What the hormones do, by body part

What they are

Hormones are chemical messengers. They travel in the blood and change how other parts of the body work. Three sex hormones do most of the work this course talks about:

• Estrogen. Before menopause, the ovaries make most of it. The adrenal glands and body fat make some too, and the placenta makes it in pregnancy.¹
• Progesterone. Made mainly after ovulation, by the empty follicle left in the ovary. The adrenal glands make a little, and in pregnancy the placenta takes over.²
• Testosterone. Made by the ovaries and adrenal glands, in much smaller amounts than in men. Most of it is turned into estrogen.³

Myth: Estrogen is the female hormone and testosterone is the male one.

That's how many of us first learned it, and it's a handy shortcut. But everyone makes both. Testosterone in women supports sex drive, energy, mood and bone and muscle strength, and men turn some of their testosterone into estrogen, which they need for growth in puberty and for sex drive.^1,3 The difference is how much, not whether.

The lessons on the menstrual cycle show how these hormones rise and fall each month. This lesson goes body part by body part, because the hormones act together and people feel the results in one place at a time.

Brain

Estrogen supports brain function, including focus.¹ In some people the brain responds unusually to the normal rise and fall of hormones, which researchers think is behind the mood changes of PMS and its severe form, PMDD. Studies point to the brain's serotonin and GABA signals.⁴

Hormones also affect appetite. One review found that estrogen tends to reduce how much people eat, while progesterone may increase appetite.⁵

Breasts

Estrogen drives breast growth at puberty, and estrogen and progesterone prepare the breasts to make milk in pregnancy.^1,2 Many people notice their breasts feel fuller or tender before a period.

Uterus and vagina

Estrogen builds up the lining of the uterus each cycle, and progesterone readies it for a possible pregnancy. In pregnancy, progesterone also keeps the uterus from contracting too early.² Estrogen keeps the walls of the vagina stretchy and moist, which is why lower estrogen around menopause can bring vaginal dryness.¹

Gut

The gut has receptors for estrogen and progesterone, so these hormones influence how fast food moves through it and how sensitive it is to pain.⁶ That is one reason digestion can change across the cycle, which the cycle section covers.

Skin and hair

Estrogen affects collagen and moisture in the skin.¹ Androgens like testosterone stimulate the skin's oil glands. When androgen levels run high, signs can include acne and oily skin, extra body or facial hair, thinning hair on the head and irregular periods. The most common cause is PMOS, the condition formerly called PCOS, which the section on when something's off covers.⁷

Bones and muscles

Estrogen helps keep bones dense and supports muscle mass and strength, and testosterone supports bone and muscle in everyone.^1,3 Low estrogen after menopause is a risk factor for osteoporosis, thin bones that break easily, and more women than men get it.⁸ The after-menopause section explains how to protect bones.

Heart and blood

Estrogen helps regulate cholesterol and blood flow.¹ The after-menopause section comes back to what this means for heart health later in life.

Sleep and body temperature

After ovulation, progesterone raises resting body temperature slightly.⁹ Many people say they sleep worst around their period, and in sleep studies, people rated their sleep quality lowest then, even though the measured sleep changed only a little.¹⁰

Across a lifetime

These hormones rise at puberty, cycle each month through the reproductive years, climb very high in pregnancy and fall during perimenopause. That fall is what brings hot flashes and vaginal dryness for many people.¹ Each of these stages has its own section in this course.

How it compares in boys and men

Men make testosterone mainly in the testicles. It drives the changes of puberty, such as muscle growth, body hair and a deeper voice, and in adults it keeps up muscle, bone strength and sex drive.³ Men have no monthly cycle. Their testosterone is highest in the morning, which is why it is usually tested then. Levels peak around age 18 and slowly fall from the 40s.³