PRODUCTION AND UTILIZATION OF MILK ATROPHIC GLAND Oest +GH+C DUCT GROWTH Ocst +Prog+Pl+ LOBULO-ALVEOLAR GROWTH PL +C MILK SECRETION Figure 1.4 The hormonal control of mammary development in rats. Oest, Oestrogen: Prog, progesterone; GH, growth hormone; PL, prolactin; C, corticosteroid 1.5 Ultrastructure of the secretory cell The structure of the secretory cell is essentially similar to that of other eukaryotic cells. In their normal state, the cells are roughly cubical, c. 10 um in cross-section It is estimated that there are c. 5 x 10 2 cells in the udder of the lactating cow. a diagrammatic representation of the cell is shown in igure 1.2d. It contains a large nucleus towards the base of the cell and is surrounded by a cell membrane, the plasmalemma. The cytoplasm contains the usual range of organelles mitochondria: principally involved in energy metabolism (tricarboxylic acid(Krebs) cycle) endoplasmic reticulum: located towards the base of the cell and to which are attached ribosomes, giving it a rough appearance(hence the term, rough endoplasmic reticulum, RER). Many of the biosynthetic reaction of the cell occur in the rer: Golgi apparatus: a smooth membrane system located toward the apical gion of the cell, where much of the assembly and 'packaging of synthesized material for excretion occurPRODUCTION AND UTILIZATION OF MILK 7 ATROPHIC GLAND Ocst + GH + C DUCT GROWTH LOBULO-ALVEOLAR GROWTH MILK SECRETION Figure 1.4 The hormonal control of mammary development in rats. Oest, Oestrogen; Prog, progesterone; GH, growth hormone; PL, prolactin; C, corticosteroids. 1.5 Ultrastructure of the secretory cell The structure of the secretory cell is essentially similar to that of other eukaryotic cells. In their normal state, the cells are roughly cubical, c. 10 pm in cross-section. It is estimated that there are c. 5 x 10’’ cells in the udder of the lactating cow. A diagrammatic representation of the cell is shown in Figure 1.2d. It contains a large nucleus towards the base of the cell and is surrounded by a cell membrane, the plasmalemma. The cytoplasm contains the usual range of organelles: 0 mitochondria: principally involved in energy metabolism (tricarboxylic acid (Krebs) cycle); 0 endoplasmic reticulum: located towards the base of the cell and to which are attached ribosomes, giving it a rough appearance (hence the term, rough endoplasmic reticulum, RER). Many of the biosynthetic reactions of the cell occur in the RER; 0 Golgi apparatus: a smooth membrane system located toward the apical region of the cell, where much of the assembly and ‘packaging’ of synthesized material for excretion occur;