From Show Me Your Glory (Gifts of Emunah) (#E-176) by Rabbi Avigdor Miller
Food is given for the purpose to gain yiras (fear of) Hashem. It’s not only that the food is a miraculous thing. What happens to the food is nissei nissim (miracles upon miracles). The food is broken up into thousands of different materials. You know how that happens? Nissei nissim! And these thousands of materials go into the blood together in a mixture and one doesn’t spoil the other.
Imagine thousands of materials now are traveling in the bloodstream to the intestines. The intestines are lined with cells that suck in certain materials. Only certain materials. The cells have such cunning arrangements that they only admit certain materials. One author said it’s because the entrance to the cell, the cell mouth, is so shaped that only configurations of that shape are able to enter. It’s tremendous.
When it finally reaches the destination, it drops off the exact package at the exact address
The molecules of the different chemicals come together in chains. Sometimes they are chains and cross chains — all kinds of designs. Also the waste materials from the cells are carried off in the bloodstream. Imagine here you have pipes leading from your house taking all the dirty water from your house. These same pipes are the pipes to which clean water comes into your house — the same pipes! The same bloodstream which is carrying off
The dead materials from each cell, the waste, is mixed together in the bloodstream with the miraculous materials that came out of your food. It’s all traveling together. When it finally reaches the destination, it drops off the exact package at the exact address. Imagine you have thousands of packages of different materials and thousands of addresses. You cannot afford to make an error. It leaves off at each address exactly what’s needed.
That’s why when you need hair, the blood vessels underneath the hair bring keratin; keratin is the material that makes hair. It also brings oil to lubricate the little well that makes up each hair. All these things, you can’t enumerate them, there are so many of them. They all come together in the bloodstream.