Slide 7: Milk Ejection

Question 1

Define milk ejection

Answer 1

The transfer of milk from the lobulo-alveolar spaces into the ducts as a result of the contraction of the myoepithelial cell surrounding each alveolus

Question 2

Milk ejection has two-components:

Answer 2

neuro-hormonal reflex:
Ø Neural (Afferent) component
Ø Hormonal (Efferent) component

Question 3

Where is prolactin secreted from?

Answer 3

Anterior pituitary

Question 4

Where is oxytocin secreted from?

Answer 4

Posterior pituitary

Question 5

Explain the nervous system of the mammary gland

Answer 5

Ø Innervation of the udder is sparse
Ø No direct innervation of the secretory cell
Ø No parasympathetic innervation
Ø Sympathetic innervation is associated with arteries
Ø Neural receptors (somatic NS) are present in the skins of the teats and udder (greatest innervation is in the teat)

Question 6

Explain the afferent (neural) component of the mammary gland

Answer 6

Ø Start with stimulation of the teat
Ø Activation of nerve receptors
Ø Nerve impulses from the receptors to the brain via the spinothalamic nerve tract.
Ø Release of oxytocin from the Posterior pituitary gland

Question 7

Explain the efferent (hormonal) component

Answer 7

Ø Start with the release of oxytocin into the blood
Ø Oxytocin travels to the epithelial secretory cell and
binds to protein receptors on the myoepithelial cell
Ø Myoepithelial cell contracts in response to oxytocin
Ø Milk expelled from epithelial cell & lumen into the ductule

Question 8

How is oxytocin secreted?

Answer 8

Oxytocin + carrier protein neurophysin (secretory granules)

Question 9

Where is oxytocin stored?

Answer 9

Stored in the neurosecretory cells in the P. pituitary gland (herring bodies)

Question 10

Oxytocin is released in ________

Answer 10

pulses (all or nothing principle)

Question 11

What is the stimulation needed to stimulate the secretion of oxytocin?

Answer 11

Oxytocin can be released without mechanical stimulation of the udder. Visual or auditory signals can result in milk letdown

Question 12

When does oxytocin peak?

Answer 12

Oxytocin peaks in blood are very sharp (1-2 min following stimulation)

Question 13

What is the half-life of oxytocin?

Answer 13

Oxytocin has short half-life in blood (90 seconds)

Question 14

Give examples to the marked differences in oxytocin release between species

Answer 14

Ø humans, rats, ruminants: peaks every 2-10 minutes

Ø Sows: a single purse during suckling

Question 15

In which animals milk ejection is less important?

Answer 15

In mammals with large cisterns, milk ejection is less important

Question 16

What happens to oxytocin release as lactation progresses?

Answer 16

the amount released and the sensitivity to it decreases

Question 17

How much oxytocin does posterior pituitary can store in women?

Answer 17

The pituitary gland contains large amount of oxytocin (3000-9000 mU) compared with the amount required to elicit rejection reflex (50-100 mU)

Question 18

What is the function of oxytocin in terms of lactation?

Answer 18

• Oxytocin increase blood flow to the breast without increasing blood pressure
• Oxytocin helps in uterus contraction (aid in uterine involution)

Question 19

Explain the steps in stimulation of milk ejection reflex (women)

Answer 19

Ø conditioned to the mother’s sensations and feelings:
Ø Touching the baby
Ø Smelling or seeing the baby
Ø hearing the baby cry

Ø A tingling sensation before or during feeding
Ø Milk flowing from her breast when she thinks of the baby or
hears him/her crying
Ø Milk flowing down the other breast when the baby is sucking
Ø milk flowing from the breast in streams if suckling is interrupted
Ø thirst during a feed
Ø Uterine pain or a flow of blood from the uterus

Question 20

What are some psychological effects of oxytocin?

Answer 20

Ø oxytocin induces state of calm and reduces stress

Ø It may enhance feelings of affection between mother and child, and promote bonding

Question 21

Explain the stimulation of milk ejection reflex (cows)

Answer 21

Ø Sight of a calf
Ø Sound of milking machine
Ø Touch (massage) of the udder

Question 22

Explain the response time for afferent & efferent pathways

Answer 22

• Nerve impulse udder to brain (afferent) 0.1 sec
• Release of oxytocin 1-2 sec
• Arterial transport of oxytocin (efferent) 19-22 sec
• Contraction of myoepithelial cell (efferent) 6 sec
• Milk ejection (efferent) 20-30 sec

Question 23

How is the inhibition of milk ejection achieved?

Answer 23

Any factor that reduces the amount of oxytocin reaching the myoepithelial cell, will inhibit milk ejection

Question 24

What are the two inhibition mechanisms of milk ejection?

Answer 24

• Peripheral inhibition: Caused by low levels of oxytocin
  reaching the moyepithelial cell
• Central inhibition: Caused by low levels of oxytocin
  secreted by the pituitary gland

Question 25

Give examples to the variations in nursing in mammals

Answer 25

Rabbit
Ø Nurse once a day
Ø Milk secretion: 250 ml in 2-5 min
Ø Response to one spurt of oxytocin

Rat
Ø Nurse every 1/2 h
Ø Oxcytocin release is delayed for 15 min after pup
attachment
Ø Oxcytocin is released every 5-12 min thereafter

Women
Ø Milk ejection (tingling sensation) occurs prior to or shortly after suckling
ØContractions last for 1 min with frequency of 4-10 contractions every 10 min
ØOxytocin blood levels rise within 1 min after stimulation and return to baseline after 6 min