Mammary Gland – Hormonal Control of Milk Secretion Flashcards
What are the four stages of the mammary cycle?
Mammogenesis, lactogenesis, weaning and involution
What happens during pregnancy?
Terminal alveoli grow into lobules. Prolactin, adrenal cortical hormones and placental lactogen (relaxin from CL in pigs) allow the synthesis of milk
What hormones are responsible for the increase in udder volume during pregnancy and the onset of milk secretion?
Increase in udder volume during pregnancy follows increase in oestrogen and placental lactogen
Onset of lactogenesis coincides with drop in circulating progesterone at parturition
What are the hormones affecting lactopoiesis?
Prolactin, oestrogen, progesterone & cortisol
What is the function of prolactin?
Prolactin regulates the production of α-lactalbulmin (involved in the production of UDP-galactose required for lactose synthesis), process is inhibited by progesterone
Prolactin is also involved in mammary involution, cessation of suckling results in a drop in prolactin secretion
What two hormones does milk secretion depend on?
Prolactin and oxytocin
What is the milk ejection reflex?
Neuroendocrine reflex that induces emptying of the mammary gland, requires sensory activation, neural activation, oxytocin release, contraction of alveoli and ducts & mechanical transfer of milk
Describe the milk reflex
Suckling stimulates sensory neurons and signals travel through afferent nerves to the hypothalamus, nerves in the paraventricular nuclei are stimulated by afferent neurons and terminals of the posterior lobe of the pituitary which release oxytocin
What does oxytocin do and where is it synthesised?
Increases pressure in the alveoli, reduces resistance in the small excretory ducts, reduces resistance in the teat canal – synthesised in the hypothalamus
Oxytocin also improves maternal-neonatal bonding
How does suckling affect dopamine?
Suckling reduces dopamine production in the hypothalamus, which allows increased prolactin secretion
What changes in metabolism occur during lactation?
Reduced fat synthesis and increased lipolysis, decreased uptake of glucose in muscle and adipose tissue, increased mammary uptake of glucose, increased uptake of amino acids in the mammary gland – regulated by prolactin, growth hormone & insulin
How does suckling cause anoestrus?
Suckling induces opioid production which blocks GnRH secretion preventing ovulation
What conditions affect lactation?
Pseudopregnancy, galactostasis (congestion of the gland combined with oedema-inflammation) & agalactia (reduced milk production)
