parturition and lactation Flashcards
most of pregnancy, the uterus is relaxed and quiescent and relatively insensitive to what hormones?
hormones that stimulate contractions, such as prostaglandins and oxytocin
two major categories of effects lead up to the intense contraction. What are they?
progressive hormone changes and progressive mechanical changes
what is the effect of progesterone throughout pregnancy?
it promotes myometrial relaxation during pregnancy (blocks contractions of labor)
how does the body override the effects of progesterone when ready to give birth?
desensitization of uterine cells to actions of progesterone
what does the desensitization of uterine cells to actions of progesterone lead to?
an increase in estrogen receptor expression
what is the effect of estrogens in pregnancy?
they increase myometrial contractility and cervical dilation
what is the effect of estrogens on the numbers of oxytocin receptors?
estrogen is going to increase the number of oxytocin receptors in the myometrium and decidual tissue
what effect does estrogen have on the release of prostaglandins?
estrogen increases the production and release of prostaglandins by fetal membranes
what are the effects of prostaglandins in pregnancy?
they stimulate strong myometrial contractions; will initiate labor
what is the synthesis of prostaglandins stimulated by?
estrogen in fetal membranes, oxytocin in uterine cells, and uterine stretch
what is the effect of oxytocin on the uterine myometrium?
it stimulates smooth muscle contraction
what is the effect of oxytocin on decidual tissue?
it stimulates PGF2alpha (prostaglandin) production
what is the primary stimulus for release of oxytocin?
distention of the cervix
what is the ferguson reflex?
a positive feedback loop to enhance labor
what is relaxin produced by?
corpus luteum, placenta, and the decidua
what is the purpose of relaxin?
it is thought to keep the uterus in a quiet state during pregnancy; may soften and help dilate the cervix
when is the maximal plasma concentration of relaxin?
weeks 38-42
what are the mechanical changes that occur that lead up to the intense contractions?
uterine size and cervical remodeling
what effect does uterine stretch have on prostaglandins?
it is going to increase prostaglandin production
what does the placenta produce that could contribute to the moment that actually initiates labor?
corticotrophin-releasing hormone (CRH)
what effect does the maternal high level of CRH have during late pregnancy?
it promotes myometrial contractions by sensitizing the uterus to prostaglnadins and oxytocin
what affect does high CRH have in fetal circulation?
it stimulates ACTH secretion in the fetus, which causes an increase in fetal adrenal cortisol production, which stimulates further placental CRH release and the ACTH in the fetus causes an increase in the fetoplacental estrogen levels, which enhances the myometrial contractions
what effect does braxton hicks contractions have on the cervix?
it begins to stretch the cervix and shorten the muscle cells; retracts the lower uterine segment and the cervix upward; cervix becomes dilated
where is a fully dilated cervix drawn up to?
just below the pelvic inlet
what effect does oxytocin have on the placental delivery?
it constricts the uterine blood vessels
what affect does nipple stimulation have on oxytocin release during placental delivery?
nipple stimulation induces oxytocin release
what does the human mammary gland contain?
15-20 lobes of glandular tissue
what does each lobe of glandular tissue consist of?
lobules that contain glandular units
what collects the milk from the lobules and brings it to the nipples?
the lactiferous ducts
each lobule consists of what?
alveoli
what is alveolar epithelium?
luminal epithelial tissue; it is the cells that are responsible for milk synthesis and secretion
what sits between the epithelial cells and the basement membrane of the alveoli and what are their purpose?
myoepithelial cells; they have a contractile function- they move milk from the alveoli into the ducts
where do the milk producing cells reside?
in the alveoli
what are the myoepithelial cells sensitive to?
oxytocin; they contract in response to oxytocin
at birth, what does the mammary gland look like?
it is mostly lactiferous ducts with a few alveoli- remains this way until puberty
under what control do the lactiferous ducts sprout and branch?
estrogen at puberty
as the menstrual cycle is established, the mammary tissue is exposed to estrogen and progesterone. What does this induce?
it induces additional ductal-lobular-alveolar growth
as the epithelial structures in the mammary gland proliferate, what happens to the adipose tissue?
it decreases
by the 3rd trimester, what happens to the parenchymal cell growth?
it slows and the alveoli become distended with early colostrum
what is a main characteristic of lactating mammary gland?
there is a large number of alveoli- minimal connective tissue separating
what hormones impact lactogenesis the most?
prolactin and oxytocin
which hormone is responsible for maintaining milk synthesis?
prolactin
which hormone is responsible for milk ejection?
oxytocin
what is the secretion of prolactin like?
intermittent/ oscillating- brought about by nursing
what are the 5 main pathways that are utilized during milk production?
secretory pathway, transcellular endocytosis and exocytosis, lipid pathway, transcellular salt and water transport, paracellular pathway
how are milk proteins moved through the cells?
secretory pathway
what pathway do immunoglobulins use?
the transcellular endocytosis and exocytosis
what activates afferent neural pathway from the breast to the spinal cord and then to the hypothalamus?
suckling stimuli
what do neurons from the spinal cord inhibit once stimulated by suckling?
they inhibit dopamine release from the arcuate nucleus- this releases the inhibition of lactotrophs and results in release of prolactin
neurons from the spinal cord that were stimulated by suckling also stimulate the production and release of what from the paraventricular and supraoptic nuclei?
oxytocin
what is the effect of the stimulation of production and release of oxytocin from the posterior pituitary?
it interacts with myoepithelial cells resulting in “let-down” of milk
neurons from the spinal cord that were stimulated by the suckling inhibit the hypothalamus’ production of what?
GnRH
what is the effect of the inhibition of GnRH production?
it results in decreased release of LH and FSH and it inhibits the ovarian cycle
what happens when the suckling stimulus is discontinued?
milk accumulates, so there is distention and mechanical atrophy of the epithelial structures; leads to rupture of the alveolar walls and compression of capillaries leading to alveolar hypoxia
what is there a high degree of with cessation of lactation?
high degree of epithelial cell death through apoptosis
what is the first stage of involution?
apoptotic cells will be seen in the lumen of the alveoli
what is the second stage of involution?
apoptosis will be accompanied by remodeling of the surrounding stroma and adipocytes
breast development at puberty depends primarily on what?
estrogen and progesterone
during pregnancy, what leads to full development of breast?
gradual increases in PRL, and hPL and very high levels of estrogens and progesterones
what are the 4 main categories of hormones that affect the breasts?
mammogenic, lactogenic, galactokinetic, and galactopoietic
what are mammogenic hormones and an example?
they promote cell proliferation e.g. estrogen
what are lactogenic hormones and an example?
promote initiation of milk production by alveolar cells e.g. prolactin
what are galactokinetic hormones and an example?
they promote contraction of myoepithelial cells and thus milk ejection e.g. oxytocin
what are galactopoietic hormones and an example?
they maintain milk production after it has been established e.g. prolactin
