Everything You Need to Know About Hormones
We have three main classes of hormones in the human body
What is a hormone?
Hormones are chemical messengers produced and released by a gland, that travel to another body site to produce an effect.
Hormones can be released and travel to their destination via the blood stream (Endocrine action). Hormones can also act much more locally. Autocrine systems are where hormones act in the cell where they were produced. Paracrine systems are where hormones act on neighbouring cells.
What types of hormones exist?
We have three main classes of hormones in the human body:
Lipid hormones (steroids and eicosanoids)
Protein hormones
Monoamine hormones (neurotransmitters and neuromodulators)
Hormones act on receptors. Hormone receptors may be inside a cell (intracellular) or on the outer membrane of a cell.
When a hormone binds to a receptor, a response is either stimulated (agonist action) or inhibited (antagonist action).
Just when you have got your head around that, the same hormone can turn functions “on” or “off” in different physiological contexts and in different body tissues.
What is a steroid hormone?
Progestogens, androgens, oestrogens, mineralocorticoids, and glucocorticoids are members of the steroid hormone family.
All steroid hormones are produced from a common building block – cholesterol.
Cholesterol can come from food sources. Our body can also synthesis cholesterol out of building blocks (acetate) from scratch. To sustain steroid hormone production, humans require “good fats” in our diet.
Steroid hormones act by entering target cells and binding to receptors in the cell control center (nucleus), where they influence DNA expression and protein production.
What are progestogens?
Progestogens are steroid hormones (or drug analogues, known as progestins) that bind to progesterone receptors.
Progestogens are produced in the adrenal cortex, the ovary (theca cells of the corpus luteum). In pregnancy, progestogens are made by the placenta.
Progesterone is the most important naturally occurring progestogen in the human female, known as the hormone of pregnancy.
Progestins (drugs that act as progestogens) are commonly used in the many methods of hormonal contraception.
What are androgens?
Androgens are steroid hormones produced from progesterone precursors. Androgens are often mis-labelled as “male hormones”. Androgens naturally occur and have important functions in females too.
The body’s principal androgens are:
5-alpha-dihydrotestosterone (DHT)
Testosterone
Androstenedione
Dehydroepiandrosterone (DHEA)
What are oestrogens?
Oestrogens are steroid hormones, primarily synthesised by the granulosa cells of the ovary.
Androgens are building blocks for oestrogen production. Androgen precursors, made in ovarian theca cells are converted to make oestrogens in ovarian granulosa cells. This two-step process is sometimes called the “two cell, two hormone system”.
Oestrogens have a huge number of functions. Important roles of oestrogens include growing a receptive uterine lining (the endometrium), stimulating female sex drive/libido, keeping the vagina moist and supple 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)
Human Chorionic Gonadotrophin
hCG is a hormone first detectable in early pregnancy, produced by trophoblast cells of an implanting embryo. hCG is known as “pregnancy hormone”.
In assisted reproduction treatments (ART), hCG can be used as a drug, to stimulate ovulation, prepare eggs for collection as an IVF “trigger” or to support a pregnancy we are trying to establish. HCG is physically very similar to Luteinizing Hormone (LH), but is more potent and longer acting than LH.
When a woman conceives, hCG is first naturally 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 helpful to evaluate the health of a pregnancy. At this time and beyond, ultrasound is reliably informative.
Thyroid hormones
Thyroid hormone action controls many aspects of cell function in all cells of the human body. Thyroid hormones influence cellular metabolism.
Thyroid hormones come in 2 forms, Thyroxine (T4) and Triiodothyronine (T3). T3 and T4 bind to proteins called Thyroid Binding Globulin (TBG), Thyroxine binding Prealbumin and Albumin. TBG is synthesised by the liver and its 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, located in the brain.
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. As a baby’s thyroid does not develop until the end of the first trimester, a mothers normal thyroid balance is critical in early pregnancy.
Why do I need thyroid monitoring after Lipiodol tubal flushing?
Lipiodol is a poppyseed oil radio-opaque contrast agent which can be used to flush and clear blockages in the fallopian tubes. Importantly, lipiodol is very high in iodine.
Iodinated contrast can disturb thyroid function, through both the Wolff-Chaikoff effect (hypothyroidism) and the Jod-Basedow effect (hyperthyroidism).
After the administration of lipiodol, thyroid function should be checked regularly. Both hypothyroidism and hyperthyroidism carry risks to a pregnancy.
Written by Dr Raelia Lew
RANZCOG Board Certified CREI Fertility specialist, Gynaecologist and the Director of Women’s Health Melbourne.
Co-host of the Knocked Up Podcast, Co-founder of Lovers intimate wellness solutions. Raelia has a PhD in Preconception Health Promotion and Genetic Screening. Raelia is a leading Australian expert in IVF and egg freezing, pioneering a bespoke model of care.