chapter 24: development. chapter 24.1: embryonic period
TRANSCRIPT
Chapter 24: Development
Chapter 24.1: Embryonic Period
First Week of Development
- Fertilization- Can occur during a 3-day window
- Early Embryonic Development- Rapid cell division- Development of inner cell mass and
trophoblast- Blastocyst implants into uterine wall
Frontal plane
1. Fertilization(occurs within uterine tube 12–24 hours after ovulation)
2. Cleavage(first cleavage completed about 30 hours after fertilization) 3. Morula
(3–4 days after fertilization)
4. Blastocyst (4 1/2–5 days after fertilization)
Uterine cavity
5. Implantation (occurs about 6 days after fertilization)
UterusEndometrium
Myometrium
OvulationOvary
Frontal section through uterus, uterine tube, and ovary
Second Week of Development
- Trophoblast penetrates uterine wall and continues to grow
- Human chorionic gonadotropin (hCG) sustains progesterone and estrogen secretion
- Inner cell mass develops into amniotic cavity and yolk sac
- Extraembryonic mesoderm begins placenta formation
Amniotic cavityFormation of yolk sac
Extraembryonic mesoderm
Third Week of Development
- Gastrulation: formation of three primary germ layers- Ectoderm- Mesoderm- Endoderm
- Mesodermal cells develop into notochord- Neural tube becomes brain and spinal cord
Third Week of Development
Umbilical vein
Umbilical arteries
Maternal blood
Amniotic cavity
Embryo
Yolk sac
Fourth-Eighth Weeks- All major organs and body systems begin to
develop- Embryo triples in size and becomes three-
dimensional (embryonic folding)
20-day embryo 24-day embryo
32-day embryo 44-day embryo 52-day embryo
Chapter 24.2-Fetal Period
Fetal Development
- Very few new structures appear and rate of body growth is very fast
- Fetus is less vulnerable to drugs, radiation, and microbes
10-week fetus 13-week fetus 26-week fetus