Embryology 3 - 8 Weeks

Front 1

Fertilisation:
Where?
What changes must Spermatozoa undergo?

Back 1

Ampullary region of the uterine tube.
Capacitation and Acrosome reaction

Front 2

Fertilisation:
Phase 1

Back 2

Penetration of the Corona Radiata.
Sperm must have undergone capacitation (removal of glycoprotein coat)

Front 3

Fertilisation:
Phase 2

Back 3

Penetration of the Zona Pellucida.
Mediated by the ligand ZP3.
Requires acrosome reaction.
When sperm comes into contact with the oocyte PM release of cortical granules.

Front 4

Fertilisation:
Phase 3

Back 4

Fusion of the Oocyte and Sperm Cell Membranes.
1. Resumption of the second meiotic division.
2. Metabolic activation of the egg.

Front 5

Blastocyst Formation:

Back 5

Inner cell mass - embryoblast - becomes embryo proper.
Outer cell mass - trophoblast - becomes placenta
End of first week.

Front 6

Uterus at time of Implantation.
Think about
Its make up, phase of the menstrual cycle

Back 6

Wall of Uterus:
1) Endometrium- mucosal lining
2) Myometrium - thick layer of smooth muscle
3)Perimetrium - peritoneal covering of the outside wall.
Mucosa in secretory phase.
Endometrium:
Compact layer, spongy layer, and thin basal layer.

Front 7

Second Week of Development:
Day 8 and 9

Back 7

Trophoblast two layers:
1) inner layer - cytotrophoblast
2) outer layer - syncytiotrophoblast
Embryoblast two layers:
1) adjacent to amniotic cavity - epiblast layer.
2) adjacent to blastocyst cavity - hypoblast
Exocoelomic Membrane lines the primative yolk sac.

Front 8

Second Week of Development:
Day 11, 12 and 13

Back 8

Blastocyst completely enveloped in the endometrium. Syncitiotrophoblasts invade into maternal arterioles - Establishment of uteroplacental circulation.
Extra-embryonic mesoderm forms the boundary of the extraembryonic cavity.
Secondary yolk sac formed from hypoblast layer.
Connecting stalk- will become ubilicus.

Front 9

Third Week of Development:
Gastrulation

Back 9

Formation of Ectoderm, Mesoderm and Ectoderm.
1) Privative streak on epiblast.
2)Cells of the epiblast migrate towards the primative streak and invaginate.
3) Displacement of the hypoblast leads to formation of the endoderm.
4) Cells betwen the epiblast and the endoderm become the mesoderm.
5) Cells remaining in the epiblast become the ectoderm.

Front 10

Third Week of Development:
Formation of the Notochord

Back 10

Prenotochordal cells invaginate into the primative node to form the prechordal plate.
Cells of the notochord detach from the endoderm and form the definitive notochord.

Front 11

Third Week of Development: Growth of the Embryonic Disc

Back 11

Gradually elongates, with broad cephalic and narrow caudal end.
Migration of cells from primative streak to cephalic region.

Front 12

Third Week of Development: Further Development of the Trophoblast.

Back 12

Primary Villi.
Mesodermal cells penetrate primary villi to become secondary villi.
Mesodermal cells differentiate into blood vessels - Tertiary Villus.

Front 13

3rd to 8th Weeks of Development:
Derivatives of the Ectodermal Germ Layer.

Back 13

Neuroectoderm forms neural plate > neural folds and neural grooves > neural tube with anteriori and posterior neuropores.
Neural crest cells - become sensory ganglia, sympathetic and enteric neurons, schwann cells and cells of adrenal medulla.

Front 14

Neural Tube defects

Back 14

Neural tube fails to form in cranial region = anencephaly.
Neural tube fails to form anywhere from cervical region caudally = spina bifida.
70% of defects prevent woth 400ug of folic acid beginning 3 months before pregnancy.

Front 15

3rd to 8th Weeks of Development:
Derivatives of the Mesodermal Germ Layer

Back 15

Cells close to the midline proliferate and formt he paraxial mesoderm.
Lateral becomes the lateral plate, which is divided into:
1) Somatic/parietal mesoderm layer.
2) Splanchnic or visceral mesoderm layer.
Intraembryonic cavity forms, lined with intermediate mesoderm.

Front 16

3rd to 8th Weeks of Development:
Praxial Mesoderm

Back 16

Organises into somitomeres.
4 occipital
8 cervical
12 thoracic
5 lumbar
8-10 coccygeal pairs. first occipital and last 5-7 coccygeal disappear, the rest form the axial skeleton.
Differentiate into:
Sclerotome - vertebrae and ribs
Dorsomedial and Ventrolateral edges- dermatome.
dermomyotome forms beneath dermotome.

Front 17

3rd to 8th Weeks of Development:
Intermediate Mesoderm

Back 17

Differentiates into urogenital structures.

Front 18

3rd to 8th Weeks of Development:
Lateral Plate Mesoderm

Back 18

-Parietal - forms lateral body wall folds/ line the peritoneal, pleural and pericardial cavities
-Visceral- forms the walls of the gut tube.

Front 19

3rd to 8th Weeks of Development:
Blood and Blood Vessels.

Back 19

-Arise from mesoderm - hemangioblasts
-hematopoietic stem cells are derived from mesoderm surrounding the aorta.

Front 20

3rd to 8th Weeks of Development:
Derivatives of teh Endodermal Germ Layer.

Back 20

-Covers the ventral surface of fthe embryo and forms the roof of the yolk sac.
-Main site of development of the gastrointestinal tract.
-Foregut, midgut and hindgut.
-Midgut communicates to the yolk sac via the vitalline duct.