Embryology

Question 1

Why do we study embryology?

Answer 1

1) Allows development of a logical framework for understanding adult anatomy
2) Bridges the gap between basic and clinical science
3) Allows clinicians to advise patients on reproduction, birth defects, prenatal development, IVF and teratology etc.

Question 2

What is embryogenesis?

Answer 2

The formation and development of an embryo

Question 3

What are the phases of embryogenesis?

Answer 3

1) Gametogenesis
2) Fertilisation
3) Cleavage
4) Gastrulation
5) Formation of a body plan
6) Organogenesis

Question 4

What is gametogenesis?

Answer 4

The formation of gametes, consisting of mitosis and meiosis

Question 5

What is spermatogenesis?

Answer 5

The formation of male gametes

Question 6

When does spermatogenesis occur?

Answer 6

Starts during puberty and continues throughout life

Question 7

What is oogenesis?

Answer 7

The formation of female gametes

Question 8

When does oogenesis occur?

Answer 8

Begins in the foetus and ends at menopause

Question 9

What is fertilisation?

Answer 9

The fusion of male and female gametes to form a zygote

Question 10

What is cleavage?

Answer 10

A series of mitotic divisions which subdivide the fertilised egg into many smaller daughter cells called blastomeres

Question 11

What is gastrulation?

Answer 11

The phase where the single layered blastocyst is reorganised into a multi-layered structure, also known as formation of a body plan

Question 12

What are the three germ layers formed during gastrulation?

Answer 12

1) Endoderm
2) Mesoderm
3) Ectoderm

Question 13

What is organogenesis?

Answer 13

The formation of organs and organ systems due to tissues maturing and becoming functional

Question 14

What is nondisjunction?

Answer 14

The failure of homologous chromosomes to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei i.e. trisomy

Question 15

What is the terminology used to describe embryonic anatomy?

Answer 15

• Cranial and caudal

- Dorsal and ventral

Question 16

What are the major primary processes that occur during embryology?

Answer 16

Cell division, differentiation, cell attachment, apoptosis, induction and cell migration

Question 17

What is induction?

Answer 17

The ability of one cell type to cause another to differentiate (can be directly or at a distance)

Question 18

What are the major secondary processes that occur during embryology?

Answer 18

Axis formation/polarity and folding/rotation

Question 19

How is development of the embryo regulated?

Answer 19

Through genetic mechanisms and epigenetic mechanisms

Question 20

How do genetic mechanisms regulate embryonic development?

Answer 20

Gene expression is tightly regulated in time and space

Question 21

How do epigenetic mechanisms regulate embryonic development?

Answer 21

Allow preferential expression of either the maternal or paternal copy of a gene

Question 22

Where does fertilisation take place?

Answer 22

The ampulla of the uterine tubes

Question 23

What are the steps involved in fertilisation?

Answer 23

1) Sperm binds in a human specific interaction with the zona pellucida glycoprotein (ZP3)
2) Acrosomal enzymes released from sperm head to allow the sperm to digest its way into the egg
3) The egg and sperm plasma membranes fuse and sperm contents enter the egg
4) Sperm entry triggers completion of meiosis 2 and the release of cortical granules by the oocyte

Question 24

What is compaction?

Answer 24

Where the blastomeres confined within the zona pellucida maximise available space by coming into closer contact with each other and beginning to form cell junctions

Question 25

What are the different parts of the blastocyst?

Answer 25

Zona pellucida, trophoblast, blastocyst cavity and inner cell mass

Question 26

What is ectopic implantation?

Answer 26

Implantation of the embryo in a location outside the uterus, which is dangerous and potentially life-threatening

Question 27

What are the common sites for ectopic implantation?

Answer 27

• Ovaries
• Uterine tubes
• Peritoneum

Question 28

Describe the 6 steps in the process of gastrulation

Answer 28

1) A primitive streak appears in the midline at the caudal end of the epiblast
2) A primitive pit and node form at the end of the primitive streak
3) Epiblast cells move through the primitive streak betwee to form the three primary germ layers
4) Hypoblast cells are replaced by the definitive endoderm
5) Cells migrate through the primitive streak between the epiblast and the definitive endoderm
6) The two germ layers become three

Question 29

How are body axes established?

Answer 29

The presence of the primitive streak

Question 30

What major tissues does the ectoderm give rise to?

Answer 30

• Epidermis of the skin (hair, nails)

- Nervous system (brain, spinal chord and peripheral nerves)

Question 31

What major tissues does the mesoderm give rise to?

Answer 31

• Bones
• Skeletal (voluntary) muscles
• Urogenital systems (kidney, ureter and gonads)
• Cardiovascular system
• Smooth muscle

Question 32

What major tissues does the endoderm give rise to?

Answer 32

• Lining of the gut tube
• Lining of the respiratory tract
• Lining of the bladder and urethra

Question 33

What changes occur to the embryo during implantation?

Answer 33

1) Uteroplacental circulation forms as the syncytioblast extends and contacts the maternal blood supply
2) The amniotic cavity is present above the bilaminar embryonic disc and the definitive yolk sac below
3) The chorionic cavity develops and encircles the entire embryo

Question 34

Where does normal embryonic implantation occur?

Answer 34

The posterior or anterior uterine wall

Question 35

What does the trophoblast give rise to?

Answer 35

• Cytotrophoblast (inner layer)

- Syncytiotrophoblast (outer layer)

Question 36

What are the two cell layers of cavities?

Answer 36

1) Amniotic sac (epiblast)

2) yolk sac (hypoblast)