Embryology

Question 1

How soon after ovulation does fertilisation occur?

Answer 1

12-24 hours

Question 2

How soon after fertilisation does implantation into the endometrium occur?

Answer 2

5 and a half to 6 days

Question 3

What is a fertilised ovum termed?

Answer 3

A zygote

A diploid cell arises from the fusion of 2 haploid gametes

Question 4

What is a morula?

Answer 4

A solid mass of cells

Question 5

How many days following fertilisation does a blastocyst form?

Answer 5

6-10 days

Question 6

What is a blastocyst?

Answer 6

A hollow ball of cells (inner cell mass and trophoblast surrounding it)

Question 7

What are chorionic villi?

Answer 7

The exchanger between the placenta and the mother

Question 8

How many days following fertilisation does a morula form?

Answer 8

4-6 days

Question 9

How is the baby’s blood replenished?

Answer 9

• From the mother’s blood via the placenta
• Blood circulations do not mix, they are separated by a thin barrier
• The barrier is permeable to most molecules (e.g. drugs) but not cells

Question 10

What are the 2 layers of the bilaminar embryo?

Answer 10

• Epiblast layer

- Hypoblast layer

Question 11

Why is it risky for a Rh- mother to have a Rh+ baby?

Answer 11

Blood circulations may mix during birth, foetal blood enters maternal circulation. Mother raises antibodies against Rh+ blood. Can put mother’s future Rh+ babies at risk (haemolytic disease of the newborn)

Question 12

What does the epiblast give rise to?

Answer 12

The embryonic ectoderm, mesoderm and endoderm

Question 13

What does the hypoblast do?

Answer 13

Participates on formation of endoderm and extraembryonic mesoderm

Question 14

At approx 10-12 days, the implanted trophoblast contains an embryo which has 2 layers. What is this embryo termed and what are the 2 layers?

Answer 14

Bilaminar embryo

Layers are the epiblast and the hypoblast

Question 15

What are the 2 types of twins?

Answer 15

1. Identical/paternal: 1 sperm, 1 egg. Zygote splits in 2. Shared placenta. Same genetic makeup.
2. Fraternal: 2 sperm, 2 eggs . Separate placentas. Different genetic makeup.

Question 16

The bilaminar embryo is a disc. it has no orientation or axis. What does the embryo develop during gastrulation?

Answer 16

1. An axis
2. The 3 embryonic cell layers: ectoderm, endoderm, mesoderm
3. Formation of a primitive streak

Question 17

How is the mesoderm formed?

Answer 17

Ectodermal cells are induced to differentiate and migrate through the primitive streak towards the hypoblast. These new cells are the mesoderm

Question 18

How is the endoderm formed?

Answer 18

Interaction between mesoderm cells and the hypoblast forms the endoderm

Question 19

What is the embryo termed once is develops the 3 embryonic layers?

Answer 19

Trilaminar embryo

Question 20

What happens during weeks 3-8 of embryo development?

Answer 20

The major organs develop from the 3 basic germ cell layers. This is termed organogenesis

Question 21

What is organogenesis?

Answer 21

The major organs develop from the 3 basic germ cell layers between weeks 3-8 of embryo development

Question 22

What is one of the first organs to be formed?

Answer 22

The central nervous system (CNS)

Question 23

What are somites?

Answer 23

Early formation of muscle

Question 24

When does the neural tube form?

Answer 24

19-20 days

Question 25

What is the neural tube?

Answer 25

The forerunner of the central nervous system

Question 26

What is a common neural tube defect?

Answer 26

Spida bifida - the neural groove persists. Folding does not occur.

Question 27

What is the neural crest derived from?

Answer 27

From ectoderm but has the characteristics of mesenchyme.

Question 28

What is the neural crest also known as?

Answer 28

Ectomesenchyme

Question 29

What does ectomesenchyme give rise to?

Answer 29

Structures in the head

Question 30

What occurs ~25 days after ovulation?

Answer 30

Embryo folds around the yolk sac, and some important organs appear (heart, liver, lungs)

Question 31

When is an embryo termed a foetus?

Answer 31

Week 9

Question 32

What is the 4th embryonic layer?

Answer 32

Ectomesenchyme

Question 33

What are stem cells?

Answer 33

Unspecialised cells ('undifferentiated') that can develop into more specialised cells

Question 34

Describe the potential of embryonic stem cells (ESCs)

Answer 34

Totipotent - can differentiate into any cell type

Question 35

Where are embryonic stem cells found?

Answer 35

The inner cell mass (ICM)

Question 36

Describe the potential of cells in the 3 germ layers

Answer 36

Pluripotent (more restricted in potential) - capable of giving rise to several cell types

Question 37

Describe the potential of adult stem cells

Answer 37

Multipotent

Question 38

What are induced pluripotent stem cells (iPSCs)?

Answer 38

Reprogramming differentiated cells to their undifferentiated state

Question 39

When does tooth development start?

Answer 39

6 weeks

Question 40

All body tissues develop from 3 primary embryonic layers. What are they?

Answer 40

- Ectoderm: outer covering - Mesoderm: middle - Endoderm: inner lining

Question 41

Which tissues develop from the ectoderm?

Answer 41

Skin, mucous membranes of the mouth and anus, brain and spinal cord (CNS), tooth enamel

Question 42

Which tissues develop from the mesoderm?

Answer 42

Most connective tissues (dermis, tendons, cartilage, bone), muscle, blood vessels, kidney and urinary system, reproductive system, serous membranes

Question 43

Which tissues develop from the endoderm?

Answer 43

Alimentary canal (pharynx-rectum), respiratory system, parts of the urogenital system

Question 44

Which structures does the ectomesenchyme give rise to?

Answer 44

- Most of the PNS: sensory and autonomic nerves - Melanocytes in skin - Adrenal medulla - Most of the mesenchyme in the head (muscles, connective tissues, most dental and periodontal tissues - EXCEPT enamel)

Question 45

Which dental and periodontal tissues are derived from the ectomesenchyme?

Answer 45

Dentine, cementum, pulp, periodontal ligament, jaw, jaw bones

Question 46

When during foetal development is the period of greatest sensitivity?

Answer 46

Weeks 3-12 (the first trimester) | Most developmental defects occur during this period

Question 47

The effects of developmental abnormalities depend on what?

Answer 47

When the changes occur i.e. what stage of development

Question 48

What usually happens if developmental abnormalities occur during the first 2 weeks of pregnancy?

Answer 48

Spontaneous abortion

Question 49

When is the period of 'functional maturity'?

Answer 49

Weeks 13-39