Estrogen: The female hormone
Estrogens are the steriods that are the female sex hormones. They are present in both females and males, but are much higher in women of reproductive age.
They are important in the formation of secondary sex characteristics (breasts, body shape) and in regulating the estrous cycle.
Low levels of estrogen have been linked with depression and mood problems. Estrogen levels vary with the estrous cycle, and many studies have confirmed that a women prefer more masculine men when ovulating. They also have a higher sex drive during this time-- and their male partners exhibit higher levels of sexual desire, attention, and jealousy than at any other time in the cycle. It makes sense; You're most concerned about sex when it's most likely to result in reproduction.

Testosterone: Sex Drive!
This is the "male" sex hormone that regulates sex drive in both males and females.
It is created in the testes and ovaries, and in small amounts in the adrenal glands. Men have about 40-60x the amount than women, although women may be more sensitive to the hormone.
In men, it is responsible for male sex characteristics-- including chest hair, increased muscle mass, deepened voice, Adam's apple, and broad shoulders and chest.
Testosterone is what gives us our libido and sex drive. Low testosterone levels can mean decreased libido for both sexes.

Dopamine & Seratonin: Pleasure
The intense feelings when we first fall in love are similar to being on cocaine. That's thanks to dopamine, the neurotransmitter that acts as the the "reward" chemical in our brain. When we see our loved one-- even a photo of them-- the dopamine areas of the brain light up. Dopamine is there to motivate us to do what's good-- in many cases, that's falling in love.

Levels of seratonin in the brain are low during new romances-- which is similar to people with Obsessive Compulsive Disorder. In fact, being in love in the early stages resembles OCD-- constant thinking about your lover, wanting to spend every moment with them, looking forward to your next meeting...

Oxytocin: Bonding
Oxytocin is a warm, fuzzy chemical important to relationships. It's what makes us form long-term bonds with our sex partner or our children. Oxytocin is released during orgasm and also during childbirth. It helps our brain form a bonding relationship. The prairie vole is one of the few animals that exhibits completely monogamous behavior-- and like us, it shares oxytocin receptors in the brain. Oxytocin release is seen in the later emotional attachment phase of relationships.

Adrenaline: Excitement
Adrenaline is released to help us flee from danger. It speeds our heartbeat up and makes us more alert. It can also trick us into thinking we are in love.That's probably because excitement, arousal, attraction, and anxiety are all related.
A study done in the 1970s by Arthur Aron and Don Dutton showed that risky situations make us more susceptible to feelings of romance and love.
Men met a woman on a rickety, high bridge, and on a lower, safer bridge. Those that met the woman on the high bridge were more likely to find the woman sexier and the situation more romantic than those on the safer bridge.
Watching a thriller can bring more feelings of love than a tame movie... adrenaline can trick us into thinking those exciting feelings we are having are related to love, not just danger.

New funny picture site: StuffOnMyRack.com