DAIRY CHEMISTRY AND BIOCHEMISTRY Friesian Cow a Morse Buffalo e Beef Co ·3 ubon Rabbit e Rats· Guinea-Pig lamster Tree shrew Body Weight (kg) Figure 1.1 Relation between daily milk yield and maternal body weight for some species (modified from Linzell, 1972) 1.4 Structure and development of mammary tissue The mammary glands of all species have the same basic structure and all are located external to the body cavity(which greatly facilitates research on milk biosynthesis). Milk constituents are synthesized in specialized epithelial cells(secretory cells or mammocytes, Figure 1.2d)from molecules absorbed from the blood. The secretory cells are grouped as a single layer around a central space, the lumen, to form more or less spherical or pear-shaped bodies, known as alveoli( Figure 1.2c). The milk is secreted from these calls into the lumen of the alveoli. When the lumen is full, the myoepithelial cells surrounding each alveolus contract under the influence of oxytocin and the milk is drained via a system of arborizing ducts towards sinuses or cisterns (Figure 1. 2a)which are the main collecting points between suckling or milking. The cisterns lead to the outside via the teat canal. Groups of alveoli, which are drained by a common duct, constitute a lobule: neighbouring lobules are separated by connective tissue(Figure 1.2b). The secretory elements are termed the " lobule-alveolar systemto distinguish them from the duct system. The whole gland is shown in Figure 1.2a Milk constituents are synthesized from components obtained from blood; consequently, the mammary gland has a plentiful blood supply also an elaborate nervous system to regulate excretion.4 DAIRY CHEMISTRY AND BIOCHEMISTRY R,~, . . Oumea-Pig Il.,lll*lcr . 1khidii:i 3 3 10.' Body Wcight (kg) Figure 1.1 Relation between daily milk yield and maternal body weight for some species (modified from Linzell, 1972). 1.4 Structure and development of mammary tissue The mammary glands of all species have the same basic structure and all are located external to the body cavity (which greatly facilitates research on milk biosynthesis). Milk constituents are synthesized in specialized epithelial cells (secretory cells or mammocytes, Figure 1.2d) from molecules absorbed from the blood. The secretory cells are grouped as a single layer around a central space, the lumen, to form more or less spherical or pear-shaped bodies, known as alveoli (Figure 1.2~). The milk is secreted from these calls into the lumen of the alveoli. When the lumen is full, the rnyoepithelial cells surrounding each alveolus contract under the influence of oxytocin and the milk is drained via a system of arborizing ducts towards sinuses or cisterns (Figure 1.2a) which are the main collecting points between suckling or milking. The cisterns lead to the outside via the teat canal. Groups of alveoli, which are drained by a common duct, constitute a lobule; neighbouring lobules are separated by connective tissue (Figure 1.2b). The secretory elements are termed the 'lobule-alveolar system' to distinguish them from the duct system. The whole gland is shown in Figure 1.2a. Milk constituents are synthesized from components obtained from the blood; consequently, the mammary gland has a plentiful blood supply and also an elaborate nervous system to regulate excretion