6 - BASIC EMBRYOLOGY SERIES.pdf

INTRODUCTION TO
DEVELOPMENTAL ANATOMY
Dr. Beda Olabu:
Basic Embryology Lecture Series

BASIC EMBRYOLOGY
Dr. Beda Olabu:

INTRODUCTION
Embryology* is the study of morphological changes
or processes that occur prenatally
Spans from gametogenesis until birth
Focusses on both the normal and the abnormal
developmental processes
Helps us to understand the anatomical basis of
congenital anomalies
3
Dr. Beda Olabu: Introduction to Embryology

INTRODUCTION
Overview of prenatal developmental periods:
Before conception:
Gametogenesis
Fertilization
After conception:
Pre-embryonic period
Embryonic period
Foetal period

INTRODUCTION
Basic embryology*
Focuses on the general principles of embryology and the
events of the early developmental stages
Systemic embryology*
Development of various body organs, according to their
organ systems
5

LECTURE SCOPE OF BASIC EMBRYOLOGY
1. Gametogenesis
2. Fertilization and its results
3. Female reproductive
cycles*
4. 1st week of development
5. Implantation & 2nd week
of development
6. Mechanisms of twinning
7. Gastrulation & derivatives
of the three germ layers
8. Neurulation process and
neural tube defects*
9. Foetal membranes and
the placenta
10. Principles of teratology
11. The foetal period
Dr. Beda Olabu: Basic Embryology

GAMETOGENESIS
Dr. Beda Olabu:

GAMETOGENESIS
Formation and development of the gametes
Occurs within the gonads (testis and ovary)
Spermatogenesis – Formation of sperms
Oogenesis – Formation of the ovum
9
Dr. Beda Olabu: Basic Embryology Series

LEARNING OUTCOMES
1. Explain the key steps in the process of spermatogenesis
2. Explain the key steps in the process of oogenesis
3. State the differences between spermatogenesis and
oogenesis
4. Highlight clinical disorders related to the process of
gametogenesis
10

PRIMORDIAL GERM CELLS
Embryonic cells that migrate into
the embryonic gonad during its
development
Become stem cells of gametes in
their respective gonads
PGCs are pluripotent cells that
arise from the walls of the yolk
sac and allantois

SPERMATOGENESIS
Occurs within the seminiferous
tubules of the testis
The process begins at puberty
Continues throughout life
It takes about 2 months to form
a single sperm
The most efficient temperature
for spermatogenesis is 34° C
The developing sperms are
supported by the Sertoli cells
12

Spermatogonia
Primary spermatocytes
Spermatocytogenesis
Spermatids
Meiosis phase I
Primordial germ cells
Differentiation
Mitotic cell
divisions*
Within testis
Meiotic cell
division* Meiosis phase II
Stem cells
Diploid
Haploid

Spermatids
Spermatozoa
Spermiogenesis
Spermiation
Storage
Decapacitation
Capacitation
Haploid

PARTS OF A MATURE SPERM
A = Head
B = Neck
C = Acrosome
X = Middle piece
Y = Principle
piece
Z = End piece
15

COMMON SPERM DISORDERS
Determined by semen
analysis
1. Teratospermia
2. Aspermia
3. Hypospermia
4. Oligospermia
5. Azoospermia
6. Asthenozoospermia
16

OOGENESIS
Takes place in the ovarian
cortex
The process begins prenatally
for all the developing oocytes
Oocyte’s meiotic cell division is
however arrested at Prophase I
The meiotic division proceeds in
“monthly” cycles after puberty
17

OOGENESIS
Multiple oocytes are
stimulated each month
Development occurs
during the 1st half of
the woman’s cycle,
then ovulation occurs
18

OOGENESIS
The oocyte is surrounded by an increasing number of
supporting cells, termed the follicular cells
19

Oogonia
Primary oocytes
Mitotic cell division
Formation of the
zona pellucida
Primordial Germ Cells
Differentiation
Surrounded by
the follicular cells

Primary oocytes
Meiosis I
Secondary oocytes
1st Meiotic arrest [P1]
Birth → Puberty
Cyclic completion
Meiosis II
2nd Meiotic arrest [M2]
Ovulation occurs
Fertilization by a sperm
Mature ovum

PARTS OF THE MATURE (GRAAFIAN) FOLLICLE
1.Secondary oocyte
2.Zona pellucida
3.Corona radiata
4.Cumulus oophorous
5.Granulosa cells
6.Follicular antrum
7.Theca interna
What is corpus luteum?

