Physiology Friday

It has been a busy morning already. Looks like we are gonna have a lot of Good Friday babies. How exciting.

With that in mind, today's cool physio is brought to you by my wife, who recently said, "I don't really know that much about menopause." Hopefully she still has a couple of years before it hits, but it's never too early to learn.

Before you completely zone out with a sigh and a "menopause is so boring," don't worry, we are gonna start off slow. This morning we are going to only hit the very cool subject of hot flashes. Oh yeah. We're gonna go there.

Some background first: menopause is when a woman's ovaries begin to fail. They no longer send out eggs and, more importantly, they don't send out their usual supply of hormones to the rest of the body. The main hormone that the ovaries are crucial for is estrogen. And today it's all about the estrogen.

You see estrogen, among the many things it does, is a muscle relaxant. It's one of the reasons women have a typically lower blood pressure than men - their blood vessels are more relaxed. It's one of the reasons women are typically more flexible. Estrogen makes those muscles a little more relaxed. Take away point: estrogen=muscle relaxant.

*(I'll explore estrogen a little more at the end, but it will be a bit more technical, so feel free to skip that part and just move on to the next paragraph)

So when a woman experience a hot flash, it is her ovaries playing the hero. They are giving a last ditch, dying effort to squeeze out whatever estrogen they can. That burst of estrogen then hits the blood vessels and causes them to dilate. When the blood vessels near the skin dilate, warm blood, right around 98 degrees, rushes to fill the empty space. Her skin turns red and she feels warm and sweaty.

And there you have it, hot flashes explained. Making the estrogen connection.

*For those of you still reading, let's take this a little further. This explains why an S3 is considered normal in an adolescent female. She has high levels of estrogen causing her heart to be more relaxed. As her estrogen levels begin to approach a more stable level, the S3 should disappear. The estrogen connection also helps explain why a pregnant woman, who has elevated levels of HCG leading to elevated estrogen, is at a greater risk for DVTs - the high estrogen relaxes veins and allows for pooling of blood and subsequently clot formation (Estrogen also causes increased production of liver proteins leading to increased clotting factors, except for XI, and so between the two factors, we see a higher incidence of DVTs in pregnant women).