Embryology: From Conception to Critical Periods
Introduction to
embryology
Dr. Sanaa Al Sharawi,
Dr.Essam Salama
Objectives
•
After this lecture you should be able to :
•
Define
Embryology.
•
Define
the developmental periods.
•
Define the
significance
of embryology.
•
Knew
the different embryological terminology.
•
Define
the
nomenclature used to describe
body parts, positions, and
relationships.
•
Describe in brief
the important events in embryology.
D
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n
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i
o
o
n
n
o
o
f
f
E
E
m
m
b
b
r
r
y
y
o
o
l
l
o
o
g
g
y
y
•
This term generally referes to
prenatal development
of embryos and
fetuses.
•
“Human embryology’’
is the science concerned with the origin and
development of a human being
starting
from a zygote
to the
birth
of
an infant.
•
Development does not stop at birth. Important changes, in addition to
growth occur after birth
(postnatal changes)
e.g.,development of
teeth
and
female breasts.
3
S
S
I
I
G
G
N
N
I
I
F
F
I
I
C
C
A
A
N
N
C
C
E
E
O
O
F
F
E
E
M
M
B
B
R
R
Y
Y
O
O
L
L
O
O
G
G
Y
Y
Importance of Embryology
:
•
The study of
prenatal stages of development
,
especially
those occurring
during the embryonic
period is to
understand the
normal body structure
and the
causes of any congenital anomalies happen.
•
So,It is concerned with
various genetic and /or
environmental factors
that disturb the normal
development producing
birth defects.
4
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v
v
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l
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p
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r
i
i
o
o
d
d
s
s
:
:
•
Developmental periods are divided
into :
1- Prenatal development :
It is the main developmental changes occurring
before birth
,
including :
•
The embryonic period :
starts from the
fertilization
to the
end of 8
th
week.
•
The fetal period :
begins from the
9
th
week
untill
birth.
2- postnatal development :
The changes occurring
after birth
, like
teeth
and
breast.
•
Prenatal development
is
more rapid
than
postnatal development and results in
more
striking changes.
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a
a
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P
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i
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o
o
d
d
s
s
o
o
f
f
H
H
u
u
m
m
a
a
n
n
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D
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v
v
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l
l
o
o
p
p
m
m
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n
t
t
•
This is the
stage of development
of an embryo
that is susceptible to
an agent, such as a
drug or virus
,
which can
lead to congenital
abnormalities.
•
Embryological Development
is
most easily disrupted
when the
tissues and organs are forming
during the embryonic period.
6
C
C
o
o
m
m
m
m
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m
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o
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g
y
y
:
:
•
Oocyte;
the
immature ovum
or
female germ cell.
•
Ovum;
the
mature female germ cell.
•
Sperm;
the
mature male germ cell.
•
Zygote;
the
fertilized ovum.
•
Cell division :
there are two types of cell division:
•
A- Mitotic :
It occurs in
the
somatic cell,
it produces
2 cells each contains
44 autosomes
and
2 sex
chromosomes
(
Diploid number
of chromosomes).
•
B- Meiotic (reduction) :
It occurs in
the
primitive
germ cells
in the testes
or
the ovaries, it includes 2
stages
1
st
& 2
nd
meiotic divisions
,
it produces
2 cells
then
4 cells
; each contains
22 autosomes
and one
sex chromosomes
(
Haploid number
of
chromosomes).
D
D
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s
s
c
c
r
r
i
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p
p
t
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v
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T
T
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r
m
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s
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o
o
:
:
•
Related to the Directions:
•
Cranial;
the top of the embryo or
the head.
•
Cephalic;
superior or
the head.
•
Caudal;
inferior or
the tail end.
•
Dorsal;
back
of the embryo.
•
Ventral;
anterior
or the belly side.
•
Medial;
near to the midline.
•
Lateral;
flank side.
D
e
s
c
r
i
p
t
i
v
e
T
e
r
m
s
:
•
Related to the Plans or sections:
•
Longitudinal;
median or sagittal.
•
Coronal;
frontal.
•
Transverse;
horizontal
Longitudinal Section
Transverse; horizontal
Coronal Section
Plans or sections:
M
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d
•
Gametogenesis.
•
Fertilization.
•
Implantation.
•
Development of the
Central Nervous System
:
begins
at
3rd week.
•
Development of
Heart
:
begins
at
3rd week.
•
Embryonic
Folding
:
4th week
11
G
A
M
E
T
O
G
E
N
E
S
I
S
•
It is the
production of mature
gametes
(sperm and ova) in the
gonads (testes in males and
ovaries in females).
•
It is divided into
:
1- Spermatogenesis.
2- Oogenesis.
12
S
S
P
P
E
E
R
R
M
M
A
A
T
T
O
O
G
G
E
E
N
N
E
E
S
S
I
I
S
S
•
It is the process
of
formation of mature
sperms.
•
Occurs
in the
semenifrous
tubules of testis.
