[MUSIC] Hello, and welcome back. Today I'm gonna discuss hormone and receptors. My colleague, Dr. St.Ledger, is gonna discuss specific example hormone receptor action, so I wanna introduce the concept. The human body is composed of trillions of cells, and all those cells need to communicate with each other. One of the ways they communicate are through chemical messengers such as hormones. Hormones are released through the endocrine system from an endocrine gland. And hormones are transported through your blood to target cells. A target cell for a specific hormone will have a receptor, which is a special protein that binds to that specific hormone. One specific type of hormone class are steroid hormones. Steroid hormones are useful as chemical messengers because they're cheap, fast and easy to make. Cholesterol's the precursor to make steroid hormones, which is readily available in your system. When steroid hormones bind to the receptor, this forms a hormone receptor complex. And this will be transported in the nucleus of the cell. And if you remember, the nucleus is where the DNA is housed. The hormone-receptor complex will activate gene expression. Some examples of steroid hormones are cortisol, estrogen, progesterone, and testosterone. This is an example of direct gene activation by steroid hormone action. You'll probably remember, gene expression is regulated by promoters and activators. And chemicals like hormones that are present in our body can affect gene expression by interacting with these sequences. If you're male, you'll make and release testosterone. And this testosterone in early development will direct your body to make primary sex characteristics associated with being male. Then at puberty that testosterone will direct gene expression so you can develop your secondary sex characteristics. Same idea in females, but with estrogen and progesterone, which allows for female specific sex characteristics. So to summarize, when an endocrine gland makes and releases a steroid hormone, that hormone will bind to specific cells that have that specific hormone receptor. Then that hormone-receptor complex enters the nucleus and binds to a region called the hormone response element. And that can interact an enhancer sequence or another regulatory sequence such as the promoter to increase gene expression. Gene expression is increased because the hormone-receptor complex activates gene transcription and translation. Many steroid hormones affect expression of genes that are linked to cell growth. You've probably heard of cortisol, it's called the stress hormone. It's released when you're under stress. However, you probably never truly thought about what stress is. Stress can be something long-term, such as not liking your living situation or constantly being unhappy at work. That's probably what you think about when I say stress. But other types of stress include just getting out of bed in the morning. Think about it. Standing up in the cold world is a lot more stressful than being cuddled up in your warm, soft blanket. So what happens early in the morning, to prepare you for the day, is your cortisol levels go up, which increases your blood pressure and your blood sugar levels. Cortisol's an important hormone because it allows your cells to communicate what's going on based on a stimulus. And that stimulus is stress. But what about even more stressful situations? For instance, you're in the jungle and a tiger is about to have you as a meal. This leads to the fight or flight response, and in that case, cortisol levels increase dramatically in response to the super stressful situation. But, so does adrenaline, or epinephrine, as it's also called. They work together to, again, increase your sympathetic nervous response, which allows your body to respond to that stimuli by increasing blood sugar levels dramatically. Heart rate and blood pressure also increase, as well as blood flow to your muscles so you can run to safety. The nervous system releases chemicals that act in a similar fashion to endocrine glands. These chemicals from the nervous system are called neurotransmitters. Neurotransmitters can act like a hormone, but they're released from cells of your nervous system called neurons. And neurotransmitters communicate in an area called a synapse. There about 50 different chemical neurotransmitters. So if you think about it, different chemicals are different conversations between your cells. So, with 50 different neurotransmitters, you can actually have 50 different conversations in your brain. And that's just looking at them independently, not how they interact with each other. One famous neurotransmitter is serotonin and another one is dopamine. Dompamine's interesting because it's linked to behaviors associated with motivation and drive, dopamine release causes you to become motivated. Whereas serotonin is often associated with removing stress, but it also has many roles that are kinda hard to pin down. Serotonin not only affects your mood, but it affects things like the movement of your GI tract, that's the movement of food through your intestines. Some people have a disease called irritable bowel syndrome, where they have irregular GI tract movements. And so whenever they have a meal, they rush to the bathroom and people with this condition say it's pretty painful and awkward. So they always have these uncomfortable bowel movements, and a lot of these people also suffer from depression. And you could argue that if after every meal you're in pain, that could lead to depression, and it would be a logical assumption. But what researchers found is that serotonin regulates bowel movements and it regulates your mood. Low levels of serotonin have been linked to depression. So when people were treated for their irritable bowel syndrome with drugs that slowed the breakdown of serotonin, not only did it help improve their GI tract movement, but it alleviated the symptoms of depression. There's an enzyme that regulates the level of serotonin called monoamine oxidase A. And an enzyme is a specialized type of protein. This enzyme, monoamine oxidase A, has been associated with behavior. Certain people have an allele called the warrior gene. That's a version of the monoamine oxidase A gene. And when this allele is coupled with abusive experiences during early childhood, it's been correlated to violent behavior in adulthood. Dr. St.Leger will discuss this more later. So to summarize, the cells of our body need to communicate. They coordinate their activities so our cells can communicate chemically. And there's two types of chemical classes that we've talked about, hormones, and I gave you examples of cortisol, testosterone, progesterone, and estrogen. And the other class of chemical messengers was neurotransmitters, and I gave you the examples of dopamine and serotonin. Chemicals can affect gene expression and ultimately, they'll affect your physiology and behavior. And remember, our behavior, such as running from that tiger in the jungle, affect your chance of survival and your chance of biological success. [NOISE]
