BLOOD





Blood:

Blood is a vital fluid that serves as a medium for transporting various substances throughout the body. It consists of two main components: plasma and cells (or cell-like bodies), including white blood cells, red blood cells, and platelets. The weight of blood in the human body is approximately 1/12 of our total body weight.

Plasma is a significant constituent of blood, accounting for approximately 55% of its volume in a normal person, while cells or cell-like bodies make up about 45% of the blood volume. It primarily consists of water, in which proteins, salts, nutrients, and wastes are dissolved. Roughly 90% of plasma is composed of water, while the remaining 10% consists of dissolved substances. Most of these dissolved substances maintain a relatively constant level, although some exhibit varying concentrations.

The composition and concentration of substances dissolved or present in plasma can vary depending on the condition of the organism and the specific area of the body under examination. These solutes can be classified into six categories:

1) Inorganic ions or mineral ions:

Inorganic ions and salts collectively account for approximately 0.9% of the plasma's weight in humans. Of this amount, more than two-thirds is composed of sodium chloride, which is commonly known as table salt. Even if the total concentration of dissolved substances remains constant, changes in the concentration of specific ions can lead to significant disturbances. The pH of human blood is typically maintained at a constant level of 7.4, as any changes in pH can impact the chemical reactions within the body.

2) Plasma proteins:

Plasma proteins constitute approximately 7-9% of the plasma's weight. Most of these proteins are synthesized in the liver. Some of the proteins, known as immunoglobulins or antibodies, are produced by lymphocytes in response to antigens. They are then transferred to the plasma and lymph. Proteins such as prothrombin act as catalysts in the blood clotting process, while fibrinogen is involved in the actual formation of blood clots. Immunoglobulins play a crucial role in the body's defense against diseases.

3) Organic nutrients:

Organic nutrients present in plasma include glucose, fats, phospholipids, amino acids, and lactic acid. Some of these nutrients enter the bloodstream through absorption in the intestines. Lactic acid is produced in muscles as a byproduct of glycolysis and is transported by the blood to the liver. Cholesterol, an important component, undergoes metabolism to some extent but also serves as a precursor for steroid hormones.

4) Nitrogenous waste products:

Plasma also contains nitrogenous waste products generated from cellular metabolism. These waste products, such as urea and small amounts of uric acid, are produced in the liver and transported through the bloodstream to organs like the kidneys, where they are eventually eliminated.

5) Hormones:

All hormones in the body are carried by the blood, making them present in the plasma. Hormones play crucial roles in regulating various physiological processes and are responsible for coordinating and controlling the functions of different organs and tissues.

6) Gases:

The plasma of the blood also contains gases such as carbon dioxide (CO₂) and oxygen (O₂). These gases are essential for cellular respiration and are transported to and from various tissues through the bloodstream.


In summary, blood serves as a vital medium for transporting essential substances throughout the body. Plasma, comprising a significant portion of the blood, consists mainly of water and contains various dissolved substances, including inorganic ions, plasma proteins, organic nutrients, nitrogenous waste products, hormones, and gases. The balance and regulation of these substances are critical for maintaining the overall health and proper functioning of the body.