principles of embryology

Question 1

What can birth defects be caused by?

Answer 1

• genetic factors
• environmental factors
• multifactorial inheritance

Question 2

What are the categories of birth defects?

Answer 2

• malformations
• disruption
• deformation

Question 3

What is a malformation? Give examples

Answer 3

• intrinsically abnormal developmental process
• e.g chromosomal abnormalities (trisomy 18)

Question 4

What is disruption? Give example

Answer 4

• extrinsic interference of the normal development process
• e.g teratogenic drug

Question 5

What is deformation? Give examples

Answer 5

• abnormal form due to mechanical factors
• e.g clubfoot (equinovarus foot)

Question 6

When is the risk of birth defects highest?

Answer 6

around week 5

Question 7

What are the developmental periods within the pre-natal period?

Answer 7

• embryonic period (0 - 8 weeks)
• foetal period (9 - 40 weeks)

Question 8

What are the developmental periods within the post-natal period?

Answer 8

• neonatal (0 - 4 weeks)
• infancy (4 - 52 weeks)
• childhood ( 2 yrs - puberty)
• adolescence (11 yrs - 19)
• adulthood (19+ yrs)

Question 9

What are the 5 early events in embyrology?

Answer 9

1. gametogenesis
2. fertilisation
3. cleavage
4. gastrulation
5. formation of the body plan

Question 10

What is a gamete?

Answer 10

cell with 23 chromosomes (haploid)

Question 11

What is gametogenesis?

Answer 11

the formation of gametes

Question 12

What is spermatogenesis?

Answer 12

the formation of male gametes

Question 13

When does spermatogenesis start and how does it vary through time?

Answer 13

• starts at puberty
  continues through life
• decreases with age

Question 14

How long does each cycle take in spermatogenesis?

Answer 14

around 64 days

Question 15

What is the typical production rate of sperm in spermatogenesis?

Answer 15

6.5 million sperm per gram of testicular tissue a day

Question 16

What is oogenesis?

Answer 16

the formation of female gametes

Question 17

When does oogenesis start and end?

Answer 17

• starts in utero
• ends at menopause

Question 18

What happens by week 28-30 in utero (oogenesis)?

Answer 18

primary oocytes begin meiosis but arrest in development until puberty

Question 19

When is the reproductive lifespan determined in females?

Answer 19

in fetal life

Question 20

What is fertilisation? Where does it occur?

Answer 20

• fusion of sperm and oocyte
• occurs in the ampulla of the uterine tube

Question 21

What does fertilisation form?

Answer 21

a zygote

Question 22

Describe a zygote

Answer 22

• diploid
• single cell embryo
• sex determination

Question 23

What does fertilisation stimulate oocytes to do?

Answer 23

complete meiosis 2

Question 24

What is cleavage?

Answer 24

repeated mitotic divisions of the zygote into blastomeres and then a blastocyte

Question 25

How is the morula formed?

Answer 25

- rapid mitotic cell division with no increase in size - 16+ cell forms morula

Question 26

What is the zona pellucida?

Answer 26

gelatinous matrix around zygote, keeps cell nice and tight (keeps us safe)

Question 27

What is the trophoblast?

Answer 27

after many divisions, the outer layer in touch with the zona pellucida gets called the trophoblast

Question 28

What does the trophoblast do?

Answer 28

- forms embryonic portion of the placenta

Question 29

Describe the trophoblast

Answer 29

- lateral cell surface express tight junctions, gap junctions and desmosomes - basal Na/K ATPase pump

Question 30

What happens in 'hatching'?

Answer 30

shedding of the zona pellucida allow future interaction with the endometrial lining of the uterus

Question 31

What are some assisted reproductive technologies?

Answer 31

- in-vitro fertilisation (IVF) - intracytoplasmic sperm injections (ICSI) - gamete or zygote intrafallopian transfer (GIFT/ZIFT)

Question 32

What happens in in IVF?

Answer 32

- trigger super ovulate (FSH, clomiphene citrate) - oocyte harvested and partnered with sperm in vitro - zygote cultured then implanted in uterine cavity

Question 33

List the components of a zygote at the beginning?

Answer 33

- polar bodies - pronuclei - zona pellucida - oolemma

Question 34

List the components of a blastocyte?

Answer 34

- zona pellucida - inner cell mass (embryoblast) - trophoblasts - blastocyst cavity

Question 35

What does the inner cell mass (embryblast) differentiate into during implantation?

Answer 35

- epiblasts and hypoblasts - they form the bilaminar germ disc

Question 36

What do the trophoblasts differentiate into during implantation?

Answer 36

- syncytiotrophoblast - cytotrophoblast

Question 37

What does the blastocyte do before implantation? When does it finally implant?

Answer 37

- floats for around 72 hours before implantation - implants 6-8 days post ovulation

Question 38

What are the two steps that happen in the implanted embryo?

Answer 38

- establish primordial uteroplacental circulation - formation of the chorionic cavity

Question 39

How does the implanted embryo establish uteroplacental circulation?

Answer 39

- maternal capillaries become sinusoids - further invasion of syncytiotrophoblast ruptures capillaries and cells - lacunae flood with maternal blood and nutrients

Question 40

In the implanted embryo, how is the chorionic cavity formed?

Answer 40

- extra-embryonic mesoderm fills space between primitive yolk sac/amniotic cavity and cytotrophoblast cells - large cavities form and become connected

Question 41

What is an extra-uterine (ectopic) pregnancy?

Answer 41

abnormal implantation of embryo

Question 42

What percentage of pregnancies are ectopic

Answer 42

2%

Question 43

What percentage of pregnancy related maternal mortality is due to ectopic pregnancy?

Answer 43

9%

Question 44

What is gastrulation and when does it occur?

Answer 44

- movement of epiblast cells through the primitive streak to form 3 primary germ layers

Question 45

Which cells do the epiblasts replace to then form the endoderm?

Answer 45

hypoblasts

Question 46

What is the ectoderm made from?

Answer 46

what's left of the epiblast layer

Question 47

What does the ectoderm go on to become?

Answer 47

- epidermis of skin (hair, nails, associated glands) - nervous system

Question 48

What does the intraembryonic mesoderm become?

Answer 48

it divides into 3 layers

Question 49

Which 3 layers does the intraembryonic mesoderm become?

Answer 49

- paraxial - intermediate - lateral plate

Question 50

What 2 layers does the lateral plate mesoderm divide into?

Answer 50

- somatic layer (dorsal) - visceral layer (ventral)

Question 51

What does the paraxial mesoderm become?

Answer 51

- axial skeleton (vertebrae) - voluntary (skeletal) muscle - part of dermis (back)

Question 52

What does paraxial mesoderm undergo further differentiation to become?

Answer 52

somites

Question 53

What do somites differentiate into?

Answer 53

- dermomyotomes - sclerotomes

Question 54

What do dermomyotomes do?

Answer 54

they form connective tissue and skeletal muscle

Question 55

What do sclerotomes do?

Answer 55

they form bone and cartilage (vertebral arch)

Question 56

What does the intermediate mesoderm become?

Answer 56

urogenital systems - kidneys, ureter, trigone of bladder - gonads, uterus + uterine tubes, superior portion of vagina, ductus deferens

Question 57

What does the somatic part of the lateral plate mesoderm become?

Answer 57

- most of dermis (not in central back) - lining of body walls - bones of limbs

Question 58

What does the visceral part of the lateral plate mesoderm become?

Answer 58

- cardiovascular system - mesothelial covering of organs - smooth muscle

Question 59

What does the endoderm become?

Answer 59

- lining of gut - lining of respiratory tract - lining of bladder and urethra