Hilchos Nidda vs reality

Hilchos Nidda is one of the most important set of laws in halacha as not only is the punishment כרת but it can severely impact the relationship between husband and wife. While many women have no problem with hilchos nidda, others have a very hard time with it, leading to halachic infertility or simply long stretches where she remains a nidda and cannot even pass an object to her husband.

To understand hilchos nidda you have to understand the female reproductive anatomy. Chazal in Maseches Nidda described the anatomy cryptically and as usual it is the source of a dispute in the rishonim how to understand the Gemara. What is very clear from the sources is that Chazal and the Rishonim, and in fact even contemporary poskim did not understand the female reproductive anatomy.

No less then the Chasm Sofer wrote the following in his chiddushim on Nidda (18a):

 מהו הפרוזדור וחדר וגג וקרקע ועליה. אחרי החקירה מפי ספרים וסופרים חכמי וספרי הניתוח א"א לנו להכחיש המציאות שאינו כפירוש רש"י ותוס' וציור מהר"ם לובלין ואין לנו אלא מה שכתב הרמב"ם
...

What is the corridor, the room, the roof, the ground and the attic [terms used by the Gemara to describe a womans reproductive anatomy]. After research from books, authors, doctors and medical books we cannot deny the fact that the reality [of a womens reproductive anatomy] is not like Rashi, Tosafos and the pictures that the Maharam Lublin provided, and all we have are the words of the Rambam.

This is quite an admission from one of the foremost poskim of the last 200 years, that Rashi and Tosafos simply didn't understand the female anatomy and therefore they didn't understand the Gemara in Nidda.

Of course the Rambams description is not completely accurate either as the Nishmas Avraham points out a number of places where the Rambam contradicts reality.

For example, the Rambam writes the following (Nidda 2:5)

To the concavity of the uterus, which is called the chamber, an artery is connected, through which the menstrual blood courses and flows through the uterus out to the cervix

We see clearly from the Rambam that he thought that there was a special artery that was the source of menstrual blood. Of course there is no such thing.

The Ramban in Chumash in Vayikra writes:

And how shall he make of it [menstrual blood] a fetus as it is a fatal drug, will kill all living creatures who drink or eat of it, etc. and it is of the wonders of the Innocent of Judgment in nature that menstruation starts as a venereal discharge. If she [the menstruating woman] looks at a light brass mirror and continues to look at it, you will see in the mirror red drops as though drops of blood, for the evil nature which harms will give birth to rebuke and the evil air will infect the mirror

You see from the Ramban that he believed that דם נדה was not regular blood and was in fact very harmful.

What we see clearly from Chazal, Rishonim and Acharonim is that they believed that there was a separate source from which דם נדה came from, the מקור and in fact, the blood is different then what they called דם מכה.

R' Wosner, a very prominent Chassidish posek (described by some in the Charedi press as the פוסק הדור) who died only a year ago, writes in the sefer שיעורי שבט הלוי describing the the female reproductive anatomy as follows:

And inside of this, deep, on the side of the back, etc., and it is called the source for this is the source of the blood, and it is called the room or uterus; the blood gathers there during approximately a month and the opening is sealed. At the time of her menstruation the opening of the cervix opens and the blood exits. In the uterus the fetus is created and the source of blood is for the purpose of creating the fetus. Therefore, while creating the fetus the woman does not see menstrual blood, for then the blood serves the purpose of creating the foetus.

This is a a very incorrect description of both the anatomy and the menstruation process and again shows that he understood that there is a separate source of menstrual blood. Here are some of the problems with what R' Wosner said:

1. the blood gathers there during approximately a month and the opening is sealed - This is simply not correct, blood doesn't gather anywhere in the uterus, rather what happens is that the uterine lining thickens and contains many blood vessels in anticipation of pregnancy. If the woman doesn't become pregnant the lining is shed which causes bleeding. 
2. The cervix is never completely sealed, it is always open 3mm or more
3. In the uterus the fetus is created and the source of blood is for the purpose of creating the foetus - This is completely and utterly wrong. The blood does nothing to create the foetus, the foetus is created by the sperm fertilising the egg. The fertilised egg is then implanted into the uterine wall where it is nourished by the blood vessels there.
4. Therefore, while creating the fetus the woman does not see menstrual blood, for then the blood serves the purpose of creating the foetus - Again this is completely wrong. A woman doesn't menstruate while pregnant because she doesn't shed the uterine lining. Rather the blood vessels in the uterus are used to nourish the baby.

It is clear that R' Wosner is basing himself on the Gemara and is either ignorant of or ignoring the medical reality.

The Shulchan Aruch (Siman 187) paskens based on the Gemara that if a woman has מכה, a wound in the uterus then she doesn't become a nidda. In fact, the contemporary poskim discuss uterine fibroids which are are benign lumps that grow on the uterus and can cause bleeding and some are מיקל in this case. Yet, the fact is that the fibroids cause bleeding from the same uterine blood vessels that cause menstrual bleeding. In fact, any wound in the uterus is causing bleeding from the same uterine blood vessels that bleed during her period.

The bottom line is that there is nothing special about menstrual bleeding, neither the source of the blood or the blood itself. It is simply blood from the blood vessels in the uterine lining that are exposed when the lining is shed. It is no different in any way then any other blood that comes out of womens body. 

The apologetic answer to explain Nidda is that the a woman becomes טמאה from menstruation because it represents the fact that an opportunity to create a new life was lost. Therefore, it only applies to her period and not to other bleeding. This sounds very nice but is clearly not what Chazal, the Rishonim and even the Acharonim believed the Torah was saying.