special topic 1 - embryonic development

Question 1

when does gastrulation occur

Answer 1

start of week 3 of embryonic development

Question 2

what are the amnion and chorion

Answer 2

the amnion is the innermost membrane surrounding and protecting the foetus and containing the amniotic fluid
the chorion is the outermost membrane that protects the amnion and embryo, and is connected to the uterine lining. has chorionic villi for nutrient exchange from placenta to uterus

Question 3

the ectoderm gives rise to (main categories)

Answer 3

the skin and all nervous tissue

Question 4

what are blastomeres?

Answer 4

early embryonic cells formed during cleavage.

Question 5

blastomeres are ____potent?

Answer 5

totipotent

Question 6

cleavage is:

Answer 6

the early rapid cell division following fertilisation, resulting in increasingly smaller cells called blastomeres

Question 7

the mesoderm gives rise to (main categories)

Answer 7

connective tissues and internal organs

Question 8

structure of the sperm

Answer 8

very small, with a head containing genetic material and a tail to swim. head has a sac with enzymes to allow it to burrow into the egg.

Question 9

what is the corona radiata, what is its function in fertilisation

Answer 9

a layer of follicular cells surrounding the zona pellucida and egg. provides a barrier that the sperm must penetrate.

Question 10

where and when does fertilisation occur (what phase)

Answer 10

in the fallopian tubes, 12-24 hours after ovulation, in metaphase II

Question 11

when is a morula formed, what are its characteristics

Answer 11

3-4 days after fertilisation.
loosely packed ball of 16-32 cells.

Question 12

what is the zona pellucida, why is it important

Answer 12

a thick glycoprotein membrane surrounding the egg,
is slippery/not sticky so ensures egg doesn’t get stuck in fallopian tubes which would result in ectopic pregnancy

Question 13

what is embryogenesis

Answer 13

formation of embryo from a fertilised egg (0-8 weeks)

Question 14

what does embryogenesis achieve

Answer 14

patterning, axis definition, rudiments of organs, gastrulation

Question 15

what is patterning

Answer 15

cells in the embryo become organised and acquire identity, forming the ‘plan’ of the developing body

Question 16

what are the 4 major axis

Answer 16

anterior - head
posterior - bottom
dorsal - back
ventral - stomach

Question 17

what germ layer would the skeleton arise form

Answer 17

mesoderm

Question 18

when can we call a fertilised egg a zygote?

Answer 18

when the male and female pronuclei fuse

Question 19

what is the difference between a polar body and a secondary oocyte or ovum, and why?

Answer 19

the polar body is the product of female meiosis I or II that is much smaller with less cytoplasm. isn’t typically fertilised.
secondary oocyte/ovum are much larger with more cytoplasm so that they are nutrient and organelle rich to support development.

Question 20

order the levels of cell potency, least to most.

Answer 20

nulli(uni)potent, multipotent, pluripotent, totipotent

Question 21

what can a multipotent cell give rise to

Answer 21

all cells of a particular tissue or organ, e.g hematopoetic stem cells

Question 22

the endoderm gives rise to

Answer 22

the innermost structures; the gut

Question 23

differentiated cells have _______ division potential

Answer 23

limited

Question 24

stem cells are defined as….

Answer 24

cells that divide to form one daughter that goes on to differentiate, and one daughter that maintains stem cell properties

Question 25

structure of a blastocyst

Answer 25

outer trophoblast cells, blastocyst cavity, inner cell mass (gives rise to embryo)

Question 26

when does the zona pallucida disappear

Answer 26

when embryo enters uterus

Question 27

role of enzymes in implantation

Answer 27

allows the blastocyst to stick in the endometrium, and ensures uterine lining doesn't slough off.

Question 28

trophoblast cells give rise to ______, and secrete what?

Answer 28

the embryonic portion of the placenta (fetal placenta). secrete enzymes and hCG

Question 29

what does the bilaminar embryonic disk consist of, what does it give rise to.

Answer 29

epiblast and hypoblast cells. epiblast cells eventually give rise to the three germ layers and amnion, while hypoblast supports and forms the endoderm yolk sac. (endoderm, but not final endoderm)

Question 30

what does the yolk sac do

Answer 30

provides nutrition for embryo while placenta is still developing

Question 31

what is the function and fate of the connecting stalk

Answer 31

the connecting stalk attaches the blastocyst to the uterine wall at the posterior end of the embryonic disc. will eventually combine with the yolk sac to form the umbilical cord

Question 32

where does the primitive streak form and travel

Answer 32

forms on the dorsal side, travels from the posterior to anterior side

Question 33

what is the primitive streaks structure and its functions

Answer 33

it is a groove on the surface of the bilaminar disc's epiblast. it allows for patterning of the embryo, defining its midline and axis. allows for invagination and gastrulation.

Question 34

what is the process of gastrulation

Answer 34

epiblast cells migrate through the primitive streak and form the mesoderm ( and final endoderm). the remaining epiblast cells become the ectoderm.

Question 35

how is embryonic folding able to occur

Answer 35

cells are moving, changing shape and size, and dividing

Question 36

describe embryonic folding, when it occurs and what it achieves.

Answer 36

occurs around week 3-4, and consists of head to tail folding in towards each other, and lateral folding of sides towards each other. results in the internal gut cavity tube, and the ectoderm around it enclosing the internal structure.

Question 37

we need stem cells for _____

Answer 37

renewal, growth, repair

Question 38

describe epidermolysis bullosa

Answer 38

a single gene defect in collagen 7. collagen 7 protein sticks epidermis to dermis, so defect results in fragile skin that sloughs off very easily. incurable, treated lifelong with pallative care.

Question 39

what is the usual stem cell potency in skin, and what is the potency aimed for in skin grafts

Answer 39

6% in normal skin, 5% minimum in grafts

Question 40

where are pluripotent cells found

Answer 40

in the inner cell mass, which can give rise to all tissue of the embryo but not extraembryonic tissues

Question 41

what are skin stem cells and where are they found

Answer 41

keratinocytes, found at bottom of epidermis and hair follicles

Question 42

what happens to skin cells as they get closer to skin surface

Answer 42

they divide and differentiate, filling with keratin and eventually losing their nuclei and dying