Everything You Need to Know About Hormones

Posted on 21 June 2022


  1. What is a hormone?

Hormones are messenger molecules produced by a body tissue, that are subsequently released, and travel to another site to produce an effect.

In the classical endocrine system, hormones are secreted and travel to their destination via the blood stream.

We now know that hormones can have more local effects to. Autocrine systems are where hormones act on different sites in the very cell where they were produced. Paracrine systems are where hormones act on neighbouring cells.

  1. What types of hormones exist?

There are three main classes of hormones in the human body.

These are:

Lipid hormones (steroids and eicosanoids)

Protein hormones

Monoamine hormones (neurotransmitters and neuromodulators)

Hormones act on receptors, which may be inside a cell (intracellular) or on the outer membrane of a cell.

By binding to a hormone recepto, a hormone can stimulate a response (acting as an agonist) or may inhibit an action (acting as an antagonist).

The same hormone can turn functions “on” or “off” differentially in different body tissues.

  1. What is a steroid hormone?

Progestogens, androgens, oestrogens, mineralocorticoids, and glucocorticoids are all part of the steroid hormone family.

All steroid hormones are produced from a common building block – cholesterol.

The body sources cholesterol from circulating lipoproteins or synthesises it from scratch from acetate. To sustain steroid hormone production, we need to have a certain amount of good fats in our diet.

All steroid hormones act by entering target cells and binding to receptors in the cell nucleus to influence DNA expression and protein production.

  1. What are progestogens?

Progestogens are steroid hormones (or drug analogues, known as progestins) that act by binding to progesterone receptors in our cells.

In the body, progestogens are produced in the adrenal cortex, the ovary (the theca cells of the corpus luteum), and, during pregnancy, the placenta.

Progesterone is the most important naturally occurring progestogen in the human female.

Progestins (drugs that act as progestogens) are commonly used in the many forms of hormonal contraception.

  1. What are androgens?

Androgens are steroid hormones produced from progesterone precursors. Androgens are often termed “male sex hormones” but also naturally occur and have important functions in females too.

The body’s principal androgens are:

5-alpha-dihydrotestosterone (DHT)



Dehydroepiandrosterone (DHEA)

  1. What are oestrogens?

Oestrogens are steroid hormones, primarily synthesised by the granulosa cells of developing ovarian follicles.

Androgens are produced first by ovarian theca cells. Androgens are building blocks for oestrogen production, which are converted to oestrogens in ovarian granulosa cells. This two step process occurs in what is known as the “two cell system”.

Oestrogens have a huge number of functions, including influencing growing a receptive uterine lining (the endometrium), increasing female sex drive/libido and stimulating fertile mucous production by glands of the cervix.

The main oestrogens in the body are:

  • 17-b-oestradiol (E2)
  • oestriol (E3)
  • oestrone (E1)
  1. Human Chorionic Gonadotrophin

hCG is a hormone produced by trophoblast cells of an implanting embryo. Commonly, hCG is known as “pregnancy hormone”.

In assisted reproduction, hCG can be used as a drug as it is physically very similar to Luteinizing Hormone (LH). hCG is in fact more potent and longer acting than LH.

When a woman conceives, hCG is detectable in her blood 10 days after ovulation and in the urine 2-4 days later. hCG levels normally double every two to three days in the first week of pregnancy and plateau after six weeks.  From this time, measuring hCG levels is not generally performed and evaluation of the pregnancy by ultrasound is most informative.

  1. Thyroid hormones

Thyroid hormone action is important for metabolism, and controls many aspects of cell function in all cells of the human body.

Thyroid hormones are known as Thyroxine (T4) and Triiodothyronine (T3). T3 and T4 circulate bound to proteins Thyroid Binding Globulin (TBG), Thyroxine binding Prealbumin and Albumin. TBG is synthesised by the liver and it’s concentration is affected by oestrogen levels, especially during pregnancy.

Homeostasis or balance of thyroid hormones is controlled via TRH and TSH release in the hypothalamus and pituitary glands.

Ideal target reference ranges for thyroid hormones and TSH levels vary for women who are not trying to conceive, for those who seek to conceive and for those who are pregnant.

  1. Why do I need thyroid monitoring after Lipiodol tubal flushing?

Lipiodol is a poppyseed oil radio-opaque contrast agent very high in iodine that can be used to outline structures in radiological investigations, including assessment of fallopian tubal patency.

Iodinated contrast can result in both the Wolff-Chaikoff effect (hypothyroidism) or the Jod-Basedow effect (hyperthyroidism).

After the administration of lipiodol, women need to have their thyroid function checked regularly for 6 months. Both hypothyroidism and hyperthyroidism carry risks to a pregnancy.

  1. Syphilis: making a comeback

Syphilis is caused by the bacterium Treponema pallidum subspecies pallidum (T. pallidum), a small, motile organism known as a spirochete.

While the mention of syphilis might conjure images of Henry VIII, it’s important to note that syphilis has unfortunately again come into circulation, perhaps with fading of safe sex messaging, powerful in the 80’s associated with the emergence of HIV.

Syphilis is transmitted by direct sexual contact with a syphilitic sore, known as a chancre. Chancres can occur on or around the external genitals, in the vagina, on the cervix, around the anus, in the rectum, or in or around the mouth. Chancres may not be obvious.

Transmission of syphilis can occur through vaginal, anal, or oral sex.

Screening for syphilis is routine for those planning a pregnancy. Pregnant women with syphilis can transmit the infection to their baby, associated with a high risk of stillbirth or neonatal death. Syphilis can be effectively treated with antibiotics.

Clinically, about 50% of people will have no symptoms and will only be diagnosed by serological testing.

  1. Why do we check rubella immunity and vaccinate before pregnancy?

Rubella is a virus, alternatively known as German Measles.

While relatively mild in adults, a mother catching rubella during pregnancy can have devastating effects for the baby including:

  • Cardiac defects
  • Eye defects including cataracts, glaucoma, chorioretinitis
  • Deafness
  • Neurological problems of brain development
  • Intrauterine growth restriction and high perinatal mortality (death around the time of birth)

Vaccination against rubella can achieve immunity for most women, conveying protection to their babies. However, as the rubella vaccine is a live attenuated virus, it can not be administered during a pregnancy.

  1. Why do we check chicken pox immunity and vaccinate before pregnancy?

Chicken pox is caused by a virus (varicella zoster or VZV) and is very dangerous for a mother to contract for the first time while pregnant, causing serious deformities in infants such as:

Skin scarring

Limb defects

Eye abnormalities

Brain and other neurological malformations

We have an effective vaccine against Varicella but it is a live attenuated virus vaccine, meaning it cannot be used during pregnancy. Some women cannot achieve immunity to VZV even after vaccination.

If you have not been effectively vaccinated and also have no natural immunity to VZV, The Australian Red Cross Blood Service can provide restricted amounts of high-titre ZIG (Zoster Immune Globulin) to offer some protection.

ZIG prevents varicella in people at high risk who report a significant exposure to varicella or herpes zoster (shingles, chicken pox reactivation) and is most effective when administered within 96 hours of the exposure.


Back to Blog