Our body is a complex system, and the deeper ourknowledge of its structure, the more amazing and mysterious it seems. The internal environment of the body, where there is a direct exchange between the cells, is the tissue fluid and lymph. How is the internal environment formed, what is its composition and function? This article will tell you about this.
The real internal environment of the body isa tissue fluid that occupies intercellular spaces. Blood as a component of the internal environment does not come into contact with the cells of the body. Capillary walls firmly separate it and retain the composition. Each cell also has a cytoplasmic membrane. Mechanisms of membrane transport provide a metabolism, but this happens through the transition of all substances into the interstitial fluid.
All cells of our body, and their order of a hundredtrillions, are surrounded by a liquid medium filled with nutrients. This is the tissue (interstitial) fluid. It has its own composition and stable isoionium (ion concentration). In our body, its volume is about 20 liters, and this is up to 29% of the total weight. Its composition is diverse and depends on the specific nature of the surrounding tissue (cerebrospinal fluid, pleural and pericardial bags). The main feature of the composition - in the intercellular fluid there are few proteins, many dissolved sugars, amino acids and enzymes. The main part is water with dissolved salts, electrolytes, oxygen, carbon dioxide, the products of vital activity of our cells.
From the intercellular space part of the tissuethe fluid flows back into the bloodstream, and part goes to the lymphatic vessels. Once in there, it becomes peripheral lymph. Passing through one or two lymph nodes, it becomes intermediate, and before returning to the bloodstream (for example, in the thoracic duct) it is already central lymph. In this case, from the peripheral to the central lymph is filled with shaped elements. In our body, the order of two liters of lymph, which consists of water and uniform elements: leukocytes, monocytes, segmented neutrophils, platelets, eosinophils and other cells. In addition, there are fats, proteins and carbohydrates in the lymph. The percentage composition of these components of lymph varies depending on its source tissues.
Our blood is enclosed in a system of blood vessels andcapillaries, and the circulatory system has a closed blood flow. It consists of a liquid fraction - a plasma - and a fraction of the shaped elements. In an adult male blood of about 40-47% of the elements, a woman - up to 42%. Blood in our body is up to 8% of the body weight, and this is 6 liters. The blood plasma has a constant composition: 91% - water, up to 8% - proteins, the rest - electrolytes, lipids, glucose, hormones and bioenzymes, vitamin complexes and dissolved gases. Form elements are specific cells (red blood cells, leukocytes, platelets).
Circulation of blood, tissue fluid and lymph inthe whole is simple and is represented in the figure. Part A illustrates blood circulation and lymph drainage, part B - how tissue fluid and lymph form. From the blood capillaries under the influence of hydrostatic and oncotic pressure, the liquid fraction of blood plasma enters the intercellular space, where it forms colloidal and fibrous formations. Some of these substances pass into cells from the tissue fluid. How does the lymph form further? Some of the liquid enters the lymphatic capillaries. The outflow of lymph is facilitated by contractile movements of the walls of the vessels and the presence of valves in them. Further, the lymph passes through the lymph nodes, where it is purified from toxins and enriched with lymphocytes, and then through the large lymphatic ducts it returns to the bloodstream. The scheme of formation of tissue fluid and lymph, its outflow is presented in the following illustration.
In the tissue, the movement of blood is not carried out by allcapillaries: some of them are closed, and some are open. It is this that explains how tissue fluid and lymph are formed in a single tissue site. In the arterial part, the fluid is filtered into the intercellular space and there is accumulation. As the pressure created by excess fluid increases, the capillaries are squeezed and "closed". In this case, other capillary fields, lymphatic, are opened. The free liquid phase of the tissue space passes into the lymphatic ducts and the pressure in this area decreases, which leads to the opening of the blood capillaries.
Description of the value of the internal environment for the normal life of our body will take more than one page. We list only the main functions: