Embryology of the humans beings anathomy.ppt

STG 2021.pdf

1. Embryology
General
1Dr Mohammed Ali Yunus Khan

2. INTRODUCTION
Every life has its minimum life span....
For survival of species there must be a mechanism for
production of new individuals...
“REPRODUCTION”
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3. 3Dr Mohammed Ali Yunus Khan

4. Embryology:
“Science concerned with origin & development of human being
from fertilization of ovum to birth of an infant”
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5. Helps us understand human anatomy better
Helps us understand why some children are born with organs
that are abnormal
May help us prevent or treat such abnormalities
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6. Human reproduction involves fusion of germ cells/gametes
•Ovum (Female gamete)
•Sperm (Male gamete)
 ‘ like that of most animals’
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7. GAMETOGENESIS :
is the process of formation and development of specialized cells
gametes (oocytes or sperms)
•Gamete maturation in male is called spermatogenesis
•Gamete maturation in female is called oogenesis
During gametogenesis:
Chromosome number is reduced by half
Shape of cells is altered
“Sperm and Oocyte are highly specialized sex cells”
Each of these cells contains:
Half the number of chromosomes (haploid number) that are
present in somatic (body) cells
Number of chromosomes is reduced during meiosis (a special
type of cell division that occurs during gametogenesis)
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8. SPERMATOGENESIS
is the sequence of events by which spermatogonia are
transformed into mature sperms
Takes place in the walls of seminiferous tubules
This maturation process begins at puberty
Events during maturation process:
•Spermatogonia are transformed into primary spermatocytes
•Each primary spermatocyte undergoes a reduction division (1
st

meiotic division)—to form two haploid secondary spermatocytes
•Secondary spermatocytes undergo a second meiotic division to
form four haploid spermatids
•Spermatids are gradually transformed into four mature sperms
by a process known as spermiogenesis
“When spermiogenesis is complete,sperms enters seminiferous tubules”
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11. Spermiogenesis Spermatozoa
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14. Oogenesis:
is the sequence of events by which oogonia are transformed into
mature oocytes (takes place in cortex of ovary)
“Maturation of oocytes begins before birth and is completed after puberty”
Events:
Oogonia (primordial female sex cells) enlarge to form primary
oocytes before birth
?Primordial follicle = Primary oocyte surrounded by single layer
of flattened follicular (connective tissue) cells
•Primary oocyte enlarges during puberty
?Primary follicle = Flattened cells surrounding primary oocyte
becomes columnar
•Primary oocyte soon becomes surrounded by a covering of
amorphous acellular glycoprotein material,zona pellucida
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18. Usually one follicle matures each month and ovulation occurs
No primary oocytes form after birth
•Primary oocytes remain dormant in ovarian follicles until
puberty
•As a follicle matures, primary oocyte increases in size
•Shortly before ovulation,primary oocyte completes first
meiotic division (to give rise to a secondary oocyte and first polar
body)
Polar body is a small, nonfunctional cell (it receives very little
cytoplasm)
•At ovulation, nucleus of secondary oocyte begins second
meiotic division(progresses only to metaphase, where division is
arrested)
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22. Fertilization
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24. Fertilization refers to penetration of an ovum (egg) by a
spermatozoon (with subsequent union of their genetic material)
Usually takes place in Ampulla of uterine tube
Prior conditions for fertilization:
•Ovum must be present in uterine tube
•Large numbers of spermatozoa must be ejaculated in the vagina to ensure
fertilization
Facts:
Woman usually ovulates one ovum(secondary oocyte) a month (it
becomes incapable of undergoing fertilization after 24 hours)
Ovum is surrounded by:
oZona pellucida (a thin layer of protein and polysaccharides)
oCorona radiata (Layer of granulosa cells)
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26. Approximation of gametes:
Transport of sperms and ova in female genital tract
 to reach uterine tube (Ampulla)
Transport of spermatozoa (events)
•Semen deposited in vagina at coitus
•Prostaglandins of semen induces powerful contraction of
uterine muscle
•Coital reflex releases oxytocin from neurohypophysis
(accentuates contraction of non – gravid uterus)
•Vaccum created in uterine cavity (between successive
contractions)
•Allows aspiration of semen passively from vagina
”1% of sperms deposited in vagina enters cervix“
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27. •Movement of sperm from cervix to oviduct is primarily by
their own propulsion (they may be assisted by uterine fluid)
After reaching isthmus sperm become less motile and cease
their migration
At OVULATION, sperm again become motile (perhaps because
of chemoattractants produced by cumulus cells surrounding
oocyte) and swim to AMPULLA
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28. Transport of Oocyte (events)
Fimbriae of oviduct begin to sweep over the surface of ovary
(shortly before ovulation)
Tube itself begins to contract rhythmically
•Oocyte surrounded by some granulosa cells is carried into the
tube by: - sweeping movements of fimbriae
and - by motion of cilia on the epithelial lining
Once oocyte is in uterine tube, it is propelled by cilia
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30. Contact and fusion of gametes:
Out of 200 to 300 million sperms (emitted at single ejaculation)
300 to 500 sperms reach ovum

