Progesterone: What Is It and What Is Its Function?

Progesterone is one of the most important hormones in women, as it regulates the process of pregnancy and the menstrual cycle. It can also be prescribed as a drug.

Written and verified by el biólogo Samuel Antonio Sánchez Amador.

Last update: 19 March, 2023

Progesterone is defined as a steroid hormone produced in the ovaries and necessary for the establishment and maintenance of pregnancy. It stimulates changes in the uterine wall and favors the implantation of the fertilized egg.

In addition to its clear physiological functions, progesterone is also used as a drug in some cases. For example, its use is widespread in hormone replacement therapy in women who have gone through the menopause and haven’t had a hysterectomy (surgical operation to remove the uterus).

Beyond the pregnancy process and its pharmacological action, progesterone also influences the development of secondary sexual characteristics in women. If you want to know more about this steroid hormone, we encourage you to continue reading, because in the following lines, we’ll take a tour of these molecules, their role, and their use in medicine.

What is a hormone?

According to the US National Library of Medicine, hormones could be simply defined as the body’s chemical messengers. These molecules, mainly protein in nature, travel through the bloodstream to tissues and organs. Among its functions we find the following:

• Growth and development of the person
• Regulation of metabolic activities, that is, the set of biochemical reactions that take place inside the body
• Balance of sexual function and reproduction of living beings
• Changing mood patterns

Thus, hormones produce changes on both a physiological and emotional level. They are released into the bloodstream by the internal secretory glands of the endocrine system and, upon reaching the target organ, they carry out their function.

Even so, not every molecule that causes a response in the body is considered a hormone. In order to be classified as such, it must meet the following requirements:

1. It needs to intervene in the metabolism.
2. It must be released into the extracellular space.
3. Diffusing into blood vessels and traveling through the blood.
4. It needs to affect tissues that may be far from the area of synthesis.
5. Its effect should be proportional to its concentration. Hormones generate physiological responses in very low amounts.
6. Regardless of its concentration, a hormone requires a receptor at a cellular level with which to interact.
7. A hormone must regulate in one way or another the functioning of the body.

What are steroid hormones?

A steroid hormone is defined as a steroid—an organic compound derived from the cyclopentanoperhydrophenanthrene or sterane nucleus—that acts like a hormone, redundant as it may seem. These molecules work together with the genetics of the organism for the sexual differentiation of the reproductive system.

Male and female hormones are no longer spoken of, but are interchangeably known as sex steroids. All these molecules come from cholesterol through the action of different enzymes and are synthesized in the gonads and adrenal glands.

In general, and depending on the receptor they bind to, steroid hormones can be classified into five types, which are the following:

1. Glucocorticoids
2. Mineralocorticoids
3. Androgens
4. Estrogens
5. Progestogens: progesterone is found here

What is progesterone?

We have finally delved far enough into the sea of terminology to come naturally to the definition of progesterone. As we have already observed throughout this journey, we are dealing with a steroid hormone from the group of progestogens.

According to scientific articles, it’s produced in large quantities in the placenta and the corpus luteum, a yellow mass in the ovary that forms just after ovulation. Approximately 25 milligrams of progesterone are generated per day at an individual level.

Hormone synthesis

Progesterone is synthesized in the ovaries under the influence of hypothalamic-pituitary hormones, mainly by the corpus luteum (luteum) that appears during the second half of the menstrual cycle and from a certain moment onwards. pregnancy through the placenta.

When pregnancy doesn’t occur at the right time during the female ovulation cycle, the corpus luteum involutes, blood progesterone levels drop, and menstruation begins. This is the cycle that happens normally every month in every woman who isn’t going to be a mother.

On the other hand, if the egg is fertilized, the trophoblast —a group of external cells of the protoembryo— begins to secrete a hormone that is integrated into the maternal circulation, whose function is to prolong the life of the corpus luteum.

Beginning in the second or third week of pregnancy, the developing placenta secretes estrogens and progesterone in collaboration with the fetal adrenal glands. From this point, the corpus luteum is no longer needed.

Thus, we can say that the corpus luteum of the ovary is the trigger, but then the placenta already fends for itself to continue producing progesterone and other estrogens until the time of birth. Cholesterol gives rise to pregnenolone, which, through metabolic pathways, ends up being transformed into progesterone.

Functions of progesterone

Let’s explore some of its functions in a cursory way:

1. Progesterone converts the endometrium, the lining of the inside of the uterus, into its secretory phase to prepare for the implantation of the embryo.
2. If pregnancy doesn’t occur, progesterone decreases in the blood, which allows the transition to female menstruation.
3. This hormone also reduces the maternal immune response during pregnancy, which allows the acceptance of the fetus in the body.
4. Progesterone decreases the contractility of uterine smooth muscle.
5. This hormone is also a neurosteroid, that is, it can be synthesized within the central nervous system. Although it may not seem like it, it affects the neuronal synapse process and its potential as a promoter of memory and cognitive abilities is being investigated.

Beyond these essential functions, we can list many more: it acts as an anti-inflammatory agent, reduces the activity of the gallbladder, and decreases smooth muscle spasms. The roles of progesterone continue to be investigated in many fields of medicine.

Progesterone in medicine

As we have said, progesterone can also be obtained synthetically due to its pharmacological potential. The drugs in this family are recommended for all those women who experience hormone insufficiency. It is also used in hormone replacement therapy.

Hormone replacement therapy in women who have gone through menopause is based on estrogens, but according to the American Cancer Society, it seems that these may increase the risk of suffering from uterine cancer, as they cause an abnormal thickening of its inner membrane.

Progesterone is indicated in these therapies to help reduce the thickening of the layers of the uterus, which should reduce the risk of suffering from this type of cancer. It should also be noted that it is prescribed in pregnant women who have abnormal menstrual cycles.

Other uses

As indicated by the aforementioned portals, its clinical use can be summarized in the following list:

• Orally in disorders linked to progesterone insufficiency, such as menstrual cycle irregularities and premenstrual syndrome.
• The vaginal route is prescribed in the following cases: replacement in episodes of ovarian deficiency, as a supplement to the luteal phase in in vitro fertilization, or in the event of threatened miscarriage.
• Topically —through the skin— its administration is recommended in female patients with benign mammary pathologies, such as mastodynia or painful mammary tension.

Progesterone is a hormone like no other

As you may have realized in this article, progesterone has so many functions that it cannot even be counted on the fingers of two hands. We all associate this hormone with female sexual cycles, but, beyond that, it also seems to play essential roles in nerve transmission and in pathologies during pregnancy.

Although progesterone can be very useful as a drug for menstrual disorders, always consult with your trusted doctor about the path to follow before any therapeutic process.