalties. It is also very dangerous as it can lead to heart attacks and strokes from an increased thickness of the blood.

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