Week 7: General Emryology

Question 1

What is the human development time of a zygote?

Answer 1

-30 hours

Question 2

What is the human development timeline of a morula (ball of cells)?

Answer 2

-30 hours to 4 days

Question 3

What is the human development time of a Blastula?

Answer 3

Day 4 to Day 7

Question 4

What is the human development timeline of a gastrula?

Answer 4

Day 7 to Week 3

Question 5

What is the human development timeframe of an embryo?

Answer 5

Week 3 to Week 8

Question 6

what is the human development timeline of a foetus?

Answer 6

-Week 8 to week 40 (birth)

Question 7

What is rostral? (Nomenclature in embryology)

Answer 7

Head end (cranial or superior)

Question 8

What is caudal? (Nomenclature in embryology)

Answer 8

Tail end (inferior)

Question 9

What is dorsal? (Nomenclature in embryology)

Answer 9

Back (posterior)

Question 10

What is ventral? (Nomenclature in embryology)

Answer 10

Front (anterior)

Question 11

What is proximal (Nomenclature in embryology)?

Answer 11

Structures near the body centre

Question 12

What is distal? (Nomenclature in embryology)

Answer 12

Structures further from the body centre (e.g. hand is distal to elbow)

Question 13

What is the order of stages from fertilisation to implantation (days 1-6) ?

Answer 13

Fertilisation, cleavage, morula, blastocyst, implantation (of blastocyst into the endometrium of the uterus)

Question 14

What is fertilisation?

Answer 14

The process where a sperm fuses with an ovum creating a zygote which eventually leads to the development of an embryo

Question 15

What is the difference between diploid and haploid? §

Answer 15

Haploid single set of chromosomes (23), Dipliod has two sets of chromosomes (23 form each parent, 46 in total)

Question 16

What is a zygote cell?

Answer 16

When the ovum nucleus and sperm head nucleus (pronuclei) fuse intermixing their chromatin, to form a diploid nucleus= zygote cell

Question 17

What are the stages of Cleavage?

Answer 17

• zygote undergoes rapid mitotic divisions (cleavage)
• 2 cell stage on day 1
• 4 cell stage on day 2
• 16 cells by day 3, this is called the Morula (solid ball of cells)

Question 18

What is a blastocyst cell?

• what is the embryoblast?
• what is the trophoblast?

Answer 18

• day 4-5, morula enters uterine cavity
• at 32 cell stage, fluid enters morula, collects between blastomeres & reorganises them around the blastocyst cavity (fluid-filled space)
• When a blastocyst cavity has formed, the tissue is called a Blastocyst (which contains 100’s of cells), from which 2 cell populations arise;
  1. Embroyblast (inner cell mast)= will become the embryo
  2. Trophoplast (outer cell layer, is blastocyst wall) = will become outer chorionic sac (surrounds foetus, site of mother-foetus nutrient/waste exchange)

Question 19

What is implantation?

Answer 19

The ovum enters the fallopian tube and travels along towards the endometrium where implants (5-6 days after fertilisation)

Question 20

What is the zone pellucida?

Answer 20

Thick glycoprotein layer surrounding the oocyte plasma membrane, by day 5 the blastocyst hatches from the Zona Pellucida by enzymatically digesting a hole and squeezing through it. This shedding of ZP is essential to permit implantation into the endometrium

Question 21

What is the inner cell mass?

Answer 21

• In the blastocyst, the Inner Cell Mass (embryoblast) will ultimately form the embryo (orientates with endometrium)
• The ICM is the source of embryonic stem cells (capable of forming all embryonic cell types)

Question 22

What is the trophoblast??

Answer 22

Outer cell layer of blastocyst (forms placenta and adnexa)

Question 23

What happens on day 6 after fertilisation?

Answer 23

-blastocyst rolls (actually grows) until Inner Cell Mass lines up with endrometrium

Question 24

What are the two distinct layers that the trophoblast form into?

Answer 24

• Cytotrophoblast (inner layer eventually forms primary chronic villi)
• Syncytiotrophoblast (outer layer, invades endometrium so direct contact with maternal blood and main communicator between foetus and mother)

Question 25

What are the two distinct layers of the inner cell mast?

Answer 25

-Epiblast- forms 3 germ layers (ectoderm)
-Hypoblast - transient layer replaced by endoderm
Together epiblast + hypoblast form the Bilaminar embryonic disc

Question 26

What is gastrulation?

Answer 26

Formation of trilaminar embryo (3 layers) (week 3)

• Early phase in mammalian embryonic development where bilaminar embryonic disc (2 layers, hypo + epi)
• three layer structure called Gastrula, eventually will form embryo’s entire body organs and tissues

Question 27

What are the three layers of the Gastrula?

Answer 27

1. Ectoderm (external layer) : epidermis (skin), nervous system (PNS, CNS), retina, nose and ears, hair, nails
2. Mesoderm (middle layer) : dermis, bones, cartilage, connective tissue, cardiovascular/reproductive/lymphatic system, muscle (Striated smooth and cardiac), kidneys and spleen
3. Endoderm (internal layer):digestive system, liver, pancreas, inner layers of lungs

Question 28

What is primitive streak formation?

Answer 28

Forms 2 germ cell layers, endoderm and mesoderm, start to organise front, head, back, tail of embryo, left/right orientation (body axis)

• migrating epiblast cells
• embryo then starts folding