Our body is a complex system, and the deeper our knowledge of its structure, the more surprising and mysterious it seems. The internal environment of the body, where there is a direct exchange between cells, is tissue fluid and lymph. How is the internal environment formed, what is its composition and functions? This article will tell about this.
The main components of the environment
The real internal environment of the body is tissue fluid, which occupies the intercellular spaces. Blood as a component of the internal environment does not come into contact with the cells of the body. The capillary walls firmly separate it and retain its composition. Each cell also has a cytoplasmic membrane. Membrane transport mechanisms provide metabolism, but this happens through the transition of all substances into the interstitial fluid.
Lymph is another component of the internal environment. From a biology course, we know that lymph is a fluid that is in the lymphatic system, the second most important body system. Simply put, these media are connected by a closed circuit: blood - interstitial fluid - cell - lymph - blood. Exactly this way is the exchange of metabolic products, hormones, biological substances and gas exchange.
Interstitial environment
All cells of our body, and about one hundred trillion of them, are surrounded by a liquid medium filled with nutrients. This is tissue (interstitial) fluid. It has its own composition and stable isoion (concentration of ions). In our body, its volume is approximately 20 liters, and this is up to 29% of the total weight. Its composition is diverse and depends on the specifics of the surrounding tissue (cerebrospinal fluid, pleural and pericardial bags). The main feature of the composition is that 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 waste products of our cells.
Intercellular fluid - a precursor to lymph
From the intercellular space, part of the tissue fluid enters the bloodstream, and part is sent to the lymphatic vessels. Once there, it becomes peripheral lymph. After 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 the central lymph. In this case, from peripheral to central lymph is filled with shaped elements. In our body, about two liters of lymph, which consists of water and shaped elements: white blood cells, monocytes, segmented neutrophils, platelets, eosinophils and other cells. In addition, fats, proteins and carbohydrates are present in the lymph. The percentage of these components of the lymph varies depending on its source tissues.
Blood - the internal environment of the body
Our blood is enclosed in a system of vessels and capillaries, and the circulatory system has a closed blood flow. It consists of a liquid fraction - plasma - and a fraction of shaped elements. In an adult man, about 40-47% of uniform elements in the blood, in a woman - up to 42%. Blood in our body is up to 8% of body weight, and this is 6 liters. 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. The shaped elements are specific cells (red blood cells, white blood cells, platelets).
Fluid cycle
The circulation of blood, tissue fluid and lymph is generally simple and is shown in the figure. Part A illustrates blood circulation and lymph outflow, part B illustrates how tissue fluid and lymph are formed. From the blood capillaries under the influence of hydrostatic and oncotic pressure, the liquid fraction of the blood plasma enters the intercellular space, where it forms colloidal and fibrous formations. Some of these substances pass into cells from tissue fluid . How is lymph formed further? Part of the fluid 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 cleaned of toxins and enriched with lymphocytes, and then through the large lymphatic ducts it returns to the bloodstream. The formation of tissue fluid and lymph, its outflow is presented in the following illustration.
Water exchange mechanism
In the tissue, blood movement is not carried out in all capillaries: some of them are closed, and part is open. This explains the formation of tissue fluid and lymph in a single tissue site. In the arterial part, the fluid is filtered into the intercellular space and it accumulates there. As the pressure created by excess fluid increases, the capillaries compress and “close”. At the same time, other capillary fields open - lymphatic. 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 blood capillaries.
Functions of blood, lymph, tissue fluid
Description of the value of the internal environment for the normal functioning of our body will take more than one page. We list only the main functions:
- Providing homeostasis of the interstitial space.
- Protein, lipid and carbohydrate metabolism.
- Gas exchange, transport of nutrient hydrolysis products.
- Redistribution of fluid.
- Humoral connection of tissues and organs, lymphatic system and blood.
- The implementation of the mechanisms of all types of immunity.
- Regulation of energy metabolism by transferring energy-providing biomolecules of adenosine triphosphoric acid.