Haemoglobin, also spelled as Hemoglobin, is a protein that is found in red blood cells and is responsible for carrying oxygen from the lungs to the body's tissues and organs. It plays a crucial role in the transportation of oxygen throughout the body.

Hemoglobin is a vital protein found in red blood cells that has the essential role of carrying oxygen throughout the body. The level of hemoglobin in the blood can be measured through a hemoglobin test. Hemoglobin is the key component of red blood cells and is primarily composed of a protein called heme. Heme has the ability to bind with oxygen, allowing it to transport oxygen from the lungs to other tissues and organs in the body. In the lungs, oxygen is exchanged for carbon dioxide, enabling the removal of waste carbon dioxide from the body.

The discovery of hemoglobin can be attributed to several scientists who made significant contributions to our understanding of this protein.

One key figure in the discovery of hemoglobin is the Italian physician and biologist Lazzaro Spallanzani. In the 18th century, Spallanzani conducted experiments on blood and observed that it changed color when exposed to air. He hypothesized that this color change was due to a substance in the blood that interacted with oxygen.

Another important scientist in the study of hemoglobin is the Swedish physician and chemist JΓΆns Jacob Berzelius. In the early 19th century, Berzelius isolated a red pigment from blood and named it "hematin." Although he did not fully understand its function, his work laid the foundation for further research on hemoglobin.

The true nature of hemoglobin was elucidated by the German physiologist and pathologist Otto Funke in the mid-19th century. Funke discovered that hemoglobin was an iron-containing protein responsible for oxygen transport in the blood. He named it "hΓ€moglobin," which later became known as hemoglobin.

Since then, numerous scientists have contributed to our understanding of the structure, function, and importance of hemoglobin in the human body. Their collective efforts have provided valuable insights into this essential protein.


Haemoglobin has several important functions in the body:

  • Oxygen Transport: The primary function of haemoglobin is to transport oxygen from the lungs to the body's tissues. It binds to oxygen in the lungs, forming oxyhaemoglobin, and releases it in areas of the body where oxygen is needed for cellular respiration.
  • Carbon Dioxide Transport: Haemoglobin also plays a role in carrying carbon dioxide, a waste product of cellular respiration, from the tissues back to the lungs, where it can be exhaled. Carbon dioxide binds to haemoglobin to form carbaminohaemoglobin.
  • Acid-Base Balance: Haemoglobin helps maintain the acid-base balance in the body by acting as a buffer. It can bind to excess hydrogen ions (H+) to help regulate pH levels and prevent acidosis.
  • Nitric Oxide Regulation: Haemoglobin is involved in regulating the release of nitric oxide (NO), a signaling molecule that plays a role in blood vessel dilation and blood pressure regulation. Haemoglobin binds to and modulates the availability of nitric oxide in the body.
  • Storage of Iron: Haemoglobin is the main site of iron storage in the body. Iron is an essential mineral involved in various physiological processes, including oxygen transport, energy production, and DNA synthesis.

These functions of haemoglobin are vital for maintaining the proper functioning of cells, tissues, and organs throughout the body.

Parts of hemoglobin

Haemoglobin consists of several components:

  • Heme: Heme is the iron-containing part of the haemoglobin molecule. It is responsible for binding and carrying oxygen. Each haemoglobin molecule contains four heme groups, and each heme group contains an iron ion at its center. The iron ion can bind to an oxygen molecule, allowing haemoglobin to transport oxygen.
  • Globin Chains: Globin chains are protein chains that surround the heme groups in the haemoglobin molecule. There are four globin chains in a haemoglobin molecule, with two alpha chains and two beta chains in adult haemoglobin (HbA). The specific combination of globin chains determines the type of haemoglobin. For example, fetal haemoglobin (HbF) has two alpha chains and two gamma chains.
  • Alpha Chains: Alpha chains are one type of globin chain found in haemoglobin. They are encoded by the HBA1 and HBA2 genes. In adult haemoglobin, there are two alpha chains.
  • Beta Chains: Beta chains are another type of globin chain found in haemoglobin. They are encoded by the HBB gene. In adult haemoglobin, there are two beta chains.

The combination of heme and globin chains forms the haemoglobin molecule, which is responsible for oxygen transport and other functions within the body.

It's important to note that there are different types of haemoglobin that can vary slightly in their composition and function. The most common types in adults are HbA, HbA2, and HbF. Each type has a specific combination of globin chains, which gives it unique properties and functions.

