General embryology
Langman’s Medical Embryology, 13th Ed
Jun Zhou (周俊）
School of Medicine, Zhejiang University
20151225
 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.
Onset of
last M.C.
Fertilization
14 days
266 days
Labor
280 days
Onset of M.C.
Ovulation
Total 38 weeks:
 Preembryonic
 Embryonic
 Fetal
period: before 2 weeks
period: 3-8 weeks
period: after 9 weeks
Preembryonic period: before 2 weeks
Embryonic period: 3-8 weeks
Fetal period: after 9 weeks
Fertilization
 Definition: the process by which the male and
female gametes(sperm and ovum) unite to give
rise to zygote
place: in the ampullary region of the oviduct
Prerequisite for fertilization:
1) maturation of oocyte
2) maturation of spermatozoa
3) capacitation and acrosome reaction of spermatozoa:
• 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
Oocyte maturation






Primordial  primary
Zona pellucida
Antrum – secondary
Cumulus oophorus
Secondary oocyte –
ovulation, polar body
Fate of oocyte
Spermatogenesis




Germ cells dormant until
puberty
At puberty become
mitotically active
sertoli cells, nutrition,
protection and
mechanical support
Unlike oogenesis, 4
gametes per clone
Spermiogenesis

Structural transformation




Condensation of the
nucleus
Reduction of associated
cytoplasm
Formation of the neck,
middle piece and the tail
Formation of the enzymerich Acrosome overlying
the head
Abnormalities of gametogenesis

Oocytes



Multiple per follicle multiple gestations
Multinucleated - die
Spermatocytes
Prerequisite for fertilization:
1) maturation of oocyte
2) maturation of spermatozoa
3) capacitation and acrosome reaction of spermatozoa:
• 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 – response
1) Cortical or zona reactions Compaction - 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
(No ZP)
Blastocoele
Inner cell mass
Trophablasts

Uterus at Time of Implantation
•Puberty – menstruation (28 days)
•Hormonal regulation
–GnRH
–FSH
–LH
•Granulosa/theca cells
–Estrogens
–Progesterones
•The endometrium of the uterus is
in the secretory phase
Implantation
-Passage through the uterine
tube
•Day 5 –Day 11 Uterus
•Orientation of implantation
- ant or post, fundus
•Trophoblasts (overlying the embryoblast
pole) attach to the endometrium,
begin to invade.
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 (most common)
Ectopic pregnancy
–Ovarian
–Abdominal
–Internal os of the cervix
•Endometrium →decidua:
-Decidua basalis
-Decidua capsularis
-Decidua parietalis
•Prerequisite:
-Endometrium is in secretory phase
-Morula/blastocyst reach the cavity of uterus on time
-Zona pellucide disappears in time
Bilaminar Germ Disc
(Second week of development)
•Implantation - sinks deeper
•The outer cell layer
–Trophoblasts
•cytotrophoblasts
•Syncytiotrophoblasts
(Syncytium)
•Inner cell mass (embryoblast)
–Fluid collection – amnion
–Epiblasts & hypoblasts
Week two – Day 9-12
•Implantation
–Covered the endometrium- fibrin plug
–Complete – slight bulge
•Trophoblasts
–Vacuoles within syncytiotrophoblastsfuse 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
–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
OBJECTIVES
1. 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