Embryology

Question 1

Answer 1

Umbilical cord H&E
The umbilical cord connects the fetus to the placenta.

It is composed of:

Amniotic Epithelium - the exterior surface is covered by a simple cuboidal epithelium.
Blood Vessels - exchange oxygen, nutrients and waste products between the fetus and the placenta.
Two Umbilical Arteries - carry deoxygenated blood from the fetus to the placenta.
Single Umbilical Vein - delivers oxygenated blood from the placenta to the fetus. It has a thick layer of circular smooth muscle unlike adult veins.
Wharton’s Jelly - the blood vessels are embedded within a matrix of embryonic mucous connective tissue.
Mostly ground substance (primarily hyaluronic acid and chondroitin sulfate) with a low abundance of collagen or reticular fibers.
Mesenchymal Cells - near the remnant of the allantois are many stellate and spindle-like (fusiform) mesenchymal cells. However, spindle-shaped mesenchymal cells are indistinguishable from resting fibroblasts.

Question 2

Answer 2

Placenta H&E

The placenta develops from both fetal (chorion) and maternal (decidua basalis) tissues. This allows the exchange of nutrients and waste between the fetal and maternal circulations.

The placenta is composed of 15 to 20 regions called cotyledons.

Villi - projections of the fetal chorion that extend into lacunae in which maternal blood flows. Exchange between the two circulations occurs through the villus wall.
Simple Cuboidal Epithelium - consists of two types of cells:
Cytotrophoblasts - cuboidal cells with pale staining cytoplasm and euchromatic nuclei. They are absent by mid to late pregnancy so are not seen in this specimen.
Syncytiotrophoblasts - multinucleated cuboidal cells with microvilli.
Stroma - mesenchymal connective tissue forms the core of villi and contains fetal capillaries and venules.
Placental Arteries - develop from arteries in the endometrium to supply maternal blood to the lacunae.
Basal Plate (Stratum Basalis) - the part of the uterus to which chorionic villi are anchored. This specimen contains only a portion of the basal plate.
Decidual Cells - clusters of large round or oval cells.
Fetal and maternal blood do not mix in the placenta.

Question 3

Answer 3

Chicken embryo H&E

Trilaminar germ disc is formed by gastrulation
→ endoderm & mesoderm & ectoderm
Epiblast is source of all germ layers in embryo

1. amniotic cavity
   (1) embryoblast differentiate into 2 layers
   ① hypoblast layer
   ② epiblast layer
   (2) together, layers form flat disc
   ① at this time, small cavity appears within epiblast
   ② this cavity enlarges & becomes amniotic cavity
2. ectoderm
   (1) towards to dorsal surface
3. neural tube
   (1) brain develops from here
   (2) 3 vesicles
   ① Prosencephalon
   ② Mesencephalon
   ③ Rhombencephalon
   (3) Later 5 secondary vesicles form
   ① Telencephalon
   ② Diencephalon
   ③ Mesencephalon
   ④ Metencephalon
   ⑤ Myencephalon
4. notochord
   (1) develops from chorda dorsalis
   (2) involved in development of vertebrae
   (3) there’s intraembryonic mesoderm on both side of notochord
   (4) development
   ① Pre-notochordal cells
   A. invaginates in primitive node
   B. move until they reach prechordal plate
   C. become intercalated in hypoblast forming notochordal plate
   ② notochordal plate proliferates & detach from endoderm
   ③ notochordal plate form solid cord of cell, notochords
5. dorsal aorta
6. embryonic mesoderm
   (1) develops between ectoderm & endoderm
   (2) paraxial mesoderm
   ① next to neural tube
   ② formed by thickened mesoderm cells close to midline
   (3) intermediate mesoderm
   ① between paraxial mesoderm & intraembryonic coeloma
   ② development of urogenital system
   (4) lateral plate mesoderm:
   ① somatopleuric mesenchyme / somatic mesoderm layer
   A. somites arises to muscular & bony structures will be formed
   ② intraembryonic coelom / intraembryonic coelomic cavity
   A. cavity between somatic & splanchnic mesoderm layer
   ③ splanchnopleuric mesenchyma / splanchnic mesoderm layer
   A. embryonic origin of second heart field, GI tract, smooth muscle, blood vessels
   B. contribute organ development
   (A) pancreas, spleen, liver
7. endoderm
   (1) towards to ventral surface
   (2) covers anterior surface of intraembryonic coeloma
   (3) contributes development of gut tube
   ① GI system arises here
8. definitive yolk sac
9. Endoderm : Division of gut tube
   (1) As a result of craniocaudal & lateral folding of embryo,
   ① Endoderm derived from gastrulation is incorporated into embryo
   ② To form Primitive gut tube
   (2) In cephalic & caudal part of embryo, primitive gut forms foregut & hindgut
   (3) Middle part remaining connected to yolk sac by vitelline duct is midgut
10. Foregut derivatives
    (1) Esophagus
    (2) Stomach
    (3) Liver
    (4) Gallbladder
    (5) Pancreas
    (6) Upper duodenum
11. Midgut derivatives
    (1) Lower duodenum
    (2) Jejunum
    (3) Ileum
    (4) Cecum
    (5) Appendix
    (6) Ascending colon
    (7) Proximal 2/3 of transverse colon
12. Hindgut derivatives
    (1) Distal 1/3 of transverse colon
    (2) Descending colon
    (3) Sigmoid colon
    (4) Rectum
    (5) Upper anal canal