What is blood?
The blood is a type of connective tissue in the body of vertebrate animals circulating in their arteries, veins and capillaries carrying the various nutrients produced by metabolism and oxygen, essential for cellular respiration.
It has a characteristic red color and is a more or less dense liquid, in which there is a vast and complex set of cells and vital substances in a constant cycle called the cardiovascular system or blood system.
Blood is vital for the functioning of the organism and it is estimated that a human body contains between 5 and 6 liters of blood, which represents 7% of its total weight.
It is possible to extract it from its natural ducts, a practice that is customary as a method of analyzing the functioning of the different hormonal and metabolic systems of the body. However, a very drastic reduction in its quantity, density or content can cause death or serious damage to different organs and tissues.
The word blood comes from the Latin sanguis and there are various theories regarding its etymological origin. One of them, documented by San Isidoro de Sevilla (560-636 AD), assures that the word originated from the adjective for “soft”, since that was the texture of said substance when the first autopsies of the history.
General characteristics of the blood
It is a liquid of red color (dark tone when it is venous blood and light tone when it is arterial blood) and of a non-Newtonian type, that is, whose viscosity varies with the temperature and the shear tension applied to it.
It is a mostly aqueous and colloidal matrix solution, whose pH range ranges from (7.36 to 7.44) and its temperature is around 37 degrees, under ordinary health conditions.
Blood is primarily composed of water (91%), proteins (8%) and some other materials dissolved in it. Its characteristic color is due to the presence of hemoglobin, a pigment that abounds in the red blood cells (erythrocytes) that compose it.
It is also made up of another large set of cells such as white blood cells (leukocytes) or platelets, as well as proteins such as enzymes, hormones, nutrients and other vital substances, such as glucose. Blood also carries waste substances, which are then filtered and discarded from the body.
Blood is composed of two distinct phases, known as blood parts and which are:
- Solid phase . These are the formal elements, that is, the solid objects dissolved in the blood, such as cells and proteins.
- Liquid phase . Also known as a serum component, it is primarily blood plasma, a yellowish substance that constitutes 55% of the blood and is slightly denser than water.
Not all blood is identical and traditionally four blood types are distinguished whose determination is congenital, that is, it does not change throughout life or is optional.
Blood transfusion, for example, should be done according to the recipient’s blood group, otherwise your body will receive different blood as if it were a foreign substance and defend itself against it.
This is due to the presence of certain defensive proteins called antigens and antibodies, which are both in red blood cells and in plasma.
These groups are:
- Group A . It has A antigens in erythrocytes and anti-B antibodies in plasma.
- Group B . It presents B antigens in erythrocytes and anti-A antibodies in plasma.
- AB group . It has both A and B antigens in erythrocytes, but no antibody in the plasma. This blood group can receive both type A and B blood and is known as a “universal receptor.”
- O group . It has no antigens neither A nor B in erythrocytes, but anti-A and anti-B antibodies in plasma. Therefore, you can donate to any other blood group, but only receive from your own. That is why he is known as a “universal donor”.
The process of blood formation is called hematopoiesis and takes place in organs and tissues specialized in this function, such as the bone marrow inside the bones, together with the liver, endocrine glands and kidneys, responsible of producing its cellular, enzymatic and aqueous component.
Red blood cells live for about 120 days, after which they are filtered by the liver for degeneration and recycling of iron, as well as expulsion of residual bilirubin when hemoglobin breaks down. They are immediately replaced by fresh blood cells that perpetuate the cycle.
The functions of the blood are diverse, namely:
- Its primary function is to serve as a transport mechanism throughout the body for both defensive and nutritive or sustenance cells and substances such as oxygen and glucose, essential for obtaining energy.
- It is essential for the cardiovascular cycle carries oxygenated blood from the lungs to the heart and the body completely, and then the filled blood CO 2 heart and thence to the lungs for reoxygenation.
- It also keeps the body temperature stable since in the presence of heat it is ventilated by widening the capillaries and exposing it to cooling through the skin, and in the presence of cold the vessels are compressed to attenuate this effect.
- It fulfills defensive functions, transporting leukocytes and platelets to the injured regions , preventing access to infections and quickly plugging damaged tissues.
Blood circulation is what keeps the body walking and the various tissues alive and nourished. The blood path reaches the most unknown regions of the body through a wide system of ducts: arteries (for oxygenated blood), veins (for deoxygenated blood) and smaller blood capillaries.
The motor of this cycle is the heart , which continuously pumps and aspirates the blood, keeping it in continuous flow from the organs and tissues to the respiratory system and back to the ends of the body.
The blood can suffer numerous diseases or ailments, grouped based on four principles of action on it:
- Diseases of hemostasis . Those that unbalance the blood content, either by overloading it with some benign element or substance under other conditions, or by subtracting it from an indispensable component. For example, diabetes.
- Erythrocyte system diseases . They afflict red blood cells, subtracting their oxygen transport capacity or shortening their half-life. For example, certain syndromes and congenital diseases of erythrocyte malformation.
- Leukocyte system diseases . They afflict the defensive system (white blood cells). For example, HIV-AIDS.
- Hematological malignancies . Types of cancer and lymphomas that impair blood quality.
The blood in the culture
Blood has played an important role in the imaginary of the human being from an early age. It has been associated with life and therefore with a certain sacred character that gave it central roles in rites, sacrifices and mythical narratives.
In Greco-Roman antiquity it was considered one of the four moods that make up the human body (in the theory of Hippocrates humors) along with yellow bile, black bile and phlegm and, therefore, determinant in health and in the character of individuals.
Numerous mythological stories give him curative or poisonous properties, depending on the creature from which it is extracted and the beings that subsist from ingesting the blood of others always had them as cursed or evil beings, as is the case with vampirism.