History of embryology

Outline
 History
 Definition of Embryology
 Techniques used in Prenatal Screening
(Humans)
 Other concepts in embryology
 Techniques used in the study of Embryonic
Development

History
 Embryonic development has been a source
of wonder…
 Aristotle’s (384-322 B.C.) studies –a shift
from superstitions to observation.
 Galen (130-200 A.D) – learned about
advanced fetuses but the minute dimensions
resisted analysis

 caused a lag in the growth of knowledge
about the embryo until the development of
microscope.
 De Graaf in 1672 – described ovarian follicle
 Hamm and Leeuwenhoek in 1677 – have seen
the sperm cells
 significance were not understood

Theory of Preformation
 Spermists - sperm contained new individual in
miniature and only nourished in the ovum
 Ovists- thought the same and that the seminal
fluid only stimulates it.
 Bonnet (1745) – discovered eggs of some insects
undergoing parthenogenesis
 Spallanzani (1729-1799) – demonstrated that
both male and female sex products are
necessary for the initiation of development

 Wolff (1733–1794) – thesis on epigenesis
(embryological development occurs through
progressive growth and differentiation)
 Von Baer (1828) – discovered mammalian egg,
first emphasized that the more general basic
features of any animal group appear earlier in
the development than do special features of
different members of the group – von Baer’s law
 Demonstrated existence of germ layers

 The formulation of cell theory by Matthias
Schleiden and Theodore Schwann laid down
the foundation of modern embryology as a
science.
 Ernst Haeckel (1834 -1919) – drafted the
Biogenetic Law of Muller and Haeckel –
Haeckel’s Law of Recapitulation
 Ontogeny recapitulates phylogeny
 Tail in vertebrates

Embryology as a science
 Embryology- study of animal development
between fertilization and birth
 May include gametogenesis
 Weismann (1834-1914) – distinguished
between soma and germ cell

Special Fields
 Descriptive embryology (1880-1890) – serial
sections and three dimensional wax plate
reconstruction
 computer softwares
 Comparative embryology (late 1800s) –
provided insights on recapitulation theory;
started with invertebrates (evolution)

 Experimental – directed to causative factors that
regulate developmental processes.
 Chemical embryology – information about the
chemical and physiological events in the embryo.
 Included the role of DNA and RNA - how it fabricates
specific chemical and structural components of embryo

 Teratology – concerned with the study of
malformations
 Reproductive biology – problems of
conception and contraception
 Developmental biology – approach, includes
even postnatal processes.

Prenatal Diagnosis
 Designed to detect
 Malformations
 genetic abnormalities
 overall fetal growth
 complications of pregnancy, such as placental or
uterine abnormalities.
 “Their use and development of in utero
therapies have heralded a new concept in
which the fetus is now a patient. “

Ultrasound
 may be transabdominal or transvaginal
(produces images with higher resolution)
 developed in the 1950s- advanced to
detection of blood ﬂow , movement of heart
valves, ﬂuid flow in the trachea and bronchi
 safe and commonly used, with approximately
80% of pregnant women US

Ultra…
 Parameters revealed :
 characteristics of fetal age and growth
 presence or absence of congenital anomalies
 status of the uterine environment, including the
amount of amniotic ﬂuid (Fig. 7.4A);
 placental position and umbilical blood ﬂow;
 whether multiple gestations are present
(Fig.7.4B).
 Among the factors used to determine proper
approaches for management of the
pregnancy.

 Fetal age and growth assessed by:
 crown-rump length during the ﬁfth to tenth weeks
of gestation.
 combination of measurements, including the
biparietal diameter (BPD) of the skull, femur
length, and abdominal circumference (Fig. 7.5).
 Multiple measures of these parameters over
time improve the ability to determine the
extent of fetal growth.

 Congenital malformations determined by
ultrasound:
 the neural tube defects anencephaly and spina
biﬁda
 abdominal wall defects, such as omphalocele and
gastroschisis ;
 Heart defects
 facial defects (cleft lip and palate).

Maternal Serum Screening
 In search for biochemical markers of fetal
status
 ﬁrst of these tests assessed serum alpha-
fetoprotein (AFP)concentrations.
 AFP produced normally by the fetal liver,
peaks at approximately 14 weeks, and “leaks”
into the maternal circulation via the placenta.

 AFP conc. increase in maternal serum in the
second trim; begin a steady decline after 30
weeks of gestation.
 AFP levels increase in amniotic ﬂuid and
maternal serum in
 neural tube defects and other abnormalities i.e
omphalocele, gastroschisis, bladder exstrophy,
amniotic band syndrome, sacro-coccygeal
teratoma, and intestinal atresia,

 AFP conc. decrease in Down syndrome,
trisomy 18, sex chromosome abnormalities,
and triploidy.
 During amniocentesis, a needle is inserted
transabdominally into the amniotic cavity
(identiﬁed by ultrasound; Fig. 7.4A) and
approximately 20 to 30 ml of ﬂuid are
withdrawn.

