Lecture 28

Question 1

What are the main anatomical parts of the mammary glands?

Answer 1

Composed of lobules that merge into alveoli (the milk producing region) then travel into the milk releasing cisterns (outer surface- highly vascularised)

Question 2

What is the first stage that is involved in the lactation provide its name, a brief description and the hormones involved?

Answer 2

MAMMOGENESIS- growth of mammary tissue

• Oestrogens- stimulate the developement of the ducts and growth of the adipose tissues
• Progesterone- stimulates the growth of glandular tissue (alveoli are responsible for secretion of milk after birth)
• Prolactin- secreted by the anterior pituitary gland, progesterone inhibits the release of prolactin during early gestation but as progesterone levels decrease more prolactin will be present. Prolactin has a role in breast development during later stages of pregnancy
• Permissive actions of certain other hormones including cortisol, T3/T4 and insulin allow progesterone and other oestrogen’s to function

Question 3

Briefly describe the second stage that is involved in lactogenesis:

Answer 3

LACTOGENESIS

• involved in the initiation of lactation including the synthesis of sugars, fats and carbohydrates
• Falling levels of progesterone before birth lead to increased prolactin and milk/colostrum synthesis
• Prolactin receptors-located on membranes of alveolar cells in the mammary glands

Question 4

What are the steps involved in the third stage of lactation?

Answer 4

GALACTOPOIESIS - maintenance of milk production

• maintenance of production occurs through prolactin
• FIL is a feedback inhibitor of lactation, if the milk is not being consumed this is released preventing the production of milk

Question 5

What is the fourth stage that is involved in lactation?

Answer 5

• milk ejection-involves neurohormonal reflex and the release of milk to the offspring, this reflex arc involves the release of oxytocin, that is promoting the synthesis and secretion of milk

Question 6

What is the role of prolactin in lactogenesis?

Answer 6

• inhibits GnRH release resulting in decreased reproductive function
• prolactin secretion decreases as lactation decreases
• somatosensory pathway important in prolactin release
• TRH and endorphins result in release of of prolactin by blocking PIF’s actions
• dominent influence in lactation is in response to the suckling response

Question 7

What is the role of GH in lactogenesis?

Answer 7

• involved in milk production
• GH acts to divert nutrients to milk production
• exogenous administration of bovine somatotropin in early lactations increases overall efficiency of milk production

Question 8

Explain the neural and hormonal events involved in the milk ejection reflex at suckling

Answer 8

• Mammary cisterns, then milk is immediately available to the infant (movement is passive)
• Removal of milk from alveoli requires neurohormonal reflex (milk ejection reflex)
• Young starts suckling on teat causing mammary glands to swell under pressure from alveolar expulsion of milk leading to contraction of myoepithelial cells leading to release of oxytocin
• above phenomenon becomes a conditioned reflex that occurs in anticipation of milk release