THE CORPUS LUTEUM
Remnants of the mature
follicle after ovulation
Consists of Granulosa
lutein & theca lutein cells
Secrete progesterone
hormone
23

OVERVIEW OF GAMETOGENESIS
SPERMATOGENESIS:
Takes place in the testis
Begins after puberty and takes
about 2 months, at 34 degrees
Supported by the Sertoli cells
Primordial germ cells →
spermatogonia → primary
spermatocytes → secondary
spermatocytes → spermatids →
spermatozoa
24

OVERVIEW OF GAMETOGENESIS
OOGENESIS:
Takes place in the ovary
Begins prenatally but is arrested,
and is completed in cycles after
puberty
Ovum is surrounded by follicular
cells and the zona pellucida
Primordial germ cells → oogonia
→ primary oocyte → secondary
oocyte → ovum
25

CLASS DISCUSSION
Outline the differences between
oogenesis and spermatogenesis
26

CLASS DISCUSSION
27
SPERMATOGENESIS OOGENESIS
Starts at puberty Starts prenatally
No meiotic arrest Two meiotic arrests
Lasts about 2 months Lasts many years
Equal meiotic division Unequal meiotic division
4 viable cells 1 viable & polar bodies

CLASS DISCUSSION
28
SPERMATOGENESIS OOGENESIS
Meiosis complete Meiosis incomplete
Both X & Y types Only X type
Motile cells Immotile cells
Continuous Cyclic (monthly)
Throughout life Stops at menopause

CLINICAL CORRELATION
29
Teratomas:
Germ cell tumors arising from
ectopic pluripotent stem cells
Contain multiple tissue lines
What would happen if PGCs do not migrate into the
developing gonad?

FERTILIZATION
Dr. Beda Olabu:

LEARNING OUTCOMES
1. Define fertilization and state where it occurs
2. Explain the sequence of events during the
process of fertilization
3. State the various outcomes of fertilization
4. Highlight the common clinical correlations
31

FERTILIZATION
Fusion of the sperm & the
ovum to form the zygote
Occurs in the ampulla of the
Fallopian tube
Illustrate parts of the Fallopian
tube using a diagram*
32

PARTS OF THE FALLOPIAN TUBE
33
Fimbria
Infundibulum
Ampulla
Isthmus
Intramural
segment
Fundus
Body
Cervix
UTERUS UTERINE TUBE (OVIDUCT)

THE PROCESS OF FERTILIZATION
1. Capacitation
2. Acrosome reaction
3. Penetration of the
oocyte coats
4. Zona reaction
34

FUNCTIONS OF ZONA PELLUCIDA
1. Prevents polyspermy
2. Ensures species specificity
3. Protects the oocyte
35

THE PROCESS OF FERTILIZATION
Only the head enters……….
5. Fusion of cell membranes
6.Completion of the oocyte
2nd meiotic division
7. Fusion of the male and the
female pronuclei
36

SUMMARY OF THE PROCESS OF FERTILIZATION
Process of fusion of the sperm
and the ovum
Occurs in the ampulla of the
Fallopian tube
Sperm penetrates the oocyte
coverings, then its nucleus fuses
with nucleus of the oocyte
The resultant new cell is called
the zygote

OUTCOME OF FERTILIZATION
1. Formation of the zygote from the ootid stage
2. Completion of oocyte 2nd meiotic division and
formation of the 2nd polar body
3. Restoration of the diploid (2n) number of chromosomes
4. Determination of embryonic sex (XX or XY genotype)
5. Genetic variation (variation of species)
6. Metabolic activation and restoration of capacity for
cell division (cleavage)
39

CLINICAL CORRELATION
1. Contraception
2. Assisted reproductive technology
3. Numerical chromosomal disorders
4. Polyspermy and molar pregnancy
40

CONTRACEPTIVE METHODS
1. Sterilization - BTL, vasectomy
2. Hormonal methods
3. Intrauterine contraceptive devices (IUCD)
4. Fertility awareness-based (natural) methods
5. Barrier methods
6. Emergency/postcoital contraception
7. Coitus interruptus
8. Lactation
41

NORMAL HUMAN KARYOTYPES
42
46XY = Male Karyotype
46XX = Female Karyotype

NUMERICAL CHROMOSOMAL DISORDERS
43
Trisomy 21: Down’s Syndrome 47XXY: Klinefelter’s Syndrome

44
45X0: Tuner’s Syndrome 47XXX = Triple X Syndrome

45
Trisomy 18: Edward’s Syndrome Trisomy 13: Patau Syndrome

MOLAR PREGNANCY
Occurs when there is an
“excess set” of paternal
chromosomes
Abnormal “vesicular”
proliferation of placental tissues
Also called hydatidiform mole
46

FEMALE REPRODUCTIVE
CYCLES
Dr. Beda Olabu:

INRODUCTION
Hormonally regulated “monthly” cycles
✓Gonadotropic hormones (from pituitary)
✓Ovarian hormones
Involves changes in the endometrium as
well as the ovary
48

LEARNING OUTCOMES
1. State the effects of FSH & LH on the ovary
2. Name the phases of the ovarian cycle and state
their hormonal basis
3. Name the phases of the endometrial cycle and state
their hormonal basis of each
4. Understand the concept of safe days and its basis
49