Three barriers protect female gametes before penetration by
fertilizing sperm:
Corona radiata
Zona pellucida
Vitelline membrane (of secondary oocyte)
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Corona radiata
Zona pellucida
Oocyte membrane

32. ”Prior to penetration spermatozoa undergo process of
CAPACITATION“
?Capacitation
Period of conditioning in female reproductive tract
Glycoprotein coat and seminal plasma proteins are removed
from plasma membrane that overlies acrosomal region of
spermatozoa
Only capacitated sperm can pass through corona cells
Dr Mohammed Ali Yunus Khan 32
Nucleus
Cell membrane
Acrosomal cap

33. Penetration of corona radiata
Liberation of Hyaluronidase from acrosomal cap helps to
disintegrate cells of corona radiata
Capacitated sperm pass freely through corona cells
Penetration of zona pellucida
•Sperm head binds to specific glycoprotein receptors – ZP3
•Acrosomal enzyme ACROSIN is released
•Acrosin (proteolytic enzyme) digests zona around sperm head
•Sperm head enters perivitelline space and contacts vitelline
membrane
This contact release lysosomal enzymes from cortical granules
lining plasma membrane of oocyte
These enzymes alters properties of zona pelucida – zona
reaction
Prevents polyspermy (inactivating receptors)
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35. Fusion of oocyte and sperm cell membranes
Adhesion (mediated in part by interaction of integrins on oocyte
and disintegrins on sperm)
Plasma membranes of sperm and Oocyte fuse
Head and tail of spermatozoon enters cytoplasm of oocyte
(plasma membrane is left behind on oocyte surface)
Further events.......
•Resumption of second meiotic division
•Nucleus of spermatozoon becomes swollen and forms male
pronucleus (tail detaches and degenerates)
•DNA of each pronuclei replicates
•Male and female pronuclei comes in close contact and lose their
nuclear envelops
•Chromosomes organize on spindle in preparation for mitotic
division
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Main results of fertilization:
Restoration of diploid number of chromosomes
Determination of sex (chromosomal)
Initiation of cleavage

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39. Developing Human
1
st
week to 3
rd
week
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Every individual spends 9 calendar months +/- 7days of its life within womb of its mother

