Conception and Biophysical changes

The Process of Fertilization Sperm and ovum unite to form a zygote Ova are fertile for 12 to 24 hours Sperm are fertile for 72 hours Takes place in the ampulla of fallopian tube

Conception Necessary functional components a. uterus b. fallopian tubes c. ovaries (eggs) d. hormones e. sperm

Preparation for Fertilization Estrogen levels increase peristalsis in fallopian tubes Fertilization usually takes place in ampulla Single ejaculation – 200 to 500 million spermatozoa Prostaglandins in semen help transport sperm

Fertilization & implantation

Figure 11-4 A. Sperm penetration of an ovum Figure 11-4 A. Sperm penetration of an ovum. The sequential steps of oocyte penetration by a sperm are depicted moving from top to bottom.

Figure 11-4 B. Sperm penetration of an ovum Figure 11-4 B. Sperm penetration of an ovum. Scanning electron micrograph of human sperm surrounding a human oocyte (750 ). The smaller spherical cells are granulosa cells of the corona radiata. Source: Used with permission from Nilsson, L. (1990). A child is born. New York, NY: Dell Publishing.

Preembryonic Stage First 14 days of human development Cleavage Blastomeres form morula Blastocyst Develops into embryonic disc and amnion Trophoblast Develops into chorion

Implantation Occurs 7 to 10 days after fertilization Blastocyst burrows into endometrium Endometrium is now called decidua

Cellular Differentiation (cont’d) Embryonic membranes begin to form Chorion(outerm membrane contribues to placental development) Amnion (inner most membranous sac) Amniotic fluid Functions –protects against physical force, maintains temperature, allows fetal movement Characteristics-clear, slightly yellow, 700- 1000cc by 3rd trimester, Abnormal variations- Yolk sac-provides early nourshment

Cellular Differentiation (cont’d) Umbilical cord Body stalk fuses with embryonic portion of placenta Provides circulatory pathway from chorionic villi to embryo One vein, two arteries Wharton’s jelly Delivers oxygenated blood to fetus Two arteries

Metabolic and nutrient exchange Maternal portion Placenta Metabolic and nutrient exchange Maternal portion Decidua basalis and circulation Fetal portion Covered by amnion (chorionic villi) Fetal surface covered by amnion

Placental Development Chorionic villi form spaces in decidua basalis Spaces fill with maternal blood Chorionic villi (provide blood supply to the embryo) Syncytium: outer layer Cytotrophoblast: inner layer Anchoring villi form septa

Figure 11-13 Longitudinal section of placental villus Figure 11-13 Longitudinal section of placental villus. Spaces formed in the maternal decidua are filled with maternal blood; chorionic villi proliferate into these maternal blood-filled spaces and differentiate into a syncytium layer and a cytotrophoblast layer.

Placental Circulation After implantation cells differentiate Trophoblast invades endometrium Opens uterine capillaries Completion of maternal-placental- fetal circulation About 17 days after conception

Figure 11-14 Vascular arrangement of the placenta Figure 11-14 Vascular arrangement of the placenta. Arrows indicate the direction of blood flow. Maternal blood flows through the uterine arteries to the intervillous spaces of the placenta and returns through the uterine veins to maternal circulation. Fetal blood flows through the umbilical arteries into the villous capillaries of the placenta and returns through the umbilical vein to the fetal circulation.

Placental Facts Size of 8-inch dinner plate Consists of 15-20 cotyledons, chorionic villi branch out from it Structure is complete at the end of 12th week gestation Grows till 20th week gestation, covers ½ of uterine surface

Placental Functions Transfers nutrients Diffuses oxygen and carbon dioxide functioning as fetal lungs Production of 4hormones hCG Progesterone Estrogens hCS/hPL Facilitates transfer of metabolic wastes from the fetus to the maternal ciruclation Transfers heat from mother to fetus.

Development of the Fetal Circulatory System Maintains blood flow to placenta Provides fetus with oxygen and nutrients Removes carbon dioxide and waste products Blood flows through umbilical vein into abdominal wall of fetus

Figure 11-15 Fetal circulation Figure 11-15 Fetal circulation. Blood leaves the placenta and enters the fetus through the umbilical vein. After circulating through the fetus, the blood returns to the placenta through the umbilical arteries. The ductus venosus, the foramen ovale, and the ductus arteriosus allow the blood to bypass the fetal liver and lungs.

Table 11-4 Embryonic and Fetal Development: What Parents Want to Know

http://www. ehd. org/resources_bpd_illustrated http://www.ehd.org/resources_bpd_illustrated.php The endowment for Human Development

Factors Influencing Development Quality of sperm or ovum Genetic code Adequacy of intrauterine environment Teratogens (any agent that interfere with a developing embryo) Organs formed primarily during embryonic development

Signs and Symptoms of Pregnancy—this is important to know Presumptive signs of pregnancy (subjective) menstrual suppression (amenorrhea, menstruation may occur after conception) nausea, vomiting, and "morning sickness" (due to increased HCG levels) frequency of micturition (uterus stretches base of bladder) tenderness and fullness of the breasts, breast pigmentation, and discharge (due to increased progesterone, estrogen) "quickening" (usually 18-20 wks. may be 16 wks. in multigravida) fatigue  

Probable signs (objective) Dark blue discoloration of the vaginal mucous membrane known as CHADWICK'S SIgn pigmentation of the skin and abdominal striae (may also occur in breasts, buttocks, and thighs) changes in the size, shape, and consistency of the uterus - HEGAR'S SIGN (lower part of the body of uterus much softer than cervix) fetal outline, distinguished by abdominal palpation and detection of a fetal part vaginally by ballottement (sudden tap on presenting part makes it rise in amniotic fluid) changes in the cervix (GOODELL'S SIGN - cervix softens due to increased vascularity edema) BRAXTON HICKS contractions (painless, cause of false labor) positive pregnancy test (increased Hcg levels, blood/serum 8-9 days after ovulation and fertilization and urine test within 2 wks of gestation)

Positive signs (diagnostic) fetal heart sounds (audible with Doppler 8-10 weeks gestation, or ultrasound) fetal movements felt by examiner x-ray- outline of fetal skeleton ultrasonic demonstration of the presence of a conceptus (6-8 wks. yields most information) fetal movements visible