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FUNCTIONAL SYSTEM “MOTHER - PLACENTA - FET” (FETOPLACENTIAL COMPLEX)

At the heart of a woman's childbearing function are:

1. Ovariomenstrual cycle

2. The process of pregnancy



Outside of pregnancy, hormonal regulation is carried out by the hypothalamic-pituitary-adrenal system, ovaries and thyroid gland.

During pregnancy, hormones of the fetoplacental complex come first.



The fetoplacental complex is a combination of two independent organisms, united by a common goal, task and end result - ensuring the normal development of the fetus.



There are two main elements of the fetoplacental complex:

1. The functional system of the mother's body

- for the fetus, it is an external environment that provides normal conditions for development.



2. Functional system of the fetus

- his activity is aimed at maintaining homeostasis.



The relationship between these systems is through the placenta.

A single hemodynamic function and the function of the placenta indicate a close relationship between the functional system of the mother's body and the functional system of the fetus.







There are 4 communication channels:

1. The transplacental humoral channel of direct and feedback.

- he is the most informative.



2. Extraplacental humoral canal

- communication is carried out through the membranes of the fetus and amniotic fluid.



3. The placental nerve canal

- information comes from bar receptors and chemoreceptors of the placenta and umbilical vessels.



4. Extraplacental nerve canal

- Information comes from the uterus and other organs in the central nervous system.



A single hemodynamic function and the function of the placenta indicate a close relationship between the functional system of the mother's body and the functional system of the fetus.



The placenta (from the Latin word "cake") was first described by Fallopius.



The placenta is a rounded flat cake with a diameter of 15-20 cm.



The thickness of the mature placenta in the center is 37-40 mm, on the periphery - 7-10 mm.



The mass of the placenta is 500-600 grams.



The total length of the villi of the placenta is

50 km

The total area of ​​the villi is 10-20 sq.m.



The placenta contains 60 ml of fetal blood, 90-100 ml of maternal blood.



The functions of the placenta:

1. The implementation of gas exchange

2. Metabolic

3. Trophic

4. Endocrine

5. Excretory

6. Barrier



The state of these functions depends on the state and intensity of the uteroplacental circulation.



Prerequisites for this are:



1. Abundant blood supply to the uterus.

There are 4 large paired sources:

uterine arteries

- ovarian arteries,

- arteries round uterine ligament,

- sacro-uterine.



Additional sources of blood circulation are:

- cystic

- rectal arteries.



2. The presence of a large number of anastomoses between the right and left half of the uterus.



3. Venous outflow is carried out in the venous plexus corresponding to arteries.



4. The special structure of the terminal arteries:



• In the thickness of the myometrium, they go in the radial direction - these are radial arteries



• In the mucous membrane (endometrium) they have a convoluted course - these are spiral arteries.

Their lumen and blood flow velocity in them depend on the amount of estrogen.



The placenta has a hemochorial type of structure, that is, the blood of the mother and fetus does not mix anywhere.







There are two independent, but closely related circles of blood circulation:

1. Uterine-placental

2. Fetal placental



The exchange of substances between them occurs through the border membrane - this is the so-called placental barrier.

It is formed by the wall of the terminal villi.



The structure of the placenta.

The placenta is formed by:

1. Chorionic membrane

(located on the fetal side)

It is formed by:

• Amnion

• Chorionic connective tissue

• Cytotrophoblast

• Syncytiotrophoblast



2. The basement membrane

(mother surface)

It is formed by:

• Syncytiotrophoblast

• Structureless fibrinoid

• Basal decidua



3. Parenchymal part

(located between the chorionic and basal membrane)

It is formed by:

• Stem villi and their branches, containing the vessels of the fetus

• The intervillous space in which maternal blood circulates freely



The fetal-placental system.

Blood volume progressively increases during pregnancy.

In the first trimester, it is 8% of the fetal mass and placenta mass, in the second - 10% (approximately 500 ml or 75-100 ml per kg of fetal mass and placenta mass).



The structure of the fetal-placental system.

• Trunk vessels

(these are arteries and veins in the thickness of the chorion plate, they are connected with the vessels of the umbilical cord)



• Peripheral vessels

(these are arteries and veins in stem villi and their branches)



• Capillary system

(in terminal villi).



Venous blood of the fetus reaches the placenta in two arteries, which in the placenta are divided into many branches.

Each artery penetrates the chorionic plate - these are trunks of the first order.

Each first order trunk is divided into two second order trunks, each of which is divided into two third order trunks.

So, dividing, these vessels reach the basement membrane, ending in the terminal villi.



The main structural unit in a mature placenta is a lobule - cotilidone - a stem villus with a first-order artery and its multiple branches.



In a mature placenta, there are from 15 to 25 lobules.



