Lactacion

Lactogenesis - Initiation of Lactation

Lactogenesis is the term meaning the initiation of lactation. This it the process of functional differentiation which mammary tissue undergoes when changing from a nonlactating to a lactating state. This process is normally associated with the end of pregnancy and around the time of parturition. Because lactogenesis is particularly dependent upon aspecific set of hormones (called the Lactogenic Complex of hormones), mammary tissue from most states of the nonlactating mammary gland also can be made to undergo some degree of lactogenesis by administration of high amounts of those hormones, even in nonpregnant animals.
This lesson includes discussions on Lactogenesis, including:

Defining Principles of Lactogenesis

Mammary Cytology Associatedwith Lactogenesis

Hormonal Changes Associated with Lactogenesis

Progesterone Involvement in Lactogenesis

The Lactogenic Complex of Hormones

Insulin

Glucocorticoids

Prolactin

Estrogen

Growth Hormone

Local Effects

Extracellular Matrix

Hormonal Induction of Lactogenesis

 
 Return to Lactation Biology Topic Areas

For more readingsee:
Tucker, HA (1994) Lactation and its hormonal control. Ch. 57, In: The Physiology of Reproduction, 2nd edition, Eds. E. Knobil, J. Neill, et al. Raven Press, Ltd., New York. p. 1065.
Oka, T, Yoshimura, M, Lavandero, S, Wada, K, Ohba, Y 1991 Control of growth and differentiation of the mammary gland by growth factors. J. Dairy Sci. 74:2788-2800.
Forsyth, IA 1989 Growth factors in mammarygland function. J. Reprod. Fert. 85:759-770.
Wilde CJ, Hurley WL 1996 Animal models for the study of milk secretion. J. Mammmary Gland Biol. Neoplasia 1:123-134.
Streuli, CH 1993 Extracellular matrix and gene expression in mammary epithelium. Sem. Cell Biol. 4:203-212.
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Defining Principles of Lactogenesis

Lactogenesis is a series of cellular changes whereby mammary epithelial cells areconverted from a nonsecretory state to a secretory state.
Lactogenesis is a two stage process :
1. Cytologic and enzymatic differentiation of alveolar epithelial cells. This coincides with very limited milk synthesis and secretion before parturition. Cytological changes associated with stage 1 of lactogenesis are described below. Enzymatic changes include increased synthesis of acetyl CoAcarboxylase, fatty acid synthetase, and other enzymes associated with lactation, and increases in uptake transport systems for amino acids, glucose, and other substrates for milk synthesis. Note that synthesis of α-lactalbumin, and therefore, lactose synthesis does not begin until stage 2 of lactogenesis. Stage 1 of lactogenesis coincides with the formation of colostrum and immunoglobulin uptake (seeThe Neonate and Colostrum Lesson).
2. Copius secretion of all milk components. In the cow this begins about 0-4 days before parturition and extends through a few days postpartum. It is not until the release of the inhibitory effects of progesterone on lactogenesis (about 2 days prepartum in many mammals) and the stimulation by the very high blood concentrations of prolactin and glucocorticoidsassociated with parturition, that copious milk secretion begins (stage 2 of lactogenesis). One exception to this timing is in women. The drop in blood progesterone concentrations does not occur in women until parturition, so that the full impact of stage 2 of lactogenesis sometimes does not occur until about 2 days postpartum. In pigs and mice, stage 2 of lactogenesis is occurring immediately priorto and at the time of parturition. It is difficult to get any mammary secretion out of a sow until parturition, whereas in the cow, substantial mammary secretion volume can be collected up to several days prepartum.

Points to consider :
• During late pregnancy the mammary gland develops the capacity to make milk, but copius milk secretion does not take place until near parturition.
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