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The function of hCG is essential to maintain the corpus luteum of pregnancy and its progesterone secretion. The immunological recognition of "nicked" forms is specially important when hCG is measured to determine the risk of a mother to carry a trisomy 21 baby ( known as the "What if, double test or triple test"), as in this chromosomal pathology, the "nicked" forms increase significantly. This gives rise to a particular tri-dimensional form of the molecule, making it often difficult to be recognised by the antibodies used for its measurement.
#Protein hormones free#
A particular form of hCG, called "nicked" hCG, is a holo-hCG or a free b sub-unit, where the bond between the 46th and the 47th aminoacid is broken. The free b sub-unit circulates also in the blood. The whole molecule of hCG is also called holo-hCG, in order to be distinguished from total hCG, currently measured in the labs, (holo-hCG + free b sub-unit). The specific b sub-unit contains 145 aminoacids and can be distinguished from the b sub-unit of LH only by 30 aminoacids in the C terminal part of the molecule. It is a heterodimer composed by two different sub-units: a and b. HCG is a glycoprotein with a molecular weight of about 43.000 daltons, produced by the syncytiotrophoblast. LH synthesis and secretion from the hypophysis is controlled by different regulators, like GnRH (gonadotropin releasing hormone of hypothalamic origin) and ovarian oestrogens and progesterone. maintaining the corpus luteum during the menstrual cycle.
![protein hormones protein hormones](https://i.ytimg.com/vi/AhVRNbcaTIA/maxresdefault.jpg)
inducing ovulation (by stimulating the cascade of proteolytic enzymes leading to the rupture of basement membrane of the follicle) and 3. promoting the androgen synthesis in the thecal cells of the ovaries and in the interstitial cells of the testicles, 2. Like FSH, LH is also present as a heterodimer with two different sub-units: a and b. LH is a glycoprotein with a molecular weight of approximately 30.000 daltons, and produced by the hypophysis. FSH synthesis and secretion by the hypophysis is controlled by different regulators, like: GnRH (gonadotropin releasing hormone of hypothalamic origin), ovarian oestrogens, activine and inhibine (both of gonadic origin). Thus, FSH is responsible for " the choice of the dominant follicle". It stimulates the aromatase activity inside the granulosa cells (the enzyme converting the androgens into oestrogens). FSH stimulates also the synthesis of its own receptor on the granulosa and Sertoli cells and the LH receptor on granulosa cells. The main function of FSH is to promote and sustain the ovarian follicular growth in women and the spermatogenesis in men. The b sub-unit (118 aminoacids) is specific for FSH. The a sub-unit (89 aminoacids) is common to all gonadotropins and also to TSH (thyrotrophic hormone). Morphologically, it is a heterodimer composed by two different sub-units: a and b. The gonadotropins include: FSH ( folliculo-stimulating hormone), LH (luteinizing hormone) and hCG (human chorionic gonadotropin).Ģ.1.1 Folliculo-stimulating hormone (FSH)įSH is a glycoprotein produced by the pituitary gland and has a molecular weight of about 30.000 daltons. These hormones are produced by different tissues (pituitary and placenta) and their main function is gonadic regulation (ovaries and testicles). On the other hand, the protein hormones are hydro-soluble and circulate freely in the blood.
![protein hormones protein hormones](https://i1.wp.com/nursekey.com/wp-content/uploads/2017/06/c18-fig-5002.jpg)
The steroids can circulate in the blood stream, only if bound to non-specific proteins like albumin, or to specific proteins like SHBG (sex hormone binding globulin). While the protein hormones weigh more than 5.000 daltons and therefore cannot penetrate the cells, they need membrane receptors. Because of their size and lipo-solubility (soluble in fat), they can easily diffuse through target cells, having consequently intra-cellular receptors. The steroids have a molecular weight of about 300 daltons, presenting thus a small size. Sexual hormones are of two types: proteins and steroids. 8th Postgraduate Course for Training in Reproductive Medicine and Reproductive Biology