1. Andrea Heinzlmann Embryology Course 2018
GASTRULATION
Andrea Heinzlmann
Embryology Course
2018

2. GASTRULATION
1. the undifferentiated blastomeres move in small masses to form sheets of cells
2. these cells differentiate into three germ layers- ectoderm, mesoderm and endoderm - these are called primary germ layers 3. these movements are called morphogenetic movements 4. the over all event is called gastrulation

3. GASTRULATION GASTRULATION:
is a process by wich the bilaminar embryonic disc is converted into a trilaminar embryonic disc
involves the movement of prospective organ forming areas from the blastodermic vesicle to their definitive positions in the embryo and their reorganisation into three primary layers

4. GASTRULATION These primary germ layers give rise to: 1. Ectoderm
2. Endoderm
3. Mesoderm

5. GASTRULATION Ectoderm forms: the outermost layer differentiates into:
1. skin
2. brain
3. spinal cord
4. nerves

6. GASTRULATION 2. Endoderm forms: the innermost layer gives rise to:
the digestive system
the respiratory systems
urinary bladder
middle part of the ear

7. GASTRULATION Mesoderm forms: the middle layer differentiates into:
1. notochord
2. muscles
3. heart
4. blood vessels
5. kidneys
6. gonads

8. GASTRULATION
GASTRULATION:
is the biginning of MORPHOGENESIS

9. GASTRULATION MORPHOGENESIS:
development of the form, structures of various organs and body parts
begins with the formation of the PRIMITIVE STREAK NB
Primitive groove Primitive pit Primitive node Oropharyngeal membrane Cardial plate Sectional edge of amniotic membrane Mesoderm Endoderm Future cloacal membrane primitive streak

10. GASTRULATION
Dorsal view of the primitive  streak at around the 17th day
Dorsal view of the primitive  streak at around the 19th day
Dorsal view of the primitive streak at around the 23rd day
Dorsal view of the primitive streak
at around the 25th day
1 2 3
Primitive streak Prechordal plate Primitive node
4 5 6
Neural plate Cloacal membrane Chordal process
1 2 3
Primitive streak Primitive node Neural tube
4 5 6
Cloacal membrane Prechordal plate Chordal process

11. GASTRULATION PRIMITIVE STREAK:
at the biginning og the 5th weekthe primitive streak (thickened linear band of epiblast) appears caudally in the median plane of the dorsal aspect of the embryonic disc
the primitive streak elongates by the addition of cells to its caudal end
the cranial ends of the primitive streak proliferates to form the PRIMITIVE NODE
A PRIMITIVE GROOVE develops in the primitive streak ending in the PRIMITIVE PIT (depression in the primitive node)
cells leave the the deep surface of primitive streak to form MESOBLAST (a loose connective network of embryonic connective tissue known as mesenchyme – which forms the supporting tissues of the embryo) NB
Primitive groove Primitive pit Primitive node Oropharyngeal membrane Cardial plate Sectional edge of amniotic membrane Mesoderm Endoderm Future cloacal membrane primitive streak
Primitive groove Epiblast Extraembryonic mesoblast Definitive endoblast Invading epiblastic cells forming  the intraembryonic mesoblast Hypoblast

12. GASTRULATION MESENCHYME:
mesenchymal cells have the potential to proliferate and diferentiate into:
fibroblasts
chondroblasts
osteoblasts

13. GASTRULATION
6. epiblast cells migrate through the primitive groove to become ENDODREM and MESODERM 7. the primitive streak actively forms mesoderm till the early part of the 4th week – then its production slows down – the primitive streak diminishes in size – becomes an insignificant structure in the sacrococcygeal region of the embryo NB
Primitive groove Primitive pit Primitive node Oropharyngeal membrane Cardial plate Sectional edge of amniotic membrane Mesoderm Endoderm Future cloacal membrane primitive streak

14. NOTOCHORDAL PROCESS AND NOTOCHORD
some mesenchymal cells migrate cranially from the primitive node and pit forming the NOTOCHORDAL PROCESS
the notochordal process acquires a lumen, the NOTOCHORDAL CANAL
the notochordal process grows cranially between the ectoderm and endoderm reaching the PRECHORDAL PLATE
The red arrow shows schematically the migration direction of the epiblast cells coming from the primitive node to form the notochordal process and later the notochord

