Embryology Flashcards
During the first week after fertilisation, the zygote travels along…?
The uterine tubes
When travelling along the uterine tubes the zygote is surrounded by what? What is its function?
A layer of glycoproteins called a zona pellucida
The zona pellucida stops the zygote from increasing in size, despite the increasing cell number due to cleavage, as it travels through the uterine tubes, so it doesn’t get stuck there, thus embedding in the tube, resulting in an ectopic pregnancy
What is the zygote nourished by as it travels down the Fallopian tubes?
Glycogen from the goblet cells of the uterine tubes, and later the secretory cells of the uterus
What is cleavage?
The mitotic cellular replication the zygote undergoes as it travels to the uterus into smaller cells called blastomeres
By three days after fertilisation how big should the zygote be, and what will it now be called?
16 cells,
Morula
What day does the blastocyst enter the uterus?
Day 4
When in the uterine cavity, the blastocyst digests its way out of:
The zona pellucida
What two masses is the blastocyst made of?
Trophoblast (outer cell mass) which becomes the chorion and placenta
Embryoblast (inner cell mass) which become the embryo, amnion and umbilical cord
What layers do the trophoblast differentiate into in week 2?
Synctio-trophoblast & inner cytotrophoblast
What is the role of the syncytiotrophoblast layer in implantation?
The syncytiotrophoblast layer forms finger like villi projections deep into the decidua (uterine endometrium) and spaces called lacunae, which fill with the mothers blood. The villi branch and contain blood vessels, thus allowing gaseous exchange between mother and foetus
The syncytiotrophoblast cells also produce hCG which prevents menustation & sustains the pregnancy by maintaining the corpus luteum
The embryoblast differentiates into two cell types, what are they and what shape do they form?
Epiblast (closest to the trophoblasts) & hypoblast (closest to the blastocyst cavity
They form a flat disc called the bilaminar embryonic disc
What is gastrulation?
The rearrangement and migration of of cells due to pre determined genetic coding to turn the bilaminar embryonic disc into a TRIlaminar embryonic disc of three primary germ layers
What is the first appearance of the three primary germ layers known as and when does it occur by?
The primitive streak
Day 15
What are the three layers of the trilaminar embryonic disc
Ectoderm: forms the epidermis layer of the skin, the hair and the nails, also forms the nervous system
Mesoderm: forms the muscle, skeleton, dermis of the skin, connective tissue, urogenital glands, blood vessels, blood and lymph cells
Endoderm: forms the epithelial lining of the respiratory, digestive and urinary systems and glandular cells of organs such as the liver and the pancreas
Describe neurulation and how it can go wrong?
The formation of the notochord, from mesodermal cells, and neural plate and therefore neural tube, occurring the in middle of the embryo and developing towards each end.
Tetratogens, diabetes or folic acid deficiency can cause neural tube defects
Describe the embryo at 4 weeks post fertilisation
There is a distinct head-rump polarity
The embryo is c shaped due to construction between the embryo and the yolk sac, which provides nutrition until the placenta takes over
Primitive beating heart present
Large liver - blood detoxification important from early on
Describe the storage functions of the placenta
The placenta stores glycogen, ready to metabolise into glucose as and the fetus requires it
Stores iron and fat soluble vitamins
Describe the endocrine functions of placenta?
Produces steroid and placental protein hormones
Steroid: oestrogen and progesterone
Placental protein hormones: hGC, hPL, PAPP-A