50
Pituitary hormones
FSH
Ovarian events
Ovarian hormones
Endometrial events
4 8 12 16 20 24 28
Folliculogenesis
Follicular
phase
Estrogen
secretion
Thickening
Ovulatory
phase
Progesterone
secretion
Glands
Proliferative
phase
Secretory
phase
Corpus luteum
Luteal
phase
Estrogen phase Progesterone phase
4
Menstrual
phase
0
FSH

FEMALE REPRODUCTIVE CYCLES
OVARIAN CYCLES:
Follicular phase
Ovulatory phase
Luteal phase
51

ENDOMETRIAL CYCLES:
Proliferative phase
Secretory phase
Menstrual phase
52

HORMONAL CYCLES:
Estrogen phase
Progesterone phase
53

THE CONCEPT OF SAFE DAYS
54

EARLY EMBRYONIC PERIOD
FIRST TWO WEEKS OF DEVELOPMENT and
IMPLANTATION
Dr. Beda Olabu:

INTRODUCTION
Prenatal developmental periods:
Before conception:
Gametogenesis
Fertilization
After conception:
Embryonic period
Foetal period

INTRODUCTION
Pre-embryonic period of development:
1. The 1st 14 days (2 weeks) after conception
2. Formation & differentiation of embryonic and
trophoblastic (placental) tissues
3. Implantation and establishment of pregnancy

LEARNING OUTCOMES
1. Explain the events and morphological changes that
occur during the 1st week of development
2. Describe the process of implantation and state the
common disorders related to this
3. Outline the events that occur in the 2nd week of and
explain the concept of the “week of twos”

1ST WEEK OF DEVELOPMENT
Occurs largely along
the Fallopian tube
Day 1 – 4/5: Within the
Fallopian tube
From day 5/6: In the
endometrial cavity

The conceptus:
1. Is propelled towards the
endometrial cavity
2. Undergoes cleavage &
morphological changes

Cleavage
ZYGOTE
STAGE
MORULA
STAGE
DAY 1 DAY 1-2 DAY 3-4
OOTID 12-32 CELLS
Compaction
2 CELLS
2-CELL
STAGE
Cleavage

BLASTOCYST
STAGE
MORULA
STAGE
DAY 3-4 DAY 5-6
Fluid accumulation
12-32 CELLS CAVITY PRESENT
Cleavage & Compaction
Cavity formation

LATE
BLASTOCYST
THE BLASTOCYST STAGE
EARLY
BLASTOCYST
DAY 5-6 DAY 6-8
Hatching Process

SUMMARY OF THE 1ST WEEK
1. Movement of the conceptus towards the endometrial
cavity (site of implantation)
2. Continuous cleavage & compaction, then hatching
3. Zygote → Two-cell stage → Morula → Blastocyst
4. Ends when the embryblastic and trophoblastic tissues
(inner and outer cell masses) have been established

PARTS OF THE BLASTOCYST
Individual cells of the blastocyst are termed blastomeres

2ND WEEK OF DEVELOPMENT
1. Implantation of the blastocyst
2. Differentiation of the embryoblastic and the
trophoblastic tissues
3. Establishment of the foetal membranes
………………..The “week of twos”………………….

IMPLANTATION
The process by which the blastocyst attaches and
embeds itself into the endometrial lining of uterine wall
Invasion of the endometrium by the blastocyst is done
by the trophoblast layer; between day 6-13
Site of implantation determines site of placentation
Commonest site = Posterior aspect of uterine fundus

RELEVANT ANATOMY OF THE UTERUS
PARTS OF THE UTERUS LAYERS OF THE UTERINE WALL
LUMEN
PERIMETRIUM
MYOMETRIUM
ENDOMETRIUM
STRATUM BASALE
STRATUM
FUNCTIONALIS

IMPLANTATION PROCESS
Hatching of the blastocyst Attachment of the blastocyst

Formation of the
syncitiotrophoblast layer
Burrowing & embedding,
guided by the trophoblast

Trophoblastic lacunae
formation
Closure and repair of the
epithelial defect

ABNORMALITIES OF IMPLANTATION
Ectopic gestation:
1. Ovarian
2. Abdominal
3. Tubal (commonest)
4. Cervical

Placenta previa:
Low lying placenta
Placenta detaches before
delivery of the baby
Risk of bleeding & still birth

Excess penetration/invasion into the uterine wall:

THE CONCEPT OF THE “WEEK OF TWOS”

THE EXTRAEMBRYONIC MESODERM

THE CHORIONIC PLATE
COMPONENTS:
1. Extraembryonic
mesoderm
2. Cytotrophoblast
3. Syncitiotrophoblast

TWO PARTS OF THE CHORIONIC LAYER
Chorion frondosum & chorion laeve

“WEEK OF TWOS”
2 Cell masses
2 poles
2 Embryonic layers
2 Cavities
2 Trophoblastic layers

