Prenatal Development and Birth Part 1 of 3

Conception Vocabulary Prenatal Development- Development of the organism that occurs before(pre) its birth (natal) Conception- The process of fertilization where a sperm cell combines with an egg cell to create a new organism Ovulation- release of an egg (ovum) from the female ovary Zygote- Term used to refer to the human organism after fertilization Mitosis- “Copy division,” the type of cell division that occurs when chromosomes are copied and divided into each new cell Differentiation- Process that occurs during cell division in which each new cell, as it divides, is committed to becoming a particular structure and serving a particular function

Conception The female reproductive system contains two Ovaries, two fallopian tubes, a uterus, a cervix and a vagina. Each ovary contains hundreds of egg cells (ova). During a woman’s menstrual cycle, about every 28 days or so, a mature ova passes through the fallopian tubes and into the uterus, this is referred to as ovulation. A normal menstrual cycle releases one ovum, but if two or more are released the offspring would be dizygotic (fraternal) twins or triplets.

Conception Cont. Typically in the upper wider part of the fallopian tube is where conception occurs. As soon as a single sperm penetrates the ovum’s outer membrane, a reaction immediately seals the membrane, making it impermeable to other sperm. This makes sure that the fertilized egg only gets 23 chromosomes from the father, and then 23 from the mother, for a total of 46. Once fertilized and sealed the zygote begins to copy and divide (mitosis) over and over again exponentially.

Conception Cont. Differentiation is when each new cells divide to form into particular structures, like the heart cell, brain cell, and muscle cells.

Stages of Prenatal Development Vocabulary Germinal Stage- The first stage of prenatal development, from conception through 2 weeks Implantation- process in which the zygote embeds itself into the inner lining of the mother’s uterus Embryonic Stage- the second stage of prenatal development, weeks 3 through 8. The embryo forms tissue representing every system and major part of the body. Miscarriage- Naturally occurring loss of pregnancy during the first 20 weeks of gestation Cephalocaudal Pattern- pattern of growth where areas in the head and upper body tend to form and grow before the areas in the lower body grow.

Stages of Prenatal Development Vocabulary Cont. Proximodistal pattern- pattern of growth where areas closer to the center of the body tend to form and grow before areas toward the extremities grow. Critical Periods- segments of time when structures are first forming and are most vulnerable to damage. Organogenesis- organ formation: Process where each major organ and system in the body differentiates within the embryo. Fetal Stage-The third and final stage of prenatal development, lasting from 8 weeks after conception until birth.

The Germinal Stage: Conception through week 2 This stage begins at conception and spans the first 2 weeks of pregnancy. Hours after conception the fertilized egg divides for the first time resulting in two identical cells. Over the next few days the zygote travels through the fallopian tube and down into the uterus. 8-12 days after conception, implantation occurs: the zygote embeds into the lining of the mother’s uterus. After implantation into the uterine lining, the placenta, amniotic sac, umbilical cord and other support structures begin to grow.

Embryonic Stage: Weeks 3- 8 Cell differentiation in this stage is especially critical. If any major genetic abnormalities exist at this point in development, a miscarriage is likely to occur. During weeks 3-4 the placenta and umbilical cord continue to form. Their function is to provide a more efficient supply of oxygen and nutrients to the growing embryo. By the end of week 4 heart tissues begins to “flutter” in a primitive heartbeat.

Embryonic Stage Cont. The Cephalocaudal Pattern (growth from upper body down) and the Proximodistal Pattern (growth from areas central outward) help estimate the critical periods in development– the times when the structures are first forming, and are at their most vulnerable. By the 8th week organogenesis is complete, each structure has differentiated within the embryo. The embryo is about 1 inch long and weighs only 1/30th of an ounce.

The fetal Stage: Week 9-birth( 38-40 weeks) This is the longest period of prenatal development. The fetus grows dramatically in size and weight. Weeks 9-12 the first movements of the arms and legs, but the mother does not feel it. The organs continue to develop enough to determine the sex of the fetus. Around weeks 17-20 the mother begins to feel the fetus rolling around and moving.

The Fetal Stage Cont. At 18 weeks the fetus weighs less than 1 pound. By 26-28 weeks the lungs are mature enough to allow successful breathing. And about 2 pounds the fetus may now be viable if born early. Not all premature babies can survive at this age. 6% chance at survival at 22 weeks 55% chance survival at 24 weeks And 92% chance of survival at 28 weeks. Infants born prior to 26 weeks suffer from respiratory distress.

The Fetus Stage Cont. During weeks 28-40 the fetus typically gains more than 5 pounds. Organs become more functional and strong The Brain develops rapidly producing more then 250,000 new cells per minute and will total over 80 billion cells by birth! At the end of a normal gestational period, the average newborn weighs 7.5 pounds and is about 21 inches in length.

Let’s Review What is the process whereby each new cell, as it divides and forms, commits to becoming a particular structure and serving a particular function? A: Organogenesis B: Mitosis C: Implantation D: Differentiation

Let’s Review Major genetic abnormalities normally lead to a miscarriage at the beginning of __________ A: Germinal Stage B: Embryonic Stage C: Fetal Stage D: Baby’s birth

Let’s Review True or False: The sex organs of the fetus can be detected by ultrasound beginning about 3-4 weeks after conception

Let’s Review A disruption to cell division during the embryonic stage is likely to have a serious negative impact because the A: Basics of all organ systems are forming during this stage B: Placenta will be injured, disrupting the flow of oxygen and nutrients to the embryo C: Functioning of organs such as the heart and lungs will be interrupted D: Fetus will fail to gain enough weight

Let’s Review True or False: The fact that infants can survive if born at 24 weeks’ gestation and weighing less than 5 pounds implies the last 16 weeks of prenatal development is not essential for the fetal health and development.