The terminal villus is the placental barrier.

By the end of pregnancy, its thickness reaches 3-5 microns.



The structure of the terminal villi.

The terminal villus consists of a stroma with a capillary.

• Stroma is collagen fibers and cells (macrophages, fibroblasts).



• The basal membrane of the trophoblast adheres to the stroma



• Cytotrophoblast

(provides immunological protection of the fetus)



• Syncytiotrophoblast



Syncytiotrophoblast is a cytoplasm that for the most part does not divide into cells.

There are "bare" zones - these are nuclear-free areas.

There are many villi and cytoplasmic outgrowths in syncytiotrophoblast - these are active absorption zones.



Syncytiotrophoblast has a high enzymatic activity, it breaks down proteins into amino acids.

Syncytiotrophoblast has the ability to synthesize complex substances from simple ones (synthesis of hormones, proteins).



Uterus-placental circle.

Comprises:

• Spiral arteries and veins

• Intervillous space



The intensity of uteroplacental circulation increases with pregnancy.

In the first trimester, it is 50 ml per minute,

at the end of pregnancy - 500-700 ml per minute.



Of the blood entering the uterus, 75-80% circulates directly at the place of attachment of the placenta - this is the so-called placental site.



The remaining 20-25% go to the uterus proper - this is a "placental discharge."



From the blood that entered the area of ​​the placental site, 400-550 ml go into the intervillous space where metabolism is carried out, and the rest of the blood goes to the nutrition of the placenta as an organ - this is a placental discharge.

Maternal blood from spiral arteries that open freely through ejected holes in the basement membrane is ejected by a powerful jet at a pressure of 70-80 mm Hg. Art. into the intervillous space and rushes up.

Near the chorionic plate, the blood turns back. At the same time, blood flow velocity and pressure are reduced.

The pressure in the intervillous space is 10-20 mm RT. Art.

Blood flows back through openings in the basement membrane into the corresponding veins.

Thus, the blood circulation in the intervillous space is supported by the pressure difference:

• In arteries 70-80 mm Hg

• In the veins of 6-8 mm Hg

• In the intervillous space of 10-20 mm RT.



Factors affecting blood flow intensity:

- maternal blood pressure

(its significant decrease or increase leads to circulatory disorders in the uteroplacental circle)



uterine contractions

(during normal contractions in the intervillous space, the pressure is 70-80 mm Hg, which leads to a temporary disturbance in blood flow)



- rheological properties of blood

- rhythmic contractions of the spiral arteries



- fruit factors

(stress state of villi, reduction of collagen fibers of villi, constancy of umbilical cord blood flow - 80 ml per minute per 1 kg of body weight).



Mechanisms for the implementation of the functions of the placenta.



1) Respiratory function

Oxygen transport occurs unilaterally by the mechanism of simple diffusion (voltage difference between carbon dioxide and oxygen in the blood).

The carbon dioxide voltage in maternal blood is 3.5 kilopascals (kPa), and in the fetal blood - 5.3 kPa.




Oxygen tension in maternal blood -

13.3 kPa, and in the fetal blood - 4 kPa.

Oxygen transport is constantly 2200-2500 ml per hour, since oxygen does not accumulate in the placenta.



2) Metabolic, trophic and barrier functions

They are carried out according to the mechanism:

- Simple diffusion

(from an area with a high concentration to an area with a lower concentration of a substance).

So transported: water, sodium, potassium, calcium, magnesium, bicarbonates, urea and gases.



- Lightweight diffusion

(its speed is greater than with simple diffusion).

So glucose, amino acids are transported.



- Ultrafiltration

(in villi and outgrowths of syncytiotrophoblast)



- Active transport



- Pinocytosis

(this is how hormones, lipids, phospholipids are transported).



The ability to penetrate substances through the placental barrier is affected by:



- Fat solubility

(directly proportional relationship)



- The shape of the molecule



- Ability to bind to plasma proteins (inversely proportional relationship)



- The degree of ionization of the molecules

(inversely proportional)

3) Endocrine function



The fetoplacental complex synthesizes classical hormones, but their secretion level is 100-400 times more intense.

The synthesis process uses maternal and fetal precursors.

Hormones of the fetoplacental complex are divided into protein and steroid.



Protein hormones:

- chorionic gonadotropin

- placental lactogen

- prolactin



They are synthesized in syncytiotrophoblast and in large quantities enter the maternal blood.

These hormones belong to the group of hormones-protectors of pregnancy.



Chorionic Gonadotropin

- This is the main protein hormone of pregnancy, close to luteinizing hormone.

It is detected in the blood of pregnant women at the time of blastocyst passage through the fallopian tube, that is, even before implantation. This is the basis for a pregnancy test.

