Parturition and Lactation Flashcards
What does parturition involve?
- Transformationi of myometrium from quiescent to highly contnractile
- Remodeling of uterine cecrtix-soften and dilate
- Rupture fetal mem
- expulsion of contents
- Return to pre pregnant state
What are the two major categories of effects leadig up to intense contractions of labor?
- progressive hormone changes
- progressive mechanical chagnes
What hormone changes occur with late pregnancy?
- Progesterone:
- promotes relaxationn and blocks contractions
- treat with nuclear progesterone antagonist increases myometrial contractility-can induce labor
- Close to labor, thought to be desensitization of uterine cells to actions of progesterone
- Fxnl rather than systemic withdrawl
- Leads to inncrease in estrogen receptor expression
What happens with estrogen followinng progesterone desensitization?
- increase in receptor expression
- Increase myometrial cotractility and cervical dilation
- Opposes actions of progesterone by increasing responsiveness to oxytocin and prostaglandins
- stimulate gap jxn formation
- increase numbers of oxytocin receptors in myometrium
- Increase production release of prostaglandins by fetal membrane
- Stimulate expression of proteolytic enzymes
What do prostaglandins do for parturition?
- Stimulate strong myometrial contractions
- initiates labor
- doses of PGF2a can induce myometrial contractions at any stage of gestation
- PGF2a potentiates oxytocin induced contractions by promoting formation of gap jxns
- Stimulates effacement of cervix in early labor
- Synthesis stimulated by estrogen inn fetal mem, oxytocin in uterine cells and uterine stretch
How long is uterus insensitive to oxytocin?
Until ~20 weeks
Estrogen incereases the oxytocin receptor numbers
What is relaxixn?
- Keeps uterus in quiescent state during pregnancy
- Max concentrations 38-42 may help soften and dilate cervix
- if elevated levels around 30 weeks assoc. with premature birth
- Produced by CL placenta and decidua
- reated to insulin
For the innitiation of labor, what hormone does the placenta produce?
- Produces CRH
- The maternal levels rise in late pregnancy and labor
- Promotes contractions
- Accumulates in fetal circulation also
When the placenta produces CRH and it accummulates in fetal circulation, what happens?
Stimulates fetal ACTH secretion
- increases fetal adrenal cortisol production and further placental CRH release
- Fetoplacental estrogen also increases
- this enhances contractility of myometrium
Where does a fully dilated cervix lie?
Drawn up just below the pelvic inlet
What is the final phase of delivery?
- Expulsion of placenta
- The uterus keeps contracting to separate placenta resulting in bleeding and clotting
- oxytocin constricts blood vessels
- Nipple stimulation induces oxytocin
what is the alveolar epithelium?
luminal epithelial cells responsible for milk synthesis and secretion
What do myoepithelial cells do?
- found btw epi cells and basememtn mem
- Contractile fxn
- Moves milk from alveoli to ducts
How does estrogen impact breast development?
- lactiferous ducts sprout and branch
- ends form small solid spheroidal masses of cells that will develop into alveoli
What is breast tissue made of at birth?
Mammary glad is almost entirely lactiferous ducts with few alveoli
As menstrual cycle is established mammary tissue is exxposed to estrogen and progesterone, this __________.
induces additional ductal lobular alveolar growth
What happens to adipose tissue in breast during pregnancy?
It decreases due to the epithelial structures proliferating and inflitration of interstitial tissues with lymphatics, plasma cells and eosinophils
What is responsible for milk ejection?
oxytocin
What maintains milk synthesis?
Prolactin & a decrease of prolactin inhibitory factor (dopamine)
What are the five main pathways that alveolar epi cells secrete milk?
- Secretory path
- Transcellular endocytosis and exocytosis
- Lipid path
- Transcellular salt and water transport
- Paracellular path
How does suckling effect hormone release?
- Stimulus from breast travels through spinal cord to hypo
- SC neurons inhibit DA rlelease, which removes inhibition of lactrophs leading to prolactin release
- SC neurons also stimulate oxytocin release from PVN and supraoptic nuclei, travels via blood to breast
- SC neurons inibit neurons in arcuate nucleus and preoptic area causing fall in GnRH, decreasing LH and FSH inhibiting ovarian cycle
How does lactation stop?
- Milk will accumulate when suckling stops, and distenstion and mechanical atrophy of epithelial structures occurs
- The alveolar walls rupture and capillaries get compressed resulting in alveolar hypoxia
- Debris is phagocytosed and lobular acinar structures shrink
- Ductal system then predominates
- Full involution can take three months
