Ch. 29 - Development Flashcards
development
series of progressive changes that leads to formation and organization of cell types
embryology
study of development prior to birth
embryo
first 8 weeks of development
fetus
week 9- birth
Periods of pregnancy
counted from first day of last menstrual period (approximately 2 weeks before fertilization) Consists of first trimester (first 3 months of pregnancy where zygote becomes embryo and then fetus), second trimester (months 4-6 with growth of fetus and expansion of maternal tissues), and third trimester (months 7-9 where fetus grows most rapidly and mothers body is preparing for labor and delivery)
what trimester does fetus grow most quickly
second
fertilization
2 gametes fuse to form new diploid cell. combines male and female genetic material and restores diploid number of chromosomes. initiates cleavage and typically occurs in widest part of uterine tube, ampulla. Oocyte viable for 24 hours following ovulation.
capacitation
physiological conditioning undergone by sperm. glycoprotein and some proteins are removed from sperm plasma membrane so sperm is capable of fertilizing secondary oocyte.
Sperm
millions deposited into vagina during intercourse and a few hundred have a chance of fertilization. It is attracted to oocyte by chemicals it releases. Only the first sperm is able to fertilize oocyte.
Fusion of sperm and oocyte
contact of sperm and oocyte plasma membranes immediately fuse. Only the sperm nucleus enters oocyte and secondary oocyte completes second meiotic division to form an ovum.
pronuclei
nucleus of sperm and ovum. each with haploid chromosomes fuse to become diploid nucleus called zygote.
cleavage
series of mitotic divisions of zygote to form blastocyst.
blastocyte
formed from mitotic division of zygote. enters lumen of uterus and by day 9,blastocyst is completely burrowed into uterine wall.
Human chorionic gonadotropin (hCG)
signals reproductive system that implantation occurred. Promotes maintenance of corpus luteum. Corpus luteum produces estrogen and progesterone to build uterine lining. It is detected by urine at the end of the second week and is the basis for most pregnancy tests. Levels eventually decline after 3 months, causing corpus luteum degeneration because by then the placenta is producing his own estrogen to maintain pregnancy.
Placenta
highly vascular structure that begins forming during second week of development. It is the site of exchange between maternal and fetal blood. It exchanges nutrients, waste, and resp. gases as well as antibodies. It produces estrogen and progesterone to maintain and build uterine lining and is ejected after birth.
Organ development
termed organogenesis; peak time of development of different organ systems. Occurs in the first trimester It is particularly sensitive to teratogens (substances that cause birth defects or death) during this time.
chromosomal abnormalities
occur regularly during gametogenesis, fertilization, or cleavage. If it is severe it will result in spontaneous abortion; (miscarriage) many within 2-3 weeks after fertilization before pregnancy is known. Up to 50% of pregnancies could be terminated from spontaneous abortion. (half from chromosomal abnormalities)
Second trimester
fetal stage; further development of all organ systems with rapid growth of fetus. Its body proportions change and progesterone levels increase
third trimester
organ systems fully functional, fetal growth rate slows, largest weight gain.
Estrogen and Progesterone: mothers body
produced by corpus luteum during first trimester and then by placenta. High levels suppress FSH and LH so that the ovarian and follicular development is arrested. It facilitates uterine, fetal, and mammary enlargement. Causes faster growing nails, fuller hair, relaxation of ligamentous joints, and functional layer growth.
Relaxin
secreted by corpus luteum and placenta. Promotes blood vessel growth in uterus.
Prolactin
increased levels produced by ant. pit. to ensure lactation occurs after giving birth
Oxytocin
produced by hypothalamus, involved in milk expulsion and uterine contractions. Increases in second and third trimesters in response to rising estrogen levels.
Uterine enlargement
begins to enlargement once implantation occurs. By 12 weeks, uterus is just superior to pubic symphysis and causes more frequent urination; especially during first and third trimester. By 16 weeks the fundus is between pubic symphysis and umbilicus and reaches umbilicus by week 22. By 9th month fundus is at xiphoid process of sternum and compresses organs.
Labor
physical expulsion of fetus and placenta. Typically at 38 weeks
Leading to Labor
increased levels of estrogen. This increases uterine myometrium sensitivity to stimulate production of oxytocin receptors on uterine myometrium. Contractions are weak and irregular at first and can happen as early as second trimmest. They become more intense and frequent with increasing estrogen and oxytocin.
Premature labor
labor prior to 38 weeks. Undesirable since infant’s body system is not fully developed, especially lungs. The more premature, the higher morbidity and mortality.
False labor
uterine contractions not resulting in 3 stages of labor; known as Braxton-Hicks contractions. Irregularly spaced and weak; do not become more frequent or intense. Pain is limited to lower abdomen and pelvis, sometimes stopping with movement. Does not lead to cervical changes.
Characteristics of true labor
uterine contractions that increase in intensity and regularity and results in changes to cervix. Mother’s hypothalamus secreting increasing levels of oxytocin and fetus also secretes oxytocin during true labor.
Prostaglandins
fatty acids and hormonelike substances whose secretion is stimulated by oxytocin. They stimulate uterine muscle contraction and soften and dilate cervix.
Initiation of true labor
positive feedback mechanism; contractions push fetus’s head against cervix stimulating stretching and dilation of cervix. This signals hypothalamus to secrete more oxytocin which stimulates placenta to secrete more prostaglandins which results in more intense uterine contractions. This continues until fetus is expelled.
stages of true labor
dilation stage, expulsion stage, placental stage and afterbirth.
Dilation stage
first stage of labor that begins with onset of regular uterine contractions. Ends when the cervix is effaced (thinned) and dilated to 10 cm. Baby’s head against cervix causes effacing and dilation, longest of 3 stages with the greatest variability.
nulliparous women
women who have not given birth before; have a longer dilation and expulsion stage.
expulsion stage
begins with complete dilation of cervix that ends with expulsion of fetus. usually 30 minutes to several hours. Uterine contractions help push fetus through vagina. Uses Valsalva maneuver “bearing down” to increase abdominal pressure.
placental stage
occurs after baby is expelled; uterus continues to contract to help compress uterine blood vessels and displace placenta from uterine wall.
Afterbirth
placenta and remaining fetal membranes; expulsion completed within 30 minutes. It is carefully examined to ensure all of it is expelled so mother does not bleed out.
Lactation
production and release of breast milk from mammary glands
prolactin
produced by ant. pit. and responsible for milk production. Surges continuing as long as baby breastfeeds.
Colostrum
produced by mammary glands during late pregnancy and first few days after birth. Rich in immunoglobulins, especially IgA. Has laxative effect, facilitating infant’s first bowel movement.
Breast milk
starts to be produced a few days postpartum and has higher fat content than colostrum. Has essential fatty acids, enzymes for digestion, and immunoglobulin and is more easily digested than breast milk substitutes. Optimal source of nutrition
milk letdown
release of breast milk; positive feedback. with suckling, mechanoreceptors in breast stimulated which sends impulses to hypothalamus to produce oxytocin. Myoepithelial cells in mammary glands contract, releasing breast milk from acini. This stimulation occurs until infant stops nursing.
