Blue Skin Pigmentation: Skin Coloration and Red Blood Cells

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Methyleneblue

Methylene blue is a dye that reverses how red blood cells respond to cyanosis: blue skin coloration. Schematic with Chem Draw 14. Copyright image by John A. Jaksich, all rights reserved.

Blue skin color is a disorder of the blood. It is an ominous sight and occurs in two types of circumstances: poisoning or birth defect.

In each case, hemoglobin molecules become methemoglobin—a molecule that cannot function in its normal roles in the circulatory system.

The transformed molecule cannot take oxygen molecules from the lungs, nor can the methemoglobin take carbon dioxide back to the lungs.

What is Hemoglobin Made of?

Hemoglobin is the stuff of our blood: It consists of red blood cells and white blood cells. The two categories may be further broken down into their functions: Red bloods cells carry oxygen and carbon dioxide within our body, and white blood cells defend us from bacteria and viruses.

Hemoglobin is a protein made up of amino acids and iron. There are four central heme molecules (that contain  iron) and two pairs of large  proteins that surround the hemes. The process of its synthesis is complex, and takes place within the bone.

Brief Overview: How Does Hemoglobin Function?

Hemoglobin is a protein that is crucial to the body’s metabolism. The molecule consists of four separate parts: a heme portion, iron, and two pairs of globular proteins. Each plays a crucial role in how the body burns calories.

As we breathe, the oxygen bonds to the iron in hemoglobin and it disperses throughout the body. Once the body utilizes the oxygen in burning carbohydrates, carbon dioxide attaches to the iron, and the body exhales it.

When hemoglobin functions normally, you may notice a healthy glow to your skin color. However, if we were somehow poisoned, the uptake of oxygen may be impeded and cyanide build-up occurs in our tissue. At an elevated level of cyanosis (at approximately 60% loss of oxygen in the tissue), death is likely.

Molecular Overview: How Hemoglobin Functions

The science behind respiration reveals itself as a complex dance of molecules. Respiration occurs when the body burns carbohydrates (simple and complex sugars) to yield energy, water, and carbon dioxide. The process of burning carbohydrates is also known as the glycolysis cycle.

Thus, we breathe oxygen, and red blood cells carry it throughout the body. The oxygen is required so carbohydrates can produce energy and produce carbon dioxide as well. The hemoglobin molecule takes carbon dioxide back to the lungs by the red blood cells and we exhale it.

respiration

The complex dance of respiration takes place with the red bloods carrying oxygen and carbon dioxide to and from the lungs. Schematic with Chem Draw 14. Copyright image by John A. Jaksich, all rights reserved.

Blue Skin: The Methemoglobin Problem?

Blue skin coloration first takes place at approximately 20% loss of tissue oxygen as the hemoglobin molecule becomes methemoglobin. The differences between hemoglobin and methemoglobin become apparent when we closely examine the chemical structures.

The heme molecules of each species appear identical, but the surrounding environments of the red blood cells act to change how the heme molecule binds oxygen and carbon dioxide as well.

Thus, hemoglobin functions with complementary structures as it acquires oxygen and releases carbon dioxide. However, it is the central iron element that becomes unable to bind either oxygen or carbon dioxide as hemoglobin changes into methemoglobin.

Despite the fact that methemoglobin cannot bond to oxygen nor to carbon dioxide, it does bond to water from its surrounding environment. By bonding to water, the methemoglobin molecule sets the process of cyanosis into play.

Managing Blue Skin

Interestingly, the treatment for Methemoglobinemia is to administer a commercial dye: Methylene Blue. The dye restores the enzyme functionality within the red blood cell, so the hemoglobin can resume its normal duties of respiration.

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