INSTRUCTOR: Hormones guide and control our lives by helping to coordinate complex processes such as growth, metabolism, and fertility.

JOANNA DAVILA: Hormones are chemical substances that are like messengers. They're designed to stimulate other organs in our body to do their job.

INSTRUCTOR: Hormones are secreted directly into the blood by the endocrine system— a group of glands throughout our bodies that respond to neurotransmitters, chemical signals that come from the brain via the nervous system.

JOANNA DAVILA: The hormonal system and neurotransmitters are separate systems, but they actually work in some similar ways in that they both are designed to affect behavior.

INSTRUCTOR: The pituitary gland is often dubbed the master gland of the endocrine system because it helps regulate the functions of the other glands. The pituitary gland produces growth hormones, puberty hormones, thyroid stimulating hormones, and antidiuretic hormones among others. A malfunctioning pituitary gland, one that produces too much or too little of these hormones, can lead to disorders throughout the endocrine system. The pituitary gland also secretes hormones that guide our emotions.

JOANNA DAVILA: Oxytocin is considered the love hormone or the cuddle hormone, the snuggle hormone, things like that. Oxytocin is released during childbirth and it's instrumental in the production of breast milk. It's released among adults with skin to skin contact, during sex, and particularly during orgasm. It functions as a way to help create a bond or an attachment between two adults.

INSTRUCTOR: Perhaps the most familiar glands in the endocrine system are the testes and ovaries. The testes secrete testosterone, a hormone that aids the development of male physical characteristics. The ovaries secrete two main hormones, estrogen and progesterone, that promote the development of female sex characteristics and ensure fertility. Concentrations of testosterone and estrogen early in life are thought to be the strongest influence on an individual's gender identity— their personal experience of the balance between male and female characteristics. Hormones can also affect the experience of people who are transgender— those uncomfortable with their assigned sex at birth.

CHARLIE: Really as long as I can remember, I felt that I somehow got sorted into the wrong box. When I started approaching puberty I knew I wanted to be a woman. It was very, very hard to wear a mask every day. When I was 19 I was like OK. I'm going to try transition.

INSTRUCTOR: Hormone replacement therapy, the supplementing or substitution of naturally occurring hormones, can help transgender people bring their physical characteristics more in line with their gender identity.

CHARLIE: I've been actively medically traditionally for almost two years now. First thing I started with was testosterone blocker. Then my doctor described me an estrogen supplement and I've been taking the two of those together. I'm moving towards having the body that I want and living the life that I want. I feel like a different person in the best way possible.

INSTRUCTOR: The thyroid gland releases hormones that control our metabolism, regulating vital body functions such as breathing, heart rate, and body temperature. The adrenal glands are best known for secreting the hormone adrenaline, which prepares your body for action in stressful situations, as well as cortisol, which helps the body respond to stress, and aldosterone, which helps control blood pressure. The most familiar expression of the adrenal hormones may be the fight or flight response— a cascade of effects that help our bodies prepare for a perceived threat and react accordingly.

GABE TOLLIVER: Some suicide bombers had infiltrated the base. We had to take up defensive positions. The struggle is not to make an emotional decision. I could have been very excited, very nervous, and shot at the first thing I saw. But I didn't.

INSTRUCTOR: Hormone levels also fluctuate over the lifespan.

JOANNA DAVILA: Adolescents and young adults are smack in puberty, typically, and so their hormones are raging. As we get older, people are still dealing with hormonal changes, particularly for women when they go through menopause, that can certainly have an effect on people's relationships.

INSTRUCTOR: At every stage of life, hormones are there to guide and shape our actions and behavior.