Varying morphology of branched organs. (A) Schematics of mouse submandibular glands from embryonic day (E) 13.5 and E16 stage embryos. Submandibular gland morphology is predominantly lobular. (B) Schematic of blood vessels from a mouse retina. The branched vascular network is completely tubular. (C) Schematics of the ureteric bud of mouse kidney from E13.5 and E18.5 stage embryos. At E13.5, mouse kidney is relatively lobular. At E18.5, the elongated collecting ducts convert kidney morphology to predominantly tubular. (D) Schematics of mouse mammary gland at young adult stage and lactation stage. At the young adult stage, the mammary gland is a tubular network. During pregnancy and lactation, dramatic remodeling occurs in the mammary gland so that lactating alveoli form at branch tips, which transforms the structure to primarily lobular.