Progesterone placental

The interaction between the adrenal cortex of the foetus and the placenta in production of steroid hormones is complex. In outline, the placenta produces progesterone from cholesterol (which is available from the maternal blood) whereas the foetal adrenal cortex produces corticosteroids and androgens from the progesterone produced in the placenta. The placenta then converts some of these androgens into oestrogens. The interplay between the placenta and the foetal adrenal cortex is acknowledged by the use of the term foeto-placental unit to describe steroido-... 

It stimulates placental progesterone synthesis and increases the secretion of placental hormones. 

The mammary gland consists of the external nipple and the system of ducts from the alveoli to the skin surface. The alveoli do not fully develop until a female experiences pregnancy and lactation. Cortisol, insulin and placental lactogen contribute to alveolar development, but estrogen and progesterone are most important. The cells that line the alveoli synthesize milk, and they are surrounded by a layer of myoepithelial cells that eject the milk. 

Devroey P, Camus M, Palermo G, Smitz J, Van Waesberghe L, Wsanto A et al. Placental production of estradiol and progesterone after ooc5de donation in patients with primary ovarian failure. Am J Obstet Gynecol 1990 162 66-70. 

The placenta produces several protein and steroid hormones (Figure 54-1). The major protein hormones are CG and placental lactogen (PL). The steroids include progesterone, estradiol, estriol, and estrone. The placenta secretes most of its products into the maternal circulation only small amounts reach the fetal circulation. Close proximity of the maternal blood vessels to the site of placental hormone production may explain some of this preferential accumulation of hormones in the maternal blood circulation. Generally, hormone production by the placenta increases in proportion to the increase in placental mass. Therefore concentrations of hormones derived from the placenta, such as PL, increase in maternal peripheral blood as the placenta increases in size CG, which peaks at the end of the first trimester, is an exception. 

One of the most important placental hormones is CG. CG stimulates the ovary to produce progesterone which, in turn, prevents menstruation thereby protecting the pregnancy. The chemistry, biochemistry, and methods for CG are discussed in the section on laboratory tests later m this chapter. 

Zander (Z2) has shown by both in vitro and in vivo experiments that much of the 20a-dihydroprogesterone produced by the fetus from placental progesterone may be reconverted to progesterone by the placenta, and thus a placental-fetal circulation is possible of some of the progesterone produced by the placenta. 

Work mentioned in Section 4.2.3. has indicated that corticotropin is involved in cortisol production in the fetus, but three reasons are there given why the control of production may be complex. At birth two of the three conditions mentioned suffer dramatic change i.e., cortisol can no longer be obtained across the placental barrier from the maternal circulation, and the abundant supply of progesterone from which cortisol might be synthesized is cut off. To maintain control in the face of changes such as these, the mechanism must surely be robust. 

Z2. Zander, J., Progesterone and its metabolites in the placental-foetal unit. Excerpta Med. Intern. Congr. Ser. 83, 715-720 (1964). 

One intriguing aspect of the enzymology of the placenta is the molecular properties of the enzymes synthesized in the placenta. The placenta contains all the enzymes that make cholesterol and progesterone. But the placental enzyme arsenal needed to convert progesterone to other steroids is incomplete, as is that of the fetus. However, if fetus and placenta are considered as a single unit, such a unit can synthesize all needed steroid hormones. The enzyme mosaic of the fetalpla-cental unit is discussed in greater detail in the chapter on steroid hormones [9]. 

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