Gland

Abstract

The first obvious statement is that the mammary gland is an intriguing structure, and that its development is one of the most fascinating aspects. During the lifetime of the animal the mammary gland probably undergoes more and greater changes in size, structure, composition and activity than any other tissue or organ. These changes start during fetal life and continue even after the gland has reached maturity since it waxes and wanes during successive reproductive cycles. In its most advanced state, that of full lactation, the gland possesses vast numbers of specialized secretory cells (parenchyma) together with supporting connective and adipose tissue (stroma); it may produce considerably more than its own weight of secretion every day or, in energetic terms, as many joules per day as it contains in its own mass. The second obvious statement is that the actual yield of milk is a function of the amount produced by each secretory cell (which must be subject to a fixed maximum, but as yet unknown, value) and the number of secretory cells. Hence those factors which determine the epithelial cell population are crucial to the control of milk production. The control of mammary growth is a complex process involving factors intrinsic to the gland (local control) or the whole animal (systemic control) as well as external influences such as environment, climate and diet. Furthermore, it now appears that the gland has an important controlling role in its own right since it has considerable influence on reproductive processes in at least one s