•
Starts
from puberty
till
old
ages.
•
It ends
by formation of
mature sperms
with
haploid
number
of chromosomes.
13
•
Results of spermatogenesis;
•
1-
Reduction of chromosomal
number
from the diploid
to
the
haploid number.
•
2-
Change
the
primitive germ cell
(spermatogonia)
to
the
motile
sperm
.
•
3-
Increase
the
number of the
sperms.
14
O
O
O
O
G
G
E
E
N
N
E
E
S
S
I
I
S
S
•
It is the process
of
formation
of mature ovum,
•
It occurs
in the
cortex of the
ovary,
•
starts;
during
fetal life,
completed
after puberty, and
fertilization
and
continues
till
menopause.
•
It ends
by formation of
mature ovum
with
haploid
number
of chromosomes.
15
F
F
E
E
R
R
T
T
I
I
L
L
I
I
Z
Z
A
A
T
T
I
I
O
O
N
N
•
Definition:
Definition:
•
It is the process during which
It is the process during which
a mature male gamete
a mature male gamete
(
(
sperm
sperm
)
)
unites
unites
with a mature
with a mature
female gamete
female gamete
(
(
oocyte)
oocyte)
to
to
form a single cell
form a single cell
(
(
ZYGOTE
ZYGOTE
).
).
•
Site :
Site :
It occurs in the
It occurs in the
uterine
uterine
tube.
tube.
•
Results of fertilization:
•
The
diploid number
of
chromosomes is
restored.
•
The sex
of the embryo is
determined.
•
Initiates
cleavage
(cell
division)
of the zygote.
•
It is the process
of
embedding
of the
blastocyct
in
the
endometrium of the uterus,
•
It
begins:
one week after fertilization.
•
It is
completed
:
by the
12th day
after fertilization
.
•
Normal site of implantation :
In the
upper part
of the
posterior surface of the body
of uterus
near the fundus.
Abnormal site of implantation (ectopic pregnancy) :
Most common type
of
ectopic pregnancies
occurs in
the
uterine tube.
17
I
M
P
L
A
N
T
A
T
I
O
N
Ectopic Implantation (Pregnancy)
•
T
h
e
u
s
u
a
l
s
i
t
e
o
f
i
m
p
l
a
n
t
a
t
i
o
n
i
s
t
h
e
p
o
s
t
e
r
i
o
r
w
a
l
l
o
f
t
h
e
b
o
d
y
o
f
u
t
e
r
u
s
(
X
)
.
•
T
u
b
a
l
p
r
e
g
n
a
n
c
y
i
s
t
h
e
m
o
s
t
c
o
m
m
o
n
t
y
p
e
o
f
e
c
t
o
p
i
c
p
r
e
g
n
a
n
c
y
(
A
)
.
•
O
v
a
r
i
a
n
p
r
e
g
n
a
n
c
y
i
s
t
h
e
l
e
a
s
t
c
o
m
m
o
n
t
y
p
e
o
f
e
c
t
o
p
i
c
p
r
e
g
n
a
n
c
y
(
H
)
.
It is The
differentiation of the cells
into
Two layers
:
(A
)
Epiblast
High columnar cells
adjacent to the
amniotic cavity.
(B)
Hypoblast
Small cuboidal cells
adjacent to
Yolk sac.
TRILAMINAR DISC
Now
the
embryonic disc
is
formed of 3 layers
:
•
Embryonic Ectoderm
•
Intraembryonic Mesoderm.
•
Embryonic Endoderm.
Cells in these layers will give
rise to
all tissues and organs
of the embryo.
R
R
e
e
f
f
e
e
r
r
e
e
n
n
c
c
e
e
:
:
•
MOORE PERSAUD
MOORE PERSAUD
“
“
THE DEVELOPING HUMAN
THE DEVELOPING HUMAN
” Clinically Oriented
” Clinically Oriented
Embryology. 7
Embryology. 7
th
th
edition
edition
21
Thank you
22
Embark on a journey through the fascinating world of embryology with Dr. Sanaa Al Sharawi and Dr. Essam Salama. Delve into the definition, significance, and developmental periods of embryology, learning about prenatal and postnatal stages, common terminologies like oocyte and zygote, and critical periods of human development. Explore how embryology helps us grasp the complexities of normal body structure, congenital anomalies, and genetic/environmental factors affecting development.
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Presentation Transcript
Introduction to embryology Dr. Sanaa Al Sharawi, Dr.Essam Salama
Objectives After this lecture you should be able to : Define Embryology. Define the developmental periods. Define the significance of embryology. Knew the different embryological terminology. Define the nomenclature used to describe body parts, positions, and relationships. Describe in brief the important events in embryology.
