Bio 202 Pregnancy Development Fall 2023 PDF

ARIZONA STATE UNIVERSITY Development & College of Letters & Sciences Pregnancy Bio 202 A natomy & Physiology II Tonya A. Penkrot, Ph.D.  Sperm Migration  Egg must be fert...

ARIZONA STATE UNIVERSITY Development & College of Letters & Sciences Pregnancy Bio 202 A natomy & Physiology II Tonya A. Penkrot, Ph.D.  Sperm Migration  Egg must be fertilized within 12 to 24 hours of ovulation, if it is to survive  Vast majority of sperm do not make it to egg destroyed by vaginal acid or drain out of vagina fail to penetrate the mucus of the cervical canal destroyed by leukocytes in the uterus half go up wrong uterine tube of the 300 million that were ejaculated, 2,000 to 3,000 spermatozoa reach the vicinity of the egg Bio 202 A&P ASU DPC T. Penkrot Development - 2  Capacitation  Spermatozoa reach uterine tube within 5 to 10 minutes of ejaculation, but cannot fertilize the egg for 10 hours capacitation – process that migrating sperm must undergo to make it possible to penetrate an egg ― plasma membrane of fresh sperm is toughened by cholesterol ― female fluids leach cholesterol from the sperm plasma membrane ― sperm membrane becomes fragile and permeable to Ca2+  Sperm remain viable for up to 6 days after ejaculation conception optimal if sperm are deposited a few days before ovulation to 14 hours after Bio 202 A&P ASU DPC T. Penkrot Development - 3  Fertilization Sperm First polar body Egg Corona radiata Zona pellucida 4 Rejected sperm 3 Fertilization membrane 2 Cortical reaction 1 Acrosomal reaction Sperm nucleus fertilizing egg Nucleus Fusion of egg Acrosome and sperm plasma m embranes Zona pellucida Cortical granules Extracellular space Egg m embrane Granulosa cells Bio 202 A&P ASU DPC T. Penkrot Development - 4  Migration of Conceptus Cleavage Blastomeres Second polar 2-celled stage 4-celled stage 8-celled stage body (30 hours) Morula Zygote (72 hours) Egg pronucleus Sperm pronucleus Zona pellucida Blastocyst Fertilization (0 hours) Ovary Maturing follicle Sperm cell Corpus luteum Implanted First polar body Ovulation blastocyst (6 days) Secondary oocyte Bio 202 A&P ASU DPC T. Penkrot Development - 5  Cleavage  Cleavage - mitotic divisions that occur in the first 3 days while the conceptus migrates down the uterine tube first cleavage occurs within 30 hrs after fertilization ― zygote splits into 2 daughter cells (blastomeres) by the time the conceptus arrives in the uterus ― within 72 hrs of ovulation ― morula stage - solid ball of 16 cells that resemble a mulberry ― still no larger than the zygote ― cleavage produces smaller and smaller blastomeres morula lies free in uterine cavity for 4-5 days ― divides into a 100 cells or so ― blastocyst Development - 6 Bio 202 A&P ASU DPC T. Penkrot  Implantation of Blastocyst Lumen of uterus Blastocyst: Blastocoel Embryonic hypoblast Trophoblast Cytotrophoblast Embryoblast Syncytiotrophoblast Endometrium: Epithelium Endometrial gland (a) 6–7 days (b) 8 days Bio 202 A&P ASU DPC T. Penkrot Development - 7  Implantation of Blastocyst  Syncytiotrophoblast grows into the uterus like little roots digesting endometrial cells along the way endometrium reacts to this injury by growing over the blastocyst and covering it ― conceptus becomes completely buried in endometrial tissue  Implantation takes about a week completed about the time the next menstrual period would have started had the woman not become pregnant Bio 202 A&P ASU DPC T. Penkrot Development - 8  Implantation of Blastocyst  Trophoblast also secretes human chorionic gonadotropin (HCG) HCG stimulates the corpus luteum to secrete estrogen and progesterone ― progesterone suppresses menstruation HCG levels rise in mother’s blood until the end of the second month ― takes over the role of the corpus luteum making HCG unnecessary ovaries become inactive for the remainder of pregnancy ― estrogen and progesterone levels rise from chorion Bio 202 A&P ASU DPC T. Penkrot Development - 9  Implanted Conceptus at 2 Weeks Cytotrophoblast Syncytiotrophoblast Germ layers: Ectoderm Mesoderm Endoderm Am nion Am niotic cavity Em bryonic stalk Allantois Yolk sac Lacuna Extraem bryonic m esoderm Chorionic villi (c) 16 days Bio 202 A&P ASU DPC T. Penkrot