The study of serous fluids (they are also called effusions) is of great diagnostic value in modern medicine. Information about these studies enables the doctor to establish a diagnosis and prescribe effective treatment in a timely manner. So let's figure out what it is, what types of serous fluid are and in what diseases they can be detected.
General information
Exudative fluid is an ultrafiltrate of human blood. This means that this substance is formed due to the filtration of blood from the bloodstream into the surrounding cavities and tissues. Moreover, in the classical sense, effusion is a liquid that accumulates precisely in the cavities of the human body. And what is collected in the tissues is called edematous fluid.
Normally, only part of the blood with a small molecular weight (water and electrolytes, for example) can pass through the pores of the capillaries. And substances with a high molecular weight (proteins, formed elements) must remain in the bloodstream. However, if there isIn the body of the inflammatory process, the wall of blood vessels is damaged, and large molecules of proteins and blood cells are able to enter the body cavity.
The concepts of serous cavities and membranes
The serous cavity is the space bounded by the serous membranes.
Serous membranes are films consisting of two sheets: parietal (located closer to the muscles) and visceral (tightly covering the internal organs).
Sheets of serous membranes are represented by the following layers:
- mesothelium;
- boundary membrane;
- fibrous collagen layer;
- superficial network of elastic fibers;
- deep longitudinal network of fibers;
- lattice layer of collagen fibers.
Mesothelium in the composition of the serous membranes performs an important function: its cells constantly produce fluid necessary for cushioning.
The visceral (organ) sheet of the serous membrane receives blood from the vessels supplying the organ it covers. And the parietal sheet receives blood supply from a wide network of anastomoses.
Serous membranes have a well-developed outflow of lymph. Therefore, the slightest violation of the lymphatic outflow can lead to the accumulation of serous fluid.
Main Functions
Why does a person need the presence of serous fluids in the cavities? To answer this question, we highlight the main functions of the effusion fluid:
- protective function - prevention of friction of organs against each other and theirtrauma;
- ensuring the dynamic properties of internal organs;
- sliding-damping function, as one of the components of the protective one.
Types of effusion
Exudative fluid is divided into two main types: transudate and exudate.
Transudate is a liquid, the accumulation of which is not associated with the presence of an inflammatory process in the body. If it collects in the tissues, this condition is called edema.
If the transudate collects in the pericardium (heart sac), there is hydropericardium, if in the abdominal cavity - ascites, in the pleural cavity - hydrothorax, around the testicle - hydrocele.
Exudate is a fluid that collects in the body cavity due to an inflammatory process.
Thus, although both transudate and exudate are two varieties of the same process, they have completely different origins, and, consequently, structure.
Transudate: causes of accumulation
The accumulation of serous fluid in the form of transudate can be caused by the following pathological conditions:
- hypoproteinemia - a decrease in the concentration of protein in the blood, mainly due to albumin; observed in glomerulonephritis with nephrotic syndrome, severe liver disease with the development of hepatocellular insufficiency, general exhaustion of the body;
- violation of lymph outflow due to blockage of lymphatic vessels;
- an increase in venous pressure that occurs during cardiacvascular insufficiency, severe liver and kidney disease.
- an increase in the concentration of sodium in the blood, observed in heart failure, nephrotic syndrome, liver failure.
- increased synthesis of aldosterone, which leads to increased absorption of sodium and water in the kidneys.
Exudate: species
When diagnosing the type of serous fluid and confirming the presence of exudate, it is necessary to indicate which type is found:
- serous - has a transparent or cloudy appearance, white;
- serous-purulent, or purulent - cloudy, yellow-green color with sediment;
- putrid - cloudy with a pungent odor;
- hemorrhagic - red or red-brown;
- hillous - hazy yellowish color;
- cholesterol - thick yellow liquid with cholesterol flakes;
- mucilaginous - with lots of mucin;
- fibrinous - incorporates fibrin strands;
- mixed forms - serous-fibrinous, mucopurulent, etc.
Transudate and exudate: differences
The differences in these two effusions are based on their concentration of protein, glucose, specific gravity of the two fluids, as well as their macroscopic characteristics (color, transparency).
As noted above, the accumulation of transudate in the cavities is in no way associated with inflammation. Therefore, the presence of differences in these two types of effusions is quite logical.
Let's start with specificweight. In exudate, it is much higher than in transudate, amounting to >1.015 and <1.015, respectively.
The level of protein in the transudate is also less than in the exudate - a true protein liquid. Its concentration is 30 g/l for exudate.
There is a special test to distinguish these two types of effusions. It is called the Riv alta test. Despite the fact that this test has been used in medical practice for more than 60 years, it is still widely used when it is necessary to differentiate two types of serous fluids. Its main advantage is the speed of obtaining results. Here, the difference between transudate and exudate is that in the presence of transudate, the sample is negative (which cannot be said about exudate).
| Transudate | Exudate | |
| Specific gravity | 1, 006–1, 015 | greater than 1, 015 |
| Protein concentration | less than 30 g/l | more than 30 g/l |
| Presence of bacteria | Not typical | Characteristic is the presence of bacteria (streptococci, staphylococci, etc.) |
| Cells that are detected in the sediment | Mesothelium, lymphocytes, maybe a small amount of red blood cells | Neutrophils, lymphocytes, a large number of erythrocytes and macrophages, eosinophils, tumor cells |
| The ratio of effusion protein concentration to blood protein concentration | < 0.5 | > 0.5 |
| Glucose concentration (mmol/l) | >5, 3 | <5, 3 |
| Cholesterol concentration (mmol/l) | <1, 6 | >1, 6 |
| The number of cells, in medicine the term "cytosis" is used | < 1×109/l | > 1×109/l |
Thus, the ability to distinguish between transudate and exudate is very important for the doctor. After all, this contributes to the correct diagnosis, and therefore, the appointment of the correct treatment.
