SYMPOSIA - Dev origins disease

Question 1

FERTILISATION - DAY 1

i) where do sperm and ovum meet? how many hours post ov?
ii) what two layers must the sperm penetrate? which meiotic divison happens after this occurs?
iii) what makes the ovum impermeable to other sperm?
iv) what is the end product? how many chromosomes?

Answer 1

i) in the ampulla of the fallopian tube 12-24hrs post ov

ii) corona radiata and the zona pellucida
- then fusion and second meiotic division

iii) acrosomal reaction
iv) zygote > 46 chromosomes

Question 2

DAYS 2-3

i) how many cells is in the embryo after 3 days? what is each cell known as? what is the solid sphere known as?
ii) what rapid process takes place? what does it involve?
iii) when is the first mitotic division?

Answer 2

i) 16 cell embryo
- each cell = blastomere / solid sphere = morula (communic via GJs)

ii) rapid cleavage of mitotic divisions
iii) 30 hours post fert

Question 3

DAYS 4-5

i) what does the morula become known as once it develops a cavity? what is the cavity called?
ii) what does the outer layer become? what does this go on to form?
iii) what happens to the rest of the cell? what does this create
iv) where is the embryo now found?

Answer 3

i) becomes a blastocyst
- cavity is blastocele

ii) outer layer = trophoblast > placenta

iii) rest of the cells are pushed up and become ICM
- creates an embryonic pole

iv) embryo is now in the uterine lumen and ready for implantation

Question 4

DAY 6-7

i) what does the embryo start to form as it implants? what does this consist of?
ii) what layer forms extra embryonic membranes? which layer forms the embryo?
iii) where does the amniotic cavity develop within?
iv) label diagram

Answer 4

i) embryo forms bilaminar disk = epiblast and hypoblast

ii) hypoblast forms extra embryonic membrane
- epiblast forms the embryo

iii) amniotic cavity develops in the epiblast mass

iv) A - syncytiotrophoblast, B - epiblast, C - hypoblast,
D - cytotrophoblast, E - amniotic cavity, E - bilaminar disk

Question 5

DAY 6-8 PRIMARY YOLK SAC

i) which membrane is derived from the hypoblast and creates the yolk sac?
ii) what does the yolk sac contain? when is it no longer needed?
iii) label diagram

Answer 5

i) exocoelomic membrane > creates cavity = yolk sac
ii) yolk sac contains nutrients that supply the embryo before the placenta functions

iii) A - exocoelomic membrane
B - primary yolk sac

Question 6

WEEK 3+

i) what develops at the start of week three? what is this process called?
ii) what initiates the process?
iii) what does the epiblast become known as? what is the hypoblast replaced with? what does this become?
iv) what ultimately happens to the hypoblast?

Answer 6

i) three layers = gastrulation
ii) primitive streak initiates

iii) epiblast is ectoderm
- hypoblast is replaced by epiblast cells = endoderm

iv) three germ layers form from epiblast and hypoblast degenerates

Question 7

WEEK 4+

i) what has happened to the flat disk by week 4?
ii) what brings the head and tail closer? what day does this happen?
iii) what brings the amniotic cavity down? what day does this happen? what does this create?

Answer 7

i) by week four flat disk has folded in two directions
ii) longitudinal folding (cephalocaudal) - day 21

iii) lateral (transverse) folding brings amniotic cavity down
- creates future gut tube inside peritoneal cavity

Question 8

MESODERM

i) what does it sit either side of?
ii) what three parts is it composed of? which is most medial and which is most lateral?
iii) what type of mesoderm forms the somites? what do somites go on to form? (2)
iv) what do the products of the somites form?
v) what does the notochord form?

Answer 8

i) sits either side of the notochord
ii) composed to paraxial (most med), intermediate and lateral plate (most lat)

iii) para axial mesoderm forms somites
- somites > dermomyotome and sclerotome

iv) dermomyotomes > conn tissue and skeletal muscle
sclerotome > bone and cartilage/vert arch

v) notochord forms intervertebral disks

Question 9

INTERMEDIATE AND LAT PLATE MESODERM

i) what system does intermediate mesoderm form? name three organs
ii) what is the lateral plate mesoderm continuous with?
iii) what two layers does the LP mesoderm differen into? what does these mesodermal cells become?

Answer 9

i) intermed mesoderm > UG system eg kidneys, gonads, UG ducts
ii) lat plate meso is continous with amniotic and yolk sac

iiI) LP differentiates into somatic and splanchnic mesoderm
- cells become membranes of body eg pericardium/pleura

Question 10

INTRAEMBRYONIC COELOM

i) which type of mesoderm do all cavities become lined with? which type of mesoderm forms the parietal layer and which forms the visceral layer?
ii) what three things does the IA coelem become? what does the bend of U become? what do limbs of U become?

Answer 10

i) all cavities become lined with lat plate mesoderm
- somatic meso > parietal layer
- splanchnic meso > visceral layer

ii) IA becomes pericardium, peritoneum and pleura
- bend of U = pericardium
- limbs of U = pleura and peritoneal cavities