This article is an excerpt from our Sefer
A. Kidneys develop sperm:
The kidneys help mature and develop the sperm cells. [According to Chinese alternative medicine the Kidney Meridian connects with the bladder and is internally-externally related. Its main functions are to store essence and dominate human reproduction and development.]
The sperm of a man derives from the brain. This does not refer to the physical development of the sperm cell, which physiologically is developed in the testis and does not come from the brain at all, but rather to the spiritual force contained within it to make it alive and capable of procreating a replica of the person who provided the sperm. In other words, the spiritual force which is expelled from the brain eventually develops into the actual physical sperm cell when it descends down the spinal cord [and into the testis].
Zera comes from all the limbs of the body: In addition to the above, man’s sperm derives from all the limbs of his body, and thus has the ability to develop all these limbs and senses within a child.
The reproduction drop [i.e. egg] of a woman derives from the brain. The order is as follows; the drop is developed from the food she eats, which in turn, then turns into blood in the liver and enters the heart. From the heart it goes to the brain, and from the brain is drawn the seeding of the drop.
 Or Torah Maggid 158
 Sh’lah Hakadosh Sha’ar Ha’osyos Erech Kedusha 400 and 430; Tanya Chapter 2 in length “The son is drawn from the brain of the father… from a drop in the brain of the father”; Torah Or Chayeh Sarah 2nd Ma’amar; Vayechi p. 210; Likkutei Torah Shelach p. 88; Matos p. 167; Shir Hashirim p. 16; Siddur Ya’avetz Mosach Hashabbos Mitos Kesef 3:1 that when it is done with holiness it comes from the level of Da’as and Bina, which is the brain
 Torah Or Chayeh Sarah 2nd Mamar p. 31 “One cannot say that even while it was in the brain it was a physical drop of seed, as if so, the brain would be lacking [each time one ejaculates]. Rather, in truth, its first drawing from the brain is merely a pull of spiritual power. Only later when it descends through the spinal cord does it change and develop into a physical drop.”; Likkutei Torah Shir Hashirim p. 16
 Torah Or ibid
 Siddur Ya’avetz Mosach Hashabbos Mitos Kesef 4:2
 Torah Or Shemos 1st Ma’amar p. 97; Eitz Chaim Shaar 39