SUMMARY OF THE MORPHOLOGICAL STAGES OF THE
CONCEPTUS DURING THE 1ST TWO WEEKS
ZYGOTE
STAGE
MORULA
STAGE
BLASTOCYST
STAGE
BILAMINAR
DISC STAGE
2-CELL
STAGE

ABNORMALITIES OF THE 2ND WEEK
Blighted ovum (abembryonic pregnancy)

ABNORMALITIES OF THE 2ND WEEK
Hydatidiform mole (Molar pregnancy)

MOLAR PREGNANCY
Occurs when there is an
“excess set” of paternal
chromosomes
Abnormal “vesicular”
proliferation of placental
tissues
84

MULTIPLE GESTATION
FOCUS ON MECHANISMS and TYPES OF TWIN
PREGNANCIES
Dr. Beda Olabu:

MULTIPLE PREGNANCIES
oTwins, Triplets, Quadruplets, Quintuplets
Types of twin gestations:
1. Dizygotic
2. Monozygotic

DYZYGOTIC TWINNING
Two ova are ovulated, & subsequently fertilized by
different sperms
Hence development begin by two zygotes
The twins are genetically different (Fraternal)
Constitute the majority of twin gestations

DYZYGOTIC TWINNING
Superfecundation:
Fertilization of two or more
ova from the same cycle
by sperms from separate
acts of sexual intercourse

MONOZYGOTIC TWINNING
An ovum is fertilized by one sperm and development
starts with 1 zygote, hence are termed monozygotic
Separation of the early embryonic cells then occurs
The splitting of embryonic cells is only possible up to
day15
Twins are classified based on the structures they share

STAGES OF EARLY DEVELOPMENT
ZYGOTE
STAGE
MORULA
STAGE
BLASTOCYST
STAGE
BILAMINAR
DISC STAGE
2-CELL
STAGE

DICHORIONIC-DIAMNIOTIC TWINS
Separate
placentas
Separate
amniotic sacs

MONOCHORIONIC-DIAMNIOTIC TWINS
Shared
placenta
Separate
amniotic
sacs

MONOCHORIONIC-MONOAMNIOTIC TWINS
Shared placenta and
amniotic sac

REVIEW OF STAGES OF EARLY DEVELOPMENT
PRIMITIVE STREAK
STAGE

CONJOINED (SIAMESE) TWINS
Separation at the primitive streak stage
(hence partial splitting of the cells of the
primitive streak)
The twins will share some body organs
All are monochorionic-monoamniotic types

Classified according to body regions shared/fused
Thoracopagus
Craniopagus

Omphalopagus Pygopagus

COMPLICATIONS OF MULTIPLE GESTATION
1. Conjoined twins
2. Prematurity
3. Low birth weight
4. Parasitic twins

Parasitic twins

5. Twin to twin transfusion syndrome

6. Intrauterine demise of one twin
Fetus Papyraceus Vanishing twin

GASTRULATION
FOCUS ON THE TRILAMINAR EMBRYONIC DISC
Dr. Beda Olabu:

INTRODUCTION
The process of formation of a three layered
embryo (the gastrula or trilaminar germ disc)
The three embryonic layers are: ectoderm,
mesoderm & endoderm
Takes place during the 3rd week of development

INTRODUCTION
Events of the third week of development set stage for
the period of organogenesis
Occasionally referred to as the “week of threes”:
1. Three embryonic layers develop from the epiblast
2. Three embryonic structures are formed: The primitive
streak, notochord and neural tube
3. Three mesodermal segments develop – the paraxial,
intermediate and lateral plate mesoderm

LEARNING OUTCOMES
1. State the formation, functions and fate of the
primitive streak
2. The events during the process of gastrulation
3. Outline the adult derivatives of each of the
three germ layers

THE PRIMITIVE STREAK
Formed by proliferation of the midline epiblast cells
Around the caudal end of the bilaminar embryo

PARTS OF THE PRIMITIVE STREAK
Primitive groove
Primitive node
Primitive pit

FUNCTIONS OF THE PRIMITIVE STREAK
1. Provide structural support to the bilaminar
embryonic disc
2. Establishes the embryonic axis and bilateral
symmetry
3. Direct the process of gastrulation

FATE THE PRIMITIVE STREAK
The primitive streak degenerates (disappears)
What would happen if these
totipotent cells persist?
Sacrococcygeal teratoma
Contain multiple tissue lines

GASTRULATION
The process of formation
of the trilaminar disc
(gastrula)
The cells of primitive streak
migrate downwards and
outwards
The cellular migration
occurs in 2 phases:

GASTRULATION PROCESS
1st phase of migration:
Displace the hypoblast
layer of cells laterally
Becomes the endodermal
layer
Extends laterally to even
form the lining of the yolk
sac

