Week 1

Question 1

What two parts make up the blastocyst?

Answer 1

trophoblast and inner cell mass

Question 2

What is the trophoblast and what does it give rise to?

Answer 2

Outer epithelial layer of the blastocyst which give rise to extraembryonic structures like placenta.

Question 3

What is the inner cell mass and what does it give rise to?

Answer 3

Embyronic stem cells of the blastocyst which give rise to the embryo.

Question 4

Which part of the blastocyst differentiates?

Answer 4

Inner cell mass

Question 5

What are the layers the inner cell mass splits into and what is in the middle of those layers?

Answer 5

The ICM splits into the epiblast and the hypoblast.

The middle of these 2 layers forms the embrypnic disc.

Question 6

Which part of the late blastocyst give rise to the embryo?

Answer 6

Only the embryonic disc

Question 7

What does the epiblast become?

Answer 7

Give rise to the 3 primary germ layers, primitive streak and distinct tissue in adults.

Question 8

What does the hypoblast become?

Answer 8

Yolk sac

Question 9

What is the bilaminar disc?

Answer 9

Refers to the embryonic disc.

Question 10

How does the primitive streak form and what is so important about it?

Answer 10

• On the upper surface (caudal end) of the bilaminar disc, a line of thickened cell appears (primitive streak).
• It defines the major body axis of the embryo.

Question 11

What does gastrulation involve?

Answer 11

Process whereby the bilaminar embryonic disc undergoes reorganisation to form a trilaminar disc.

Question 12

How is the primitive node and primitive groove formed?

Answer 12

• At the cranial end of the embryonic disc, the primitive streak expands to create the primitive node (circular depression)
• The depression continues along the midline of epiblast towards the caudal end of the primitive streak forming a primitive groove. (invagination of primitive streak)

Question 13

How is the trilaminar embryonic disc formed? (3)

Answer 13

• First, cells of the epiblast migrate medially and through primitive groove into hypoblast (displacing them- they become part of the yolk sac instead) to form embryonic endoderm (MET process).
• Later cells move into the space btw epiblast and endoderm to become embryonic mesoderm.
• Cells left in the epiblast become embryonic ectoderm.

Question 14

What is the primitive node and what is its importance?

Answer 14

• Fluid filled groove (cells at the bottom have cilia which rotate in same direction)
• Important for setting up left-right symmetry.

Question 15

What are th 3 hypotheses for breaking symmetry?

Answer 15

• Morphogen hypothesis
• Nodal vesicular parcel hypothesis
• Two cilia hypothesis

Question 16

Explain the morphogen hypothesis. (2)

Answer 16

• Growth factors/molecules are secreted into the fluid and are pushed to the left.
• They bind to receptors on the cells on the left and activate signal transduction pathways telling them they are on the left side.

Question 17

Explain the nodal vesicular parcel hypothesis.

Answer 17

• Similar to morphogen hypothesis but molecules are in vesicles.

Question 18

Explain the two cilia hypothesis. (3)

Answer 18

• There are 2 types of cilia (ones at the ring don’t rotate, ones at the bottom rotate)
• Rotating node push fluid from right to left causing left cilia to bend to the left which activates signal transduction to let it know its on the left.
• No fluid bending right nodes so it knows its on the right.

Question 19

How does the notochord form? (4)

Answer 19

• Formed through migration of cells through the primitive node (mesodermal).
• This forms a hollow tube which extends towards the cranial end of the embryo and form cartilage structure in the middle of embryonic disc.
• While primitive streak regresses and lengthens towards the caudal end.
• The hollow tube fuses with the endoderm to form the notochordal plate which eventually come together formaing the notochord.

Question 20

What is the importance of neural tube?

Answer 20

• Important for induction of neural tube (neuralation).

Question 21

How does the neural plate form? (3)

Answer 21

• Induced by notochord.
• Ectodermal cells differentiate into thick plate of pseudostratified, columnar neuroepithelial cells (neuroectoderm).
• It resides btw the cranial end of embryo and the primitive node.

Question 22

What is neurulation?

Answer 22

Process of neural plate becoming neural tube.

Question 23

How does the neural tube form? (2)

Answer 23

• Notochord give signals to cells in ectoderm to start thickening (neural plate) and invaginating to form a neural groove.
• The neural fold on either side of the neural grove progress towards each other and fuse.

Question 24

What is the neural crest and what do they become? (3)

Answer 24

• Particular group of cells which reside at the peaks of the neural folds.
• They form a layer over the top of the neural tube.
• These cells develop into most of the peripheral nervous system.

Question 25

What does the neural tube give rise to?

Answer 25

The central nervous system

Question 26

Which germ layer gives rise to the epidermis?

Answer 26

Embryonic ectoderm

Question 27

What other cells are in the epidermis?

Answer 27

Melanocytes and langerhans cells

Question 28

Which germ layer gives rise to the dermis?

Answer 28

Mesoderm (except face: neural crest)

Question 29

What is the embryo like at the end of 3rd week?

Answer 29

Flat, ovoid, trilaminar disc

Question 30

When does body folding occur and what happens? (6)

Answer 30

• 4th week
• Embryo grows rapidly (the longitudinal end grows slightly faster than the transverse/upper layer grows faster than lower layer causing disc to bend).
• Differential growth of various tissues
• Embryonic disc and amnion: high growth rate
• Yolk sac: almost no growth
• Developing notochord, neural tube and somites stiffen dorsal axis

Question 31

When does yolk sac disappear?

Answer 31

When placenta forms

Question 32

What 3 parts is the mesoderm divided into?

Answer 32

• Paraxial
• Intermediate
• Lateral

Question 33

What does the paraxial mesoderm become? (2)

Answer 33

• dermis of skin, axial skeleton, axial limb muscles

- forms the somites in the trunk region which will produce muscle, bone and dermis

Question 34

What does the intermediate mesoderm become?

Answer 34

• Urogenital system

Question 35

What does the lateral mesoderm become? (5)

Answer 35

• Somatic (parietal) and splanchnic (visceral) mesoderms
• Ventro-lateral body wall (connective tissue not muscle) ~SO
• heart and vasculature ~SP
• wall of gut ~SP
• bones of the limbs (not the axial skeleton bones) ~SO

Question 36

What does somitogenesis involve? (3)

Answer 36

• Somites forming regularly from below where the head forms through MET
• Somites reorganises into epithelial dermamyotome and mesenchymal sclerotome
• Forms dermatome (dermis), myotome (muscle) and sclerotome (skeleton)

Question 37

What makes up the urogenital system?

Answer 37

• kidneys
• gonads
• respective duct glands

Question 38

What makes up the mullerian duct?

Answer 38

• oviduct, uterus, upper vagina

Question 39

What makes up the wolfian duct?

Answer 39

• epididymis, vas deferens, seminal vesicle

Question 40

What does SRY gene do? (3)

Answer 40

• Drives genital ridge to develop into testis, which produce:
• AMH: degeneration of mullerian duct
• Testosterone: wolffian duct develops

Question 41

What happens if AMH is mutated?

Answer 41

Leads to both male and female reproductive tract.

Question 42

What are 2 parts involved in development of the cardiovascular system?

Answer 42

• Vasulogenesis: assembly of blood vessel from mesodermally derived cells. Requires recruitment of mesodermal progenitors to the endothelial cell lineage and organisation of their progeny into microvessels (occurs only during embryogenesis).
• Angiogenesis: blood vessle formation from pre-existing vasculature. Organisation into a precise spatial pattern within a particular tissue (occurs during embryogenesis and in adults).