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Reproductive Module Dr.Halima Babiker
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Overview of Steroid Hormones Steroid hormones: produced in the adrenal cortex, testis, ovary, and some peripheral tissues (adipose tissue, the brain!) All steroid hormones are derived from cholesterol and differ only in the ring structure and side chains attached to it.
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Steroid hormones The core of steroids is composed of seventeen carbon atoms bonded together that take the form of four fused rings. carbon Three cyclohexane rings (designated as rings A, B, and C ) and one cyclopentane ring (the D ring). cyclohexanecyclopentanecyclohexanecyclopentane The steroids vary by the functional groups attached to this four ring core and by the oxidation state of the rings. oxidation state oxidation state
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C B A D
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steroids based upon their chemical composition Examples Number of carbon atoms cholesterol 27 cholic acid cholic acid 24 progesterone 21 testosterone 19 estradiol 18
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Types of steroid hormones Glucocorticoids; cortisol is the major representative in most mammals Mineralocorticoids; aldosterone being most prominentAndrogens such as testosteroneEstrogens, including estradiol and estrone Progestogens (also known a progestins) such as progesterone
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Steroid hormones Are not packaged, but synthesized and immediately released Enzymes which produce steroid hormones from cholesterol are located in mitochondria and smooth ER Steroid hormones are not water soluble so have to be carried in the blood complexed to specific binding globulins. Corticosteroid binding globulin carries cortisol Sex steroid binding globulin carries testosterone and estradiol
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Functions of Steroid Hormones Steroid hormones play important roles in: - carbohydrate regulation (glucocorticoids) - mineral balance (mineralocorticoids) - reproductive functions (gonadal steroids) Steroids also play roles in inflammatory responses, stress responses, bone metabolism
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Steroid hormone synthesis A series of enzymatic steps in the mitochondria and ER of steroidogenic tissues convert cholesterol into all of the other steroid hormones and intermediates. The rate-limiting step in this process is the transport of free cholesterol from the cytoplasm into mitochondria This step is carried out by the Steroidogenic Acute Regulatory Protein (StAR)
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CholesterolCholesterol is precursor for 5 steroid hormone classes Progestagens (e.g. Progesterone)Progesterone Glucocorticoids (e.g. Cortisol) Mineralcorticoids (e.g. Aldosterone) Androgens (e.g. Testosterone) EstrogensEstrogen Synthesis sites Adrenal cortex: Glucocorticoids, Mineralcorticoids Women Corpus luteum: Progestagens Ovary: EstrogensEstrogen Men Testis: TestosteroneTestis
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Enzymes involved in steroid biosynthesis Desmolases (or lyases): these enzymes catalyse reactions which result in the removal of parts of the original cholesterol side- chain. This involves hydroxylation and requires a cytochrome P- 450, molecular oxygen (O2) and (NADPH) as a cofactor. These enzymes are located in the mitochondria. Hydroxylases : these enzymes are membrane-bound and are present either in the mitochondrial or in the microsomal fraction of the cell. They also require a cytochrome P-450, molecular oxygen and NADPH, as for lyases. Hydroxysteroid dehydrogenases (oxido-reductases): these enzymes catalyse reversible reactions.They are found both in the cell cytosol and in the microsomal fraction. Aromatase: conversion of the A-ring to a phenolic structure (i.e. with a phenolic HO-group at C-3), a process known as " aromatization ",
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21-hydroxylase
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Steroid Hormone Synthesis
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Functions of Hormones Derived from Cholesterol ProductFunctions Progesterone prepares uterus lining for implantation of ovum Glucocorticoids (cortisol) promote gluconeogenesis; anti-inflammatory Mineralocorticoids (aldosterone) maintains blood volume and blood pressure by increasing sodium reabsorption by kidney
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Androgens (strongest = testosterone) (strongest = testosterone) development of male secondary sex characteristics Estrogen development of female secondary sex characteristics; prevents bone resorption Vitamin D (not a steroid hormone) intestinal calcium absorption; promotes bone formation; prevents phosphate loss by kidneys ProductFunctions Functions of Hormones Derived from Cholesterol
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Catabolism of stroids Steroids are oxidized mainly by cytochrome P450 oxidase enzymes. cytochrome P450 oxidasecytochrome P450 oxidase These reactions introduce oxygen into the steroid ring and allows the structure to be broken up by other enzymes, to form bile acids as final products. bile acidsbile acids These bile acids can then be eliminated through secretion from the liver in the bile. liverbileliverbile
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Over use of anabolic steroids
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Home work No 1 (Assignment ) Write About Major pathway for steroid hormones biosynthesis
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