2nd phase of migration:
The cells sandwich themselves
between the formed endoderm
& the remaining epiblast cells
Become the mesodermal layer
This later divides into three

Remaining epiblast constitute
the ectodermal layer
The structure is now called
gastrula (trilaminar germ disc)
All its layers arise from the
epiblast layer

SUMMARY OF GASTRULATION
Ectoderm, mesoderm & endoderm

DERIVATIVES OF THE GERM LAYERS
1. Ectoderm layer:
Protecting & communicating
layer
Differentiates into two parts:
1. Neuroectoderm: Nervous
system (both PNS & CNS)
2. Surface ectoderm: epidermis
of the skin

2. Endoderm layer:
A nourishing layer
Becomes incorporated into
the embryo during folding
Constitutes the lining of the
primordial gut
Gives rise to epithelial lining &
glands of digestive &
respiratory systems

Differentiation of the mesoderm layer:

3. Mesoderm layer:
(a) Paraxial mesoderm
Undergoes segmentation to
form the somites
Somites differentiate into:
1. Sclerotome: Axial skeleton
2. Myotome: Skeletal muscles
3. Dermatome: Trunkal dermis

3. Mesoderm layer:
(b) Intermediate mesoderm
Urinary system
Reproductive system

3. Mesoderm layer:
(c) Somatic mesoderm
Appendicular skeleton
Dermis

3. Mesoderm layer:
(d) Splanchnic mesoderm
Smooth musculature
Cardiac musculature
Visceral C.T

THE GERM LAYERS & THEIR DERIVATIVES

GASTRULATION DISORDERS
Caudal dysgenesis (Sirenomelia)

NEURULATION
FOCUS ON FORMATION OF THE NEURAL
TUBE & NEURAL TUBE DEFECTS
Dr. Beda Olabu:

INTRODUCTION
Neurulation is the process of formation of the neural
tube
The neural tube is the primordium of the central
nervous system – brain and spinal cord
Occurs during the 3rd to 4th week of development
There is primary and secondary neurulation processes

LEARNING OUTCOMES
1. State the formation, functions and fate of
notochord
2. Describe the process of primary and secondary
3. Highlight on the common neural tube defects
4. Outline the derivatives of the neural crest cells

THE NOTOCHORD
Special cartilaginous
structure
Lies within the midline
of mesoderm layer

FUNCTIONS OF THE NOTOCHORD
1. Provide structural support
2. Define the embryonic axis
3. Induce neurulation
4. Basis for axial skeleton

FATE OF THE NOTOCHORD
Degenerates
Form the nucleus
pulposus of the
intervertebral discs
If it fails to degenerate?

CHORDOMAS

NEURULATION
Process of formation of
the neural tube
Primordium of CNS
Leads to formation of
neural tube & neural crest
Primary & secondary…..

PRIMARY NEURULATION
Neurulation by notochordal induction
Involves the cranial ectoderm

SECONDARY NEURULATION
Neurulation by mesenchymal condensation
Forms the caudal neural tube (without neural plate)

NEURULATION PROCESS
The notochord induces the overlying ectoderm to
form neuroectoderm (and surface ectoderm)

OVERVIEW OF NEURULATION PROCESS
Induction by the notochord
Form the neuroectoderm &
surface ectoderm
Thickening (= neural plate)
Neural groove & neural folds
Fusion to form the neural tube
(and neural crest)

NEURAL CREST DERIVATIVES
In the peripheral nervous
system
In the integument system
In the endocrine system
In the heart
In the craniofacial region

ANOMALIES ASSOCIATED WITH NEURAL
CREST CELLS
1. Congenital aganglionic megacolon
2. Disorders of skin pigmentation
3. 1st pharyngeal arch syndromes
4. Cardiac malformations

FOETAL MEMBRANES
AMNION, YOLK SAC, ALLANTOIS & CHORION
Dr. Beda Olabu:

INTRODUCTION
Structures that cover
the foetus
Are of zygotic origin
Part of the POCs
Are extraembryonic

INTRODUCTION
FOUR COMPONENTS:
1. Amnion
2. Yolk sac
3. Allantois
4. Chorion

LEARNING OUTCOMES
For each foetal membrane, state:
1. When and how the membrane is formed
2. The roles/functions of the foetal membrane
3. The eventual fate of the foetal membrane
4. Clinical aspects regarding the foetal membrane

THE AMNION
Forms in the ICM during the 2nd
week of development
By migration of the amnioblast
cells from the epiblast layer
Secrete (amniotic) fluid into
the amniotic cavity

THE AMNIOTIC SAC
The size increases as the pregnancy advances

SOURCES OF AMNIOTIC FLUID
EARLY SOURCES:
Secretions of amnioblast
cells
Maternal tissue fluid (by
diffusion)
LATER SOURCES:
Fetal urine
Foetal secretions: from
foetal skin, lungs and GIT

