Slide 7: Milk Ejection Flashcards
Define milk ejection
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
Milk ejection has two-components:
neuro-hormonal reflex:
Ø Neural (Afferent) component
Ø Hormonal (Efferent) component
Where is prolactin secreted from?
Anterior pituitary
Where is oxytocin secreted from?
Posterior pituitary
Explain the nervous system of the mammary gland
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)
Explain the afferent (neural) component of the mammary gland
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
Explain the efferent (hormonal) component
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
How is oxytocin secreted?
Oxytocin + carrier protein neurophysin (secretory granules)
Where is oxytocin stored?
Stored in the neurosecretory cells in the P. pituitary gland (herring bodies)
Oxytocin is released in ________
pulses (all or nothing principle)
What is the stimulation needed to stimulate the secretion of oxytocin?
Oxytocin can be released without mechanical stimulation of the udder. Visual or auditory signals can result in milk letdown
When does oxytocin peak?
Oxytocin peaks in blood are very sharp (1-2 min following stimulation)
What is the half-life of oxytocin?
Oxytocin has short half-life in blood (90 seconds)
Give examples to the marked differences in oxytocin release between species
Ø humans, rats, ruminants: peaks every 2-10 minutes
Ø Sows: a single purse during suckling
In which animals milk ejection is less important?
In mammals with large cisterns, milk ejection is less important
What happens to oxytocin release as lactation progresses?
the amount released and the sensitivity to it decreases
How much oxytocin does posterior pituitary can store in women?
The pituitary gland contains large amount of oxytocin (3000-9000 mU) compared with the amount required to elicit rejection reflex (50-100 mU)
What is the function of oxytocin in terms of lactation?
- Oxytocin increase blood flow to the breast without increasing blood pressure
- Oxytocin helps in uterus contraction (aid in uterine involution)
Explain the steps in stimulation of milk ejection reflex (women)
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
What are some psychological effects of oxytocin?
Ø oxytocin induces state of calm and reduces stress
Ø It may enhance feelings of affection between mother and child, and promote bonding
Explain the stimulation of milk ejection reflex (cows)
Ø Sight of a calf
Ø Sound of milking machine
Ø Touch (massage) of the udder
Explain the response time for afferent & efferent pathways
- 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
How is the inhibition of milk ejection achieved?
Any factor that reduces the amount of oxytocin reaching the myoepithelial cell, will inhibit milk ejection
What are the two inhibition mechanisms of milk ejection?
- 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