Abnormal levels of haemoglobin can indicate certain health problems. The normal range of haemoglobin levels can vary slightly depending on factors such as age and gender. In general, a healthy haemoglobin level for males aged 19-65 years is between 13.1 and 17.5 grams per deciliter of blood (g/dL).

Haemoglobin is responsible for both the red color of blood and the blue blood of aristocrats. Without blood cells, the resulting plasma is a pale yellow color. Haemoglobin combines with oxygen, allowing blood to carry 70 times more oxygen than if it was simply dissolved. It is essential for physically active animals and larger organisms to survive. It has been suggested that without haemoglobin, humans would not have achieved any activities beyond those of a lobster, or if they had, they would have had a body as small as a fly's.

Haemoglobin is found in the red cells of the blood and is the main site of iron in the body. It is present in all vertebrate species and is synthesized in the developing red cells in the bone marrow of adult humans. While many worms have haemoglobin, other organisms, including most mollusks, have different oxygen-carrying pigments that are more primitive and have not survived in higher forms of evolution.

In addition to distributing oxygen to the tissues, haemoglobin also serves as an important oxygen store. Healthy humans have about 15 grams of haemoglobin per liter of blood, and it can bind with 200 milliliters of oxygen per liter. When the body is at rest, only about one-quarter of the available oxygen in arterial blood is removed by the tissues, with the remaining three-quarters returning to the lungs in venous blood. This reserve of oxygen supply is crucial during conditions of work and exercise. In a typical total blood volume of 5 liters, there is approximately 0.75 liters of oxygen combined with haemoglobin in the blood, which is similar to the amount of gas in the lungs. Without these oxygen stores, brain function would cease almost immediately if breathing were to stop.

The amount of oxygen dissolved in the blood plays a minimal role in oxygen carriage to the tissues. The amount depends on the pressure of oxygen in the lungs. Breathing pure oxygen increases the amount of dissolved oxygen significantly and can contribute significantly to the body's oxygen supply. However, breathing high-pressure oxygen carries significant hazards and is only used in certain conditions when haemoglobin is severely deficient.

Each haemoglobin molecule consists of four iron-containing parts (haems) and four protein chains (globins). The presence of iron in blood was discovered in 1747, and the chemical structure of haemoglobin was fully elucidated in the 1960s. Each haemoglobin molecule can combine with four oxygen molecules, and the degree of combination depends on the pressure of the gas. Haemoglobin saturation is not linearly related to oxygen pressure, which allows it to defend the oxygen supply against interruptions of breathing or oxygen shortage while promoting oxygen off-loading in the body.

The combination of haemoglobin and oxygen is weak, and oxygen can be pulled from the blood when the surrounding oxygen pressure is low. In metabolizing tissues, the low oxygen pressure draws oxygen from its combination with haemoglobin, allowing it to enter the cells. Consequently, venous blood contains less oxygen saturation than arterial blood, giving it a bluish color. Haemoglobin can also combine with carbon dioxide to form carbaminohaemoglobin, which is another way carbon dioxide is transported in the body.

Human red cells have a lifespan of approximately 120 days before being broken down. The haemoglobin is broken down into haem and globins, with the haem further split into iron and bilirubin. Bilirubin contributes to the pale color of plasma and is excreted in the bile, giving it its color. In the intestines, bilirubin is acted upon by bacteria, forming stercobilinogen, which gives feces its characteristic color. Some stercobilinogen is reabsorbed into the bloodstream and excreted in the urine as urobilinogen. Haemoglobin breakdown products are responsible for the colors of plasma, bile, feces, and urine.

Abnormal haemoglobins can cause various diseases, with the abnormality usually occurring in the globin part of the molecule. These diseases can affect the ability of haemoglobin to combine with oxygen and cause deformations in red blood cells. Examples include sickle cell disease, thalassemia, and abnormalities in enzymes associated with haemoglobin.

If you want to learn more about haemoglobin, you can check out the following sources:

  1. Healthline - What is Hemoglobin? Normal Levels and Potential Problems (Published on July 12, 2023)
  2. Wikipedia - Hemoglobin
  3. MedicineNet - Hemoglobin: Normal, High, Low Levels by Age, Test, Deficiency (Published on March 7, 2024)
  4. Verywell Health - Hemoglobin Levels: High vs. Low, Symptoms, and Risk Factors (Published on January 11, 2024)
  5. PMC - Hemoglobin: Structure, Function and Allostery


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