AMNIOTIC FLUID CIRCULATION
AMNIOTIC FLUID WITHIN THE AMNIOTIC CAVITY
Amnioblast
Cells
Maternal
Fluid
Foetal
Urine
Foetal
Secretions
FLUID WITHIN FOETAL BLOOD CIRCULATION
Foetal swallowing
Intestinal absorption Foetal kidneys
Foetal urine
PLACENTAL CIRCULATION
Umbilical arteries
Umbilical vein

FUNCTIONS OF THE AMNIOTIC FLUID
Protective/shock
absorption
Lubricates the fetal skin
to prevent drying
Musculoskeletal
development
Permit symmetrical growth
of the foetus
Thermoregulation
Lubricate the birth canal
Promote expansion of the
lung alveoli

FATE OF THE AMNION
Tears around the time of delivery during
“rupture of membranes”
The membrane is expelled “after birth”
together with the placenta

CLINICAL CORRELATIONS
1. Amniocentesis
2. Oligohydramnios
3. Polyhydramnios
4. Amniotic band disruption syndrome (ABDS)

AMNIOCENTESIS
Obtaining
amniotic fluid for
testing
Screening for
fetal anomalies

OLIGOHYDRAMNIOS
Amniotic fluid volume is
less than expected for the
gestational age
Often less than 500mL
List possible causes of
oligohydramnios

CAUSES OF OLIGOHYDRAMNIOS (DRIPPC)
Demise/Drugs
Renal abnormalities (hence reduced urine output):
agenesis, dysplasia, cystic kidney diseases, PUVs,
urethral atresia
Intra-uterine growth restriction (IUGR)
Premature rupture of membranes (PROM & PPROM)
Placental insufficiency
Chromosomal anomalies: Trisomy 13; Trisomy 18

COMPLICATIONS OF OLIGOHYDRAMNIOS
1. Pulmonary
hypoplasia
2. Foetal limb
anomalies
3. Foetal demise

POLYHYDRAMNIOS
Amniotic fluid volume is
more than expected for
the gestational age
Generally AFI >25 cm
List possible causes of
polyhydramnios

CAUSES OF POLYHYDRAMNIOS
Categories:
More than 50% is
idiopathic
Maternal causes: DM,
CCF
Multiple foetal causes:
Common foetal causes:
CNS anomalies
Anomalies that lead to
gastrointestinal obstruction
Multiple pregnancy
Cardiac anomalies
Trisomy 21(or 18 and 13)

COMPLICATIONS OF POLYHYDRAMNIOS

AMNIOTIC BAND SYNDROME
Comprises a wide spectrum
of abnormalities
Result from entrapment of
various fetal body parts in a
disrupted amnion
Multiple defects can occur

AMNIOTIC BAND SYNDROME

YOLK SAC (UMBILICAL VESICLE)
Formed in the 2nd week of
development
By migrating cells from the
hypoblast layer
Later by endodermal cells

FUNCTIONS OF THE YOLK SAC
Early nutrient supply
Site of early hemopoiesis
Gives rise to the PGCs
(primordial germ cells)

OVERVIEW OF EMBRYONIC FOLDING
The embryo folds both longitudinally (cranio-caudal axis)
and laterally (transverse axis)
As the embryo folds, the dorsal part of the yolk sac is
longitudinally incorporated into the developing baby
Discuss with your neighbor the key outcomes of each of
the embryonic folding processes

OUTCOME OF EMBRYONIC FOLDING
Transverse embryonic folding:

OUTCOME OF EMBRYONIC FOLDING
Cranio-caudal embryonic folding:

THE FATE OF THE YOLK SAC

FATE OF THE YOLK SAC
Dorsal part is incorporated
into the embryo during
folding (to become the
primordial gut)
Ventral part degenerates

FATE OF THE VITELLINE DUCT

YOLK SAC: CLINICAL CORRELATES
Vitelline duct anomalies
Meckel’s diverticulum Vitelline fistula Vitelline cyst Fibrous cord

THE ALLANTOIS
An extension of the yolk sac,
into the connecting stalk
Similar functions as yolk sac*
Contribute to formation of
the umbilical vessels

FATE OF THE ALLANTOIS
Lower part incorporated to
form the urinary bladder
Upper part degenerates as
the urachus
Becomes the median
umbilical ligament

CLINICAL CORRELATIONS
Persistence of the
allantois lead to
Urachal anomalies
Commoner types are:
Urachal fistulas
Urachal cysts

THE CHORIONIC PLATE
COMPONENTS:
1. Extraembryonic
mesoderm (somatic L)
2. Cytotrophoblast
3. Syncitiotrophoblast

TWO PARTS OF THE CHORION
Chorion frondosum & chorion laeve

FUNCTIONS OF THE CHORION
Chorion frondosum forms the
foetal component of the
placenta
Chorion protects the embryo
Haemopoietic centre

