Embryology And Fertilisation Flashcards
Why is semen alkaline?
Neutralises acidic vaginal fluid
Approx how many sperm are left by the infundibulum?
1000
What kills off the sperm
Stuck in vaginal mucus
Lost in cervix
Absorbed by white blood cells
(Contraception)
Why do sperm rub against the tube walls
Removal of the glycoprotein coat of the acrosome.
Called capacitation
What is the acrosome
Cap like structure around sperms nucleus
What does the sperm secrete after capacitation
Hyaluronidase
What does hyaluronidase do
Breaks down hyaluronic acid (such as the layer that protects the egg)
What is the Corona radiata
Layer of follicular cells around the egg
What is the zona pellucida
Extracellular matrix of glycoproteins
What are the stages of the acrosomal reaction
- Release of acrosin from the sperm
- Creation of actin anchors from the sperm that anchors and binds ZP3 proteins.leading to fusion of sperm and egg plasma layers - SPERM BINDING
What is the cortical reaction
Rise in internal egg calcium leads to fusion of granules with the egg cell membrane
What does the cortical reaction create
The hyaline layer
What does the hyaline layer do
Prevents more than one sperm from fertilising the egg
What happens inside the egg while the hyaline layer is being created
Meiosis II - creation of the 23 chromosome female pronucleus
What happens to the male and female pro nucleii
Dissolve the nucleus envelope and mitotic spindle weaves the chromosomes into complimentary pairs
What is the moment the zygote is formed called
Syngamy (single cell!)
Name the two outer layers of the egg
Corona radiata and zona pellucida
Where is the most likely place for fertilisation to take place?
Ampullary region of the fallopian tube
How many hours after fertilization has the zygote hit the 4 cell stage
40 hours
How many hours after fertilization has a zygote hit two cells
30 hours
What process in the zygote separates inner cells from outer cells in the blastocyte?
Compaction
What is the mullerian duct system responsible for the development of?
Uterus, cervix and upper two thirds of the vagina
What is a 16 cell blastocyst called
Morula (mulberry shaped)
What is the outside layer of the blastocyst called
Trophoblast
Embryoblast become what
Fetus
What cells invade the uterine wall at implantation
Syncytiotrophoblast
How many cells has a zygote at 3 days after fertilization
12-16
What structure secretes hCG in early pregnancy
Syncytiotrophoblast
A failure of cortication results in what?
Polyspermia
On day 8 what layer does the blastocyst attach to?
Decidua basalis
Name the segments of the trophoblast
Cytotrophoblast (mono nucleus)
Syncytiotrophoblast (many nucleii)
Explain the decidual reaction
High progesterone enlarges decidual cells and coats them in a sugar rich, fatty fluid.
Initially only occurs at decidua basalis, but eventually spreads throughout all of the decidua
What develops around day 14 outside the blastocyte
Primary villi start to grow, forming lacunae (empty spaces) and encouraging growth of blood vessels into the lacunae (this eventually creates a large pool of blood, the junctional zone)
What happens around day 14 inside the blastocyst
Formation of the bilaminar embryonic disc
What is found within the yolk sac
Vitelline fluid
What cells line the outside of the yolk sac
Hypoblasts
What is the initial stages of the embryos germ layers?
Epiblast
What lines the amniotic cavity
Epiblast cells
What do extraembryonic mesoderm cells do
Line the outside of the cytotrophoblast and create space for the chorionic cavity
What does the embryoblast become
Epiblast and hypoblast
In what direction does the primitive groove form
Caudal to cranial
What makes up the primitive streak
Primitive groove
Primitive pit
Primitive node
Name the layers of the trilaminar disc
Endoderm
Mesoderm
Extoderm
What are the two bilaminar areas in the trilaminar membrane
Oropharyngeal membrane (mouth)
Cloacal membrane (anus and genitourinary tracts)
What does the notochord do
Transient solid rod
Influences embryo folding
Secretes sonic hedgehog (diffuses out and allows cells to know where they are in 3 dimensional space
What does the mesoderm differentiate into on day 20
Paraxial, intermediate, lateral
Explain neurulation
Neural plate - neural groove (with neural folds) - neural tube (between mesoderm and ectoderm)
What happens in the junctionional zone at the end of week 3?
