Fertilisation & Embryogensi Flashcards
what is fertilisation
the fusion of gametes, sperm and egg to form a zygote.
with a complete set of chromosomes.
where does the sperm travel to once it has entered the female reproductive tract.
once entered after sexua intercourse, it travels through the cervix into the uterus, guided by chemical signals.
when is the secondary oocyte released from the ovary
during ovulation.
how are the egg cells recognised by the sperm
they are recognised by the protective membrane (w/ glycoproteins) - the zona pellucida, where the sperm binds to.
what allows the sperm to penetrate the zona pellucida
the acrosome on the sperm, releases proteolytic enzymes to penetrate the zona pellucida.
- the enzymes include hyaluronidase and acrosin.
what triggers the completion of meiosis 2, and what is formed
the fusion of the sperm and egg triggers the completion of M2.
- forming a mature egg and a second polar body.
how is the zygote formed
when the nuclei of the sperm and egg fuse, combining their genetic material = zygote.
How many weeks does enbryogenesis occur for
first 8 weeks of development after fertilisation.
what stage is zygote when in the first 12-24 hours after it is formed.
and what happens
spent in cleavage, where the zygote undegoes rapid mitotic divisions.
with each round of division, the cell no. doubles = exponentially increasing in number.
what is the morula
the zygote after multiple divisions, gets to the 32 cell stage. but the cell is limited by the - zona pellicuda - how big it can grow.
after the cells in the morula start to diferentiate, what are the 2 layers that develop.
the outer shell layer - the trophoblast - sphere formed.
and the inner collection of cell - the inner cell mass, which is pushed off to one side.
what is the fluid-filled cavity in the differentiating morula
the blastocoel.
what does the trophoplast allow for the blastocyst do.
- what is the process called.
the trophoblast, develops into structures that help the gowing enbyro implant itself in the mother’s uterus linning.
- implantation.
what is blasulation and what happens
AKA - blastocyst formation
blastulation - when the inner mass of cells form a hollow ball.
they later begin to differentiate, and eventually become the enbryo.
the innner cells start to differentiate - what can be another name for this process, and what else happens.
can be called the enbryoblast (blast = to make), here the zona pellicuda also disappears, allowing the blastocyst to grow and change shape, and adhere with the uterine lining. (implantation).
what type of cells are the inner cell mass in the blastocyst.
they are pluripotent cells, which will eventually turn into any body tissue.
what is the blastocyst known as in non-mammal animals
the blastula
why does implantation into the uterus occur
for nutrient exchange between the uterus and the blasocyst.
what are the layers of the bilaminar disc
the bilaminar disc is made up of epiblast and the hypoblast,
the hypoblast faces the blastocoel, whilst the epiblast faces the other direction.
when is the bilaminar disc formed.
and decribe its structure
formed from further differentation of the inner mass cells in the second week.
- its a flat disc of cells, in the developing sphere, that splits the environment into 2 cavities.
what are the cavities called that form on the epiblast and hypoblast side
hypoblast side (botton part of the cell) = primitive yolk sac.
epiblast side - amniotic cavity. which eventually surrounds the fetus.
which of the two, epiblast and hypoblast dont contribute to the embryo
the hypoblast.
in week 3 of development, gatrulation occurs.
decribe the rough idea of it.
the development or gastrulation of germ layers orrurs and the cell mass is now called the gastrula.
- the primitive streak and the notochord are formed.
the anatomy is basically an inner tube (our digestive tract) and a series of tubes that wrap around it.
what actually forms these tubes.
the germ layer dfferentiates into the -
- ectoderm
- mesoderm
- endoderm
what is the primitive streak and how is it formed.
the fertilisation of a thickened structure forms along the middle in the epiblast.
- it has a caudal (tail) end and a cranial (rostel/head) side,
what is the thickened structure that forms the primintive streak made up of.
we just looking at moving celles here, from the epiblast to the original epiblast and hypoblast layer.
what is the main function of the primitive stream
it defines the midline and seperates the left and right, with the caudal and cranial end.
how is the ectoderm layer formed.
some of the epiblast cells stay on the surface ( continue to border the amniotic cavity) and don’t move through the primitive streak.
- these become the ectoderm, eventually forming:
- epidermic (outer layer of the skin)
- hair, brain, spinal cord, peripheral nervouse system.
