Embryology Flashcards
what is the zona pellucida?
a thick transparent membrane surrounding an ovum before implantation
what does sperm bind to during fertilisation?
the zona pellucida glycoprotein (ZP3)
where the acrosome?
at the head of the sperm
where are acrosomal enzymes released from?
the sperm head
what do acrosomal enzymes do when they are released from the sperm head?
they allow the sperm to digest into the egg
what does sperm entry trigger?
completion of meiosis 2 and the release of granules by oocyte
what do the granules released from oocytes do?
they cause the fertilised oocyte to harden up to prevent more sperm entering/polysperming and break down ZP3 receptor
many smaller daughter cells formed when the zygote undergoes mitotic divisions
blastomeres
blastomeres up to the 8 cell stage are thought to be…?
totipotent
what is mitotic nondisjunction?
The failure in mitosis for the two members of a chromosome pair to separate (to disjoin) normally so that both chromosomes go to one daughter cell while none go to the other daughter cell.
what are blastomeres?
the individual daughter cells from the zygote divisions
how many blastomeres make up a morula?
16+
name of outer cell mass
trophoblast
name of inner cell mass
embryoblast
when does the thing become a blastocyst?
when there is a separation between the inner and outer layer
what happens when the blastocyst gets so big?
it breaks free from the zona pellucida
where does implantation usually happen?
on the anterior or posterior uterine wall
typically, by what day does implantation happen?
day 6
as the trophoblast attaches to the uterine wall, the trophoblast separates into?
the cytotrophoblast and the syncytiotrophoblast
as the embryo attaches to the uterine wall, the embryo organises itself into what two layers? at what stage?
the epiblast and the hypoblast
day 7.5 - bilaminar embryo
epiblast
the dorsal surface of the embryo
hypoblast
the ventral surface of the embryo
what completes implantation?
closure by fibrin coagulum
day 9 - two cavities are formed?
amniotic cavity (epiblast) and primitive yolk sac (hypoblast)
epiblast cell shape?
tall columnar cells
hypoblast cell shape?
cuboidal cells
what does hCG stand for?
human chorionic gonadotropin
what does hCG stimulate?
the corpus luteum which secretes oestrogen and progesterone
what replaces the corpus luteum?
the placenta
when does the bilaminar embryo need its own uteroplacental circulation?
day 12
where do vacuoles appear in?
in the syncytiotrophoblast
what happens when the vacuoles in the syncytiotrophoblast unite?
they form lacunae
where does maternal blood flow into to establish the embryos uteroplacental circulation?
into lacunae to diffuse to the embryoblast
where does the primitive streak appear from?
the midline at the caudal end of the epiblast
three parts of the primitive streak
primitive pit, primitive node and primitive groove
what is found at the cranial end of the primitive streak?
primitive pit and node
what is gastrulation?
the movement of epiblast cells through the primitive streak to form the three primary germ layers
what establishes the body axes?
the primitive streak
how many days in does gastrulation happen?
14-15
what replaces hypoblast cells?
definitive endoderm
what replaces the epiblast cells?
ectoderm
what are the names of the three germ layers?
ectoderm, mesoderm and endoderm
what is the fate of the ectoderm?
produces the epidermis of skin (also hair, nails and associated glands) and the nervous system (brain, spinal cord, peripheral nerves)
what is the fate of the mesoderm?
it becomes divided into three regions across both sides of the notochord
what are the 3 mesoderm regions?
paraxial, intermediate and lateral (visceral and somatic)
fate of the paraxial mesoderm?
axial skeleton, voluntary skeletal muscle, part of dermis (back)
fate of the intermediate mesoderm?
urogenital systems such as kidney and ureter and gonads and associated structures
fate of the somatic lateral plate of mesoderm
makes most of dermis, lining of body wall and part of limbs
fate of visceral lateral plate of mesoderm
makes the cardiovascular system, mesothelial covering of organs and smooth muscle
fate of the endoderm
lining of the gut tube, respiratory tract and bladder and urethra