Definition of Embryology Definition of Embryology This term generally referes to prenatal development of embryos and fetuses. Human embryology is the science concerned with the origin and development of a human being starting from a zygote to the birth of an infant. Development does not stop at birth. Important changes, in addition to growth occur after birth (postnatal changes) e.g.,development of teeth and female breasts. 3
SIGNIFICANCE OF EMBRYOLOGY SIGNIFICANCE OF EMBRYOLOGY Importance of Embryology : The study of prenatal stages of development, especially those occurring during the embryonic period is to understand the normal body structure and the causes of any congenital anomalies happen. So,It is concerned with various genetic and /or environmental factors that disturb the normal development producing birth defects. 4
Developmental periods : Developmental periods : Developmental periods are divided into : 1- Prenatal development : It is the main developmental changes occurring before birth, including : The embryonic period : starts from the fertilization to the end of 8th week. The fetal period : begins from the 9th week untill birth. 2- postnatal development : The changes occurring after birth, like teeth and breast. Prenatal development is more rapid than postnatal development and results in more striking changes.
Critical Periods of Human Development Critical Periods of Human Development This is the stage of development of an embryo that is susceptible to an agent, such as a drug or virus, which can lead to congenital abnormalities. Embryological Development is most easily disrupted when the tissues and organs are forming during the embryonic period. 6
Common terminology : Common terminology : Oocyte; the immature ovum or female germ cell. Ovum; the mature female germ cell. Sperm; the mature male germ cell. Zygote; the fertilized ovum. Cell division : there are two types of cell division: A- Mitotic : It occurs in the somatic cell, it produces 2 cells each contains 44 autosomes and 2 sex chromosomes (Diploid number of chromosomes). B- Meiotic (reduction) : It occurs in the primitive germ cells in the testes or the ovaries, it includes 2 stages 1st & 2nd meiotic divisions, it produces 2 cells then 4 cells ; each contains 22 autosomes and one sex chromosomes (Haploid number of chromosomes).
Descriptive Terms of the embryo : Descriptive Terms of the embryo : Related to the Directions: Cranial; the top of the embryo or the head. Cephalic; superior or the head. Caudal; inferior or the tail end. Dorsal; back of the embryo. Ventral; anterior or the belly side. Medial; near to the midline. Lateral; flank side.
Descriptive Terms: Descriptive Terms: Related to the Plans or sections: Longitudinal; median or sagittal. Coronal; frontal. Transverse; horizontal
Plans or sections: Transverse; horizontal coronal section through embryo Longitudinal Section Coronal Section
Major events during embryonic period Major events during embryonic period Gametogenesis. Fertilization. Implantation. Development of the Central Nervous System : begins at 3rd week. Development of Heart : begins at 3rd week. Embryonic Folding : 4th week 11
GAMETOGENESIS GAMETOGENESIS It is the production of mature gametes (sperm and ova) in the gonads (testes in males and ovaries in females). It is divided into: 1- Spermatogenesis. 2- Oogenesis. 12
SPERMATOGENESIS SPERMATOGENESIS It is the process of formation of mature sperms. Occurs in the semenifrous tubules of testis. Starts from puberty till old ages. It ends by formation of mature sperms with haploid number of chromosomes. 13
Results of spermatogenesis; 1- Reduction of chromosomal number from the diploid to the haploid number. 2- Change the primitive germ cell (spermatogonia) to the motile sperm. 3- Increase the number of the sperms. 14
OOGENESIS OOGENESIS It is the process of formation of mature ovum, It occurs in the cortex of the ovary, starts; during fetal life, completed after puberty, and fertilization and continues till menopause. It ends by formation of mature ovum with haploid number of chromosomes. 15
FERTILIZATION FERTILIZATION Definition: It is the process during which a mature male gamete (sperm) unites with a mature female gamete (oocyte) to form a single cell (ZYGOTE). Site : It occurs in the uterine tube. Results of fertilization: The diploid number of chromosomes is restored. The sex of the embryo is determined. Initiates cleavage (cell division) of the zygote.
IMPLANTATION It is the process of embedding of the blastocyct in the endometrium of the uterus, It begins: one week after fertilization. It is completed : by the 12th day after fertilization. Normal site of implantation : In the upper part of the posterior surface of the body of uterus near the fundus. Abnormal site of implantation (ectopic pregnancy) : Most common type of ectopic pregnancies occurs in the uterine tube. 17
Ectopic Implantation (Pregnancy) The usual site of implantation is the posterior wall of the body of uterus (X). Tubal pregnancy is the most common type of ectopic pregnancy (A). Ovarian pregnancy is the least common type of ectopic pregnancy (H).
It is The differentiation of the cells into Two layers : (A) Epiblast High columnar cells adjacent to the amniotic cavity. (B) Hypoblast Small cuboidal cells adjacent to Yolk sac.
TRILAMINAR DISC Now the embryonic disc is formed of 3 layers : Embryonic Ectoderm Intraembryonic Mesoderm. Embryonic Endoderm. Cells in these layers will give rise to all tissues and organs of the embryo.
Reference Reference : : MOORE PERSAUD THE DEVELOPING HUMAN Clinically Oriented Embryology. 7th edition 21
Thank you 22
