Steroid hormones constitution

Steroid hormones regulate a very extensive assembly of functions in numerous corporal tissues. Estrogens, the steroid hormones to which the majority of this chapter is dedicated, regulate from basic functions related to reproduction, the development of the skeleton, the maintenance of arterial tension, or diverse nervous functions. The molecular studies on the mechanism of action of estrogens have set the foundations that will permit us to understand how they carry out such diverse functions in such dissimilar tissues as well as how some substances that act through the estrogen signaling pathway can exercise opposite functions in different tissues. In this respect, there are five facts of particular importance that constitute the central nucleus of this revision ... 

The remaining steroid lipids constitute two main classes of steroid hormones sex hormones and adrenocortical hormones. The sex hormones include androgens (testosterone, androsterone), estrogens (estrone, estradiol), and progestins (progesterone). The adrenocortical hormones include mineralocorticoids (aldosterone) and glucocorticoids (hydrocortisone). 

The yams constitute a tropical and warm-temperate family known as a source of food and for the sapogenins from which steroid hormones are synthesized. 

Steroid hormones can increase and decrease the level and/or activity of a large number of proteins in eukaryotes. Steroid hormones were first discovered in humans, where they play essential roles in development, differentiation, homeostasis, and endocrine therapies. However, current interest in steroid hormones is increasing because they constitute excellent model systems for examining the control of gene expression. Many human pathologies result from the inappropriate expression of protein(s). Thus, to treat disease states, it is critical to understand the normal processes governing how, when, and how much of the information encoded in the DNA of cells is transcribed to mRNAs and eventually into proteins, which perform most of the functions of cells. Steroid hormones provide excellent model systems with which to address these clinically relevant questions. 

As indicated in Table 45.1, the liver produces a number of transport or binding proteins and secretes them into the blood. The major protein synthesized is albumin, which constitutes approximately 60% of the total plasma protein, but because of its relatively small size (69 kDa) is thought to contribute 70 to 80% of the total osmotic pressure of the plasma. Albumin, like most plasma proteins, is a glycoprotein and is a carrier of free fatty acids, calcium, zinc, steroid hormones, copper, and bilirubin. 

Avian lysozyme is a particularly good example with which to illustrate how such a control system works. The lysozyme gene is expressed in different ways in different tissues of the domestic fowl. In the tubular gland cells of the hen oviduct, expression is induced by steroid hormones (Palmiter, 1972), but the same gene is expressed constitutively in macrophages using the same promoter (Hauser el al., 1981). Its expression is also developmentally regulated. 

The value of such color reactions is limited to indicating the presence of steroid substances. Since there is growing evidence that cholesterol constitutes the precursor for the steroid hormones (Bloch, 1950), the presence of cholesterol in the droplets provides the possibility of such... 

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