Prenatal Development

Prenatal Development

Conception

Stages (NOT Trimesters)

• Germinal/Blastocyst/Zygote Stage– Begins with Conception and ends with implantation– 0-(8-14) days-first two weeks– Egg and sperm meet (Zygote)

• travel down the fallopian tube to the uterus and implants– ~ 3-4 days after conception

• Differentiation of cells begins• eventually becoming the blastocyst: embryonic disk and

trophoblast– Amnion, Chorion, & Placenta

– 30-50% of all conceptions end– Death??– 12-17 conceptions are male to 1 female-WHY?

Conception

Stages (NOT Trimesters)

• Embryonic Period– Begins with implantation and ends with

ossification (calcification) of the bones.– 2-8th week– First two (or so) weeks: Embryonic disk

forms 3 layers:• Ectoderm-Nervous system & skin• Mesoderm-Muscles, skeleton, circulatory system• Endoderm-digestive system, lungs, urinary tract,

glands– Second month: systems become more

complex & defined

Stages (NOT Trimesters)

• Embryonic Period (cont)– Organogenesis complete (heart beat)– Skeleton complete– Sexual differentiation between 7-10 weeks

• Female unless presence of presence of Gene, SRY, is present on the short arm of the Y chromosome

• Differentiation of gonads into testes– 25-50% of all pregnancies terminate

spontaneously• Death?

Stages (NOT Trimesters)

• Fetal Period– Begins with ossification of the bones and ends with

birth– Purpose is for growth (in size and complexity) and

connections– 9-38 weeks +/- 2 weeks– 5% born on due date– Less than ¼ conceptions make it to delivery– From last menstrual period→40 weeks– At Birth 106 males to 100 females– But, at 1 year 96 males to 100 females

• Page 88-92 of your text- pics BUT DON’T FOCUS ON TRIMESTERS. FOCUS ON PERIODS

Sonograms

Critical Period

• What is it?

• Embryonic Period??

Critical Period

• Embryonic Period– Cell differentiation is occurring,

organogenesis, skeleton forming, timing is all genetically programmed.

• Cephalocaudal- Head to toe

• Proximal-Distal- Inside to out

• At birth approximately 19-21 inches

• At birth approximately 6-8 ½ lbs

• 7 ½ white> Af Am>Native Americans & Latino Americans

Development and Growth

Group Exercise

Group Exercise

• The mother can feel movement• Implantation occurs• The groundwork for all body structures is laid.• The placenta is connected to the developing organism by

the umbilical chord• The baby has reached the age of viability• A mass of cells drifts down and out of the fallopian tubes

and attaches itself to the wall of the uterus• The ectoderm, mesoderm, and endoderm are formed• Organs, muscles, and nervous system start to become

organized and connected• The embryonic disk (blastocyst) is formed• The developing organism is sensitive to sound and light

Group Exercise• The mother can feel movement (fetal)• Implantation occurs (germinal)• The groundwork for all body structures is laid

(embryonic).• The placenta is connected to the developing organism by

the umbilical chord (germinal)• The baby has reached the age of viability (fetal)• A mass of cells drifts down and out of the fallopian tubes

and attaches itself to the wall of the uterus (germinal)• The ectoderm, mesoderm, and endoderm are formed

(embryonic)• Organs, muscles, and nervous system start to become

organized and connected (fetal)• The embryonic disk (blastocyst) is formed (germinal)• The developing organism is sensitive to sound and light

(fetal)