To understand the Qur’aanic verse concerning the above concepts, it is important to know that chemical reactions occur in the intestines and that, from there, substances extracted from food pass into the blood stream via a complex system; sometimes by way of the liver, depending on their chemical nature. The blood transports them to all the organs of the body, among which are the milk-producing mammary glands.
In simple terms, certain substances from the contents of the intestines enter into the vessels of the intestinal wall itself, and these substances are transported by the blood stream to the various organs.
This concept must be fully appreciated if we wish to understand the following verse in the Qur’aan:
"And verily in cattle there is A lesson for you. We give you to drink Of what is inside their bodies, Coming from a conjunction Between the contents of the Intestine and the blood, A milk pure and pleasant for Those who drink it." [Al-Qur’aan 16:66] [Translation of this Qur’anic verse is from the book "The Bible, the Qur’an and Science" by Dr. Maurice Bucaille]
"And in cattle (too) ye Have an instructive example: From within their bodies We produce (milk) for you To drink; there are, in them, (Besides), numerous (other) Benefits for you; And of their (meat) ye eat." [Al-Qur’aan 23:21]
The Qur’aanic description of the production of milk in cattle is strikingly similar to what modern physiology has discovered.