CONCEPTION AND FETAL DEVELOPMENT MNCN Chapter 4

CELLULAR DIVISION Mitosis Meiosis Oogenesis Spermatogenesis

FERTILIZATION Sperm and ovum unite to form a zygote Takes place in ampulla of fallopian tube High levels of estrogen during ovulation help ovum move and thin cervical mucous for sperm

OVA AND SPERM Ovum fertile for hours Sperm can survive up to 72 hours (most healthy at 24 hours) Sperm must undergo capacitation and acrosomal reaction

Twins Occur in 1 in 80 pregnancies Fraternal (dizygotic) Identical (monozygotic)

AFTER FERTILIZATION Development divided into two phases Cellular multiplication Cellular differentiation

Development of endometrium and embryo Under influence of progesterone, endometrium thickens and increases vascularity for implantation Maternal part of placenta develops from decidua basalis

About 10 to 14th day after conception, blastocyst differentiate into primary germ layers All tissues, organs develop from three germ cell layers

CELLULAR DIFFERENTIATION Embryonic membranes Chorion Amnion Amniotic fluid

PLACENTA Functions: fetal respiration, nutrition, and excretion and produces glycogen, cholesterol and fatty acids, ad hormones hCG, hPL estrogen and progesterone Duncan vs. Schultz Umbilical cord 2 umbilical arteries 1 umbilical vein Fetal circulation

Pregnancy calculation 10 lunar months: 40 weeks or 280 days Calculated from onset of last normal menstrual period to time of birth

EMBRYO AND FETAL DEVELOPMENT 3 stages of development Preembryonic: 1 st 14 days Embryonic: day 15 through 8 th week: tissues differentiate into essential organs. Main external features develop and most susceptible to teratogens Fetal stage: end of 8 th week until birth (9-40 weeks

Fetal Development At 8 weeks, resembles human being Circulatory system through umbilical cord well established Every organ system and external structure is present

12 weeks Will have spontaneous movements Begins to produce urine Fetal heart can be heard by electronic devices

20 weeks Muscles well developed; active and mother feels movement (quickening) Body covered with vernix caseosa; Alveoli in lungs are just beginning to form

28 weeks Viable but respiratory and circulatory systems physiologically immature If born, will require immediate and prolonged intensive care to survive

38 to 40 weeks Considered full term Assumes position of comfort, usually head down Well-flexed extremities and head

Malformations and factors that may affect development Quality of sperm or ovum Quality of genetic code established at fertilization Adequacy of intrauterine environment

Teratogens: agents that can cause development of abnormal structures Has greatest effect on cells undergoing most rapid growth, which is first months of pregnancy

Prenatal Deficiency in vitamins and folic acid can increase incidence of neural tube defects Fifth lunar month: period of maximum brain growth: Inadequate maternal nutrition can lead to learning disabilities Maternal hyperthermia during first trimester can cause CNS defects