Embryology Flashcards
What is nondisjunction?
Failure of sister chromatids to separate during cell division
Can lead to trisomy
What happens during fertilisation?
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)
What are the stages of embriogenesis?
Gametogenesis Fertilisation Cleavage Gastrulation Embryonic folding Organogenesis
What does the trophoblast split into?
Cytotrophoblast
Syncytiotrophoblast
What does the ‘inner cell mass’ split into?
Epiblast layer
Hypoblast layer
What are the 3 primary germ layers?
Ectoderm
Mesoderm
Endoderm
What is the fate of the ectoderm?
Epidermis of the skin
Nervous system
What is the fate of the mesoderm?
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
What is the fate of the endoderm?
Lining of gut tubes, respiratory tract and bladder/urethra
during weeks 0-3 of development it is known as?
conceptus/embryo
during which weeks is it known as an embryo?
0-3 weeks
During which weeks is the embryonic period?
weeks 3-8
during which weeks is it known as the fetal period?
weeks 9-40
what happens during gametogenesis?
The gametes are formed.
Mitosis happens first then meiosis.
what is mitosis?
Cell division to produce two identical daughter cells
what is meiosis?
cell division to produce 4 haploid cells called gametes
how many chromosomes does a gamete have?
half: 23
the formation of male gametes is known as?
the formation of female gametes is knowns as?
spermatogenesis
oogenesis
How long does the production of a male gamete take and what is the production rate?
each cycle takes 64 days
production rate = 6.5 million sperm per gram of testicular tissue per day
when do primary oocytes begin meiosis?
by week 28-30 of development, they then lie dormant till puberty
what is trisomy 21 and how is it caused?
an additional copy of chromosome 21 causing down syndrome.
caused by nondisjunction
what is fertilisation?
Fusion of the sperm and oocyte to form a zygote
what is a zygote?
a diploid single celled embryo
what happens during cleavage?
rapid mitotic cell division with no overall increase in size/volume
what happens during gastrulation?
formation of the germ layers (in weeks 3) and the body axes are established
what occurs on day 0?
fertilisation
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.
what is the name of the enzyme the sperm releases to digest its way into the egg?
acrosomal enzyme
what does sperm penetration cause?
completion of meiosis 2 and release of cortical granules by the oocyte to make the zona pellucida impenetrable
where does fertilisation usually occur?
in the ampulla of the uterine tube
where does cleavage happen?
as the egg makes its way through the uterine tubes to get to the uterus.
up to what stage is the zygote totipotent?
up to the 8 cell stage blastomere.
what is mosaicism?
a condition where an individuals cells don’t all contain identical chromosomes.
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.
what is a morula
16+ blastomeres
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
by which day does implantation occur?
day 6
where does implantation occur?
the posterior uterine wall - normally
the epiblast makes up which surface of the embryo?
dorsal
the hypoblast makes up which surface of the embryo?
ventral
when is implantation complete?
day 9
which two cavities are formed on day 9?
the amniotic cavity and the primitive yolk sac
what happens on day 12?
uteroplacental circulation is established and extraembryonic mesoderm develops and degenerates forming the chorionic cavity
when is the primitive streak formed?
week 3
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
where is the primitive pit and node?
the caudal end of the primitive streak
what does the epiblast become?
the primary germ layers
