Reproductive Hormones

Female Reproductive Hormones

FSH and LH stimulate the ovaries to produce mature gametes, as well as to synthesize and secrete oestrogen, the main female reproductive hormone. Women have two ovaries on either side of the uterus. The tubes that connect the ovaries to the uterus are called fallopian tubes or uterine tubes.

Menstrual cycle reproductive hormones functions

The levels of LH, FSH, oestrogen and progesterone in the bloodstream go through a cycle every month called the menstrual cycle. The first menstrual period happens between the ages of 11 and 15 and continues to recur every month until the beginning of menopause between the ages of 45 and 55. Each cycle normally lasts an average of 28 days (21-35 days).

The events that transpire during the menstrual cycle can be described in the context of two separate cycles, the ovarian and the uterine cycles.

The ovarian cycle

The ovarian cycle consists of two phases. The follicular phase, and the luteal phase. Ovulation occurs between these two phases. It marks the end of the follicular phase and the start of the luteal phase. The follicular phase marks the beginning of a new cycle as follicles begin to mature and prepare to release an oocyte.

There is minimal FSH, LH, and oestrogen in the blood at the start of a new cycle, so many follicles begin to grow independently of these hormones. Because oestrogen levels are low, there is little negative feedback acting on the HPG axis, leading to an increase in FSH and LH levels. These increase the follicle's growth and the production of oestrogen. During each menstrual cycle, only one dominant follicle can continue to grow and be released. As oestrogen levels rise to moderate levels, negative feedback decreases FSH levels, allowing just the dominant follicle to survive, which is now capable to grow independently of FSH. Follicular oestrogen gradually rises and because there is minimal progesterone in the system at this time, it exerts positive feedback on the HPG axis, triggering an upsurge in LH levels. The follicle releases the mature oocyte into the fallopian tube in response to the LH surge. This process is called ovulation. For around 24 hours, the oocyte remains viable for fertilization.

The uterine cycle

The uterine cycle describes the events that occur inside the uterus during the menstrual cycle, and it consists of three phases: menstruation, the proliferative phase, and the secretory phase.

• Menstruation signifies the start of a new menstrual cycle. It happens without fertilization after the corpus luteum has regressed, and the uterine lining has started to shed. Menstrual bleeding normally lasts 2-7 days, with the average woman losing between 10-80ml of blood.

• Following menstruation, the proliferative phase occurs concurrently with the follicular phase of the ovary, preparing the reproductive tract for fertilization and implantation. Oestrogen causes the uterine lining to thicken, as well as the secretion of a thin alkaline cervical mucus that aids sperms' entrance into the uterus.

• The secretory phase occurs along with the luteal phase. Progesterone promotes the thickening of the uterine lining as well as the development of secretory glands. In the presence of oestrogen, progesterone induces the cervix to generate a thick acidic mucus that inhibits any further sperms from entering. These two hormones also stimulate breast tissue growth and other metabolic changes that slightly raise the average body temperature.

Menstrual cycle hormone graph

The female reproductive hormone cycles outlined above are summarized in the graph below.

Therapeutic Reproductive Hormones Functions

Exogenous hormones can be used in certain scenarios for therapeutic purposes, like Hormone replacement therapy (HRT) or Transgender hormone therapy (THT).

Hormone Replacement Therapy

Hormone replacement therapy (HRT) is an effective treatment for the symptoms of menopause. HRT can also help with other long-term health issues connected with menopause, including lowering the risk of osteoporosis, cardiovascular disease, and stroke. The goal of HRT is to supplement the reduced hormone levels caused by menopause.

When the ovaries cease producing eggs, menopause has started. The hormones oestrogen and progesterone are lowered in the blood as a result of menopause. In addition to subfertility, menopause can cause symptoms such as hot flushes, dryness of the vagina and weakening of the bones. HRT works by replenishing these hormones to some degree to lower menopausal symptoms and health concerns.

Transgender Hormone Therapy

Transgender hormone therapy (THT) is a type of hormone therapy in which sex hormones and other pharmacological drugs are given to transgender people to match their secondary sexual traits more closely with the gender they identify themselves with. This sort of hormone therapy is classified into two groups based on whether the target of the treatment is masculinization or feminization:

1. In the form of masculinizing hormone therapy, transgender males or transmasculine persons are administered testosterone and anti-oestrogen drugs.
2. In contrast, feminizing hormone treatment involves the administration of oestrogen and anti-testosterone medications to transgender women or transfeminine persons.