41. Gestation period is subdivided into three stages
I.Germinal period (begins at fertilization)
1
st
to 3
rd
week of development
Includes:
Cleavage division of zygote
Formation of Morula
Blastocyst and its implantation
Differentiation of trophoblasts and chorion
Appearance of bilaminar and then trilaminar germ disc
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42. II.Embryonic period
Extends from 4
th
to 8
th
week
Characterised by:
Changes of shape and external appearance of embryo
Germ layers undergoes differentiation
Most of tissues and organs of body are formed
Period of teratogenicity (chances of congenital anomalies)
III.Foetal period
Extends from 3
rd
month up to termination of pregnancy
Characterised by:
Rapid growth of foetus
Complete development of placenta
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43. Pre implantation development
Cleavage division
Process of repeated segmentation of zygote within zona
pellucida in rapid succession
Gives rise to increasing number of small cells known as
BLASTOMERES
Stages:
a)2 cells stage
Two cells derived from 1
st
cleavage division of zygote are
unequal in size (Larger cell divides first)
b) 3 cell stage
c) 12 – 16 cell stage (mass is called MORULA )
All cells are apparently similar in size and shape
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46. As cleavage division continues:
Zygote gradually migrates from ampulla of uterine tube and
reaches uterine cavity (approximately 3 days after fertilization)
Transport of zygote is facilitated by Ciliary beats and
contraction of musculature of tube
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47. Formation of Blastocyst
Fluid from uterine lumen passes through zona pellucida and
outer cells of morula
Fluid appears in inter-cellular spaces between inner cell mass
and outer cell mass
Continuous accumulation of fluid converts morula into fluid
filled single cavity BLASTOCELE
Cells of outer cell mass forms wall of blastocyst (consists of
flattened cells = TROPHOBLAST)
Cells of inner cell mass known as EMBRYOBLAST ( attached
as a clump of cells to one pole of blastocyst)
Formation of blastocyst takes place between 4
th
and 5
th
day after
fertilization
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49. Implantation of blastocyst
Includes:
Dissolution of zona pellucida
Orientation and adhesion of blastocyst onto endometrium
Trophoblastic penetration into endometrium
Migration of blastocyst into endometrium
Spread and proliferation of trophoblast (which envelops and
specifically disrupts and invades maternal tissues)
Zona pellucida disappears at the end of 5
th
day of fertilization
(assisted by trypsin like enzyme)
oBlastocyst is hatched from zona
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50. Hatching of BLASTOCYST
Blastocyst
Zona pellucida
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51. Cytotrophoblast cells give rise to syncytiotrophoblast
?SYNCYTIOTROPHOBLAST = Multinucleated mass of cytoplasm
Syncytiotrophoblast secretes numerous hormones
It also secretes human chorionic gonadotrophin (hCG),
hCG can be detected in maternal urine from as early as 10
days after fertilization (forms the basis for tests for early pregnancy)
Flanges of syncytial trophoblast grow between cells of uterine
luminal epithelium towards underlying basal lamina
Implantation continues with erosion of maternal vascular
endothelium and glandular epithelium
Blastocyst occupies an uneven implantation cavity in stroma
This type of implantation is INTERSTITIAL
Implantation takes place on 6
th
or 7
th
day after fertilization
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55. Normal site of Implantation:
Usually blastocyst is attached to the junction of fundus and
posterior wall of body of uterus
Implantation anywhere in upper part of uterine cavity is
considered as normal
Abnormal Implantation:
Extra – uterine pregnancy (ectopic)
•Ovary
•Abdominal cavity
•Uterine tube ( may cause rupture of uterine tube endangering
life of mother)
Intra - uterine abnormal site
•Lower part of uterine cavity (overlapping internal os) Placenta
praevia
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56. Abnormal sites of implantation 56Dr Mohammed Ali Yunus Khan

