Hormones extensively regulate the reproductive system of the human body and one such hormone is luteinizing hormone. That important hormone is vital to ensuring a healthy reproductive system, with different roles in men and women's bodies. Having your reproductive health under control requires understanding that important hormone.
Luteinizing hormone (LH) is produced in the anterior pituitary gland, and released. This hormone is called a gonadotrophic hormone because of its role in controlling female ovary function and male testing, known as gonads.
Structure:
LH is a glycoprotein with a heterodimeric nature. -monomeric unit is a molecule of glycoproteins; one alpha and one beta subunit form the complete, functional protein.
Compared to other glycoprotein hormones, follicle-stimulating hormone (FSH), thyroid - stimulating hormone (TSH), and human chorionic gonadotropin ( hCG), the structure is similar. The protein dimer contains 2 non - covalently connected glycopeptidic subunits (labeledalpha-and beta-subunits).
The LH, FSH, TSH, and hCG alpha subunits are similar and contain 92 amino acids in humans but 96 amino acids in nearly all other vertebrate species (glycoprotein hormones do not occur in invertebrates).
The beta subunits are complex. LH has a 120 amino acid (LHB) beta subunit that confers its specific biological action and is responsible for the specificity of the interaction with the LH receptor. This beta subunit contains an amino acid sequence exhibiting broad homologies to that of the hCG beta subunit and both stimulating the same receptor. Nevertheless, the hCG beta subunit contains an additional 24 amino acids and the two hormones differ in their sugar moiety composition.
The varying composition of these oligosaccharides affects bioactivity and degradation speed. The biological half - life of LH is 20 minutes, shorter than that of FSH (3–4 hours) and hCG (24 hours) The biological half - life of LH is 23 subcutaneous hours or 10 - 12 hours of terminal half - life.
Luteinizing Hormone Function
lh function in women and males:
For women, the ovaries are stimulated by the hormone to produce estradiol. A increase for luteinizing hormone allows the ovaries to release an egg during ovulation within two weeks of a woman's cycle. If fertilization occurs, the luteinizing hormone will stimulate the luteum corpus which produces progesterone to help the pregnancy.
In males, the luteinizing hormone stimulates testosterone production in the testes from Leydig cells. Testosterone, in effect, increases sperm development and helps accentuate male features — like a deep voice or facial hair growth.
Disorders of the Luteinizing Hormone
Individuals with high luteinizing hormone levels can experience infertility, since the hormone directly affects the reproductive system. For females, too high levels of luteinizing hormones are often related to polycystic ovary syndrome, which produces abnormal levels of testosterone. Many genetic conditions can also cause high levels of the hormone, such as Turner syndrome or Klinefelter syndrome. Individuals who have these conditions often cannot replicate.
Low luteinizing hormone levels can also cause infertility, because insufficient levels can limit sperm production or ovulation cycle. Too little luteinizing hormone prevents ovulation in women, or causes a gonadotropin releasing hormone (GnRH) secretion deficiency in men.
FAQs on Luteinizing Hormone
1. What is Luteinizing Hormone (LH) and where is it produced in the body?
Luteinizing Hormone, commonly known as LH, is a crucial glycoprotein hormone. It is synthesised and secreted by the gonadotropic cells located in the anterior pituitary gland. LH is classified as a gonadotropin, meaning it acts on the gonads (testes in males and ovaries in females) to regulate reproductive functions.
2. What is the primary function of Luteinizing Hormone (LH) in the male reproductive system?
In males, Luteinizing Hormone acts on the Leydig cells (also known as interstitial cells) of the testes. Its primary function is to stimulate these cells to synthesise and secrete androgens, with testosterone being the most important one. Testosterone is essential for spermatogenesis (sperm production) and the development of secondary sexual characteristics.
3. What is the role of Luteinizing Hormone (LH) in the female menstrual cycle?
In females, LH plays a vital role throughout the menstrual cycle. Its most critical function is inducing ovulation, which is the release of a mature egg from the ovarian follicle. A rapid and significant increase in LH levels, known as the 'LH surge', triggers this event. Following ovulation, LH stimulates the remaining follicular cells to develop into the corpus luteum, which then secretes progesterone to prepare the uterus for pregnancy.
4. How does the function of Luteinizing Hormone (LH) differ from Follicle-Stimulating Hormone (FSH)?
While both LH and FSH are gonadotropins produced by the anterior pituitary, their functions are distinct but complementary. The key differences are:
- In Females: FSH stimulates the growth and maturation of ovarian follicles, while LH triggers ovulation and promotes the formation of the corpus luteum.
- In Males: FSH acts on Sertoli cells to support spermatogenesis, whereas LH acts on Leydig cells to stimulate testosterone production.
Essentially, FSH is primarily involved in gamete (sperm and egg) maturation, while LH is involved in ovulation and sex hormone production.
5. Why is the 'LH surge' considered a critical event for ovulation?
The 'LH surge' is the pivotal trigger for ovulation. This rapid increase in LH concentration, which typically occurs mid-cycle, causes the mature Graafian follicle to rupture and release its ovum (egg). Without this surge, the follicle would not rupture, and ovulation would not occur, making conception impossible. The surge is a result of a positive feedback mechanism where high levels of estrogen from the maturing follicle stimulate the pituitary gland to release a large amount of LH.
6. What health conditions can be indicated by abnormally high levels of LH?
Consistently high levels of Luteinizing Hormone can indicate an issue with the gonads, a condition known as primary hypogonadism. This means the ovaries or testes are not responding correctly to LH stimulation. Specific conditions include:
- In females: Polycystic Ovary Syndrome (PCOS), premature ovarian failure, or menopause.
- In males: Primary testicular failure (e.g., due to Klinefelter syndrome or physical damage).
- In both sexes, a pituitary gland tumour could also be a cause.
7. What are the consequences of having low levels of Luteinizing Hormone?
Low levels of LH, often caused by a problem with the pituitary gland or hypothalamus (secondary hypogonadism), can lead to insufficient stimulation of the gonads. This results in:
- In females: Failure to ovulate (anovulation), leading to irregular or absent menstrual cycles and infertility.
- In males: Decreased testosterone production, which can cause reduced libido, fatigue, muscle loss, and impaired sperm production.
8. How is the secretion of Luteinizing Hormone regulated in the body?
The secretion of LH is precisely controlled by a negative feedback loop. The hypothalamus releases Gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary to secrete LH. In males, the testosterone produced by the testes in response to LH then inhibits the secretion of both GnRH and LH. In females, progesterone and estrogen (except during the pre-ovulatory phase) also inhibit GnRH and LH release, maintaining a hormonal balance throughout the menstrual cycle.
