Placenta Steroid hormones

Steroid hormones are produced by the adrenal cortex, testes, ovaries, and placenta. Synthesized from cholesterol, these hormones are lipid soluble therefore, they cross cell membranes readily and bind to receptors found intracellularly. However, because their lipid solubility renders them insoluble in blood, these hormones are transported in the blood bound to proteins. Furthermore, steroid hormones are not typically preformed and stored for future use within the endocrine gland. Because they are lipid soluble, they could diffuse out of the cells and physiological regulation of their release would not be possible. Finally, steroid hormones are absorbed easily by the gastrointestinal tract and therefore may be administered orally. 

Cholesterol, mostly esterified, is utilized in the buildup of cell biomembranes. Besides, cholesterol is a precursor to biologically important steroid compounds bile acids (in liver), steroid hormones (in adrenal cortex, male and female sexual glands, and placenta), and vitamin D3, or cholecalciferol (in skin). 

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-... 

The male and female gonads, as well as the placenta of pregnant females and, to a lesser extent, the adrenal cortex, produce a range of steroid hormones which regulate the development and maintenance of reproductive and related functions. As such, these steroid sex hormones have found medical application in the treatment of various reproductive dysfunctions. 

Gases, nutrients, hormones, electrolytes, antibodies and waste products are transported across the placenta. Many drugs and infectious agents can also cross the placenta. Maternal transfer of steroid hormones across the placenta is limited. When natural or synthetic steroid hormones do cross the placenta, developmental toxicity can result. Furthermore, hormones produced by the fetal placenta also play an important role in parturition. 

Mitochondrial system The function of the mitochondrial cyto chrome P450 monooxygenase system is to participate in the hydroxylation of steroids, a process that makes these hydropho bic compounds more water soluble. For example, in the steroid hormone-producing tissues, such as the placenta, ovaries, testes, and adrenal cortex, it is used to hydroxylate intermediates in the conversion of cholesterol to steroid hormones. The liver uses this system in bile acid synthesis (see p. 222), and the kidney uses it to hydroxylate vitamin 25-hydroxycholecalciferol (vitamin D, see p. 384) to its biologically active 1,25-hydroxylated form. 

Steroid hormones are biosynthesized from cholesterol in the adrenal cortex, gonads, and placenta. These steroids are important hormones for many specific physiological processes. 

Exposure, Intake, and Effects of Toxic and Essential Elements Assessment of steroid hormone disruption in placenta as indicator tissue for monitoring fetal and maternal environment. Biomonitoring of metals is included with evaluation of dietary metal intake (European Commission 2004). 

SULT 2A and 2B sulfotransferase subfamily members sulfate the 3P-hydroxyl group of a variety of steroid hormones. Dehydroepiandrosterone (DHEA) is the prototypical substrate for the SULT 2 enzymes. However, other hydroxysteroids such as testosterone and its phase I hydroxylated derivatives are substrates for these enzymes. The SULT 2 sulfotransferases also are responsible for the sulfate conjugation of a variety of alcohols and xenobiotics that have undergone phase I hydro-xylation, including the polycyclic aromatic hydrocarbons (PAHs). The SULT 2 enzymes exhibit different patterns of tissue expression. SULT 2A1 is expressed primarily in the adrenal cortex, brain, liver, and intestine, while SULT 2B1 is expressed in the prostate, placenta, and trachea. 

The blastocyst is a hollow, fluid-filled ball of approximately 1000 cells. The cells that form the outer layer are referred to as trophoblasts and will ultimately develop as extraembryonic tissues (e.g., placenta), while the cells of the inner cell mass are omnipotent (i.e., stem cells) and form the embryo. Depending on the species, the blastocyst arrives at the uterus within 5-10 days of fertilization, whereupon it hatches from the zona pellucida and implants into the uterine wall, which has been preconditioned by ovarian-derived steroid hormones (see Chapter 33). Shortly after implantation, the inner cell mass undergoes gastrulation to form a trilaminar embryo composed of three primary germ layers, the ectoderm, mesoderm, and endoderm. 

The nuclear vitamin D receptor was originally studied in intestinal mucosa, hut has subsequently been found in a variety of other tissues that have therefore been shown to be vitamin D-responsive, including kidneys, bone, parathyroid gland, -islet cells of the pancreas, pituitary, placenta, uterus, mammary glands, skin, thymus, monocytes, macrophages, and activated T lymphocytes. Like other steroid hormone receptors, it is a zinc finger protein it has the same high affinity (of the order of 10 " M) for both calcitriol and ercalcitriol. 

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. 

CAS 57-83-0. C2II I, ),. The female sex hormone secreted in the body by the corpus luteum, adrenal cortex, or placenta during pregnancy. It is important in the preparation of the uterus for pregnancy and for the maintenance of pregnancy. It exists in two crystalline forms (a- and (i ) of equal physiological activity. Progesterone is believed to be the precursor of the adrenal steroid hormones. 

Phospholipids and glycosphingolipids are amphipathic lipid constituents of membranes (Chapter 10). They play an essential role in the synthesis of plasma lipoproteins (Chapter 20) and eicosanoids (Chapter 18). They function in transduction of messages from cell surface receptors to second messengers that control cellular processes (Chapter 30) and as surfactants. Cholesterol is mainly of animal origin and is an essential constituent of biomembranes (Chapter 10). In plasma, cholesterol is associated with lipoproteins (Chapter 20). Cholesterol is a precursor of bile acids formed in the liver of steroid hormones secreted by adrenals, gonads, and placenta and 7-dehydrocholesterol of vitamin D formed in the skin. In tissues, cholesterol exists primarily in the unesterified form (e.g., brain and erythrocytes), although appreciable quantities are esterified with fatty acids in liver, skin, adrenal cortex, and plasma lipoproteins. 

Biosynthesis of steroid hormones from cholesterol. The different pathways occur to varying extent in adrenals, gonads, and placenta. The systematic names for cytochrome P-450 enzymes, namely CYP followed by a number, are given in parentheses. CYPI1B2 and CYP17 possess multiple enzyme activities. [Reproduced with permission from P. C. White and P. W. Speiser, Congenital adrenal hyperplasia due to 21-hydroxylase deficiency. Endocrine Reviews 21,245 (2000).]... 

Steroid hormones are extracellular messengers elaborated by the gonads and the adrenal cortex, plus the placenta in pregnant females. A general feature of steroid hormones is that they are not stored for release after synthesis. Levels of circulating hormones are controlled primarily by their rates of synthesis. This, in turn, is often controlled by signals from the brain. 

If implantation occurs, human chorionic gonadotropin, produced initially by the trophoblast and later by the placenta, maintains steroid hormone synthesis by the corpus luteum during the early stages of pregnancy. Thereafter, the placenta itself becomes the major site of estrogen and progesterone synthesis. 

Human placenta ha,s been recognized as a source of chorionic gonadotropin.s and steroid hormones. Since the development of the placental cholinergic system follows... 

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