Development - 10  Placenta and Embryonic Membranes Maternal blood in placental sinus Uterus Developing Chorionic placenta villus Umbilical blood vessels Yolk sac Amnion Chorion Amniotic cavity (a) Bio 202 A&P ASU DPC T. Penkrot Development - 11  Placenta and Embryonic Membranes Maternal Maternal vein artery Myometrium of uterus Chorionic Placental villus sinus Maternal blood Umbilical cord Umbilical arteries Umbilical vein Placenta Yolk sac Allantois Umbilical cord Amniotic fluid in amniotic cavity Amnion Chorion Lumen of uterus Bio 202 A&P ASU DPC T. Penkrot Development - 12  Fetus  By the end of 8 weeks all organ systems are present individual is about 3 cm long now considered a fetus bones have begun to calcify skeletal muscles exhibit spontaneous contractions ― too weak to be felt by the mother heart, beating since the 4th week, now circulates blood heart and liver are very large forming the prominent ventral bulge head is nearly half the total body length Bio 202 A&P ASU DPC T. Penkrot Development - 13  Embryonic Membranes  Several accessory organs develop along side the embryo – placenta, umbilical cord, and four embryonic membranes – amnion, yolk sac, allantois, and chorion  Amnion - transparent sac that develops from epiblast grows to completely enclose the embryo and penetrated only by the umbilical cord fills with amniotic fluid Bio 202 A&P ASU DPC T. Penkrot Development - 14  Prenatal Nutrition  During gestation the conceptus is nourished in three different, overlapping ways: uterine milk – glycogen-rich secretion of the uterine tubes and endometrial glands trophoblastic nutrition - conceptus consumes decidual cells of the endometrium ― progesterone from corpus luteum stimulates decidual cells to proliferate ― they accumulate a store of glycogen, proteins, and lipids ― as conceptus burrows into the endometrium, the syncytiotrophoblast digests them and supplies the nutrients to the embryoblast ― only mode of nutrition for the first week after implantation ― remains dominant source through the end of 8 weeks ― wanes as placental nutrition increases Bio 202 A&P ASU DPC T. Penkrot Development - 15  Prenatal Development  Conceptus – all products of conception – the embryo or fetus, the placenta, and associated membranes blastocyst – the developing individual is a hollow ball the first 2 weeks embryo - from day 16 through 8 weeks fetus – beginning of week 9 to birth neonate - newborn to 6 weeks Bio 202 A&P ASU DPC T. Penkrot Development - 16  Hormones of Pregnancy  Human chorionic gonadotropin (HCG) secreted by blastocyst and placenta detectable in urine 8 to 9 days after conception by home pregnancy test kits stimulates growth of corpus luteum ― secretes increasing amounts of progesterone and estrogen  Estrogens increases to 30 times normal by the end of gestation corpus luteum is source for first 12 weeks until placenta takes over gradually from weeks 7 to 17 causes tissue growth in the fetus and the mother Bio 202 A&P ASU DPC T. Penkrot Development - 17  Hormones of Pregnancy  Progesterone secreted by placenta and corpus luteum suppresses secretion of FSH and LH preventing follicular development during pregnancy suppresses uterine contractions prevents menstruation, thickens endometrium stimulates development of acini in breast in another step toward lactation  Human chorionic somatomammotropin (HCS) placenta begins its secretion about 5th week ― increases steadily until term in proportion to placental size ― effects seem similar to growth hormone, but weaker ― seems to reduce the mother’s insulin sensitivity and glucose usage leaving more for the fetus Bio 202 A&P ASU DPC T. Penkrot Development - 18  Other Hormones of Pregnancy  Woman’s pituitary gland grows about 50% larger during pregnancy produces markedly elevated levels of thyrotropin, prolactin, and ACTH  Thyroid gland becomes 50% larger under influence of HCG, pituitary thyrotropin, and human chorionic thyrotropin from placenta increases metabolic rate of mother and fetus  Parathyroid glands enlarge and increase osteoclast activity  ACTH stimulates glucocorticoid secretion serve primarily to mobilize amino acids for fetal protein synthesis  Aldosterone secretion rises promoting fluid retention increasing