PRENATAL PERIOD

THE STAGES OF PRENATAL DEVELOPMENT

1. Germinal Period - (First 2 weeks after conception)

a) creation of the zygote 

b) continued cell division 

c) the attachment of the zygote to the uterine wall. 

The following are the details of development during this period:

a. 24 to 30 hours after fertilization the male (sperm) and female (egg) chromosome unite

b. 36 hours the fertilized ovum, zygote, divides into two (2) cells;

c. 48 hours (2 days)-2 cells become 4 cells

d. 72 hours (3 days) - 4 cells become small compact ball of 16-32 cells

e. 96 hours (4 days) - hollow ball of 64-128 cells

f. 4-5 days - inner cell mass (blastocyst) still free in the uterus

g. 67 days - blastocyst attaches to the wall of uterus

h. 11-15 days - blastocyst invades into urine wall and becomes in it (implantation)

• Blastocyst- the inner layer of cells that develops during later into the embryo

• Trophoblast-  the outer layer of cells that develops also during the germinal period later provides nutrition and support for embryo.

2.  Embryonic Period (2-8 weeks after conception)

Cell differentiation

a. Embryo's endoderm - inner layer of cells, develops into the digestive and respiratory systems

b. Embryo's ectoderm - the outermost layer which becomes the nervous system, sensory receptors (eyes, ears, nose) and skin parts (nails, hair)

c. Embryo's mesoderm - the middle layer which becomes the circulatory, skeletal, muscular

excretory and reproductive systems.

    Life-support systems for the embryo develop

a. Placenta - consist of disk-shape group of tissues in which small blood vessels from the mother and the offspring intertwine but do not join.

b. Umbilical cord - contains two arteries and one vein that connects the baby to the placenta.

c. Amnion - is a bag or an envelope that contains clear fluid in which the developing embryo floats.

c. Organs appear (organogenesis - process of organ formation)

3. Fetal Period (2 months to 7 months after conception) 

   - growth and development continue dramatically during this period.

Teratology and Hazards to Prenatal Development

          Teratology is the field that investigates the causes of congenital (birth) defects. A teratogen is that   which cause birth effects. It comes from Greek word "tera" which means "monster".

Below are the clusters of hazards to prenatal development:

1. Prescription and nonprescription drugs - one of the examples of prescriptive drugs is Antibiotic

because it can be harmful.

2. Psychoactive drugs - these include nicotine, caffeine and illegal drugs such as marijuana, cocaine and heroin.

3. Environmental hazards - these include radiation in jobsites and X-rays, environmental pollutants, toxic wastes, and prolonged exposure to heat in saunas and bath tubs.

4. Other maternal factors such as Rubella (German measles), syphilis, gentitl herpes, AIDS, nutrition, high anxiety and stress, age (too early or too late, beyond 30).