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Prolactin has a wide variety of effects. It stimulates the mammary glands to produce milk (): increased serum concentrations of prolactin during pregnancy cause enlargement of the mammary glands and prepare for milk production, which normally starts when levels of progesterone fall by the end of pregnancy and a suckling stimulus is present.
In these cases, high perceived pressure raises cortisol levels inside the body. [18] [21] The elevated level of the stress hormone affects the secretion of lactogenic hormones in the mother, which delays the onset of lactation. [22] Women who underwent a c-section are more likely to experience DOL compared to women who delivered vaginally.
Prolactin, produced by the pituitary gland, is essential for initiating and maintaining milk production. Its levels increase during pregnancy to prepare the breasts for milk production and remain high after childbirth to continue supporting breastfeeding.
High levels of prolactin during pregnancy and breastfeeding also increase insulin resistance, increase growth factor levels (IGF-1) and modify lipid metabolism in preparation for breastfeeding. During lactation, prolactin is the main factor maintaining tight junctions of the ductal epithelium and regulating milk production through osmotic balance.
By the twentieth week of gestation, mammary glands have reached a sufficient level of development to generate milk components as a result of stimulation by prolactin. [33] Post-lactational involution refers to the process of breast tissue returning to its normal state after milk production stops due to a decrease in prolactin levels. [33]
A prolactin cell (also known as a lactotropic cell, epsilon acidophil, lactotrope, lactotroph, mammatroph, mammotroph) is a cell in the anterior pituitary which produces prolactin (a peptide hormone) in response to hormonal signals including dopamine (which is inhibitory), thyrotropin-releasing hormone and estrogen (especially during pregnancy), which are stimulatory.
Estrogen and progesterone cause the secretion of high levels of prolactin from the anterior pituitary, [32] [33] which reach levels as high as 20 times greater than normal menstrual cycle levels. [31] IGF-1 and IGF-2 levels also increase dramatically during pregnancy, due to secretion of placental growth hormone (PGH). [34]
Mechanical detection of suckling increases prolactin levels in the body to increase milk synthesis. Excess prolactin may inhibit the menstrual cycle directly, by a suppressive effect on the ovary, or indirectly, by decreasing the release of GnRH. [2] Suckling is a pivotal factor in maintaining lactational amenorrhea postpartum.