Embryology Flashcards
how many weeks does the pre-embryonic stage of development last?
0-3 weeks
what weeks does the embryonic stage of development last?
weeks 4-8
in oogenesis what does the oogonium develop into?
1 ovum and 3 polar bodies
what develops into 4 sperm in spermatogenesis?
spermatogonium
what two things fuse in the egg during fertilisation?
the( pro)nuclease of the egg and sperm
apart from the (pro)nucleus what else can be transferred in fertilisation?
the mothers mitochondrial DNA, meaning mitochondrial disease can be passed from parent to child
what does the diploid zygote form?
a morula (solid ball of cells)
what does it nutrition become difficult for the morula and how is this problem overcome?
as the morula increases in size getting nutrition to the core becomes difficult so a cavity develops- blastocystic cavity
in a blastocyst what cells is the outer lining made of?
trophoblasts
where does fertilisation occur in the uterus?
at the distal ends of the uterine tubes
where in the womb does the blastocyst settle?
in the endometrium, an inner lining of blood vessels that grow under the influence of hormones
around what day has the blastula formed and reached the uterine cavity?
day 5 or 6
what is an ectopic pregnancy?
this occurs if the cilia function is abnormal and unable to transport the blastocyst to the uterus so it implants in the uterine tube. this is known as a tubular pregnancy and can often rupture
what do the trophoblasts form during implantation in week 2?
the divide forming two layers that makes up the chorion
what are chorionic villi?
the chorion develops finger like processes that aides in implantation
what does the chorion do?
> implants
forms part of the placenta
secretes human chronic gonadotropin (HCG) which keeps the endometrium in place during pregnancy
what is the decidua basalis?
part of the endometrium deep to the implanted conceptus
what do the inner cell mass form in week two?
the bilaminar disc
in week 2 what two cavities are formed?
the amniotic cavity and yolk sac
what are the main functions of the placenta?
> foetal nutrition
transport of waste and gases
immune protection
describe the maternal surface of the placenta
the decidua basalis is rough and has maternal blood vessels
describe the foetal side of the placenta
it is smooth and contains the end of the umbilical cord
when is the placenta matured?
weeks 18-20
describe the conditions in a dizygote/fraternal multiple birth
2 ova are released and are fertilised by two sperm creating two separate zygotes that have different genetic make up. this can run in families.
in week 2 what are the names of the two layers of cells in the inner cell mass between the cavities?
the epiblast (in amniotic cavity) and the hypoblast (in the yolk sac cavity)
describe monozygotic twins
there is one ovum that is fertilised by one sperm that develops into to one zygote that then splits into to 2 and each cell develops into a different embryo.
in what week are the germ layers developed?
week 3
what is the primitive streak?
this is formed by cells dividing at a faster rate than the rest of them and develops in the midline of the epiblast.
where do the epiblast cell migrate to in week 3?
they migrate into the space in between the epiblast and the hypoblast layers, displacing the hypobalst
name the three germ layers
ectoderm, mesoderm and endoderm
describe the development of the notochord
the cells forming the primitive streak sink down to form a solid tube between the mesoderm and endoderm, this is the notochord.
how is the neural tube formed?
the notochord sends signals to the ectoderm and a neural plate begins to form. this plate sinks down until the edges of the plate come together to form a tube between the ectoderm and mesoderm.
what induces the mesoderm to thicken?
the neural tube
name the three section that the mesoderm divides into
the paraxial mesoderm
the intermediate plate mesoderm
the lateral plate mesoderm
what does the lateral plate mesoderm split to for?
the somatic and splanchnic mesoderm
what is the space formed between the splanchnic and somatic mesoderm?
the intraembryonic coelom
what mesoderm goes on to form the somites?
the paraxial mesoderm
what is formed from the intermediate plate mesoderm?
the urogenital system (kidneys and repro)
in the lateral folding of the embryo what surrounds the whole embryo?
the ectoderm
what forms the pleural cavity?
when the embryo folds laterally the space between the somatic and splanchnic mesoderm (intra-embryonic celom) forms the pleural space.
what does the endoderm go on to form?
the gut
name the three sections that the somites split into in week 4 to 8.
the dermatome, myotome and sclerotome.
what do each of these sections of somites go on to form?
> dermatome: dermis of the skin
myotome: muscles
sclerotome: bones
what is teratology?
the study of when things go wrong in development
what is a teratogen?
this is an environmental factor that causes abnormal development.
give some examples of environmental teratogens
> drugs > alcohol > tobacco > infectious agents > rubella > herpes .....
name some genetic factors that could affect development
too many chromosomes
too few chromosomes
structural changes to genetic make up
when is the greatest sensitivity to teratogens?
weeks 3-8
what factors does the risk posed by a teratogen depend on?
> exposure during critical periods of development
dosage of drug/chemical/factor
genetic constitution of the embryo (some are more susceptible than others at the equivalent dose)
what pre-natal tests would be carried out to check for developmental abnormalities?
> blood test
ultrasound scan at 12 weeks
invasive tests such as a chorionic villus sampling)
what does the transverse septum “shelf” develop into?
it’s four components fuse together to form the diaphragm, separating the thorax and the abdomen
describe the development of the pleura
the lung buds punch into the visceral mesoderm. the mesoderm covering the outside of the lung develops into the visceral pleura and the somatic mesoderm covering the body wall on the inside becomes the parietal pleura.
where is the oesophagotracheal septum?
it develops between the trachea and oesophagus, separating them into the trachea ventrally and the oesophagus dorsally.
what is an atresia?
this is when an orifice or passage in the body is closed or absent
what is a fistula?
an abnormal/surgically made passage between a hollow or tubular organ and the body surface/ between two hollow or tubular organs. it is between two epithelial surfaces.
what are accessory lobes?
they are extra lobes such as the azygos lobe that has no clinical impact.
what is angenesis of the lung?
when the lung tissue has not fully developed
where is the septum transversum originally located?
opposite C3-C5 somites
what does the septum transversum bring with it when it migrates?
spinal root C3-C5 (the root values of the phrenic nerves)
what is a sliding hiatus hernia?
this is what causes heart burn
what is a paraoesophageal hernia also known as?
a rolling hernia