CLINICAL UTILITY OF THE CHORION
For diagnosis of early
pregnancy:
1. Laboratory detection of
beta hCG (from urine or
blood samples)
2. Sonographic visualization
of the gestational sac
(chorionic cavity)

For diagnosis of an
early pregnancy:
1. Laboratory detection of
beta hCG (from urine or
blood samples)
2. Sonographic visualization
of the gestational sac
(chorionic cavity)

Chorionic villous sampling:

THE PLACENTA
A fetomaternal
organ
Foetal: Chorionic
frondosum
Maternal part:
Decidua basalis

FUNCTIONS OF THE PLACENTA
Exchange – Oxygen, carbon dioxide, nutrients,
antibodies
Endocrine – hCG, estrogen, progesterone, hPL
Metabolic – Glycogen

STRUCTURAL ANOMALIES OF THE PLACENTA
Excess penetration/invasion into the uterine wall:

Placenta
Previa
Battledore
Placenta
Bi-lobed
Placenta

Circumvallate
Placenta
Placenta
Velamentosa
Placenta
Succenturiata

FOETAL PERIOD OF DEVELOPMENT
FOCUS ON THE 9TH WEEK UNTIL BIRTH
Dr. Beda Olabu:

INTRODUCTION
Prenatal developmental periods:
Before conception:
Gametogenesis
Fertilization
After conception:
Embryonic period
Foetal period

1. Main characteristics of the foetal period
2. Methods of assessing foetal growth
3. Prenatal diagnosis of birth defects
4. Key features in various foetal periods
5. Factors which influence foetal growth
LEARNING OUTCOMES

1. Rapid growth of the body organs
✓ 1st trimester – hyperplasia
✓ 2nd trimester – hyperplasia & hypertrophy
✓ 3rd trimester – hypertrophy
2. Marked increase in height and weight
✓ In the 3rd trimester, weight triples and length doubles
as body stores of protein, fat, iron and calcium increase
CHARACTERISTICS OF THE FOETAL PERIOD

3. Ossification
4. Fat deposition

5. Reduced head dominance (compared to the rest
of the body)

Ossification centers for long bones and cranium appear
Head is ½ of the crown heel length
Face is recognizably human
Hepatosplenic phase of hemopoiesis
Intestines return to the abdomen
Urine formation
Gender of the external genital becomes distinguishable
WEEK 9 – 12 OF DEVELOPMENT

Rapid growth occurs
Ossification is active
Head becomes relatively small compared to the 12th
week fetus: longer limbs
Face changes: eyes are anterolateral, ears almost in
place
14 weeks:
 Limb movements are coordinated
Slow eye movements

Rapid growth occurs
Ossification is active
Head becomes relatively small
compared to the 12th week fetus: longer
limbs
Face changes: eyes are anterolateral,
ears almost in place
Limb movements are coordinated
Slow eye movements

Growth slows
Fetal movements can be felt by
mother
Skin covered by vernix caseosa
Uterus formed, vagina canalized
Eye brows and head hair visible
Fetal skin covered by lanugo
Brown fat is formed (site of heat
production)
Descent of the testes

Weight gain occurs
Wrinkled skin, translucent
Skin is pink
Rapid eye movements; Blink startle 21-23 weeks
Finger-nails present
Type II pneumocytes start to secrete surfactant

Lungs and pulmonary vasculature adequately formed
CNS can regulate body temperature and breathing
Eyelids open at 26 weeks
Toe nails are visible
Subcutaneous fat present (3.5% of body weight), making
skin smooth
Bone marrow takes over hematopoiesis at 28 weeks

Pupillary light reflex can be elicited
Upper and lower limbs now have a chubby
appearance
Fat is now 8% of body weight

Firm grasp by fetus
Spontaneous orientation to light
Fat is about 16% of the body weight (fat increases
at 14g per day)
At 36 weeks abdominal circumference same as
head circumference
Breasts protrude in both males and females

CLASS DISCUSSION
Outline the factors that influence
fetal growth
203

Genetic factors: Race; Chromosomal disorders
Hormonal factors: Fetal thyroid hormone
Environmental factors: uterine environment,
maternal systemic disease, Smoking)
FACTORS THAT INFLUENCE FOETAL GROWTH

Infectious agents (TORCH-S)
Diet and nutrients
Social and emotional stress
Drug and smoking
Teratogens and toxins
Altitude and temperature
Ionizing radiation
FACTORS THAT INFLUENCE FOETAL GROWTH

Fundal height:
Estimates the size of
the uterus
ASSESSMENT OF FOETAL GROWTH

Fetoscopy:
Measures the
foetal heart rate

Ultrasonography:
Use of ultrasound
Provides a more
elaborate assessment
Many indications

