BBC Sounds, Music, Radio, Podcasts. Chris, it's the bleak midwinter. January. How are you feeling? I don't mind it. It's a bit dark, but I'm not done with it yet. Winter is still novel. You know, a frosty morning in my household is still like, ooh, it's snowed. Yeah, I know what you mean. A frozen puddle.

Enormous fun. The crunch of frosty leaves under first. It's weird. The liquid stuff isn't liquid. And the smoke comes out of your mouth. I mean, how amazing is that? Yeah. You know, by April, I am done. I'm properly done with April. But January is still quite fun. I'm still into it. Well, that's good because we're here for our daily dose alongside everyone in January, whether they're enjoying the crispy coldness or whether they're not enjoying it at all. One thing I do enjoy is learning new things. I think that's actually the whole meaning of life. You've got to go out different to the way you came in, haven't you? You've got to learn some stuff. I think when you train as a doctor, you think you're sort of maybe going to learn everything because there's a lot to learn.

And then you realize you don't know anything. So I try and stay open and curious, even in the dark

winter months. It's still fun to learn new things, isn't it? It's good to push against that.

Break them up like the icy puddles.

Well, in today's daily dose, we're looking back on an episode of What's Up Docs that I think you and I really learned a lot in.

Is that fair to say? I mean, we, you know...

I knew nothing about this. I think that is approximately right. We had a couple of lectures in medical school, but really everything

felt fresh and new. We're looking back on our episode on menstrual health with the brilliant

Dr. Chi Eziapha, who is an old friend, and she flipped the perspective in terms of looking

at the human menstrual cycle in terms of the evolutionary benefits that it brings

and how powerful and important it is to the survival of the species.

So many animals and mammals have an estrus cycle, but humans have a menstrual cycle. So the menstrual cycle

is a process which runs about a month long,

where there are messages released from the brain and hormones released as a result,

and communication between the brain and the ovaries, and that causes changes in the body.

One of the important changes is that one of the eggs in the ovary matures and is then released and pass down the fallopian tubes.

Another important change is that the lining of the womb thickens.

And if that egg is not fertilized that month, then the womb lining is released along with some blood

and fluid, and that's what we call a period.

Okay. So what's unique to humans and bats in these other species

is that we have this thing called spontaneous decidualization.

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