Secondary villi grow into the primary villi, creating the fetal contribution to the placenta and the villous capillary system
What does gastrulation do
Gives the embryo it’s specific head to tail and front to back orientation
What is the movement of epiblast cells towards the primitive streak called
Invagination
What are the trophoblastic primary villi composed of
Cytotrophoblastic core covered by syncytiotrophoblast
What is the first step of gastrulation
Formation of the primitive streak
What is the source of germ layers during gastrulation
Epiblast
What does the exocoeleomic membrane derived from
Hypoblasts
How long does spermatogenesis take
74+4 days
Where does the diaphragm originate from
Septum transversum of the fourth pharyngeal arch
What is the origin of the renal tubules
Metanephric blastema
What stimulates the mesonephric ducts
Androgens
What stimulates the paramesonephric ducts
Oestrogen
What causes regression of the paramesonephric ducts
Mullerian inhibiting substance
What do the paramesonephric ducts become in men
Appendix testes
What does the wolffian ducts become in females
Atrophy to Gartner’s duct, suspensory ligaments of the ovary
What does the ectoderm become?
EXOSKELETON - skin, eye lens, external auditory meatus, adrenal medulla, nerve systems, appendages
What does the mesoderm become
SKELE and MUSCLES dermis, urogenital ( kidney, repro), bone, muscle, vascular, lymph and spleen, adrenal cortex
what does endoderm become
INNER = ORGANS eustachion tube, middle ear, GI tract, liver, endocrine bits, resp system, bladder
What is the notochord from
mesoderm
what does lateral mesoderm become
skeletal limbs
what does intermediate mesoderm become
urogenital system
what does paraxial mesoderm become
axial skeleton (somites become vertebral colum)
what does the neural crest (ectoderm) become
cranial bones
What are the parts of the pharangeal apparatus
Arches (mesoderm) Pouches (endoderm) clefts (ectoderm)
Pharangeal arch 1 =
CN V (trigeminal) - muscles of mastication
Pharangeal arch 2 =
CN IIV (facial) - muscles of facial expression
pharangeal arch 3 =
CN IX (glossopharangeal) - swallowing (stylopharangeus) + hyhoid bone
pharangeal arch 4 + 6=
CN X - Vagus nerve, (voice box,) larynx musces, some swallow`
pharangeal pouch 1 =
eustachion tube
Pharangeal pouch 2
palentine tonsil
pharangeal pouch 3
inferior parathyroid + thymus
pharangeal pouch 4 + 6
superior parathyroid, ultimobranchial body
Pharangeal arch 1
maxillary arches
Pharangeal arch 2
regresses
pharangeal arch 3
internal and common carotids
pharangeal arch 4
L = aorta arch R = subclavian
Pharangeal arch 6
pulmonary arteries, L forms ductus arteriosus
when does fetal heart start beating
day 22
What is the allantois
connects yolk sac to hind-gut (endoderm). becomes median umbilical ligament.
what produces HCG
syncytotrophoblast
which fetal cells connect to maternal cells/blood
syncytotrophoblast
What is another word for paraxial mesoderm
Splanchnic mesoderm
What is another name for parietal mesoderm
Visceral mesoderm
When does the neural tube close
Day 25 head end day 28 tail end
What forms the somites
Paraxial mesoderm
What connects the yolk sac to the midgut
Vitteline duc
Where is the mesentery from
Mesoderm
What does the septum transversum become when it meets the pleuroperitoneal fold?
Diaphragm
What happens if there is a failure of the septum transversum and ventral pleuroperitoneal fold to meet
Congenital diaphragmatic hernia
What does the buccopharangeal membrane break down to become
Stomodeum
Where does the respiratory diverticulum form from
The endoderm of the foregut
Where do the ventral and dorsal pancreatic buds form
The fore gut endoderm
What grows down to divide the cloaca
Urogenital septum
When does the superior mesenteric artery form?
Week 5
Where does the gut go as it forms?
Between weeks 6 + 10 lengthen and twist out into the umbilical cord.
Then from week 10 return.
If not, omphalos.
What happens if the vitiline duct doesn’t disappear?
Meckel’s diverticulum
Where is Meckel’s diverticulum
50cm back from ceacum, on the illeum.
What is liver made of
Mix of mesoderm and endoderm.
Most of billiary tree is endoderm
Special fetal blood making cells are mesoderm
What does the liver divide the ventral mesogastrium into
Falciform ligament, + lesser omentum
What does the dorsal mesogastrium become
Greater omentum (4x mesoderm layers)
What makes up the muscles and cartilage of the chest wall
Splanchnic mesoderm
What cavity do lungs grow into
Intraembryonic cavity
