Albumin: what is it and what functions does it have in the human body


Blood is a liquid connective tissue that circulates through the vessels and capillaries, veins and arteries of all vertebrate animals. Human beings have an average of 5 liters of blood in the body, and our heart pumps about 70 milliliters for each beat, that is, almost all of the blood present in the entire body in a single minute.

Blood, in addition to the red blood cells that give it color, also carries with it many other molecules with different physiological functions. This is the case of blood or plasma proteins, which are responsible for the transport of lipids, hormones, vitamins, minerals and various actions of an immunological nature.

In the following lines we are going to collect the characteristics of the most prevalent blood protein and, surely, the most important. Stay with us, because this time we dissect the secrets of albumin and its medical implications.

What is albumin?

Albumin is a small, relatively symmetric protein found in multiple structures of animal origin: blood, milk, egg white, and the seeds of certain plants. In humans, it represents 54.3% of plasma proteins, that is, it is the most abundant of all (3.5-5 g / dl).

It may sound a bit strange to say that albumin is the most abundant plasma protein, since we are all used to thinking of hemoglobin as the queen of blood proteins, right? It is curious to know that hemoglobin is not considered in this group since it is transported within red blood cells, not in plasma. For this reason, no matter how abundant it is within these cell bodies (450 mg / ml), it is not conceived as a plasma protein per se.

Next, we present a series of relevant data to contextualize the importance of albumin in the human body:

  • The liver produces 9 to 12 grams a day of this complex substance.
  • Approximately 60% of the albumin is located in the extravascular space, that is, outside the blood vessels.
  • Given its strong negative charge, albumin is a water soluble protein.
  • Its life cycle in the bloodstream is 12 to 20 days.
  • Its renewal rate is 15 grams per day. Unlike other substances, there are no reserves of albumin anywhere in the human body.

The most important function of albumin is the regulation of oncotic pressure, necessary for the proper distribution of fluids in and out of tissues. We are going to stop for a moment on this singular term, as it is of great medical and biological interest.

Albumin and its functions

Oncotic pressure is medically defined as the osmotic pressure of a colloidal solution or dispersion. The difference between receiving this information and not knowing anything is small, which is why we offer a slightly kinder meaning for the general public: it is about a type of osmotic pressure caused by the difference in plasma proteins between blood plasma (within blood vessels) and interstitial fluid (space between cells, one sixth of body tissues).

As blood capillaries are not very permeable to large plasma proteins (such as albumin), these tend to remain inside the plasma instead of being distributed through the interstitium. Due to this protein concentration gradient (greater in blood than in interstitial fluid), water enters the blood vessels seeking to “balance” this difference. In summary we can say that this event maintains the correct distribution of body fluids in our body and allows their movement.

Even so, maintaining oncotic pressure simply by its presence in plasma is not the only function of albumin. Among many others, we can list the following:

  • It facilitates the metabolism and detoxification of various substances, such as bilirubin, metals, ions or enzymes.
  • It promotes the elimination of free radicals, harmful products generated during cellular respiration.
  • It carries thyroid and fat-soluble hormones.
  • It carries free fatty acids and unconjugated bilirubin, in addition to many other substances.
  • Control the pH.

What is the albumin blood test?

As redundant as it may sound, it is necessary to clarify that the albumin blood test measures the amount of albumin in the patient’s blood. It is a measurable quantification of liver function, since being synthesized in the liver, it provides information on its status and functioning.

On the other hand, a low level of albumin in the blood can also be indicative of kidney function failures, as in these cases this protein is excreted with the urine when it should not (an event known as albuminuria). A healthy kidney in no case allows albumin to pass from the blood into the urine.

In general, this test is recommended to patients who come to the clinic for jaundice or yellowing of the skin (increased levels of bilirubin in the tissues), weight loss, tiredness, dark-colored urine, or pain under the skin. the right rib, the site of the liver.

The normal serum albumin concentration is 3.5 to 5 grams per deciliter. A value lower than normal is known as hypoalbuminemia and may indicate any of the following disorders that we summarize briefly in the following lines.

1. Liver cirrhosis

This condition is the final consequence of a previous pathology in which the liver cells have been destroyed, which has caused their replacement by scar tissue, reducing the effectiveness of the organ itself.

The World Health Organization (WHO) estimates that 27,000 people die annually in high-income countries from this condition which, to no one’s surprise, is linked to chronic alcoholism. Liver cirrhosis is not the only condition that generates alcoholism, since it is estimated that more than 5% of all deaths in the world are due to its consumption (neither more nor less than 3,000,000).

2. Malnutrition

More than 462 million people in the most disadvantaged areas of the planet show signs of nutritional insufficiency. Hypoalbuminemia is one of them, as it occurs due to a lack of protein intake.

Albumin is synthesized in the liver from amino acids obtained due to the metabolism of dietary proteins, which is why the low values ​​of the same and malnutrition of the patient are clearly linked.

3. Other causes

Although malnutrition and liver cirrhosis are usually the most common causes of a lack of albumin in the blood, there are many other conditions that cause it. We present to you, to close today’s topic, some of the most relevant:

  • Some type of kidney dysfunction, such as an infection in the kidneys.
  • Liver cancer. More than 800,000 people are diagnosed with this condition annually.
  • Congestive heart failure or pericarditis.
  • Stomach problems, such as lymphomas or Inflammatory Bowel Disease (IBD). This is usually accompanied by nausea, vomiting, and diarrhea.
  • As a side effect of other diseases or the intake of certain drugs.

It should be noted that in patients with hypoalbuminemia may consider the administration of albumin for medical purposes. Its dose and rate of administration depend on the conditions of the individual, which consist of blood pressure, pulse, hemodynamic status, hemoglobin and hematocrit concentrations, plasma protein content (the oncotic pressure described above) and the degree of venous and pulmonary congestion. A total of 125 grams of albumin can be administered every 24 hours.

Summary

As we have seen in this space, the albumen it is the protein most present in blood plasma and performs multiple functions: from the transport and metabolism of various substances to the maintenance of oncotic pressure, this molecule is essential for the correct physiological balance of the body.

Whether due to excessive excretion by the kidneys or poor synthesis in the liver, a lack of serum albumin can translate into swelling of certain areas of the body, fatigue, muscle weakness and many other clinical signs. Despite the fact that this condition can be caused by many events, alcoholism and malnutrition are two of the most common. Once again, we see that each particle that makes up our body is essential for the maintenance of the physiology and functions of our body.

Bibliographic references:

  • Albumin (blood), Mhealth.
  • Albuminuria, NIDDK.
  • Hankins, J. (2008). Role of albumin in water balance. Nursing (Spanish Ed.), 26 (10), 42-43.
  • Hypoalbuminemia, chemocare.com.
  • Oncotic pressure, Clínica Universidad de Navarra.

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