Fertilisation to trilaminar Flashcards
What does the sperm bind with on the surface of the egg?
The zona pellucida glycoprotein (ZP3)
How does the sperm enter the egg?
It releases acrosomal enzymes from the acrosome of the sperm head
How does the egg cell prevent polyspermy?
Sperm penetration causes cortical granules in the cytoplasm to release their contents which hardens the zone pellucida
What does sperm entry trigger in the egg cell?
Completion of meiosis 2
Release of cortical granules by oocyte
What occurs when the sperm and egg bind?
The sperm contents enter the egg
Where does fertilisation occur within the uterine tube?
Ampulla
What is the name given to the smaller daughter cells of the fertilised egg?
Blastomeres
What happens to the overall size of the ovum during mitosis?
It stays the same
What is the definition of totipotent?
Can differentiate to form any type of adult cell, as well as embryonic and placental cell. Blastomeres up to the 8 cell stage are thought to be totipotent
What is mosaicism?
When non-disjunction occurs during the first cell division, not during gametogenesis, so only some cells contain the increased number of cells. In trisomy 21, this leads to less prominent features
What is meant by a morula?
When the ovum contains 16 or more blastomeres
What occurs during compaction of the morula?
Blastomeres come into closer contact and form cell junctions, outer cells that are in contact with the zone pellucida form extensive gap junctions
How many cells are in a blastocyst?
70-100
What are the 4 regions of a blastocyst?
Trophoblast layer
Inner cell mass
Blastocyst cavity
Zona pellucida
What does the trophoblast layer form?
The placenta
What does the inner cell mass form?
Embryo
What occurs during hatching?
Trophoblasts release enzymes that begin to break down the zone pellucida. Embryonic contractions allow for hatching as the zone pellucida is released
In what does the ovum mature?
A preovulatory follicle
What happens to the preovulatory follicle after ovulation?
It forms a corpus luteum, a temporary gland that secretes progesterone, maintaining the thick endometrial lining for implantation
What are the 2 layers formed from the trophoblast layer?
Cytotrophoblast
Syncytiotrophoblast
What forms the syncytiotrophoblast?
A single, multinucleate cell
What hormone does the syncytiotrophoblast form?
Human chorionic gonadotrophin
What is the function of Human chorionic gonadotrophin?
Stimulates the corpus luteum to thicken the endometrial lining and is the basis of pregnancy tests
What 2 layers does the embryo split into?
Epiblast
Hypoblast
What surface of the embryo is the epiblast?
Dorsal surface
What surface of the embryo is the hypoblast?
Ventral surface
On what day does the bilaminar embryo form?
Day 7.5
What 2 cavities form on day 9?
Amniotic cavity from the epiblast
Primitive yolk sac (Exocoelomic cavity) from the hypoblast
What occurs in the syncytiotrophoblast on day 9?
Vacuoles appear and unite to form lacunae
What closes the site of embryonic implantation of the endometrium?
A fibrin coagulum
What is the name of the hypoblast membrane that surrounds the yolk sac?
Exocoelomic (Heuser) membrane
What fills the trophoblastic lacunae on day 12?
Maternal sinusoids formed from nearby capillaries pass blood into the trophoblastic lacunae, establishing a uteroplacental circulation
What layer forms around the exocoelomic membrane?
Extraembryonic mesoderm
What are the 3 components of the extra embryonic mesoderm?
Extraembryonic somatic mesoderm (Outer)
Extraembryonic splanchnic mesoderm (Inner)
Extraembryonic cavities
What happens to the embryonic mesoderm on day 13?
The extraembryonic splanchnic mesoderm degenerates to form the chorionic cavity
What structure forms to connect the embryo and trophoblast layer?
Connecting stalk
What is the exocoelomic cyst?
The remnants of the primary yolk sac, found in the chorionic membrane. A secondary yolk sac forms within the embryo
During what week does the primitive streak form?
Week 3
What are the 3 parts of the primitive streak?
Primitive pit at the cranial end
Primitive node at the cranial end
Primitive groove at the caudal end
What is established by the formation of the primitive streak?
The body axes
What occurs during the first stage of gastrulation?
Epiblast cells move through the primitive streak and replace the hypoblast layer with a definitive endoderm layer
What occurs during the second layer of gastrulation?
More epiblast cells move in through the primitive streak and move in-between the epiblast layer and definitive endoderm to form three layers
What are the 3 layers of the trimlaminar embryo?
Ectoderm
Mesoderm
Endoderm
What 2 membranes form on the trilaminar embryo?
Oropharyngeal membrane (Cranial end)
Cloacal membrane (Caudal end)
What structures form from the ectoderm?
Epidermis of the skin, hair, nails and associated glands
Nervous system; brain, spinal chord and peripheral nerves
what are the 3 regions of the mesoderm?
Paraxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm
What are the 2 layers of the lateral plate mesoderm?
Somatic layer
Visceral layer
What is the notochord?
A flexible, rod-like structure that forms from mesodermal cells that forms the spinal chord in vertebrates
What structures form from the paraxial mesoderm?
Axial skeleton, skeletal muscle and parts of the dermis of the back
What structures form from the intermediate mesoderm?
Urogenital systems; kidney, ureter, gonads and associated structures
What structures form from the somatic layer of the lateral plate mesoderm?
Most of the dermis, lining of body wall and parts of limbs
What structures form from the visceral layer of the lateral plate mesoderm?
Cardiovascular system, mesothelial covering of organs and smooth muscle
What structures form from the endoderm?
Lining of the gut tube
Lining of the respiratory tract
Lining of the bladder and urethra