mother’s blood volume  Relaxin, secreted by corpus luteum and placenta Bio 202 A&P ASU DPC T. Penkrot Development - 19  Hormone Levels and Pregnancy Human chorionic gonadotropin Relative hormone levels Estradiol Progesterone Parturition Ovulation 0 4 8 12 16 20 24 28 32 36 40 Weeks after beginning of last menstrual period Bio 202 A&P ASU DPC T. Penkrot Development - 20  Adjustments to Pregnancy Lung Xiphoid process Pericardium Breast Liver Stomach Gallbladder Greater omentum Small intestine Ascending colon Descending colon Uterus Umbilical cord Ilium Ovary Ovary Uterine tube Inguinal ligament Round ligament of uterus Urinary bladder Pubic symphysis Bio 202 A&P ASU DPC T. Penkrot Development - 21  Childbirth - Parturition  In the seventh month of gestation, the fetus normally turns into the head-down vertex position most babies born head first head acting as a wedge that widens the mother’s cervix, vagina, and vulva during birth  Fetus is a passive player in its own birth expulsion achieved by contractions of mother’s uterine and abdominal muscles fetus may play a role chemically by stimulating labor contractions sending chemical messages that signify when it is developed enough to be born Bio 202 A&P ASU DPC T. Penkrot Development - 22  Uterine Contractility  Braxton Hicks contractions – relatively weak contractions of the uterus over the course of gestation strengthen late in pregnancy - false labor contractions transform suddenly into more powerful labor contractions  Parturition - the process of giving birth ― marked by the onset of true labor contractions  Progesterone and estradiol balance may be one factor in this pattern of increasing contractility progesterone inhibits uterine contractions, but declines after 6 months estradiol stimulates uterine contractions, and continues to rise Bio 202 A&P ASU DPC T. Penkrot Development - 23  Uterine Contractility  As pregnancy nears full term - posterior pituitary releases more oxytocin (OT), uterus produces more OT receptors  Conceptus may produce chemical stimuli promoting its own birth fetal cortisol rises and may increase estrogen secretion by the placenta fetal pituitary produces oxytocin, but may stimulate fetal membranes to produce prostaglandin  Uterine stretching thought to play a role in initiating labor stretching of smooth muscle increases contractility of smooth muscle Bio 202 A&P ASU DPC T. Penkrot Development - 24  Labor Contractions  Labor contractions begin about 30 minutes apart and eventually occur every 1 to 3 minutes periodically relax to increase blood flow and oxygen delivery to placenta and fetus contractions strongest in fundus and body of uterus ― weakest in the cervix ― pushes fetus downward Bio 202 A&P ASU DPC T. Penkrot Development - 25  Labor Contractions  Cervical stretching induces a neuroendocrine reflex through the spinal cord, hypothalamus, and the posterior pituitary posterior pituitary releases oxytocin  Cervical stretching → oxytocin secretion → uterine contraction →cervical stretching  Woman feels need to “bear down” contraction of these muscles aids in expelling the fetus especially when combined with the Valsalva maneuver for increasing intra-abdominal pressure Bio 202 A&P ASU DPC T. Penkrot Development - 26  Pain of Labor  Pain of labor is due at first mainly to ischemia of the myometrium muscles hurt when they are deprived of blood each contraction temporarily restricts uterine circulation  As fetus enters the vaginal canal, the pain becomes stronger stretching of the cervix, vagina, and perineum sometimes tearing of the vaginal tissue episiotomy may be necessary Bio 202 A&P ASU DPC T. Penkrot Development - 27  Stages of Labor  Labor occurs in three stages: dilation expulsion placental stage  Duration of each stage tends to be longer in primipara ― woman giving birth for the first time  Than in multipara ― woman who has previously given birth Bio 202 A&P ASU DPC T. Penkrot Development - 28  Stages of Labor - Early Dilation (a) Early dilation stage Uterus Placenta Umbilical cord Cervix Vagina  Longest stage – lasting 8 to 24 hours  Dilation of cervical canal and effacement (thinning) of cervix to reach 10 cm - diameter of fetal head  Rupture of fetal membranes and loss of amniotic