HRR: female repro physiology IV Flashcards
Where is oxytocin made?
Mostly in the paraventricular nucleus of the hypothalamus, but some in peripheral tissues.
What triggers the production of oxytocin?
Uterine cervix expansion.
In terms of oxytocin, what happens in the third trimester?
Estrogen increases oxytocin receptors and sensitivity, allowing oxytocin to have more effect.
Describe how oxytocin is able to produce contractions.
- Oxytocin stimulates an increase in intracellular calcium.
- Calcium activates calmodulin.
- MLCK is stimulated.
- Myosin light chain is phosphorylated.
- Myosin and actin can interact, producing smooth muscle contraction.
Around labor, what happens with oxytocin receptors in the myometrium?
There is a sharp, steady increase in oxytocin leading up to labor, which then drops back down after delivery.
Around labor, what happens with oxytocin receptors in the mammary gland?
There is a gradual steady increase leading up to labor, followed by a quick drop after delivery. The oxytocin receptors will then start rising again and eventually level off during lactation.
What kinds of receptors are largely found around the nipple?
Mechanoreceptors (stimulated by suckling!).
Describe the milk ejection reflex.
- Suckling or psychogenic stimulus (crying) stimulates the breast.
- Stimulus travels to the hypothalamus.
- Oxytocin and prolactin are triggered for release from the posterior pituitary and anterior pituitary.
- Prolactin causes milk synthesis.
- Oxytocin causes milk ejection.
Oxytocin is needed for milk ___, while prolactin is needed for milk ___
Ejection, synthesis.
Describe the role of oxytocin in milk ejection.
Oxytocin travels to the breast and stimulates contraction of myoepithelial cells surrounding the acini and ducts in the breast. The contraction moves milk to the nipple where it can be ejected.
Prolactin is mostly made in the…
Anterior pituitary.
Describe how we regulate prolactin.
- Dopamine binds D2 receptors on pituitary lactotrophs.
- PKA is inhibited.
- Lactotroph hyperpolarization decreases prolactin secretion/transcription of prolactin gene.
What is the effect of dopamine on prolactin?
It mediates a tonic inhibition of prolactin.
What can increase prolactin secretion/transcription?
Estrogen.
What happens with the pituitary during pregnancy?
Hypertrophy! Enlarges by like 30% thanks to high estrogen levels.
Describe prolactin levels during pregnancy.
Rise steadily throughout pregnancy; if not nursing, levels return to baseline about 2 weeks after delivery. If nursing, prolactin will stay elevated.
What does suckling do to dopamine?
Decreases it, allowing for prolactin release.
What can increase prolactin levels?
Estrogen, pregnancy, exercise, surgery, trauma, sickness, etc.
How does prolactin cause milk production?
It stimulates transcription of various genes like casein and lactalbumin. This allows for fatty acid and lactose synthesis and milk production.
What is lactational amenorrhea?
During lactation, a nursing mother may not have menses. This is because the high levels of prolactin cause GnRH pulses to be inhibited, leading to low LH/FSH and decreased chances for ovulation.
What is a prolactinoma?
A pituitary tumor producing prolactin.
What are manifestations of a prolactinoma?
Hyperprolactinemia. It can enlarge breast tissue, cause cessation of the menstrual cycle, inappropriate milk production without pregnancy, and gonadal dysfunction in men.
