Amblerous water

The amniotic fluid can be considered as a large part of the extracellular fluid of the fetus, since its osmotic indices, electrolyte and biochemical composition are identical to the fetal plasma.

Normally, the amount of amniotic fluid is 0.5-1.5 liters, varies depending on the gestational age. It should be noted that the physiological development of the fetus depends to a large extent on the usefulness of the amniotic fluid.

Functions of amniotic fluid

Amniotic fluid performs a number of important functions in the development of the fetus, namely:

• creates conditions for unimpeded movement of the fetus and the development of its musculoskeletal system;
• water, which swallows the fetus, contribute to the development of the digestive tract;
• supplies the components vital to the nutrition of the fetus;
• maintains constant intrauterine pressure, thereby reducing the loss of pulmonary fluid, a component necessary for lung development (Nicolini, 1998);
• protects the fetus from numerous exogenous influences;
• protects the umbilical cord from compression;
• the constant temperature of the amniotic fluid helps maintain the body temperature of the fetus;
• bacteriostatic properties of amniotic fluid reduce the risk of possible infection of the fetus.

Physiology of amniotic fluid

The main sources of amniotic fluid formation are the respiratory system, fetal kidneys, umbilical cord, exfoliated skin epithelium, mucous membrane of the cheeks, urinary and sexual organs of the fetus, fetal surface of the amnion and chorion cells.

The process of formation and evacuation of amniotic fluid from the amnion is fast enough. So, a complete exchange of water occurs in 3 hours, and the exchange of dissolved substances - for 5 days.

It should be noted that the factors that regulate the exchange of amniotic fluid have not yet been fully studied. Brace (1997) identifies 6 possible ways of movement of amniotic fluid.

Movement of amniotic fluid is carried out from mother to fetus, from the fetus to the amniotic cavity and again into the mother's body.

Excretion of water takes place by placental and paraplacental routes. In the first case, they are excreted through the fetal organism during respiratory movements (by ingestion). Thus, approximately 600-800 ml of liquid per day passes through the lungs of the fetus. Part of the water is utilized by the skin and respiratory tract and is subsequently removed through the umbilical cord and the placenta. In this way, about 40% of the amniotic fluid is excreted.

Ways of movement of amniotic fluid

Ways of movement of amniotic fluid	Volume, ml / day
	To the fetus	Into an amniotic fluid
Fetal Ingestion	500-1000	-
Oral secretion	-	25
Secretion through the respiratory tract	170	170
Urination of the fetus	-	800-1200
Intramembranous movement through the placenta, umbilical cord and fetus	200-500	-
Transmembranous movement from the amniotic cavity to the uterine flow	-	10

Most of the amniotic fluid is excreted paraplacental way, namely through the intercellular spaces into the blood vessels of the smooth chorion, the decidual envelope and the venous system of the mother.

Chemical composition of amniotic fluid

The amniotic fluid contains 98-99% of water, 1-2% is a dense residue, half of which is organic compounds, and half are inorganic.

The study of the composition of amniotic fluid showed that in the amniotic fluid contains 27 amino acids and 12 protein fractions.

In amniotic fluid, all fractions of lipids were also found; mono-, di-, triacylglycerides, cholesterol and its esters, fatty acids and all classes of phospholipids.

Carbohydrate metabolism of amniotic fluid is not fully understood.

In addition, amniotic fluid contains acid hydrolase, alkaline and acidic phosphatase, beta-glucuronidase, hyaluronidase, hexosamidinamidase, lactate dehydrogenase, isocitrate dehydrogenase, carbonic anhydrase, glucose-6-phosphatase, glucose-6-phosphate dehydrogenase and other enzymes.

Also in the amniotic fluid a significant amount of biologically active substances, in particular histamine, dopamine, catecholamines, serotonin, has been detected.

Histamine is synthesized both in the body of the mother and the fetus and takes part in the regulation of embryonic growth processes. In turn, dopamine in amniotic fluid in a significant amount is detected immediately before childbirth. The concentration of catecholamines increases with the duration of pregnancy, which is a reflection of the maturation of the sympathetic autonomic nervous system of the fetus. Serotonin is actively secreted into the amniotic fluid by the fetus and its concentration rises with increasing gestation. The serotonin content in the amniotic fluid has a diagnostic value: its decrease is one of the earliest manifestations of compensatory reactions to intrauterine hypoxia.

The amniotic fluid has a high hormonal activity. They contain the following hormones: chorionic gonadotropin, placental lactogen, adrenocorticotropic hormone, prolactin, somatotropic hormone, thyroxine, insulin, and steroid hormones. The main source of steroids is the placenta. In it there is a consecutive transformation of cholesterol into pregna nolone, then into progesterone, from which fetal corticosteroids are synthesized.

In amniotic fluid, all fractions of estrogens are determined in concentrations that significantly exceed the latter in the blood of the mother and fetus. In the physiological course of pregnancy, the amount of estrogen in the amniotic fluid progressively increases. The increase in the level of estrogen is due to estriol, which enters the amniotic fluid with fetal urine by direct absorption from the circulatory system.

The composition of amniotic fluid includes almost all corticosteroids. Most of them are of fruit origin. It is known that an increase in the concentration of cortisol in the amniotic fluid is an integral part of the mechanism of normal delivery and the index of maturity of the fetus.

[1], [2], [3], [4], [5], [6]