Biokimia Reproduksi

Biochemistry Aspect In Human Reproduction

Lastri Mei Winarni

2 Aspect Today

• Hormone Reproductive System• Regulation Of Ovarian Hormonal

Activity

Hormon Of The Reproductive System

• The hormones of the reproductive system of vertebrates (sex hormones) are steroids that are secreted, like those of the adrenal cortex, by tissues derived from the coelomic epithelium.

• Both types of secretory tissues also share biosynthetic pathways

Female Hormones

• The sex hormones, together with the hypothalamic region of the forebrain and the pituitary gland, form a regulatory system, which is most complex in the female mammal.

• It is common for sexual activity of vertebrates to be cyclical and for the cycles to be coordinated with the seasons of the year; this ensures that the young are born at the most favourable time.

In mammals, however, reproduction is complicated by

the need to provide for the intrauterine life of the

developing fetus and to ensure that interference by another

generation of embryos cannot occur

Estrogen

• Hormones are secreted from the mammalian ovary by the ovarian follicle, or vesicle, including the granulosa cells immediately surrounding the ovum, or egg, and the cells of the theca, which forms a supporting outer wall for the follicle.

• The main estrogen secreted is called β-estradiol.

• The close relationship between the female and the male sex hormones is revealed by the fact that testosterone (the main male hormone) is an intermediate compound in the pathway that leads to the synthesis of estradiol, although another route, which avoids the formation of testosterone, is possible

• Other estrogens are also known; the most familiar ones in man and other mammals, estrone and estriol, are much less active than estradiol, estriol being the weakest.

• Estrone can be converted to estradiol and vice versa in the ovary and in other tissues; e.g., estradiol is converted, particularly in the liver, to estriol, which is an excretory product.

• The metabolism of these compounds is complex; they may be combined in part with other substances, or they may pass through the bile into the intestine for reabsorption and circulation through the body before excretion in the urine occurs.

• Their urinary concentrations provide an important clinical index of reproductive function

Progestin

• Progestins, of which the most important is progesterone, are concerned with the maintenance of pregnancy.

• Progesterone, therefore, evolved in viviparous mammals; i.e., those that produce living young.

• Its chemical origin is demonstrable, since it is also an important intermediate compound in the biosynthetic pathways leading to corticoid and estrogen production.

• Mammals thus converted to hormonal use a substance that was synthesized by vertebrates long before the evolution of terrestrial vertebrates

• Some progesterone is probably formed in the ovarian follicle, but the main site of production is the corpus luteum, which is formed by a transformation of the follicle after ovulation; the secretory cells are formed from granulosa cells.

• The functions of the two important follicular phases, preceding and following ovulation, therefore, are continuous.

• The hormone is metabolized in several ways, but one important product is pregnanediol; formed mainly in the liver, it appears in part in the urine, where it can be measured to determine the degree of ovarian function.

In General

• The vertebrate reproductive cycle depends upon delicate interrelationships between the sex hormones and the pituitary gonadotropic hormones (FSH and LH)

• Broadly speaking, FSH (follicle-stimulating hormone), with some support from LH (luteinizing hormone), promotes growth and secretory activity of the follicle.

• The increasing output of estrogen from the ovary eventually tends, by feedback to the pituitary gland, to reduce FSH output and to stimulate the secretion of LH; it is a sudden peak release of the latter hormone that evokes ovulation in many mammals

Regulation Of Ovarian Hormon Activity

• Apart from the very important role the ovaries play in reproductiveprocesses, it means storing and periodic releaseof oocytes, they also produced the steroid hormones, estradiol and progesterone, essential for reproduction, secondarysexual characteristic and function of the women’s organs.

• The substrate to steroid hormones production is cholesterol mainly coming from plasma lipoproteins.

• The cholesterol is transported into mitochondria by the steroidogenic acute regualatory protein (StAR) where the pregnenolon is synthesized.

• Pregnenolon is then translocated out of mitochondria to the smooth endoplasmic reticulum where the sex steroid hormones production take place.

• The major source of hormone production are follicles.

• The process of follicles maturation, ovulation, corpus luteum formation and regression is influenced gonadotropin secretion and their activity as well as sensitivity of the granulose cells and theca cells which are the major source of hormone production in the maturing follicles.

• The granulose cells produce estrogens, and the theca cells androgens.

• The latter are also produced in stroma cells which can be devided into the secondary interstitial cells (derived from theca) and hilum cells.

• Endocrine function of the ovaries differ markedly within the age of woman and come under periodic changes (the menstrual cycle) during the whole reproductive age in women.

• The menstrual cycle is regulated by mutual interaction between hypothalamus-pituitaryovarian axis.

• Two gonadotropins follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are involved in follicular growth and development and as a result steroidogenesis.

• The ovaries have their own paracrine and autocrine system.

• The role of it is modulation of gonadotropin activity, follicular development and steroid production.

• Inhibins, activins and follistatin are peptides synthesized by granulosa cells in response to FSH and secreted into the follicular fluid and blood.

• They influence FSH secretion and action.

• Insuline-like growth factors (IGF) are peptides that stimulates granulose cell proliferation, aromatase activity and progesterone synthesis.

• Other intraovarian factors are transforming growth factor (TGF) family and epidermal growth factor (EGF) family and other peptides that play important role in all functions of the ovary.