fertilisation and embryogenesis

Question 1

what are the requirements for conception

Answer 1

functioning gametes

patent reproductive pathway

Question 2

how long can the gametes survive if fertilisation doesn’t occur

Answer 2

sperm - 5 days

egg - 1 day

Question 3

describe the process of a sperm entering an egg

Answer 3

sperm has hydrolytic enzymes that act on the zona pellucida and vetelline layer of the egg
once it has entered a chemical reaction occurs which causes the plasma membrane to thicken so no more sperm can enter

Question 4

what happens if more thsn one sperm fertilises an egg

Answer 4

this is abnormal and abnormally fertilised eggs are not viable
can cause a molar pregnancy

Question 5

what is the pronuclei

Answer 5

when the sperm has entered the egg and there are two nuclei in the egg

Question 6

when does the first cell division occur

Answer 6

day 2

Question 7

what day does the morula form

Answer 7

day 4

Question 8

when does the blastocyst form

Answer 8

by day 5

Question 9

what is the structure of a blastocyst

Answer 9

outer trophoblast layer

inner cell mass/endoderm

Question 10

what is adhesion

Answer 10

trophoblast adheres to endometrium

Question 11

what is hatching

Answer 11

trophoectoderm cells produce protease to dissolve zona pellucida (protective layer)

Question 12

what is apposition

Answer 12

trophoblast cells adhere to epithelial layer of endometrium

Question 13

when does hCG get produced

Answer 13

when apposition occurs

Question 14

what is invasion

Answer 14

trophoblast proliferates and differentiates
crosses epithelium BM and invades endometrial stroma
forms placenta
remodels uterine spiral arteries

Question 15

what are the four steps of implantation

Answer 15

hatching
apposition
adhesion
invasion

Question 16

what is required for invasion to take place

Answer 16

the endometrium needs to have under gone decidualisation

transformation of endometrium into a vascular receptive tissue for blastocyst invasion

Question 17

what regulates the steps of implantation

Answer 17

hormones 
cytokines
growth factors 
regulators 
free oxygen radicals

Question 18

what hormone mediates decidualisation

Answer 18

progesterone

Question 19

what changes to the endometrium occur in decidualisation

Answer 19

stromal cells differentiate from elongated fibroblast like cells to rounded epithelial decidual cells
angiogenesis
increase in macrophages, lymphocytes, leukocytes

Question 20

what is the process of placentation

Answer 20

invading trophoblast forms primary villi
secondary villi infiltrate the embryonic mesoderm
tertiary villi have developed capillaries
the cytotrophoblast remodels spinal arteries to increase blood flow to embryo

Question 21

what is a mature placenta formed from

Answer 21

chorionic villi
intervillous space
placental septae
cotyledons

Question 22

what are the functions of the placenta

Answer 22

immunological barrier 
gas exchange 
nutrient exchange 
waste excretion 
endocrine functions 
secretion of hCG to maintain pregnancy

Question 23

what is embryogenesis

Answer 23

first 8 weeks of development

Question 24

when is the bilaminar disk formed and when does it differentiate into the trilaminar disk

Answer 24

formed week 2-3

differentiates into trilaminar disk week 3-4

Question 25

what is the structure of the bilaminar disk

Answer 25

made up of epiblast and hypoblast | two cavities form either side of it

Question 26

where are the amniotic and yolk sac cavities in relation to the hypoblast and epiblast

Answer 26

amniotic cavity is between the epiblast and endometrium | yolk sac cavity is below the hypoblast

Question 27

what forms the bilaminar disk

Answer 27

pluripotent cells of the inner cell mass of the blastocyst

Question 28

what happens to the epiblast layer of the bilaminar disk

Answer 28

undergoes gastrulation to form the three germ layers

Question 29

what is the process of gastrulation

Answer 29

primitive streak appears at caudal end of epiblast epiblast cells displace hypoblast cells forming the endoderm epiblast cells migrate through primitive streak and form mesoderm remaining epiblast becomes endoderm

Question 30

what are the three layers in the trilaminar disk

Answer 30

ectoderm mesoderm endoderm

Question 31

what does the ectoderm form

Answer 31

``` epidermis central and peripheral nervous system hair nails neuroendocrine organs enamel of teeth ```

Question 32

what does the mesoderm form

Answer 32

``` dermis MSK structures CVS kidneys ureters trigone of bladder gonads adrenal cortex visceral and parietal linings ```

Question 33

what are the mesoderm subunits

Answer 33

paraxial intermediate lateral plate

Question 34

what part of the mesoderm forms kidney, ureter and gonads

Answer 34

intermediate mesoderm

Question 35

what is a dizygotic pregnancy

Answer 35

two or more eggs fertilising and implanting | note: different eggs

Question 36

what is a monozygotic pregnancy

Answer 36

one embryo splitting produces identical twins less common

Question 37

what does dichorionic diamniotic mean

Answer 37

twins with separate placentas and amniotic sacs

Question 38

what does monochorionic diamniotic mean

Answer 38

twins that share a placenta but have separate amniotic sacs | most common

Question 39

what does monochorionic monoamniotic mean

Answer 39

twins that share a placenta and an amniotic sac

Question 40

what are conjoined twins

Answer 40

twins that share a placenta, amniotic sac and have joined up organs

Question 41

how does egg splitting in monozygotic twins impact on placental/amniotic sac sharing

Answer 41

later splitting = less separated if egg splits early twins will have separate placenta and amniotic sac if egg implants in womb then splits there will be a shared placenta and separate amniotic sacs if the egg implants then splits later on there will be a shared placenta and sac