57. Trophoblast differentiates into two layers:
•Cytotrophoblast - an inner layer of mononucleated cells
Syncytiotrophoblast - an outer multinucleated zone without
distinct cell boundaries
Embryoblast differentiates into two layers:
Hypoblast = a layer of small cuboidal cells adjacent to
blastocyst cavity
Epiblast = a layer of high columnar cells adjacent to amniotic
cavity
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59. Most characteristic event occurring during 3
rd
week of
gestation is gastrulation
? Gastrulation Process that establishes all three germ layers
(ectoderm, mesoderm, and endoderm) in the embryo
Gastrulation begins with formation of primitive streak on the
surface of epiblast
Primitive streak clearly visible as a narrow groove with slightly
bulging regions on either side in (15- to 16-day embryo)
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61. Epiblast cells arising from primitive streak replaces hypoblast
cells as = Embryonic endoderm
Some cells comes to lie between epiblast and endoderm to
form = Intra embryonic mesoderm
Remaining cells in epiblast forms Ectoderm
Cells in these layers will give rise to all of the tissues
and organs in the embryo
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63. Placenta
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64. ? Placenta
Organ that facilitates nutrient and gas exchange between
maternal and fetal compartments
Formed by two components :
Fetal component = Trophoblast & Extra embryonic mesoderm
Maternal component = Uterine endometrium
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65. Development of placenta
By beginning of 3
rd
week
Trophoblast is characterized by:
Primary villi (cytotrophoblastic core covered by a syncytial layer)
Later....
Mesodermal cells penetrate core of primary villi and grow
towards decidua
?Decidua
Endometrium after implantation is called decidua
Newly formed structure is known as a secondary villus
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67. By end of 3
rd
week
Mesodermal cells in the core of villus begin to differentiate
into blood cells and small blood vessels
The villus is now known as a tertiary villus or definitive
placental villus
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70. Further development.....
Cytotrophoblastic cells in the villi penetrate progressively into
overlying syncytium (until they reach maternal endometrium)
Forming a thin outer cytotrophoblast shell
Cytotrophoblastic shell gradually surrounds trophoblast
entirely
Attaches chorionic sac firmly to maternal endometrial tissue
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72. Types of Villi
Stem (Anchoring) villi
Villi that extend from chorionic plate to decidua basalis
(decidual basalis : part of endometrium where placenta will form)
Free (terminal) villi
Those villi that branch from sides of stem villi
(through which exchange of nutrients and other factors will occur)
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73. Placental membrane
In Placenta:
Maternal blood circulates through intervillous space
Fetal blood circulates through blood vessels in villi
Maternal and fetal blood do not mix with each other (they are
separated by a membrane)
oMembrane made up of layers of wall of villus
Layers...(from fetal side)
i.Endothelium of fetal blood vessels and its basement membrane
ii.Surrounding mesoderm
iii.Cytotrophoblast and its basement membrane
iv.Syncytiotrophoblast
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75. Functions Of Placenta
CO2
WATER
UREA
WASTE PRODUCTS
HORMONES
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76. Full term placenta:
Discoid in shape
15 – 25 cm in diameter
3 cm thick
500 – 600 g in weight
At birth it is torn from uterine surface
It is expelled from uterine cavity 30 minutes (appoximately)
after birth of child
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77. Two surfaces (when examined after expulsion)
Maternal surface
Slightly bulging areas called cotyledons (15 – 20 ) covered by
thin layer of decidua is recognizable
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78. Fetal surface
Smooth in appearance
Covered entirely by chorionic plate
Chorionic vessels converging towards umbilical cord is seen
Chorion in term is covered by amnion
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Twinning

81. ? Twinning
When a mother give birth to two young individuals in
single pregnancy
•Most primates (including man) are monovulatory
? Monovulatory
Shed a single ovum in each ovarian cycle
Birth of a single offspring is the rule
Twinning and multiple births are accidental and sporadic
Influenced by genetical and environmental factors
”Twinning occurs at frequency of about 1 in 80 births“
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82. Twinning may be Dizygotic (or) Monozygotic
Dizygotic twinning:
Two ova are discharged at same time in a single ovarian cycle
Ova are fertilized by two different sperms
Resulting twins are fraternal (unlike)
Twins may be of same or different sex
Possess separate placentae and separate chorionic sacs
”Most Frequent Form Of Twinning“
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83. Monozygotic twinning:
•Two embryos are derived from single ovum
Fertilized by a single sperm
Possesses:
Similar genetic constitution
Similar in appearance & structure
Belongs to same sex
TYPES:
Monozygotic Bichorionic
Monochorionic Biamniotic
Monochorionic Monoamniotic
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84. Monozygotic Bichorionic
During two cell stage of cleavage division
Blastomere cells (totipotent) develop into two separate
blastocyts
Implanted separately in uterine endometrium
Posseses:
Separate placentae
Separate chorionic sacs
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85. Inner cell mass
Amniotic cavity
Yolk sac
Monozygotic Bichorionic 85Dr Mohammed Ali Yunus Khan

86. Monochorionic Biamniotic
Innercell mass is separated completely into two equal parts
Each part develops into a separate embryo
Possesses:
Single placenta
Common chorionic sac
Separate amniotic sacs
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87. Inner cell mass
Blastocyst cavity
Common chorionic cavity
Common placenta
Monochorionic Biamniotic
Amniotic cavity
Amniotic cavity
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88. Monochorionic Monoamniotic
Two separate organising centres appear in disc (e.g., primitive
streak)
Differentiates into two separate embryos
Twin embryos lie within:
Common chorionic sac
Enveoped by:
oSingle amniotic membrane
Possesses:
One placenta
Two umbilical cords
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89. Blastocyst cavity
Amniotic cavity
Common chorionic cavity
Common chorionic cavity
Monochorionic Monoamniotic
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90. Twin defects
Conjoined twins
May be due to partial splitting of primitive node and primitive
streak
Thoracophagus
Pygopagus
Craniopagus
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91. Chang and Eng Bunkers
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92. 21 childrens
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