  Eggs are giant cells Egg coat  Mammals = Zona pellucida AND cumulus cells Polar body

     Capacitation of sperm Spermatozoa reach uterine tube within 10 minutes of ejaculation To fertilize ovum, they must undergo capacitation  takes 10 hours Sperm fertile for 48 hours after ejaculation Conception optimal if sperm are deposited 48 hours before ovulation to 14 hours after 28-2

• Binding to ZP3 induces the acrosome reaction.

• Proteolytic enzymes released by the acrosome digest a hole through the zona pellucida

Fig. 29.2

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 The blastula has a trophoblast and ICM

   Attaches to uterine wall 6 to 12 days after ovulation Syncytiotrophoblast - multinucleate mass grows “roots” and digests its way into endometrium  

secretes human chorionic gonadotropin (HCG)

becomes chorion Endometrium completely encloses embryo 29-6

 Mammals have the same gastrulation movements as reptiles and birds even though there is no yolk

  Arrangement of blastomeres into 3 primary germ layers    Ectoderm Mesoderm Endoderm Flattening of embryoblast into embryonic disc  Cells sink into primitive streak (a groove) and spread laterally as mesoderm layer  as mesenchyme cells 29-8

    Formation of organs from primary germ layers   at 8 weeks, all organs are present in 3 cm long fetus heart is beating and muscles exhibit contracts Derivatives of ectoderm 

epidermis, nervous system

, lens and cornea, internal ear Derivatives of mesoderm 

skeleton

,

muscle

, cartilage,

blood

,

blood vessels

, lymphoid tissue, gonads and ducts,

kidneys

and ureters Derivatives of endoderm 

gut and respiratory epithelium, liver, bladder and urethra

29-9

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   HCG (human chorionic gonadotropin)   secreted by trophoblast within 9 days of conception prevents involution of corpus luteum Estrogens  increases to 30 times normal before birth  corpus luteum is source for first 12 weeks until placenta takes over  causes uterine, mammary duct and breast enlargement Progesterone     secreted by placenta and corpus luteum suppresses secretion of FSH and LH preventing follicular development prevents menstruation, thickens endometrium stimulates development of acini in breast 28-11

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  Blastocyst implants outside uterus   1 out of 300 pregnancies most cases occur in uterine tube (tubal pregnancy)  tubal obstruction from previous pelvic inflammations increase risk Tube ruptures by 12 weeks   conceptus may reimplant in abdominopelvic cavity  anywhere it finds an adequate blood supply  usually requires an abortion 9% of abdominal pregnancies result in live birth by cesarean section 29-13

  Trophoblastic nutrition - conceptus nourished by digestion of endometrial cells (first 8 weeks)  progesterone stimulates decidual cells of uterus Placental nutrition - conceptus nourished from mother’s bloodstream through placenta 29-14

The placenta is an organ derived from both maternal and fetal-derived tissues.

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 Age based terminology     Blastocyst is less than 2 weeks old Embryo is from 2 to 8 weeks old  Three embryonic tissue layers have formed Fetus is 9 weeks to birth  Organs have begun to form Neonate - newborn to 6 weeks 28-16

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    Progesterone inhibits contractions Estrogen stimulates contractions Near full term - posterior pituitary releases more oxytocin, uterus produces more receptors   directly stimulates myometrial contractions stimulates fetal membranes to produce prostaglandins synergists of oxytocin Stretching  increases contractility of smooth muscle  role in initiating labor 28-18

 Contractions begin 30 minutes apart and eventually occur every 1-3 minutes  periodically relax to  blood flow to placenta and fetus  contractions strongest in fundus and body of uterus, pushes fetus into cervix  Self-amplifying cycle of stretch and contraction  positive feedback cycles increase contractions   cervical stretching  contraction  repeat oxytocin secretion  reflex arc from uterus  spinal cord  uterine abdominal skeletal muscles 28-19

  Widening of cervical canal by effacement (thinning) of cervix to reach 10 cm -- diameter of fetal head Rupture of fetal membranes and loss of amniotic fluid 28-20

Dilation reaches 10 cm in 24 hours or less in primipara (first baby) and in as little as few minutes in multipara 28-21

  Time baby’s head enters vagina until delivery  up to 30 minutes Valsalva maneuver helps to expel fetus 28-22

 Uterine contractions continue causing placental separation 28-23

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Ductus venosus Ductus arteriosus Foramen ovale 29-27

    Umbilical arteries and veins become ligamentous Ligamentum venosum (liver) Fossa ovalis (heart) Ligamentum arteriosum (vessels) 29-28

