Prenatal Development

PRENATAL DEVELOPMENT: STRUCTURE AND PROCESS

  • The 10 major components covered:
    1) Anatomy of the female reproductive system
    2) Gametes (sex cells)
    3) The 3 stages of prenatal development
    4) The menstrual cycle
    5) Fertilization
    6) Chromosomal and genetic abnormalities
    7) Germinal stage
    8) Embryonic stage
    9) Teratogens
    10) Fetal stage

ANATOMY OF THE FEMALE REPRODUCTIVE SYSTEM

  • Major parts:

    • Vagina

    • Cervix

    • Uterus

    • Fallopian tubes

    • Ovaries

  • Functions:

    • Vagina: birth canal; passage for menstrual flow and intercourse

    • Cervix: lower part of uterus that opens during birth

    • Uterus: where the developing embryo/fetus grows

    • Fallopian tubes: where fertilization typically occurs; where eggs travel

    • Ovaries: store eggs and release them during the menstrual cycle

GAMETES (SEX CELLS)

  • Gametes are aka sex cells.

  • The egg (ovum) and sperm are each a sex cell.

  • Chromosome numbers:

    • Each gamete contains 23 chromosomes.

    • When egg and sperm unite, the zygote contains 46 chromosomes.

  • The chromosomes contain the genes that determine our individual features.

THE 3 STAGES OF PRENATAL DEVELOPMENT

  • Germinal stage

  • Embryonic stage

  • Fetal stage

  • Chronological order: Germinal → Embryonic → Fetal

  • Typical duration:

    • Germinal: begins at fertilization and lasts about 2 weeks; the zygote becomes a morula then a blastocyst.

    • Embryonic: lasts about 6 weeks (the next stage after germinal).

    • Fetal: lasts about 30-32 weeks (approximately until birth).

MENSTRUAL CYCLE

  • Sequence:

    • The uterine wall thickens in preparation for embedding a fertilized egg.

    • An ovary releases an egg.

    • The egg travels through the Fallopian tube.

    • If no sperm fertilizes the egg, the egg is discharged and the menstrual cycle ends (menstruation).

FERTILIZATION

  • Process:

    • Sperm travel up the Fallopian tube toward the egg; the egg is traveling down the tube.

    • When a sperm penetrates the egg, the nucleus of the sperm and the nucleus of the egg fuse.

    • This fusion is fertilization.

    • The resulting new organism is called a zygote.

CHROMOSOMAL AND GENETIC ABNORMALITIES

  • Abnormalities often involve more or less genes or defects in chromosomes.

  • Genetic variations and chromosomal anomalies can cause developmental concerns.

GERMINAL STAGE

  • Key events:

    • Begins with fertilization.

    • The new organism = zygote.

    • Zygote starts as 1 cell, then divides to 2, 4, 8, 16 cells.

    • At this point it’s called a morula.

    • Morula changes shape: most cells on outside, some on inside; becomes a blastocyst.

    • The blastocyst embeds in the uterine wall; outer cells become the placenta and inner cells become the embryo.

EMBRYONIC STAGE

  • Core processes:

    • Cell differentiation occurs: different cells take on different functions.

    • The body’s systems begin to develop (e.g., nervous system, other organ systems).

    • The placenta develops to supply nutrients and oxygen, remove waste; it serves as the connection between mother and embryo.

    • The embryo consumes what the mother consumes.

  • Key implications:

    • Critical period for organ development; vulnerability to teratogens is high during this stage.

TERATOGENS

  • Definition: Teratogens are substances or conditions outside the placenta that can harm the developing embryo/fetus.

  • Common examples: Alcohol, nicotine, infectious diseases, malnutrition, untreated diabetes, very stressful maternal environments, etc.

  • Embryonic stage as the peak vulnerability window due to rapid development of multiple systems.

  • Consequences: Intellectual disabilities, physical birth defects, language delays, hyperactivity, etc.

FETAL STAGE

  • Characteristics:

    • Primarily a period of fine tuning and rapid growth.

    • The fetus grows quickly in size.

    • It becomes more active, develops reflexes, and responds to external stimuli (e.g., mom’s voice).

CORRECTING FALSE STATEMENTS

  • Common false statements corrected:

    • The cervix is aka the birth canal. (Correction: The birth canal is primarily the vagina; the cervix is the lower part of the uterus that opens during birth.)

    • After fertilization, the vagina remains closed until birth. (Correction: The cervix remains closed until birth.)

    • Fertilization occurs in an ovary. (Correction: Fertilization typically occurs in the Fallopian tube.)

    • The ovaries store the sperm cells and release them into the fallopian tubes. (Correction: Ovaries store eggs; testes/epididymis store and mature sperm; sperm are released into the reproductive tract by ejaculation, not from the ovaries.)

    • The gonads (egg and sperm) are aka the sex cells. (Correction: The gametes produce sex cells, which are the eggs and sperm.)

    • When egg and sperm unite it results in 64 chromosomes. (Correction: It results in 46 chromosomes.)

    • The 3 stages of development are the 1st, 2nd, and 3rd trimesters. (Correction: Prenatal stages are germinal, embryonic, fetal; trimester terminology refers to pregnancy periods, not prenatal stages.)

    • The embryonic stage begins with fertilization and ends with embedding in the uterine wall. (Correction: Germinal stage begins with fertilization; embryonic stage follows germinal and ends with the formation of major organs.)

    • The longest lasting stage is the germinal stage. (Correction: The fetal stage lasts the longest.)

    • The embryo is most vulnerable to teratogens only in the fetal stage. (Correction: The embryonic stage is the peak vulnerability window.)

    • Teratogens are anything in the genes that can harm development. (Correction: Teratogens are external agents, not genes.)

    • In the germinal stage, the fetus is very active, develops reflexes, and responds to stimuli. (Correction: The fetus becomes active and responsive primarily in the fetal stage; early germinal stage activity is minimal.)

  • Bonus questions:

    • All mammals, including humans, reproduce via what?

      • Internal fertilization

    • About how many sperm are released upon ejaculation?

      • 250,000,000

    • When fertilization occurs:

      • 2 literally become 1