3. Embryology
Embryo
Greek word “Embryon”= unborn
The branch of biology that deals with the
formation, early growth, and development
of living organisms.
3
11. End result of first
week.
implanted
blastocyst
11
12. 2nd week (week of two’s)
Trophoblast differentiates into two layers:
cytotrophoblast and syncytiotrophoblast.
Embryoblast forms two layers:
epiblast and hypoblast. (Bilaminar)
Formation of 2 cavities:
amniotic and yolk sac cavities.
12
20. Which is the most important time
of human life?
"It is not birth, marriage, or death, but
gastrulation, which is truly the most
important time in your life."
Lewis Wolpert (1986)
20
22. Notochord formation
Days 16-18
Primitive node epiblast
cells invaginate and
migrate anteriorly
towards prochordal
plate – Notochordal
process.
Represents early
midline axis of the
embryo
22
23. Neurulation
Notochord induces the
overlying ectoderm to
thicken and
differentiate into
neural plate.
Neural groove
Neural tube
23
35. Development of Branchial arch
Neural crest cells migrate into the head
and neck region (4th
week)
35
36. The endodermal wall of the foregut is
separated from the surface ectoderm by a
layer of mesoderm.
Soon after, the mesoderm is arranged in
the form of six bars.
5th
arch soon degenerates.
36
37. Pharyngeal arch components
A typical pharyngeal
arch contains:
Cartilaginous rod
(skeleton of arch)
Muscular component
Nerve
Artery
37
38. Derivatives of branchial arches
Head and neck region of human beings
develop from these branchial arches.
Skeletal derivatives
Muscular derivatives
Nerves supply
Arterial supply
38
43. Arterial derivatives
Arch I : Part of the maxillary artery
Arch II : Hyoid and stapedial arteries
Arch III : Part of the carotid system
Arch IV : Left side-arch of aorta, Right
side-right subclavian artery
Arch VI : Pulmonary arteries
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45. Pharyngeal pouches
The endoderm of
the pharynx lines
the internal
aspects of
pharyngeal arches
and passes into
balloon like
diverticula called
pharyngeal
pouches
45
46. Pharyngeal Grooves or Clefts
These grooves
separate the
pharyngeal arches
externally
Out of four pairs
only first pair
persists as the
external acoustic
meatus.
46
47. Pharyngeal Membranes
The endoderm of the
pouches contacts the
ectoderm of the
pharyngeal grooves and
form the double layered
pharyngeal membranes.
First pharyngeal
membrane becomes the
tympanic membrane,
others obliterate 47