1 - Prenatal Human Development

Question 1

What does the development of the oral facial region begin with?

Answer 1

Proliferative period:
lasts 2 weeks
in this time: -Fertilisation
-implantation
-embryonic disk formation

Question 2

Origin of Tissues

Answer 2

Begins w/fertilasation of egg/ovum:

• sperm contacts egg in distal part of uterine tube
• fertilisation occurs in upper 3rd of fallopian tube

After fertilisation - zygote is formed, in centre is DNA

Question 3

1st week of development - Preimplantation period

Answer 3

Fast cell division
Primary division - 2 new cells
followed by 4 cell stage, then 8 cell stage
in the next cell is the MORULA - ball of cells

Question 4

What is the morula?

Answer 4

A ball of cells formed in the uterine tube (13 - 32 cells)
it grows + migrates to the nucleus
Morula differentiated + cavitates into a blastocyst

Morulas cell’s undergoes 2 types of differentiation:
inner cell mass - growing on interior of blastocoel
Trophoblasts - growing on exterior

Question 5

Embryonic stage - weeks 2-8

Implantation stage

Answer 5

Blastocyst digests uterine endometrium = deeper penetration

Question 6

2nd week of development

Answer 6

Proliferation - blastocyst increases in size

• blastocyst cavity forms
• differentiation of inner cell mass begins
• This results in formation of bilaminar embryonic disk (2 cell layers)

2 cells layers: -Upper epiblast (ecto, meso + endoderm)
-Lower Hypoblast (extra embryonic mesoderm)
Above the disk:
-upper amniotic cavity
-Lower yolk sac

Trophoblast begins to differentiate - Forming a primitive placenta - embryo connects to it via a stalk

Question 7

Gastrulation Stage

Answer 7

Primitive Plaque - towards 14 days primitive ectoderm thickens
Primitive groove is formed:
-In cranial edge Primitive NODE is formed
-Both cells acquire mitotic activity = penetrating between ecoderm + endoderm

Question 8

3rd week of development

Answer 8

Bilaminar disk converts into trilaminar disk : Ectoderm
Endoderm
Formation of primitive streak is Mesoderm
critical for this formation

Epiblast cells migrate towards hypoblast via primitive streak

Mesoderm has twofold origin:

• Majority is derived from proliferation of ectoderm inwards
• Smaller part forms later, then the migrating cells of neural crests

Question 9

Late 3rd Week/Early 4th week

Answer 9

Embryo forms a simple bilaminar disk developed to obtain 3 different forms
there are 3 fateful moments:
Notochord formation - Organiser of the whole embryo

Pharyngeal Membrane formation - Beginning of primary mouth

Neural plate foemation - Incentive for formation of tissues, organs + organ systems

Question 10

4th week of development

Answer 10

Mesoderm forms either the : Notochord - formed by mesodermal cells of the primitive node
38 somite pairs - give rise to most skeletal structures of head,
neck + trunk
Ectoderm cells differentiate to form Neuroectoderm
-Then forms the neural plate - thickens w/proliferation
-This Invaginated centrally to form Neural Groove
-Groove deepens + is surrounded by 2 neural folds
-Neural crest cells develop from Neural Folds

Question 11

Foetal Period - 8th week until birth

Answer 11

Foetal period - Period of organ growth + psychological maturation
Includes development of these systems:
Nervous
Cardiovascular
Gastrointestinal
Muscular 
Vascular

Question 12

Neurulation

Answer 12

Formation of Brain + Spinal cord
Conversion of neural plate into Neural tube

1:Notochord induces formation of N.S
-signals ectoderm to form neural plate
plate folds upon itself to form neural tube

2: As neural tube forms - group of cells separate from neuroectoderm
- Cells migrate + differentiate within developing embryo - basis for nerve structures

In head region:
Neural crest cells differentiate to form Head CT
embryonic CT elsewhere is derived from mesenchyme