15. NOTOCHORDAL PROCESS AND NOTOCHORD
The chordal process at  roughly the 21rst day (Stage 7)
 The chordal process at  roughly the 19th day (Stage 7
The chordal process at  roughly the 19th day (Stage 7)
 The chordal process at roughly the 21rst day (Stage 7)
1 3
Chordal process Embryonic endoblast
Chordal process Primitive node Embryonic endoblast Amniotic cavity
5 6 7
Body stalk Extraembryonic mesoblast Allantois
Amniotic cavity Body stalk Extraembryonic mesoblast Allantois
The chordal process at  roughly the 23rd day (Stage 8)
 The chordal process at  roughly the 23rd day (Stage 8)
Fused chordal process Prechordal plate Pharyngeal membrane Embryonic endoblast Amniotic cavity Neural groove
Canalis neurentericus Intraembryonic mesoblast Cloacal membrane Umbilical vesicle  Allantois

16. NOTOCHORDAL PROCESS AND NOTOCHORD
 The chordal process at  roughly the 25th day (Stage 9)
The chordal process at  roughly the 28th day (Stage)10)
 The chordal process at  roughly the 25th day (Stage 9)
 The chordal process at  roughly the 28th day (Stage 10)
Chordal process Embryonic endoderm Amniotic cavity Neural groove Body stalk Intraembryonic mesoblast Prechordal plate
Chordal process Embryonic endoblast Amniotic cavity Neural tube Body stalk Intraembryonic mesoblast Prechordal plate
Pharyngeal membrane Cloacal membrane Aortae  Umbilical veins Cardiogenic plate Allantois
Pharyngeal membrane Cloacal membrane Aortae Umbilical veins Cardiogenic plate Allantois

17. NOTOCHORDAL PROCESS AND NOTOCHORD
PRECHORDAL PLATE
is an important organizer of the head region
it is attached to the ovarlaying ectoderm – these fused layers, the ecto – and endoderm form the OROPHARYNGEAL MEMBRANE (located at the future site of the oral cavity)

18. NOTOCHORDAL PROCESS AND NOTOCHORD
4. some mesenchymal cells from the primitive streak and the notochordal process migrate laterally and cranially between the ecto – and endoderm reaching the margins of the embryonic disc 5. these mesenchymal cells are continous with the extraembryonic mesoderm – which covers the amnion and the umbilical vesicle NB
Primitive groove Primitive pit Primitive node Oropharyngeal membrane Cardial plate Sectional edge of amniotic membrane Mesoderm Endoderm Future cloacal membrane primitive streak

19. NOTOCHORDAL PROCESS AND NOTOCHORD
6. some mesenchymal cells from the primitive streak migrate cranially on each side of the notochordal process and around the prechordal plate – these cells meet each other to form the CARDIOGENIC MESODERM in the cardiogenic area (primordium of the heart)

20. NOTOCHORD NOTOCHORD: is a cellular rod
extends from the oropharyngeal membrane to the primitive node
Induces the overlying ectoderm to form the NEURAL PLATE (primordium of the central nervous system)
defines the axis of the embryo
serves as the basis for the development of the axial skeleton (bone, head, vertebral column)
indicates the future site of the vertebral bodies
Dorsal view of the primitive  streak at around the 17th day
Dorsal view of the primitive  streak at around the 19th day
Dorsal view of the primitive streak at around the 23rd day
Dorsal view of the primitive streak
at around the 25th day
1 2 3
Primitive streak Prechordal plate Primitive node
4 5 6
Neural plate Cloacal membrane Chordal process
1 2 3
Primitive streak Primitive node Neural tube
4 5 6
Cloacal membrane Prechordal plate Chordal process

21. VERTEBRAL COLUMN forms around the notochord
the notochord degenerates and disappears as the bodies of the vertebrae form
parts of the notochord persist as the NUCLEUS PULPOSUS of each intervertebral disc

22. NOTOCHORDAL PROCESS AND NOTOCHORD
CLOACAL MEMBRANE:
caudal to the primitive streak
Indicates the future site of the anus

23. NOTOCHORDAL PROCESS AND NOTOCHORD
ALLANTOIS:
appears approx. Day 16 as a small diverticulum
extends from the caudal wall of the umbilical vesicle into the connecting stalk
involved with early blood formation
associated with the urinary bladder

24. THANK YOU FOR YOUR ATTENTION!

25. BIBLIOGRAPHY
The developing human : clinically oriented embryology by Moore, Keith L
Langman's Medical Embryology Thomas W. Sadler
Essentials of Domestic Animal Embryology, 1st Edition, Poul Hyttel, Fred Sinowatz, Morten Vejlsted, Keith Betteridge

26. BIBLIOGRAPHY https://www.youtube.com/watch?v=dAOWQC-OBv0