This post originally appeared on Sanandi.com
This week we’re talking about how our reproductive systems work.
This system is an interesting one because we don’t all have the same parts—the difference between male and female reproductive systems is pretty substantial.
These systems work together to create life and without their differences, we wouldn’t be here. It’s a complicated, inter-working structure and this article offers a basic overview of how each system works individually and then together to further our species.
Because women have the job of growing and birthing children, the system is necessarily more complicated than the male system, so we’ll start there.
The Female Reproductive System
The female reproductive system has two ovaries, two fallopian tubes, the uterus, and the vagina. Eggs are are in the produced the ovaries and travel through the fallopian tubes to the uterus. The uterus is the site for the growth of a fetus.
A single ovary has several hundred eggs, these eggs are present at birth—that means that a woman pregnant with a baby girl is also carrying the eggs that will mature into her grandchildren.
A birth, there are upwards of 2 million eggs in a girl’s ovaries and by the age of puberty there are less than half a million. Only 1-2 of these eggs ever reach maturity during a monthly cycle but many more are sacrificed each time. Throughout a woman’s life, only 300-400 follicles are mature, which means she has 300-400 chances to conceive a child before menopause.
Each mature egg is released from an ovary, travels through the fallopian tube and into the uterus where, if it is not fertilized, it will die and the uterine lining that had been building to be ready for new life will shed. If the egg is fertilized, it will implant into the uterine lining and a fetus will grow.
The Monthly Cycle
On average, a woman’s reproductive cycle is about 28 days long (like the moon!) and although every woman is different, this cycle can be broken up into two phases.
These two phases are the follicular phase and the luteal phase.
The follicular phase is from day 1 to day 14 and the luteal phase is from day 15 to day 28.
Day one of the menstrual cycle is the first day of bleeding and the beginning of the follicular phase. Bleeding lasts for about one week while the uterine lining sheds after being unfertilized. Then, still during this phase, estrogen increases and the new egg begins to mature. The increase in estrogen initiates growth of a new uterine lining and a readying of the body to accept a fertilized egg.
The follicular phase ends and the luteal phase begins with ovulation. This is where estrogen spikes, the mature egg finds its way through the fallopian tubes into the soft cushiony uterus and is ready to be fertilized and implanted.
At this point, the body starts to produce an increased amount of progesterone—which is the antagonist to Estrogen. The progesterone helps keep the uterine lining nice and habitable for the potential baby, it builds it a bit more and promotes growth of blood vessels and storage of nutrients in the endometrium.
If the egg is unfertilized within a few days, the system will stop producing the progesterone. The endometrium will die without the continuing progesterone and it will shed, along with the mature egg. That shedding is the beginning of the next cycle.
However, if the egg is fertilized, it will implant into the uterine lining and the reproductive system will continue to produce progesterone for up to 7 weeks to make the young embryo comfortable, until the placenta has grown enough to take over.
The Male Reproductive System
This system is so much simpler—simply put, men don’t have the potential of life and death to contend with every month.
The male reproductive system contains the scrotum, vas deferens, penis, prostate and bladder.
The scrotum holds the testes and functions to keep the temperature of the testes around 96 degrees Fahrenheit by dropping when it gets too hot and retracting into the body when it gets too cold. This is because sperm and the male hormone testosterone are made in the testes and they’re sensitive to the temperature of their environment.
It takes 74 days for sperm to become viable for reproduction, and they’re made on a consistent basis rather than being there when the boy is born.
When a man ejaculates he releases, on average, about 100 million sperm. Many of them are weak, and most die pretty quickly. They thrive in warm, moist places though and can live for up to 5 days inside of a woman’s uterus—searching for the egg.
How Fertilization Works
Fertilization, to me, is mind blowing.
A singular sperm has to make its way through essentially a vast open space to find a singular egg, and then the egg has to allow it to come inside—that’s right ladies, your eggs have a choice about the little zygote that makes it through her walls. I have to wonder how she sets her standards.
To put this into context, the size of an egg is about the size of the period at the end of this sentence. A sperm though, you need a microscope to see it.
Now, look down for a second and check out the size of your lower belly, where your uterus is/would be. See? Mind blowing. Sperm literally has 5 days at most, to make what amounts to an odyssey—yet incredibly, we all exist.
In reality, these two tiny things find each other—and here’s where it gets so cool—using scent.
The egg, pulling a classic first date move, releases pheromones to let the sperm know where she is. Now, it’s not exactly like the sperm has a sniffer, but they do have olfactory receptors (actually, every cell in your body has olfactory receptors) that allow them the pick up the trace.
Basically imagine that the egg is noodling around smelling good, making her home all nice for a visitor, and all the sudden she’s got tiny sperm bumping her to let them in. She chooses the one she likes and they settle in together and become a new thing.
What questions do you have about the Reproductive System? Let us know in the comments below.