PREGNANCY & HUMAN DEVELOPMENT

Fertilization oocyte viable 12 - 24 after ovulation sperm retain fertilizing power within female reproductive tract 12 - 48 hours some “super sperm” viable for 72 hours about 5 days a month that pregnancy can occur

Sperm Transport acidity within the vagina is hostile to sperm & some leak from vagina or die almost immediately many cannot penetrate cervical mucus in uterus thousands are killed by leukocytes only a few thousand finally reach uterine tubes

Capacitation membranes must become fragile so that hydrolytic enzymes in their acrosomes can be released

Acrosomal Reaction acrosomal reaction: release of acrosomal enzymes that occurs in immediate vicinity of oocyte hundreds of acrosomes must rupture to break down intercellular cement of oocyte single sperm makes contact with oocyte

Sperm Penetration nucleus is pulled into oocyte cytoplasm only one sperm is allowed to penetrate Fusion of nuclear material occurs to complete fertilization

Preembryonic Development fertilized egg is now called a zygote

1. Cleavage & Blastocyst Formation cleavage: period of rapid mitotic divisions following fertilization daughter cells become smaller & smaller results in a high surface-to-volume ratio for greater uptake of oxygen & nutrients

blastomeres: 2 identical cells by 36 hours 4 identical cells by 60 hours 8 identical cells by 72 hours morula: berry-shaped 100 cell 4-5 days

Implantation 6 days after ovulation implantation begins completed by 14 day

Placentation formation of placenta highly vascular fully functional as nutritive, respiratory, excretory, & endocrine organ by end of 2nd month of pregnancy some harmful substances can pass placental barriers

teratogens: may cause severe congenital abnormalities or even fetal death alcohol, nicotine, drugs, infections

Events of Embryonic Development

Formation & Roles of Embryonic Membranes amnion: sac that becomes filled with amniotic fluid which bathes cells provides buoyant environment & protection against physical trauma helps maintain temperature as kidneys develop urine is added to fluid water portion is exchanged 3 hours

yolk sac: blood cell formation & produce gonads chorion: forms placenta allantois: constructs umbilical cord becomes part of bladder

Gastrulation: Germ Layer Formation Ectoderm Mesoderm Endoderm

Ectoderm all nervous tissue skin, hairs, sebaceous & sweat glands, & nails tooth enamel epithelium of: oral & nasal cavities, anal canal, pineal & pituitary glands

Mesoderm skeletal, smooth, & cardiac muscle cartilage, bone & other CT blood, bone marrow, lymph tissue ureters, kidneys, gonads

Endoderm epithelium of digestive tract liver, pancreas thyroid, parathyroid, & thymus glands

Effects of Pregnancy on Mother

Anatomical Changes breasts enlarge & areolae darken “mask of pregnancy” pigmentation of facial skin uterus enlarges lordosis placenta produces the hormone relaxin, that causes ligaments to relax & become flexible for child birth weight gain about 25 lbs

Gastrointestinal System excessive salivation morning sickness: increase of hormones heartburn: esophagus & stomach is crowded constipation: motility of digestive tract declines

Urinary System urination more frequent & sometimes uncontrollable uterus compresses bladder kidneys also have to dispose of fetal wastes

Respiratory System lung volume decreases nasal stuffiness

Cardiovascular System total body water rises as safeguard against blood lose during birth blood volume increases 25 - 40 % blood pressure & pulse rise uterus presses on pelvic blood vessels, venous return from lower limbs may be impaired & result in varicose veins

Birth 280 days after conception Parturition Birth 280 days after conception

Initiation of Labor last few weeks of pregnancy estrogen reaches highest levels myometrium becomes increasingly irritable & weak which may cause Braxton Hicks contractions or false labor oxytocin is released by posterior pituitary which causes expulsive contraction of true labor

Stages of Labor

Dilation time from labor’s onset until cervix is fully dilated (10 cm) contractions begin in upper part of uterus & move downward toward vagina contractions 15 - 30 minutes apart & last for 10 - 30 sec. contractions become more vigorous & rapid

infant’s head is forced against cervix causing it to soften & become thinner amniotic fluid breaks lasts 6-12 hours

Expulsion from full dilation to delivery contraction every 2 - 3 minutes & lasting 1 minute lasts 20 minutes to 2 hours crowning episiotomy may be performed to reduce tearing umbilical cord is clamped & cut

Placental delivery of placenta within 15 minutes of birth important that all placental fragments be removed called afterbirth