Stem cells are cells with a capacity to self-renew and to generate daughter cells that can differentiate into different cell lineages to form all the cell types that are found in the mature tissue. The activity of mammary stem cells and their mitotic progeny is fundamental to normal mammary growth, differentiation and regeneration in successive cycles of pregnancy, lactation and involution. The isolation and characterization of mammary stem cells is fundamental to understanding mammary gland development and tissue homeostasis as well as breast oncogenesis.

Endothelium is not only a layer of cells separating lumen of vessel from surrounding tissues. It begins to notice its role in many biological processes. This paper presents the role of endothelium and vessels in development, tissues and organs formation and maturation.