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-   -   HCG hormone (http://www.biochemistry4all.com/forums/showthread.php?t=6900)

نجــد 07-25-2007 12:23 AM

HCG hormone
 
Human chorionic gonadotropin
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Human chorionic gonadotropin (hCG) is a peptide hormone produced in pregnancy, that is made by the embryo soon after conception and later by the syncytiotrophoblast (part of the placenta). Its role is to prevent the disintegration of the corpus luteum of the ovary and thereby maintain progesterone production that is critical for a pregnancy in humans. hCG may have additional functions, for instance it is thought that it affects the immune tolerance of the pregnancy. Early pregnancy testing generally is based on the detection or measurement of hCG. Because hCG is produced also by some kinds of tumor, hCG is an important tumor marker, but it is not known whether this production is a contributing cause or an effect of tumorigenesis



Pregnancy test


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A pregnancy test is a test to determine whether or not a woman is pregnant.
The earliest test for pregnancy is a rosette inhibition assay for early pregnancy factor (EPF). EPF can be detected in blood within 48 hours of fertilization

Most chemical tests for pregnancy look for the presence of the beta subunit of hCG or human chorionic gonadotropin in the blood or urine. hCG can be detected in urine or blood after implantation, which occurs six to twelve days after fertilization



Timing of test
False negative readings can occur when testing is done too early. Quantitative blood tests and the most sensitive urine tests usually detect hCG shortly after implantation, which can occur anywhere from 6 to 12 days after ovulation

False positivesEvaportation lines may appear on many home pregnancy tests if read after the suggested 3–5 minute window or reaction time, independent of an actual pregnancy. Therefore, it is imperative that a pregnancy test be interpreted within the reaction time specified by the test manufacturer
.




Structure of HCG hormone

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hCG is an oligosaccharide glycoprotein composed of 244 amino acids with a molecular mass of 36.7 kDa.
It is heterodimeric, with an α (alpha) subunit identical to that of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH) and β (beta) subunit that is unique to hCG.
• The α (alpha) subunit is 92 amino acids long and has dimensions 60x25x15 angstroms (6x2.5x1.5 nm).
• βhCG is encoded by six highly homologous genes which are arranged in tandem and inverted pairs on chromosome 19q13.3
The two subunits create a small hydrophobic core surrounded by a high surface area to volume ratio 2.8 times that of a sphere. The vast majority of the outer amino acids are hydrophilic.



Function


hCG interacts with the LHCG receptor and promotes the maintenance of the corpus luteum during the beginning of pregnancy causing it to secrete the hormone progesterone. Progesterone enriches the uterus with a thick lining of blood vessels and capillaries so that it can sustain the growing fetus. Due to its highly negative charge hCG may repel the immune cells of the mother, protecting the fetus during the first trimester. It has also been hypothesized that hCG may be a placental link for the development of local maternal immunotolerance. For example, hCG-treated endometrial cells induce an increase in T cell apoptosis (dissolution of T-cells). These results suggest that hCG may be a link in the development of peritrophoblastic immune tolerance and may facilitate the trophoblast invasion which is known to expedite fetal development in the endometrium.

It has also been suggested that hCG levels are linked to the severity of morning sickness in pregnant women..

Because of its similarity to LH, hCG can also be used clinically to induce ovulation in the ovaries as well as testosterone production in the testes. As the most abundant biological source is women who are presently pregnant, some organizations collect urine from gravidae to extract hCG for use in fertility treatment.




Tumor marker


β-hCG is also secreted by some cancers including choriocarcinoma, teratoma with elements of choriocarcinoma (this is rare), and islet cell tumor.



Use as medication


hCG is extensively used as a parenteral fertility medication in lieu of luteinizing hormone. In the presence of one or more mature ovarian follicles, ovulation can be triggered by the administration of hCG. As ovulation will happen about 40-45 hours after the injection of hCG, procedures can be scheduled to take advantage of this time sequence. Thus, patients who undergo IVF, typically receive hCG to trigger the ovulation process, but have their eggs retrieved at about 36 hours after injection, a few hours before the eggs actually would be released from the ovary.
As hCG supports the corpus luteum, administration of hCG is used in certain circumstances to enhance the production of progesterone.
In the male, hCG injections are used to stimulate the leydig cells to synthesize testosterone. The intratesticular testosterone is necessary for spermatogenesis from the sertoli cells. Typical indications for hCG in men include hypogonadism and fertility treatment.



Production

Like other gonadotropins, hCG can be extracted from urine or by genetic modification.





Use with anabolic steroids


In the world of performance enhancing drugs, hCG is increasingly used in combination with various Anabolic Androgenic Steroid (AAS) cycles.
When AAS are put into a male body, the body's natural negative feedback loops cause the body to shut down its own production of testosterone via shutdown of the HPTA (hypothalamic-pituitary-testicular axis). High levels of AASs that mimic the body's natural testosterone trigger the hypothalamus to shut down its production of gonadotropin-releasing hormone (GnRH) from the hypothalamus. Without GnRH the pituitary gland stops releasing luteinizing hormone (LH). LH normally travels from the pituitary via the blood stream to the testes where it triggers the production and release of testosterone. Without LH, the testes shut down their production of testosterone, causing testicular atrophy.
In males, hCG mimics LH and helps restore / maintain testosterone production in the testes. As such, hCG is commonly used during and after steroid cycles to maintain and restore testicular size as well as endogenous testosterone production. However, if hCG is used for too long and in too high a dose, the resulting rise in natural testosterone will eventually inhibit its own production via negative feedback on the hypothalamus and pituitary.

الريمـ 07-25-2007 02:13 AM

يسلمو ورود ،،،،

الحاج حلاوه 07-25-2007 02:55 AM

موضوع رائع من عضوه رائعه تسلمى ياورود

نايف 07-25-2007 10:36 AM

موضوع رائع ومميز

نجــد 07-25-2007 02:48 PM

Marmoora
الحاج حلاوة..
نايف

اشكركم على مروركم الكريم.......نورتونا

جــود 07-28-2007 04:45 AM

اييييييييييييييه ياورود تتذكرين ايام الفلويد

شكلك غاشته منه


خخخخخخخخخخخخخخ


يسلمووووووووووووو ورود عالموضوع ..


برايفت ورود..

تحبيني مثل ماتحبين الهرمونات ؟؟ خخخ

نجــد 07-28-2007 04:29 PM

حراااااااااااااااام عسولة لا والله ماغشيته:stink::stink::stink:>>>>اللي يسمع يقول خذينا موسوعه عنه:sad::sad:

وبعدين عااادي واذا غشيته؟؟!!:biggrin::biggrin:>>>> يكفي اني الوحيدة اللي خذيت 10 من 10 بالربورت خخخخ بزرااااان:rabbi::rabbi:


يابعد من قااام وقعد...علي ماعلي....................بدون قرعة خخخخخخ:blush::blush::blush::blush:

الريمـ 07-29-2007 09:50 PM

يوه يوه فرحانه فيها هالعشره
اقول اسكتي فرقي عنك انا والعسوله كم بوينت<< بدت الغيره هههههههه

نجــد 07-29-2007 10:12 PM

اقتباس:

يوه يوه فرحانه فيها هالعشره
اقول اسكتي فرقي عنك انا والعسوله كم بوينت<< بدت الغيره هههههههه
الغيرة تحرق ديره مرمورا خخخخخخخخخخخخخخخخخ

SeR_TaL 08-02-2007 10:13 AM

تسلمي على الموضوع


الساعة الآن 05:46 AM

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