MAMMARY GLANDS AND LACTATION

16. The Mammary Glands = Milk Glands

• Specialized skin glands

  • Present in both male and female

  • Normally only function in the female

  • Vary among species (number, locations, openings per teat)

• Produce colostrum and milk

• Very important during neonatal period

17. Mammary Gland Development

• Develop in response to hormones produced at puberty:

  • Prolactin

  • Growth hormone

  • Estrogen

  • Progesterone

  • Thyroid-stimulating hormone

  • Adrenocorticotropic hormone

• Levels of various hormones must be balanced precisely for complete development

18. Lactation

• The process of milk production

• Begins toward end of pregnancy

• Obvious at time of parturition

• Hormones involved in starting lactation:

  • Prolactin

  • Growth hormone

  • Hormones from adrenal cortex

19. Colostrum

• Pre-milk secretion

• Contents:

  • Larger amounts of proteins, lipids, and amino acids than milk

  • High levels of various essential vitamins

  • Laxative effect to help clear newborn's meconium

  • High levels of specific antibodies (passive immunity)

20. Maintenance of Lactation

• Once begun, lactation continues as long as mammary gland is emptied regularly

  • Physical stimulation of the teat combined with regular milk removal

• Lactation will gradually cease due to:

  • Lack of hormonal stimulation

  • Increased pressure in mammary gland

  • Involution of the mammary gland = "dries up"

21. Milk Letdown

• Immediate effect of nursing or milking

• Steps for milk letdown:

  1. Milk accumulates in alveoli and small ducts

  2. Physical stimulation of nipple or teat sends sensory nerve impulses to brain, to release oxytocin

  3. Oxytocin causes contraction of myoepithelial cells around alveoli and small ducts

  4. Milk is squeezed down into large ducts and sinuses