Embryology Flashcards

1
Q

What is nondisjunction?

A

Failure of sister chromatids to separate during cell division
Can lead to trisomy

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2
Q

What happens during fertilisation?

A

Sperm bind to zona pellucida
Acrosomal enzymes are release by the head of the sperm (digests into the oocyte)
Sperm and oocyte plasma membranes fuse
The oocyte completes meiosis 2 and releases cortical granules (making ZP impenetrable)

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3
Q

What are the stages of embriogenesis?

A
Gametogenesis
Fertilisation
Cleavage
Gastrulation
Embryonic folding
Organogenesis
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4
Q

What does the trophoblast split into?

A

Cytotrophoblast

Syncytiotrophoblast

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5
Q

What does the ‘inner cell mass’ split into?

A

Epiblast layer

Hypoblast layer

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6
Q

What are the 3 primary germ layers?

A

Ectoderm
Mesoderm
Endoderm

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7
Q

What is the fate of the ectoderm?

A

Epidermis of the skin

Nervous system

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8
Q

What is the fate of the mesoderm?

A

Paraxial mesoderm- axial skeleton, skeletal muscle and part of dermis of the back

Intermediate mesoderm- urogenital systems

Lateral plate mesoderm

  • somatic part: most of dermis, lining of body wall and contributes to limbs
  • visceral part: cardiovascular system, smooth muscle, mesothelium
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9
Q

What is the fate of the endoderm?

A

Lining of gut tubes, respiratory tract and bladder/urethra

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10
Q

during weeks 0-3 of development it is known as?

A

conceptus/embryo

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11
Q

during which weeks is it known as an embryo?

A

0-3 weeks

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12
Q

During which weeks is the embryonic period?

A

weeks 3-8

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13
Q

during which weeks is it known as the fetal period?

A

weeks 9-40

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14
Q

what happens during gametogenesis?

A

The gametes are formed.

Mitosis happens first then meiosis.

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15
Q

what is mitosis?

A

Cell division to produce two identical daughter cells

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16
Q

what is meiosis?

A

cell division to produce 4 haploid cells called gametes

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17
Q

how many chromosomes does a gamete have?

A

half: 23

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18
Q

the formation of male gametes is known as?

the formation of female gametes is knowns as?

A

spermatogenesis

oogenesis

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19
Q

How long does the production of a male gamete take and what is the production rate?

A

each cycle takes 64 days

production rate = 6.5 million sperm per gram of testicular tissue per day

20
Q

when do primary oocytes begin meiosis?

A

by week 28-30 of development, they then lie dormant till puberty

21
Q

what is trisomy 21 and how is it caused?

A

an additional copy of chromosome 21 causing down syndrome.

caused by nondisjunction

22
Q

what is fertilisation?

A

Fusion of the sperm and oocyte to form a zygote

23
Q

what is a zygote?

A

a diploid single celled embryo

24
Q

what happens during cleavage?

A

rapid mitotic cell division with no overall increase in size/volume

25
what happens during gastrulation?
formation of the germ layers (in weeks 3) and the body axes are established
26
what occurs on day 0?
fertilisation
27
what happens during fertilisation?
the sperm binds with the zona pellucida glycoprotein. the head of the sperm releases acrosomal enzymes to digest into the egg the egg and sperm membrane fuse and the sperm contents enter the egg.
28
what is the name of the enzyme the sperm releases to digest its way into the egg?
acrosomal enzyme
29
what does sperm penetration cause?
completion of meiosis 2 and release of cortical granules by the oocyte to make the zona pellucida impenetrable
30
where does fertilisation usually occur?
in the ampulla of the uterine tube
31
where does cleavage happen?
as the egg makes its way through the uterine tubes to get to the uterus.
32
up to what stage is the zygote totipotent?
up to the 8 cell stage blastomere.
33
what is mosaicism?
a condition where an individuals cells don't all contain identical chromosomes.
34
how is mosaicism caused?
by mitotic nondisjunction in a zygote which already has trisomy 21 - resulting in some cells being normal and some having trisomy.
35
what is a morula
16+ blastomeres
36
what are the first two layers and cavity formed called? | note this is still contained inside the zona pellucida
the outside layer = trophoblast inside layer = embryoblast Blastocyst cavity
37
by which day does implantation occur?
day 6
38
where does implantation occur?
the posterior uterine wall - normally
39
the epiblast makes up which surface of the embryo?
dorsal
40
the hypoblast makes up which surface of the embryo?
ventral
41
when is implantation complete?
day 9
42
which two cavities are formed on day 9?
the amniotic cavity and the primitive yolk sac
43
what happens on day 12?
uteroplacental circulation is established and extraembryonic mesoderm develops and degenerates forming the chorionic cavity
44
when is the primitive streak formed?
week 3
45
explain where the following cavities are in relation to the bilaminar embryonic disc: - amniotic cavity - definitive yolk sac - chorionic cavity
amniotic cavity = above the disc definitive yolk sac = below the disc chorionic cavity = encircles the entire embryo
46
where is the primitive pit and node?
the caudal end of the primitive streak
47
what does the epiblast become?
the primary germ layers