General embryology

Jun Zhou ( 周俊）

School of Medicine, Zhejiang University

20121225

Langman’s Medical Embryology, 9th Ed

Fertilization

14 days

Onset of last M.C.

266 days

280 days

a science which study the processes and regulations of development of human fetus.(from 1 cell (zygote) to (5-7) x1012 cells)

In general the length of pregnancy is considered to be 280 days or 40 weeks after the onset of the last menstruation, or more accurately, 266 days or 38 weeks after fertilization.

Labor

Preembryonic period: before 2 weeks

Embryonic period: 3-8 weeks

Fetal period: after 9 weeks

Total 38 weeks:

Embryonic period: 3-8 weeks

Fetal period: after 9 weeks

Preembryonic period: before 2 weeks

Fertilization

Definition: the process by which the male and female gametes(sperm and ovum) unite to give rise to zygoteplace: in the ampullary region of the oviduct

conditions: 1) maturation of oocyte 2) maturation of spermatozoa

3)  capacitation and acrosome reaction of spermatozoa: R5

• capacitation factor: secreted by epi. cells of oviduct, capacity

of releasing acrosome enzymes

4)  quality and quantity of spermatozoa:

• 2-6 ml, 100,000,000/ml,

• <1.5 ml; or <10,000,000; abnormal sperm >30%; or

capacity for mobile< 70%

5)  meeting of sperm and ovum within 24 hrs

Processes of fertilization:

•Phase I–penetrate the corona radiata, acrosomal release

•Phase II–ZP with receptors – zona pellucida spongy – the release of local enzymes

•Phase III–Success formation of zygote

• Entry – response1) Cortical or zona reactions -Comp

action - impermeable to more sperm

2) Oocyte finishes 2nd meiotic division

3) Female /Male pronucleus

4) Metabolic activation of the egg

• Results of fertilization– Diploid– Genetic sex– Cleavage

Cleavage •Mitosis and cytoplasmic division•Blastula - blastomeres•Morula

–inner cell mass•embryoblast

–outer cell rim•trophoblasts

•Blastocyst –Blastocoele–The cells of morula secrete fluid–Zona pellucide disappears

•Puberty – menstruation (28 days) •Hormonal regulation

–GnRH –FSH–LH

•Granulosa/theca cells–Estrogens –Progesterones

•The endometrium of the uterus is in the secretory phase

Uterus at Time of Implantation

Implantation

-Passage through the uterine tube•Day 5 –Day 11 Uterus•Orientation of implantation•Location - ant or post, fundus•Trophoblasts overlying the embryoblast pole attach to the endometrium, erosion into deep uterine vessels

Processes

zona pellucide disappear → polar trophoblast touch the endometrium→secrete enzymes →dissolve the endometrium → embedded into endometrium → coagulation plug seal the space

•Implantation site–Normal:ant or post wall of the uterus–Abnormal

–Tubal–Internal os of the cervix–Ovarian–Abdominal

•endometrium →decidua: -decidua basalis

-decidua capsularis

-decidua parietalis

•conditions: -endometrium is in secretory phase

-morula reach the cavity of uterus on time

-zona pellucide disappears in time

•Implantation - sinks deeper•The outer cell layer

–Trophoblasts•cytotrophoblasts•syncytiotrophoblasts

•Inner cell mass (embryoblast)–Fluid collection – amnion–Epiblasts & hypoblasts

Bilaminar Germ Disc

(Second week of development)

Week two – Day 9-12

•Implantation–Covered the endometrium- fibrin plug–Complete – slight bulge

•Trophoblasts–Vacuoles within syncytiotrophoblasts- fuse and form lacunar networks–Uteroplacental circ

•Extra-Embryonic Mesoderm–btwn troph & cavity–Somatic/splanchnic

Week 2 – Day 13-14

•Trophoblasts–Primary villi

•Yolk sac–Primary to seconday–Chorionic plate–Connecting stalk

The Bilaminar Embryo•Disc btwn

–Amnion–Yolk sac

•Bilaminar disc–Epiblasts–Hypoblasts

End of the Week of Twos•2 major cell masses

–Trophoblasts –Inner cell mass

•Trophoblasts–Cytotrophoblasts–Syncytiotrophoblasts

•Embryonic Cavities–Amniotic cavity–Yolk sac

•Germ Disc–Epiblasts–Hypoblasts

OBJECTIVES1. The definition of Embryology

2. The major phases of fertilization and the site where fertilization typically occurs

3. Endometrial changes that enable implantation and the hormones that modulate this change

4. Normal sites of implanation and the most abnormal sites

5. Morphologic changes in the zygote that occur enroute to the uterus

6. The development roles of the inner cell mass and the outer cell mass

7. Bilaminar germ discs