When things go wrong
If cells are deprived of oxygen, instead of using aerobic (with oxygen) metabolism to function, the cells use the anaerobic (without oxygen) pathway to produce energy. Unfortunately, lactic acid is formed as a by-product of anaerobic metabolism.
This acid changes the acid-base balance in the blood, making it more acidic, and can lead to a situation in which cells begin to leak toxic chemicals into the bloodstream, causing blood vessel walls to become damaged. The anaerobic process ultimately leads to the death of the cell. If enough cells die, organs start to fail, and the body starts to fail and, eventually, death occurs.
Think of the cardiovascular system of the body as similar to the oil pump in your car. For efficient functioning, the electrical pump needs to work to pump the oil, there needs to be enough oil, and the oil lines need to be intact. If any of these components fail, oil pressure falls and the engine may be damaged. In the body, if the heart, blood vessels, or bloodstream (circulation) fail, then eventually, death occurs.
Where things go wrong
The oxygen delivery system to the body's cells can fail in a variety of ways.
- The amount of oxygen in the air that is inhaled can be decreased.
- Examples include breathing at high altitude or carbon monoxide poisoning.
The lung may be injured and not be able to transfer oxygen to the blood stream. Examples of causes include:
The heart may not be able to adequately pump the blood to the tissues of the body. Examples of these causes examples include:
- Heart attack in which muscle tissue is lost and the heart cannot beat as strong and pump blood throughout the body.
- A rhythm disturbance of the heart occurs when the heart can't beat in a coordinated way.
- Inflammation of the sac around the heart (pericarditis) or inflammation of the heart muscle due to infections or other causes, in which the effective beating capabilities of the heart are lost.
There may not be enough red blood cells in the blood. If there aren't enough red blood cells (anemia), then not enough oxygen can be delivered to the tissues with each heart beat. Examples of causes may include:
- acute or chronic bleeding,
- inability of the bone marrow to make red blood cells, or
- the increased destruction of red blood cells by the body (an example, sickle cell disease).
There may not be enough other fluids in the blood vessels. The blood stream contains the blood cells (red, white, and platelets), plasma (which is more than 90% water), and many important proteins and chemicals. Loss of body water or dehydration can cause shock.
The blood vessels may not be able to maintain enough pressure within their walls to allow blood to be pumped to the rest of the body. Normally, blood vessel walls have tension on them to allow blood to be pumped against gravity to areas above the level of the heart.
This tension is under the control of the unconscious central nervous system, balanced between the action of two chemicals, adrenaline (epinephrine) and acetylcholine. If the adrenaline system fails, then the blood vessel walls dilate and blood pools in the parts of the body closest to the ground (lower extremities), and may have a difficult time returning to heart to be pumped around the body.
Since one of the steps in the cascade of events causing shock is damage to blood vessel walls, this loss of integrity can cause blood vessels to leak fluid, leading to dehydration which initiates a vicious circle of worsening shock.