   Transitional period  first 6-8 hours heart and respiratory rate  temperature falls   and body periods of sleeping and gagging on mucus and debris feed every 3 to 4 hours during 6 week neonatal period Respiratory adaptations of newborn   onset of breathing due to CO 2 accumulation great effort to inflate lungs for first few breaths Immunological adaptation  maternal antibody, IgG, diffuses across placenta  provides 6 mo of protection from most infectious diseases while fetal production   IgA in breast milk can protect newborn from gastroenteritis 29-29

   Colostrum forms in late pregnancy    similar to breast milk; contains 1/3 less fat, thinner first 1 to 3 days after birth contains IgA protection from gastroenteritis 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 Myoepithelial cells surround secretory cells in acinus   contract to squeeze milk into duct milk flow within 30-60 seconds after suckling begins 28-30

  First 6 weeks after delivery Anatomy and physiology return to normal   involution of uterus  to pre-gravid weight in 4 weeks  accomplished by autolysis by lysosomal enzymes  vaginal discharge called lochia breastfeeding promotes involution  suppresses estrogen secretion  stimulates oxytocin which causes myometrial contraction 28-31

   Midlife change in hormone secretion   due to age related depletion of follicles occurs with menopause (cessation of menstruation); average age of 52 Results  atrophy of uterus, vagina and breasts   skin becomes thinner, bone mass declines, and risks of cardiovascular disease increase hot flashes (sudden dilation of cutaneous arteries) occur several times a day HRT = hormone replacement therapy 28-32

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  Digestive System   nausea  first few months constipation and heartburn due to   intestinal motility  pressure on stomach Metabolism  BMR  may stimulate appetite  healthy weight gain - 24 lb.

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 Nutrition    placenta stores nutrients for 3rd trimester  protein, iron, calcium, phosphates vitamin K  reduces risk of hemorrhages in neonatal brain folic acid  prevent neurological disorders  spina bifida, anencephaly  supplements must be started before pregnancy 28-35

 Circulatory System   mother’s blood volume and cardiac output - rises 30%  due to fluid retention and hemopoiesis  by full term, placenta requires 625 mL of blood/minute hemorrhoids and varicose veins  from pressure on large pelvic blood vessels 28-36

 Respiratory System   minute ventilation  about 50%  demands of fetus, higher maternal metabolic rate  ventilation adjusted to keep P CO 2 respiratory rate  lower than normal  difficult to breathe deeply 28-37

 Urinary System    salt and water retention  due to aldosterone and steroids GFR  by 50% and output is slightly elevated   mother disposes additional metabolic wastes frequency of urination  due to bladder compression 28-38

 Integumentary Systems    stretch marks  due to dermal stretching linea alba may become dark (linea nigra) temporary chloasma or “mask of pregnancy”  blotchy darkening of skin over nose and cheeks 28-39

  Parturition  process of giving birth  by contraction of uterine and abdominal muscles Braxton Hicks contractions  throughout gestation  strengthen late in pregnancy - false labor 28-40

   Ischemia of myometrium Stretching of cervix, vagina and perineum  episiotomy prevents tearing Large fetal head in a narrow pelvic outlet 28-41

   Lactation  synthesis and ejection of milk from mammary glands in breast Ducts grow and branch  due to high estrogen levels in pregnancy Followed by budding and development of acini at the ends of the ducts  due to progesterone 28-42

  Colostrum forms in late pregnancy    similar to breast milk; contains 1/3 less fat, thinner first 1 to 3 days after birth contains IgA protection from gastroenteritis Synthesis is promoted by prolactin (from pituitary)   synthesis of hormone begins 5 weeks into pregnancy, by full term it is 20x normal level steroid hormones from placenta oppose it until birth 28-43

  At birth, prolactin secretion drops, but  20 times after nursing  without nursing, milk production stops in 1 week 5-10% of women become pregnant while nursing  inhibition of GnRH and reduced ovarian cycling 28-44

  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 Myoepithelial cells surround secretory cells in acinus  contract to squeeze milk into duct  milk flow within 30-60 seconds after suckling begins 28-45

    Supplies antibodies and colonizes intestine with beneficial bacteria Colostrum and milk have a laxative effect that clears intestine of meconium (green, bile-filled fecal material in newborn) Nursing woman can produce 1.5L per day 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) 28-46

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     1 out of 8 American women Tumors begin with cells from mammary ducts  may metastasize by lymphatics Symptoms may include palpable lump, skin puckering, skin texture and drainage from nipple Most breast cancer is nonhereditary  some stimulated by estrogen Risk factors include   aging, ionizing radiation, carcinogenic chemicals, alcohol, smoking and fat intake 70% lack risk factors 28-48

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