Embryology Introduction

Question 1

When is the pre-embryonic phase?

Answer 1

0-3 weeks

Question 2

When is the embryonic phase?

Answer 2

4-8 weeks

Question 3

When is the foetal phase?

Answer 3

9-40 weeks

Question 4

How are the gametes sperm and ovum produced?

Answer 4

Spermatogonium and oogonium due to meiosis

Question 5

Describe fertilisation

Answer 5

Several sperm surrounds ovum, only one penetrates - (pro) nucleus of the sperm enters and fuses with the (pro) nucleus of the ovum to give diploid cell - Zygote

Question 6

What is a summary of week 1 of pre-embryonic phase?

Answer 6

Zygote is formed and divides to form a blastocyst
Moves through uterine tube and reached uterine cavity

Question 7

What is the first cell of the body?

Answer 7

Zygote

Question 8

How is morula formed?

Answer 8

A solid ball of cell formed by mitosis of cells from zygote

Question 9

Describe a zygote

Answer 9

First cell in the body - 23 chromosomes of mum and 23 of dad
Mitochondria and cell organelle from mum

Question 10

Who are mitochondrial diseases inherited from?

Answer 10

Inherited from the mother

Question 11

What is the blastocystic cavity?

Answer 11

Cavity develops as morula increases with number of cells - nutrition to central core starts becoming difficult

Question 12

Describe a blastocyst

Answer 12

Has blastocystic cavity
Cells accumulate at one end to form an inner cell mass
Outer layer of cells is called the throphoblast

Question 13

Describe timing of zygote to blastocyst

Answer 13

Ovum released from ovary
Fertilisation in fallopian tube
Zygote
Then after 3 days morula
By day 5 morula reached inside of uterus cavity an becomes blastocyst

Question 14

What is lining the uterine tube?

Answer 14

Cilia

Question 15

How could an ectopic pregnancy occur?

Answer 15

If cilia function is abnormal

Question 16

What is the summary of week 2 of pre-embryonic phase?

Answer 16

Implantation occurs in the uterine endometrial layer and placenta begins to develop
Cells that later form embryo form a bilaminar disc
Sacs, membranes and cord to nourish the human conceptus start to form

Question 17

Describe trophoblast forming chorion?

Answer 17

Trophoblast divides to form 2 layers - chorion
Develops finger like processes called chorionic villi

Question 18

What does a chorion do?

Answer 18

Implantation process - chorionic villi burry into endometrium
Forms part of placenta in due course
Secretes human chorionic gonadotropin (HCG) used to detect pregnancy

Question 19

When does implantation begin?

Answer 19

At 7 days blastocyst begins to burrow into uterine wall and chorion plays important role in burrowing

Question 20

What is the decidua basalis?

Answer 20

Part of the endometrium deep to the implanted conceptus

Question 21

Describe endometrium after implantation has occurred?

Answer 21

Has myometrium, endometrium and decidua basalis (with maternal blood vessels)
NCG secreted by chorion to help maintain decidua
Maternal blood levels of HCG increases at 12 weeks gestation

Question 22

What happens to the inner cell mass of blastocyst?

Answer 22

Cells of inner cell mass form a 2 layered flat disc called a bilaminar disc and 2 cavities begin to form

Question 23

What are the cavities which from from bilaminar disc?

Answer 23

Amniotic cavity with epiblast
Yolk sac with hypoblast

Question 24

What are the main functions of the placenta?

Answer 24

Foetal nutrition
Transport of waste and gases
Immune etc

Question 25

Describe the foetal part and surface of the placenta

Answer 25

Smooth with foetal blood vessels and end of umbilical cord

Question 26

Describe the maternal part of the placenta

Answer 26

decidua basalis of endometrium is rough and has maternal blood vessels

Question 27

When does placenta mature?

Answer 27

18-20 weeks

Question 28

What are the two types of twins/multiple births?

Answer 28

Fraternal/ dizygotic Identical/ monozygotic

Question 29

What is a summary of week 3 of pre-embryonic phase?

Answer 29

Formation of the germ layers - gastrulation Formation of the neural tube - neurulation Development of somites Early development of cardiovascular system

Question 30

What is the primitive streak?

Answer 30

Formed in the midline of the epiblast by dipping in of cells - invagination Once forms then axis of the embryo is formed

Question 31

Describe gastrulation

Answer 31

Formation of 3 germ layers Epiblast cells migrate to lie in between epiblast and hypoblast layers Cells then displace hypoblast and forms 3 germ layers Trilaminar disc is formed

Question 32

What are the 3 layers formed making the trilaminar disc?

Answer 32

Ectoderm Mesoderm Endoderm

Question 33

What does each germ layer form?

Answer 33

Ectoderm - epidermis of skin and nerves Mesoderm - heart muscle, bones and connective tissue Endoderm - respiratory system and gut

Question 34

Describe the process of neurulation

Answer 34

Neural tube formation Notochord formation - cells sink down from primitive streak to form solid tube then notochord Then a neural plate in the ectoderm which sinks down to form neural tube and notochord induces ectodermal cells in midline to from a neural tube

Question 35

What is the effect of neural tube on the mesoderm?

Answer 35

Mesoderm thickens and separates into 3 parts and lateral plate mesoderm splits

Question 36

What are the 3 parts the mesoderm splits into called?

Answer 36

Paraxial mesoderm Intermediate plate mesoderm Lateral plate mesoderm

Question 37

Describe formation of somites?

Answer 37

Paraxial mesoderm forms somite formation - 43 pairs of somites

Question 38

What are the names of the 3 divisions of the somite?

Answer 38

Dermatome Myotome Sclerotome

Question 39

What does each division of somite develop into?

Answer 39

Dermatome - dermis of skin Myotome - muscles Sclerosis - bones including the vertebrae

Question 40

When does the heart start to beat?

Answer 40

Days 24

Question 41

What does the intermediate plate mesoderm form?

Answer 41

Urogenital system - kidneys and repro.

Question 42

What does lateral plate mesoderm form?

Answer 42

Body cavity and coverings

Question 43

What happens during the embryonic/ organogenetic period?

Answer 43

Folding into a tube - lateral folds Neural tube forms forebrain, hindbrain, spinal cord Gut formation Limb buds from Neck development

Question 44

What is teratology?

Answer 44

Study of when things go wrong during development

Question 45

What are teratogens?

Answer 45

Environmental factors that cause abnormal development

Question 46

How can you diagnose malformations prenatally?

Answer 46

Blood - AFP US scan at 12 weeks Invasive tests - chorionic villus sampling and amniocentesis

Question 47

How can you diagnose malformation postnatally?

Answer 47

Hip stability Testes Fingers and toes Hearing