How is the mesoderm layer formed
when some cells move through the primitive streak, and spread out across the middle of the streak to form the mesoderm.
- later developing into the muscles, bones,connective tissue, circulatory system, notochord, kidney, gonads etc.
how is the endoderm layer formed
when some cells push furhter down the primitive streak (closest to the hypoblast) to form the endoderm,
- forming the lining of the digestive tract, stomach, colon, liver, pancreas, bladder and lungs.
what is the notochord formed, and what is its purpose
the mesoderm forms a thin rod of cells, called the notochord, which is a defining feature in the chordate phylum.
provides structural support in embyros. and (in vertebrates), it is later replaced by the vertebral column.
what is the neural plate, and what is it’s purpose.
when neuroectodermal tissues differentiate from the ectoderm into the neural plate.
the neural plate envelope seperates the ectoderm from the NP
the NP folds with the midline to form the neural tube. the closure going both forward (toward the head) and backwards (towards the tail), until fully fused.
what are the neural components created in response to actions of the notochord
the neural plate (NP)
the neural tube (NT)
the neural crest (NC)
what is the purppose of the NT.
once the tube has fused it disconnects from the crest and epidermis.
- the anterior of the tube = develops intothe brain
- the posterior = spinal cord.
developing the central nervous system
what is the neural crest, and what is it’s purpose
as the NP folds, towards the end the NP boarders get pulled with it, and form a layer of cells above the NT, called the NC.
sometimes aka the 4 germ layer, the cells differentiate to form most of the PNS, schwann cells, and even some bones and connective tissue of the face.
what is the process of the start of the development of the nervous system in ebryogenesis
Neurulation
once the neural tube is folded, what does the medoderm subdivide into, and what else happens
the notochord degenerates, and continues as the nucleus pulposus of the invertebral discs.
the mesoderm subdivides into the axial, paraxial, intermediate and lateral plate mesoderms.
which specific mesoderm subdivision does the notochord come from
the axial mesoderm
what does the parximol mesoderm give rise to
the somites. which go on to differentiate into muscle, catrilage, bone and dermis.
- somite derivatives create a segmented body plan.
what does the intermeditate mesoderm give rise to
our urogenital system - out kidneys, gonands, adrenal glands and the ducts that connect them.
what does the lateral plate mesoderm, give rise to
the heart - the first organ to develop, the blood vessels, body wall, and the muscle in our organs.
during organogeneis, the endoderm rolls into tubes, what do they form.
and what divisions does it have.
the rolling tube of the endoderm, becomes the digestive tract.
this is subdivided into the foregut, midgut and the hindgut.
what organs do the subdivision of the digestive tract give rise to.
foregut - eosophogus, stomach and part of the duodenum, and the respiratory bud (-> lungs)
midgut - the second half of the duodenum, 2/3 of the transverse colon, the cecum and the appendix and the ascending colon.
hindgut - the other 1/3 of the transverse colon, descending colon, sigmoid colon and the upper anal canal.
what happens in gut formation
the primitive gut tube, is connecting to the ectoderm to form the mouth and the anus.
what events in the human embryonic development occur in weeks 1-2
Ferilisation, cleavage and implantation.
what events in the human embryonic development occur in weeks 3-8
Gastrulation, neurulation and early organogenesis.
what events in the human embryonic development occur in weeks 9-38
continued organ development, maturation, growth in the fetal stage.
What is polyspermy
when one egg is fertilised by more than one sperm, the resulting zygot will have have too many chromosomes, and can result in a miscarriage.
what are the 2 mechanisms to prevent polyspermy
fast-block: immediately after the first sperm enters the egg, there’s a rapid change in the elctrical charge of the egg’s membrane, preventing other sperm from fusing.
slow-block (cortical reaction): egg releases enzymes that modify the zona pellucida, making it impermiable o additional sperm.
the germ layers that formed during gastrulation, can deivide animals into 2 broad categories.
what are they, and what germ layers do they have.
diplobastic and tripliblastic.
diploblastic animals hage 2 germ layers - the ectoderm and endoderm.
triploblastic - all 3 germ layers (e,e,m)
so these different categories of animals have different foundations for develkoping tissued and organs in their embryos.
