I've heard mention in the past of an amino acid pool in the body. Can't remember if that is what Kiefer mentioned in that podcast or not. The body has all sorts of storage and recycling mechanisms for bodily resources.The autophagy help with recycling of garbage materials into usable resources for the body, such as amino acids. Sorry I don't have more info, but that may have been what he is talking about, not sure.
I believe Keifer was talking about the splenic bed in the body, but I have seen no research that the spleen is responsible for anything other than red blood cell and monocyte storage. And I can't get any hits on Google for it either.