The peak of secretion of this hormone occurs at 7-16 weeks of gestation (supports the function of the corpus luteum in the ovary), at 34 weeks it actively stimulates the fetal adrenal glands.



The functions of chorionic gonadotropin:

1) ensuring the adaptation of a woman's body to pregnancy



2) inhibits the immunological reactions of rejection of the fetal egg (that is, provides tolerance)



3) reduces the contractile activity of the myometrium (stimulates the corpus luteum to the synthesis of progesterone)



4) ensures the correct formation of the sex glands in the fetus

Placental lactogen.

It is detected in the blood from 5-6 weeks of pregnancy, its level rises to 37 weeks.



Functions:

1) luteotropic effect (stimulates the synthesis of sex hormones in the corpus luteum)



2) reduces uterine contractility



3) lactogenic effect (prepares the mammary glands for lactation)



4) lipolytic effect (provides a high level of free fatty acids)



5) diabetogenic effect



6) stimulates protein synthesis



Thus, it affects all types of metabolism and the fetal mass depends on its level.



Prolactin.



Functions:

1) is involved in fetoplacental osmoregulation



2) is involved in the production and maturation of pulmonary surfactant.





Steroid hormones:

- progesterone

- estrogens



Progesterone.



The peak of secretion occurs at 16 weeks, then its level rises to 37 weeks, and then drops.



Functions:

1) increases the activity of beta-adrenergic receptors



2) reduces the activity of alpha-adrenergic receptors



3) provides decidual transformations



4) myometrium and provides implantation



5) reduces uterine contractility



6) causes hyperpolarization of the membranes.



Estrogens.

estradiol

estron

estriol



By the time of full-term pregnancy, they dominate.



Estrogens are synthesized from the precursor of cholesterol - the maternal cholesterol, which enters the maternal part of the placenta, turns into progesterone and goes into the blood of the fetus.

In the adrenal glands of the fetus, it passes into the predecessors of male sex hormones - dehydroepiandrosterone, androsterone and testosterone, which again enter the placenta.

In the fetal part of the placenta, estrogens are synthesized from them.



The amount of estrogen formed depends on:

• number of predecessors

• functional activity of the adrenal glands of the fetus



The biological effect of estrogen:



1) increases the activity of alpha-adrenergic receptors



2) reduces the activity of beta-adrenergic receptors



3) causes hyperplasia and hypertrophy of myometrial cells (increase in uterine mass from 50 grams before pregnancy to 1.5 kg at the end of pregnancy, growth of blood vessels and nerve endings)



4) activates blood circulation, increases the degree of oxygen consumption by myometrium



5) activate the synthesis of enzymes



6) activate the synthesis of contractile proteins in the myometrium (actin and myosin), DNA and RNA synthesis



7) contribute to the accumulation of energy substances in the myometrium (ATP, glucose, phospholipids)



8) contribute to the accumulation of trace elements in the myometrium



9) activate the formation of specific proteins - receptors for prostaglandins and oxytacin



10) sensitize the neuromuscular apparatus to substances that cause uterine contractions (to uterotonics)



11) block enzymes that destroy uterotonics



12) reduce the resting potential, initiate the action potential



13) increase the formation in the hypothalamus of biologically active substances (prostaglandins, catecholamines, oxytacin)



Thus, estrogens contribute to the accumulation of energy and contractile proteins in the myometrium and prepare the uterus for active contractions.



Hormonal immunological relationships in the fetoplacental complex.



A fetal egg carries maternal and paternal (foreign) antigens.

Thus, the fetus is an allograft.



Even a physiologically occurring pregnancy is accompanied by sensitization as a result of the ingress of fetal antigens into the blood of the mother, for which antibodies are produced.



With a physiologically ongoing pregnancy, rejection of the ovum does not occur, since active immunosuppression is formed.

Of great importance in its development are hormones of the fetoplacental complex.



Immune response suppression mechanisms:

1) During pregnancy, lymphoid tissue is rearranged - suppressor cells are mobilized.

Placenta synthesizes maturation stimulants of T-suppressors (embryonic alpha-fetoprotein).



2) All placental hormones have a moderate nonspecific immunosuppressive effect.



3) Increased glucocorticoid activity of the adrenal glands of the fetus in the second and third trimester.



4) The appearance of factors that block alloantibodies in the blood of a pregnant woman already at an early date is a complex of embryonic substances that are secreted by the fetoplacental complex.



5) Local processes occurring in the placental area.



The placenta is an immunoadsorbent that prevents the penetration of maternal lymphocytes and anti-fetal antibodies due to:

• High concentration of hormones



• Structureless fibrinoid and cytotrophoblast



• High proteolytic properties of cytotrophoblast



• Due to the near-fetal antigenic protection zone (fetal antigens in the amniotic fluid divert maternal antibodies to themselves).
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