Amniocentesis
 a needle is inserted transabdominally into the
amniotic cavity (identiﬁed by ultrasound; Fig.
7.4A)
 20 to 30 ml of ﬂuid are withdrawn.
 not usually performed before 14 weeks
gestation
 risk of fetal loss 1%

 fluid analyzed for
AFP and acetyl-
cholinesterase
 fetal cells in the
amniotic fluid
recovered for
metaphase
karyotyping and
other genetic
analyses
 major
chromosomal
alterations, such
as translocations,
breaks, trisomies,
and monosomies,
can be identified.

Chorionic villus sampling
 CVS involves inserting a needle
transabdominally or transvaginally into the
placental mass and aspirating approximately
5 to 30 mg of villus tissue
 Reserved only for high risk pregnancy

Fetal Therapy
 FETAL TRANSFUSION
 In cases of fetal anemia produced by maternal
antibodies or other causes, blood transfusions for
the fetus can be performed. Ultrasound is used to
guide insertion of a needle into the umbilical cord
vein, and blood is transfused directly into the
fetus.

 FETAL MEDICAL TREATMENT
 Treatment for infections, fetal cardiac
arrhythmias, compromised thyroid function, and
other medical problems is usually provided to the
mother and reaches the fetal compartment after
crossing the placenta. In some cases, however,
agents may be administered to the fetus directly
by intramuscular injection into the gluteal region
or via the umbilical vein.

 FETAL SURGERY
 Because of advances in ultrasound and surgical
procedures, operating on fetuses has become
possible.
 “Modern medicine has also made the fetus a
patient who can receive treatment, such as
transfusions, medications for disease, fetal
surgery, and gene therapy.”
 www.scribd.com/doc/7733260/Langmans-Medical-Embryology

Other concepts in
Embryology
 Totipotency – capability to form all possible
types of cells - zygote
 Pluripotency – all possible cell types with
some exceptions – placental stem cells
 Multipotency – multiple types of cells but not
all possible types – adult stem cells
 Monopotency – one particular cell type -
monocyte

 Gurdon and
colleagues
use somatic
cells of
Xenopus to
show somatic
pluripotency

Types of Stem Cell Source Potency
1. Early Embryonic
Stem Cell
Newly fertilized egg
that starts to divide
TOTIPOTENT! They can
become any kind of cell in
the body
2. Blastocyst
Embryonic
Stem Cell
Inner cell mass of
blastocyst (7 days after
fertilization)
PLURIPOTENT! they have
the ability to become
almost any kind of cell in
the body
3. Fetal Stem Cell Fetus ( 8 weeks after
fertilization)
PLURIPOTENT!
4. Umbilical Cord
Stem Cell
Blood from the
umbilical cord
MULTIPOTENT! can
differentiate into only a
limited range of cell types
(blood & immune cells)
5. Adult Stem Cell From developed
tissues
UNIPOTENT!
MULTIPOTENT!

 Restriction - reduction of developmental
options
 Determination – commitment to single
developmental fate
 Formation of cornea
 Differentiation – formation of specialized cell

 Morphogenesis – entire group of processes
that mold internal and external configuration
of an embryo (axes)
 Role of homeotic genes

 Apoptosis - genetically determined cell death
 Induction – embryonic signal calling; effect of
embryonic tissue on another
 Regulation
 Morphogenetic fields
 Regeneration

 Recapitulation - Biogenetic law
 Growth
 Differential growth
 Determinate growth
 Indeterminate growth

Methods in the Embryology
 Microcinematography
 Fixed Material
 Histochemical Methods – chem. activity
 Autoradiography - isotopes
 In situ hybridization – for RNA
 Tracing Methods – using dyes
 HRP - injected
 Japanese quail cells
 Retroviruses – carry reporter gene

 Immunological
 Microsurgical
 Ablation
 Transplantation
 Explantation
 Autografting
 Heterografting
 Xenografting

 Culture techniques
 Biochemical and molecular techniques
 Isoenzymes
 PCR
 Irradiation techniques
 Use of mutants
 Transgenic animals

References
 Carlson B.M. 2003. Patten’s Foundations of
Embryology. 6th
Ed. New York: McGraw-Hill,
Inc. Book Company
 www.scribd.com/doc/7733260/langmans-medical
-embryology

History of embryology

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History of embryology