DAIRY CHEMISTRY AND BIOCHEMISTRY Weaning 10 0 100 Figure 1.3 Time-course of mammary development in rats(from Tucker, 1969) The substrates for milk synthesis enter the secretory cell across the basal membrane(outside), are utilized, converted and interchanged as they pass inwards through the cell and the finished milk constituents are excreted into the lumen across the lumenal or apical membrane. Myoepithelial cells (spindle shaped)form abasket around each alveolus and are capable of contracting on receiving an electrical, hormonally mediated, stimulus, there- by causing ejection of milk from the lumen into the ducts. Development of mammary tissue commences before birth, but at birth he gland is still rudimentary. It remains rudimentary until puberty when rery significant growth occurs in some species; much less growth occurs in other species, but in all species the mammary gland is fully developed at puberty. In most species, the most rapid phase of mammary gland develop- ment occurs at pregnancy and continues through pregnancy and partur ition, to reach peak milk production at weaning. The data in Figure 1.3 the development pattern of the mammary gland in the rat, the species has been thoroughly studied in this regard Mammary development is under the regulation of a complex set of hormones. Studies ng endocrinectomy(removal of different endocrine organs) show that the principal hormones are oestrogen, progesterone growth hormone, prolactin and corticosteroids( Figure 1.4)6 DAIRY CHEMISTRY AND BIOCHEMISTRY 3 t-” 10 0 0 100 200 Days Figure 1.3 Time-course of mammary development in rats (from Tucker, 1969). The substrates for milk synthesis enter the secretory cell across the basal membrane (outside), are utilized, converted and interchanged as they pass inwards through the cell and the finished milk constituents are excreted into the lumen across the lumenal or apical membrane. Myoepithelial cells (spindle shaped) form a ‘basket’ around each alveolus and are capable of contracting on receiving an electrical, hormonally mediated, stimulus, there￾by causing ejection of milk from the lumen into the ducts. Development of mammary tissue commences before birth, but at birth the gland is still rudimentary. It remains rudimentary until puberty when very significant growth occurs in some species; much less growth occurs in other species, but in all species the mammary gland is fully developed at puberty. In most species, the most rapid phase of mammary gland develop￾ment occurs at pregnancy and continues through pregnancy and partur￾ition, to reach peak milk production at weaning. The data in Figure 1.3 show the development pattern of the mammary gland in the rat, the species that has been thoroughly studied in this regard. Mammary development is under the regulation of a complex set of hormones. Studies involving endocrinectomy (removal of different endocrine organs) show that the principal hormones are oestrogen, progesterone, growth hormone, prolactin and corticosteroids (Figure 1.4)