Lesson 8: Embryonic & Fetal Development, Pregnancy, Parturition, & Lactation

State the names of and describe the events that occur for mother and baby during each stage of pregnancy.

1) FERTILIZATION- sperm's nucleus enters the egg, which triggers completion of meiosis II and the formation of of the HAPLOID OVUM. 2) CONCEPTION - when haploid nuclei of sperm and mature ovum join forming a single diploid cell, THE ZYGOTE. 3) CLEAVAGE - First 4 days, divisions creating a series of identical cells. No growth, traveling down oviduct. 4) Multiple cleavages, lead to a MORULA, a ball of 32 identical cells. 5) On the 4th day, it gets swept into the uterus, undergoes BOTH DIFFERENTIATION (cell specialization and function) and MORPHOGENESIS (dramatic developmental changes in shape and form). For mothers, ectopic pregnancy is a rare, but possible occurrence, if morula stays in oviduct. 6) Week 1-2 - PRE-EMBRYONIC STAGE: The first stage is to become a BLASTOCYST, then implantation to the endometrium. 7) Week 2 - The the cell mass becomes the EMBRYONIC DISK and differentiates into two cell types - ENDODERM (outermost: will become skin, nervous system, hair, organs) and ECTODERM (innermost: will become liver, pancreas, vagina, glands) 8) Week 3-8 - EMBRYONIC STAGE: Developing human is called an EMBRYO. This stage begins when the MESODERM (middle: will become muscle, bone, kidney, testes, ovaries) forms between the endo and ectoderms and the blastocyst becomes a GASTRULA. 9) Week 4 - After gastrulation, the ectoderm creates neural tissue and the gastrula is now called the NEURULA, and the beginning of the nervous and optic systems are created. 10) 4 EXTRAEMBRYONIC MEMBRANEs & PLACENTA form to facilitate development and birth: a. AMNION - Bag of waters - urine removal, shock absorption, moisturization. b. ALLANTOIS - temporary membrane that helps form the blood vessels of the umbilical cord. c. YOLK SAC - becomes part of the digestive tract, produces fetal blood cells, and gonad germ cells. d. CHORION - the source of human chorionic gonadotropin (hCG), a hormone that supports pregnancy for the first 3 months. e. PLACENTA & UMBILICAL CORD - The cord is the two-way lifeline that connects the placenta to the embryo's circulation. The placenta is the entire structure that forms from embryonic and maternal tissue. It's a filter that permits the exchange of nutrients, gases and antibodies between mother and embryo, but not large proteins or blood cells. 11) Week 5-8 embryo becomes distinctly human: four limbs are formed with fingers and toes, tail regresses, circulatory system is functional. Gender development begins at 6 weeks. For mothers, spontaneous pregnancy termination and miscarriage 20% common at this point. 12) Week 9-Birth - FETAL DEVELOPMENT stage: human is now called a fetus. Mother is now showing physical changes: morning sickness, tired, increased appetite, increased waistline. 13) Month 3: kidneys develop, sex can be determined visually by genitalia. 14) Month 4: Liver and bone marrow produce blood cells, face takes final form, ears and eyes become fixed. Fetus is 6 inches. Mother: increased - waist, breast size, appetite, weight gain. 15) Month 5: fetus begins to move, heartbeat can be heard with stethoscope, body is covered with LANUGO (soft, downy hair). 16) Month 6: lungs produce surfactant, and fetus could survive outside uterus. Weighs 1.5 lbs. 17) Months 7-9: rapid growth, loosing downy body hair, moves into position - head down toward uterus. Weight 6-7.5 lbs. Mother: all above, progressive discomfort, constipation, increased urinary frequency, hair loss/gain.

Once an oocyte is fertilized by a spermatozoon, it begins a series of events designed to maintain its development. What is the correct sequence for the events?

1. Cleavage 2. Compaction 3. Blastocyst Formation 4. Hatching 5. Implantation

blastocyst

A morula turns to a blastocyst after it is swept into the uterus. It's comprised of an outer sphere (trophoblast), a hollow central cavity, and a group of cells called the inner cell mass (the future embryo)

yolk sac

PART OF THE UMBILICUS. Forms a small sack that hangs from the embryo's ventral surface; becomes part of the fetal digestive track; source of germ cells that migrate into gonads. FUNCTION: VITAL SOURCE OF PRECURSOR CELLS

State the names of and describe the events that occur for mother and baby during each stage of the birthing process.

When the fetus' pituitary gland is mature, a series of events occur that trigger labor to begin. Several glands within the fetus and the placenta work together to secrete etrogen, prostaglandins and OXYTOCIN receptors. These, along with the mother's oxytocin stimulate the uterus to contract rhythmically, called LABOR. STAGE 1: DILATION - first phase of labor (6-12 hrs) contractions increase over time, pushing fetus' head against cervix. Widens to 10 cm to accommodate baby's head which causes water to break. STAGE 2: EXPULSION - second phase (>1 hr) from full cervical dilation through actual delivery. Contractions strengthen, and woman experiences intense urge to assist. Baby's head appearing at labia is crowning. When the head is expelled, nose and mouth are cleared of mucus to facilitate breathing. Once baby is out, umbilical cord is clamped to force baby to breathe. STAGE 3: AFTERBIRTH - third phase (>30 min) Contractions continue after baby is expelled in order to detach placenta from the uterus and expel placenta and umbilical cord - AFTERBIRTH. Breast-feeding is a multi-stage process of nurishing the infant. During pregnancy, high concentrations of estrogen and progesterone cause the woman's breasts to enlarge in preparation for LACTATION (milk production). During the first 1-2 days after birth, the breasts produce COLOSTRUM, a watery milk that is rich in antibodies but low in fat and lactose. This helps the newborn until it's own immune system kicks in. MILK LETDOWN/EJECTION is triggered by oxytocin in response to the infant suckling.

morula

a ball-shaped mass of about 32 identical cells present in the oviduct

allantois

a temporary membrane that serves as a source of vital cells because it helps form the blood vessels of the umbilical cord. FUNCTION: PART OF THE UMBILICUS

cell cleavage

cell division accompanied by reduction in size

Events after oocyte is fertilized

cleavage, compaction, blastocyst formation, hatching, implantation

aminion

the "bag of waters" lines the amniotic cavity, absorbs physical shocks, insulates the fetus and keeps it from drying out serves as a membrane to remove urine and exchange for the mother's blood. FUNCTION: CUSHION

placenta

the entire structure that forms the embryonic tissue and maternal tissue, and provides a means for the exchange of nutrients and wastes between mother and fetus.

chorion

the outermost layer; source of human chorionic gonadotropin; also forms structures that will be part of the exchange mechanism in the placenta. FUNCTION: EXCHANGE

trophoblast

the outermost sphere of cells in a blastocyst

umbilical cord

the two-way life line that connects the placenta to the embryo's circulation