fluid Bio 202 A&P ASU DPC T. Penkrot Development - 29  Stages of Labor -- Late Dilation (b) Late dilation stage Pubic symphysis dilation reaches 10 cm in 24 hours or less in primipara (first baby) and in as little as few minutes in multipara Bio 202 A&P ASU DPC T. Penkrot Development - 30  Stages of Labor - Expulsion (c) Expulsion stage  Begins when the baby’s head enters vagina lasts until the baby is expelled up to 30 minutes  Crowning – when the baby’s head is visible delivery of the head is the most difficult part nose and mouth suctioned before delivery to clear airway  After expulsion, attendant drains blood from umbilical vein into baby clamps umbilical cord in two places, and cuts cord between clamps Bio 202 A&P ASU DPC T. Penkrot Development - 31  Placental Stage Uterus (d) Placental stage Placenta (detaching) Umbilical cord  Uterine contractions continue causing placental separation  Membranes (afterbirth) inspected to be sure everything has been expelled Bio 202 A&P ASU DPC T. Penkrot Development - 32  The Puerperium  First 6 weeks postpartum (after birth) are called the puerperium period in which the mother’s anatomy and physiology stabilize and the reproductive organs return nearly to the pregravid state (condition prior to pregnancy) ― involution – shrinkage of the uterus  involution is achieved by autolysis (self-digestion) of uterine cells by their own lysosomal enzymes  for about 10 days produces a vaginal discharge – lochia  bloody at first and then turns serous  Breast-feeding promotes involution suppresses estrogen secretion which would make the uterus more flaccid stimulates oxytocin secretion which causes myometrium to contract and firm up the uterus sooner Bio 202 A&P ASU DPC T. Penkrot Development - 33  Lactation  Lactation – the synthesis and ejection of milk from the mammary glands lasts as little as a week in women who do not breast- feed their infants can continue for many years as long as the breast is stimulated by a nursing infant or a mechanical device (breast pump) women traditionally nurse their infants until a median age of about 2.8 years Bio 202 A&P ASU DPC T. Penkrot Development - 34  Colostrum and Milk Synthesis  Colostrum forms in late pregnancy similar to breast milk in protein and lactose, but contains 1/3 less fat first 1 to 3 days after birth thin watery consistency and a cloudy yellow color contains IgA to protection the baby from gastroenteritis  Prolactin (from anterior pituitary) promotes milk synthesis inhibited by dopamine when not pregnant synthesis of hormone begins 5 weeks into pregnancy, by full term it is 10 to 20 times normal level ― little effect on mammary glands until after birth milk synthesis also requires growth hormone, cortisol, insulin, and parathyroid hormone to mobilize necessary amino acids, fatty acids, glucose, and calcium Bio 202 A&P ASU DPC T. Penkrot Development - 35  Colostrum and Milk Synthesis  At birth, prolactin secretion drops to nonpregnancy levels  Every time the infant nurses prolactin levels jump to 10 to 20 times this level for the next hour stimulates the synthesis of milk for the next feeding without nursing, milk production stops in 1 week  Only 5-10% of women become pregnant while breast- feeding inhibition of GnRH and reduced ovarian cycling natural means of spacing births Bio 202 A&P ASU DPC T. Penkrot Development - 36  Milk Ejection  Milk is continually secreted into the mammary acini, but does not easily flow into the ducts  Milk ejection (letdown) is controlled by a neuroendocrine reflex infant’s suckling stimulates sensory receptors in nipple, signaling hypothalamus and posterior pituitary to release oxytocin oxytocin stimulates myoepithelial cells around each acinus contract to squeeze milk into duct ― milk flow within 30-60 seconds after suckling begins Bio 202 A&P ASU DPC T. Penkrot Development - 37  Breast Milk  Breast milk changes composition over the first two weeks varies from one time of day to another at the end of a feeding there is less lactose and protein, but six times the fat  Cow’s milk not a good substitute 1/3 less lactose but 3 times as much protein harder to digest and more nitrogenous waste (diaper rash) Bio 202 A&P ASU DPC T. Penkrot Development - 38