View synonyms for hemoglobin


[ hee-muh-gloh-bin, hem-uh- ]


, Biochemistry.
  1. the oxygen-carrying pigment of red blood cells that gives them their red color and serves to convey oxygen to the tissues: occurs in reduced form deoxyhemoglobin in venous blood and in combination with oxygen oxyhemoglobin in arterial blood. : Hb


/ mə-glō′bĭn /

  1. An iron-containing protein present in the blood of many animals that, in vertebrates, carries oxygen from the lungs to the tissues of the body and carries carbon dioxide from the tissues to the lungs. Hemoglobin is contained in the red blood cells of vertebrates and gives these cells their characteristic color. Hemoglobin is also found in many invertebrates, where it circulates freely in the blood. It consists of four peptide units, each attached to a nonprotein compound called heme that binds to oxygen.
  2. See Note at red blood cell


  1. A complex organic molecule (see also organic molecules ) containing iron that carries oxygen in the blood .

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Hemoglobin gives blood its characteristic red color.

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Other Words From

  • he·mo·glo·bic [hee-m, uh, -, gloh, -bik], he·mo·glo·bin·ous [hee-m, uh, -, gloh, -bi-n, uh, s], adjective

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Word History and Origins

Origin of hemoglobin1

First recorded in 1865–70; earlier hematoglobulin; hemo-, globulin

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A Closer Look

Ninety percent of the protein in red blood cells is made up of hemoglobin, the main oxygen transport molecule in mammals. A protein with four iron-containing subunits called hemes, hemoglobin is a complex molecule with a complex function. It must bind to oxygen in the lungs, then release that oxygen in the tissues, then bind to carbon dioxide in the tissues and release it in the lungs. Hemoglobin accomplishes oxygen transport by changing its structure, and even its substructures, around the oxygen-binding heme groups, making them more or less accessible to the environment. When oxygen binds to at least one of the heme groups (as happens in the oxygen-rich lungs), all of the heme groups become exposed to the environment and bind oxygen easily. The bond between oxygen and heme is a loose one, however, so that the oxygen can break free in the tissues, where the concentration of oxygen is relatively low, and thereby become available for use in the cells. When the last of the four heme subunits loses its oxygen, the structure of hemoglobin changes again, so that the size of the opening from the environment to the heme groups decreases, making it difficult for an oxygen molecule to rebind to the hemoglobin. In this way, hemoglobin stops itself from competing with the tissues for needed oxygen. When the red blood cell carrying hemoglobin returns to the lungs, where oxygen concentration is high, the cycle of oxygen binding, transport, and release starts again. Normally, iron binds with oxygen to form rust (iron oxide), but the structure of hemoglobin prevents this from happening, since it would inactivate the heme subunits. Carbon dioxide does not bind the heme in hemoglobin, but rather the amino groups at the ends of the hemoglobin's protein subunits. Hemoglobin transport is only one of a number of bodily mechanisms by which carbon dioxide travels from the tissues to the lungs for release to the air.

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Compare Meanings

How does hemoglobin compare to similar and commonly confused words? Explore the most common comparisons:

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Example Sentences

The volunteers continued using insulin while their blood was checked for changes to T cells and levels of hemoglobin A1c, or HbA1c, which tells how well-controlled glucose is in the blood.

Three years later, that group experienced drops in blood glucose, as measured by hemoglobin A1c.

At this pace, it will burn through its deep reserve of oxygen—provided by extra-large volumes of blood and hemoglobin—more slowly.

Targeting sickle hemoglobin directly has proved problematic given the large abundance of hemoglobin in the blood that would potentially require modification.

From Ozy

The next parameter is tissue oxygenation in the leg muscles, as measured with near-infrared spectroscopy, which basically involves shining infrared light through the skin and measuring how much is absorbed by oxygen-rich hemoglobin.

A single drop of a less-than-lily-white ancestral hemoglobin somewhere along the line?

A red blood cell having no hemoglobin is also called a ghost.

You can't fully understand how hemoglobin molecules interact until you've seen them depicted through a classical pas de deux.

In both conditions chemic tests will show hemoglobin, but in the latter the microscope will reveal the presence of red corpuscles.

In the lungs hemoglobin forms a loose combination with oxygen, which it readily gives up when it reaches the tissues.

Increase of hemoglobin, or hyperchromemia, is uncommon, and is probably more apparent than real.

Clinical study of the blood may be discussed under the following heads: I. Hemoglobin.

In mild cases a slight decrease of hemoglobin is the only blood change noted.


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