Chapter 23: Pregnancy, Growth & Development Pregnancy is the presence of a developing offspring in the uterus Growth is an increase in size and entails increases in cell numbers and cell sizes Development is the continuous process by which an individual changes from one life phase to another and involves two phases Prenatal period – fertilization to birth Postnatal period – birth to death

Pregnancy Fertilization (aka conception) Union of egg and sperm cells Occurs in the Fallopian tube Journey from cervix to uterine tube takes less than an hour Oocyte survives only 12-24 hrs after ovulation Sperm may live 24-72 hrs within female Page 895: morning sickness Page 896-897: ARTs

Period Of Cleavage & Implantation The first division of the zygote (fertilized egg) will occur about 30 hours after fertilization. Division continues as the zygote moves down toward the uterus. Implantation in the uterus occurs about 6-7 days after fertilization Period Of Cleavage & Implantation

Fertilization sperm cell reaches corona radiata of egg acrosome releases enzymes sperm cell penetrates zona pellucida sperm cell’s membrane fuses with egg cell’s membrane

Implantation Blastocyst secretes enzyme that digests the endometrium allowing it to bury into the uterine wall Layer of cells called trophoblast helps form the placenta and secretes hCG which helps maintain the corpus luteum and thus the pregnancy

Page 900: Twins Page 901: Ectopic Pregnancy Page 900-901: Preimplantation Genetic Diagnosis Page 903: Hormonal Testing Pregnancy tests test for the presence of hCG

Hormonal Changes During Pregnancy Main hormonal secretions: secretion of hCG maintains corpus luteum corpus luteum secretes estrogens and progesterone placenta secretes large amounts of estrogens and progesterone which stimulate and maintain uterine lining, inhibit FSH and LH, inhibit uterine contractions, and enlarge reproductive organs Additional hormonal secretions: relaxin from corpus luteum inhibits uterine contractions and relaxes pelvic ligaments placental lactogen stimulates breast development aldosterone promotes sodium retention PTH maintains calcium concentrations in blood

Embryonic Stage Beginning of the 2nd week through the 8th week Heart begins to beat during 5th week Beginning of the 2nd week through the 8th week

Placenta Embryonic Testing may include Chorionic Villus Sampling Reddish brown disc Approximately 20 cm long and 2.5 cm thick Connection between embryo and uterine wall Chorion is embyonic portion of placenta Embryonic Testing may include Chorionic Villus Sampling

Amnion About the 2nd week a membrane called the amnion develops around the embryo Fluid called the amnionic fluid fills the area between the embryo and amnion

Ammniocentesis 15-20 wks Approximately 2 Tbsp (30 mL) fluid removed Used to determine genetic abnormalities

Umbilical Cord The umbilical cord forms from the amnion and chorion Is about 55 cm long and 1 cm in diameter Inserts into center of placenta and connects to abdomin of embryo Contains 2 arteries and 1 vein Transports blood between embryo and placenta

Summary Of Embryonic Period Most critical period of development All major organs are formed About 30 mm long and weighs about 5 g Time during which teratogens (drugs, viruses, radiation, etc..) are most likely to cause birth defects

Teratogens & Embryonic Developement

Thalidomide 1957-1966

Fetal Stage 9th week until birth Rapid growth; head becomes more proportional to rest of body Bones begin to ossify Mother feels 1st fetal movements around 5th month (once called quickening) Fine downy hair called lanugo covers body Vernix caseosa covers body – mix of sebum and epidermal cells – protects skin from amniotic fluid Nervous & Circulatory systems 1st to develop during embryonic period and Digestive & Respiratory systems are last to develop during fetal period. Premature babies often have respiratory difficulties because their lungs are not yet producing surfactant

Trimesters Pregnancy is divided into 3 distinct time periods called trimesters Each trimester is 3 months in length. 1st trimester – embryonic period and beginning of fetal stage – Rapid development of organ systems 2nd trimester – middle of fetal period – adding details to organ systems 3rd trimester – end of pregnancy – adding fat

Fetal Blood And Circulation oxygen and nutrients diffuse into the fetal blood from the maternal blood waste diffuses into the maternal blood from the fetal blood Fetal blood and maternal blood DO NOT mix

Fetal Cardiovascular Adaptations fetal blood has greater oxygen-carrying capacity umbilical vein carries oxygenated blood from placenta to fetus ductus venosus conducts half the blood from umbilical vein to inferior vena cava; liver is bypassed foramen ovale conveys blood from right atrium to left atrium; lungs are bypassed ductus arteriosis conducts some blood from pulmonary trunk to aorta; lungs are bypassed umbilical arteries carry blood from internal iliac arteries to placenta

Position Of Full-term Fetus Fetal position before labor is head down toward cervix facing the spine Breech babies are positioned with buttocks downward toward cervix Position Of Full-term Fetus

Birth Process Also called Parturition Involves two stages: Labor – Events that occur in preparation for delivery of the fetus Cervical changes & uterine contractions Delivery – the actual expulsion of the fetus & placenta from the body

Birth Process Factors contributing to the labor process: as birth approaches, progesterone levels decrease prostaglandins synthesized which may initiate labor stretching uterine tissue stimulates release of oxytocin from posterior pituitary gland (pitocin is a synthetic form of oxytocin and is used to induce labor) oxytocin stimulates uterine contractions fetal head stretches uterus positive feedback results in stronger and stronger contractions and greater release of oxytocin

Stages In Birth - Labor Baby is in head down position and is occupying the lower part of the womb – “baby has dropped” “false labor” may occur

Stages In Birth - Labor Thinning & dilation of the cervix May begin a week or two before actual birth Thinning of cervix referred to as effacement Cervix will dilate to 10 cm. Muscle contractions of uterus occur Amnion ruptures (“water breaks”)

Stages In Birth - Delivery Contractions intensify and fetus is expelled Episiotomy may be performed to aid in delivery of fetus Expulsion of the placenta - afterbirth

Cesarean Birth Conjoined twins as shown on page 921 would need to be born through cesarean birth.

Postnatal Developement Neonatal period – birth to 4th week Infancy – 4th week to one year Childhood – one year to puberty Adolescence – puberty to adulthood Adulthood – adolescence to old age Senescence – old age to death