ASSESSMENT BY ULTRASOUND

SONOGRAPHIC ESTIMATION OF GESTATIONAL AGE
MEAN SAC DIAMETER CROWN-RUMP LENGTH

SONOGRAPHIC ESTIMATION OF GESTATIONAL AGE
FL BPD & HC AC

Sampling techniques
Invasive methods
1. Amniocentesis
2. Chorionic villous
sampling
3. Percutaneous
cordocentesis
PRENATAL DIAGNOSIS OF CONGENITAL
ANOMALIES

Imaging techniques
Non-invasive
1. Obstetric ultrasound (for
anomaly scan)
2. Obstetric MRI
PRENATAL DIAGNOSIS OF CONGENITAL
ANOMALIES

PRINCIPLES OF TERATOLOGY
MECHANISMS & CAUSES OF BIRTH DEFECTS
Dr. Beda Olabu:

Teratology:
Study of birth defects
Teratogen:
An agent that causes congenital defects
Congenital anomaly:
A structural defect that someone is born with
DEFINITIONS OF TERMS

Malformation: A primary structural defect resulting
from a localized error of morphogenesis (intrinsic)
Disruption: Specific abnormality that results from
disruption of normal developmental processes.
Deformation: An alteration in shape / structure of
previously normally formed part (extrinsic)
Syndrome: A recognized pattern of malformations with
a given etiology
DEFINITIONS OF TERMS

1. General principles of teratology
2. Common mechanisms of birth defects
3. Common morphological defects
4. Causes of birth defects
5. Prenatal diagnosis of birth defects
LEARNING OUTCOMES

2-3% of live newborns have birth defects
Wide spectrum
Multiple defects can occur – syndromes
Shows geographical and ethnic differences
GENERAL PRINCIPLES OF CONGENITAL
ANOMALIES

 Failed induction to form an organ
 Persistence of an embryonic structure
 Inadequate/failed cellular migration
 Excessive migration of cells/tissues
 Developmental arrest
COMMON MECHANISMS OF CONGENITAL
ANOMALIES

 Incomplete/partial separation
 Defective septation of an organ/embryonic structure
 Failed/inadequate/excess tissue resorption
 Failure to fuse/merge
 Abnormal union/merging
COMMON MECHANISMS OF CONGENITAL
ANOMALIES

CONJOINED TWINS
Thoracopagus Craniopagus Omphalopagus

LIMB ANOMALIES
Club foot (CTEV) Polydactyly Syndactyly

CNS ANOMALIES
Spina bifida Hydrocephaly Encephalocele

CRANIOFACIAL DEFECTS
Cleft lip & palate Ankyloglossia Micrognathia

DEFECTS OF THE URINARY SYSTEM
Horse-shoe
kidney
Pelvic/ectopic
kidney
Extrophy of the
urinary bladder

ANOMALIES OF MALE GENITALIA
Hypospadia Ambiguous
genitalia
Cryptochirdism

ANOMALIES OF FEMALE GENITALIA
Mullerian duct anomalies Ambiguous genitalia

ABDOMINAL WALL DEFECTS
Prune-Belly Umbilical
hernia
Gastroschisis

GASTROINTESTINAL ANOMALIES
Omphalocele Gut malrotation Merkel’s
diverticulum

GASTROINTESTINAL ANOMALIES
Congenital
pyloric stenosis
(Gut) atresia Aganglionic
megacolon

ANOMALIES OF THE RESPIRATORY SYSTEM
Tracheo-esophageal fistula Pulmonary agenesis

CARDIOVASCULAR DEFECTS
Ventricular
septal defect
Tetralogy of
Fallot
Coarctation of
the aorta

ANOMALIES OF THE SKIN
Albinism Vitiligo Ichthyosis

ANOMALIES OF THE BREAST
Amastia Inverted nipple Polymastia

Idiopathic - 50%
Genetic factors - 18%
Environmental factors - 7%
Multifactorial (genetic & environmental) - 25%
CAUSES OF CONGENITAL ANOMALIES

Mechanical factors
Chemicals/drugs
Physical factors
Maternal infections and diseases
ENVIRONMENTAL FACTORS

Critical period of
development
Genetic susceptibility
of the embryo
Dosage of the factor
ENVIRONMENTAL FACTORS

1. Death – abortion or miscarriage
2. Malformation
3. IUGR – intrauterine growth retardation
4. Functional defects in the newborn
5. Normal newborn
CONSEQUENCES OF EXPOSURE TO A TERATOGEN

CONSEQUENCES OF EXPOSURE TO A TERATOGEN

GENETIC FACTORS
Chromosomal defects Gene Mutations
Numerical
Trisomy 21
45X0
XXY
Trisomy 18
Trisomy 13
Structural Autosomal
OR
Sex-Linked
Dominant
OR
Recessive

AUTOSOMAL DOMINANT
Congenital aniridia Achondroplasia

AUTOSOMAL RECESSIVE
Phocomelia Albinism

X-LINKED RECESSIVE
Ichthyosis vulgaris Hemophilia

6 - BASIC EMBRYOLOGY SERIES.pdf

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