Definition
The luteinizing hormone, LH (translated “yellowing hormone”) acts on the gonads in humans and fulfills important functions for the reproductive ability (so-called fertility). In women it is essential for ovulation and in men for the maturation of sperm. It is a so-called peptide hormone, which consists of protein. It is produced in the anterior lobe of the pituitary gland (the pituitary gland), the stimulus for this is provided by another, higher-level hormone, gonadoliberin (GnRH).
Mode of action
Luteinizing hormone regulates the synthesis and secretion of sex hormones in the gonads of men and women. In this respect it is essential for the reproductive ability of both sexes. In men, LH acts on so-called Leydig cells in the testicles and thus promotes the synthesis and release of testosterone.
In the female cycle, the LH plays an important role by triggering ovulation through a sudden increase around the 12th – 14th day of the cycle. After ovulation, the auxiliary cells of the egg cell remain in the mucous membrane of the ovary, which now form the so-called corpus luteum. For this reason, this hormone is also called yellowing hormone (luteinizing hormone).
The corpus luteum now produces progesterone, stimulated by the LH. This hormone prepares the lining of the uterus for pregnancy or for an egg, which can implant itself when fertilised. If the egg is not fertilized, the corpus luteum recedes and the resulting lack of progesterone finally leads to menstruation.
Values
For LH, it is not possible to specify a standard value that applies in principle. The concentration of LH ́s in the blood depends first of all on whether a woman or a man is involved. Besides the norm ranges of the LH ́s differ depending on whether it concerns a girl before puberty, a sexually mature woman or a woman beyond the menopause.
Also within the female cycle different norm values are valid in different phases. The concentration of the hormone in the blood is given in the unit IU/l (International Units per liter). In women, the normal value in the first phase of the cycle (day 1 to approximately day 12-14) is in the range of 1.9-12.5 IU/l.
Shortly before ovulation, during the LH peak (a sudden rise in LH that triggers ovulation), the concentration is 8.7-76.3 IU/l. So-called ovulation tests measure this value and thus indicate the woman’s fertile days when she wants to have children. In the second half of the cycle, the normal range is between 0.5-16.9 IU/l.
After the menopause, a value of 15.9-54.0 IU/l is normal. In children before puberty the value can be up to 6 IU/l. In men, a blood concentration of 1.5-9.3 IU/l is normal.
Basically it can be said that LH is released pulsatile, i.e. in relapses. Therefore, several measurements on the same day can give different results, as it is not a continuous process. Also, different laboratories have different standard values, which should be taken into account in the interpretation.
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