Changes

===Involution===

===Involution===

As the requirement for milk by the neonate decreases, suckling is less frequent. Consequently, there is a buildup of pressure in the mammary gland causing secretory cells to become increasingly less functional - '''pressure atrophy'''. Secretory cells then remain non-functional until a subsequent pregnancy, at which time prolactin, glucocorticoids and placental lactogen restimulate alveolar milk synthesis. During involution, immune cells such as lymphocytes and macrophages invade the mammary tissue.  These produce immunoglobulins in the subsequent lactation. Involution is critical to allow the replacement of senescent secretory cells which are lost by apoptosis.

As the requirement for milk by the neonate decreases, suckling is less frequent. Consequently, there is a buildup of pressure in the mammary gland causing secretory cells to become increasingly less functional - '''pressure atrophy'''. Secretory cells then remain non-functional until a subsequent pregnancy, at which time prolactin, glucocorticoids and placental lactogen restimulate alveolar milk synthesis. During involution, immune cells such as lymphocytes and macrophages invade the mammary tissue.  These produce immunoglobulins in the subsequent lactation. Involution is critical to allow the replacement of senescent secretory cells which are lost by apoptosis.