Embryology Flashcards
When is considered the first day of pregnancy
The first day of the last period
What is in the head of sperm
Acrosome and nucleus
What is in the mid-piece of sperm
Mitochondrion (around 100)
What is in the tail of sperm
Fragella (9+2 arrangement of microtubule)
What is the secondary oocyte locked at
Metaphase II
Name the 2 layers the sperm has to penetrate to fertilize the ovum
Corona Radiata and Zona Pellucida
Name the 2 reactions to prevent multiple fertilzation of a single ovum
Cortical reaction and Zona reaction
What is the Cortical reaction caused by. And the effect?
By release of secretory granule to make the surface, or accurately, perivitelline space inpenetrable
What is the Zona reaction caused by and the effect
By hydrolytic enzyme and to remove the ligand on Zona pellucida to make it inpenentrable
What happens to the nuclei of the fertilized Oocyte
It continues the meiosis II
Where are the remaining nuclei formed by meiosis II of oocyte
They become polar body
What will happen after formation of oocyte nuclei
Approximation of pronuclei (from sperm and ovum)
On 8th hour, what important event happens.
What is it about
Why is it important
cleavage.
Forming new daughter cells (blastomeres) with little or no growth in early embryo
To restore normal cytoplasm:nucleus ratio
Active transcription and protein synthesis
Maternal recognition of pregnancy
Cell fate determination
What is the names when the early embryo contains 16 blastomeres and ~100 respectively
Morula; Blastocyst
What is compaction
Forming tight junctions betwen blastomeres to maximize cell-to-cell contact
What is blastogenesis
What is observable change
When does it take place
It means formation of blastocyst
At morula stage, cavity starts to appear
–> forming blastocyst with a well-defined inner cell mass (embryoblast) and outer cell mass which has flattened cells forming the epithelial wall of blastocyst (trophoblast)
–> On day 5,The blastocyst hatches from zona pellucida and can implant on uterus endometrium on day 6
Name 3 cases for monozygous twins to occur
- division of the early embryo to form 2 embryo
- Division of 2 inner cell mass without dividing trophoblast
- Incomplete division of inner cell mass to form the co-joined twins
What does hatching means.
What is the fate if it fails
What is the fate if it takes place too early
It means the blastocyst will hatch from the Zona Pellucida to get prepared for implantation.
Failure causes infertility
Too early causes ectopic implantation
Where should implantation take place. Where does it mostly take place in ecotopic implantation
When does it take place
Uterus
Tubal pregnancy (Mostly Ampulary, ie site of fertilization)
Day 6
What is the characterisitic of syncytiotrophoblast.
What hormone does it create
What is it’s origin
Syncytiotrophoblast is multinucleated, and is cancer-like and invades the endometrium of uterus
Human Chorionic Gonadotrophin (HCG)
It is by cytotrophoblast
What are bilaminar layer and the cavities formed
Epiblast –> Amniontic cavity
Hypoblast –> Yolk sac
What is surrounding the primitive yolk sac
Heuser’s membrane
What is formed in the syncytiotrophoblast and anastomose with maternal blood sinusoids
trophoblastic lacunae
Due to a reason, there is space between the cytotrophoblast and the bilaminar disc. What is the reason and what fills up the space
The cytotrophoblast grows faster than the inner cell mass.
Extraembryonic mesoderm
Within the extraembryonic mesoderm, a cavity forms. What is that cavity and what are the 2 layers forming that cavity
Chorionic cavity
Somatic mesoderm and splanchnic mesoderm
What are the fate of the somatic mesoderm and splanchnic mesoderm respectively
Somatic mesoderm forms the chorion, the precursor of placenta
Splanchnic mesoderm: Wrap around the amniotic caivty and yolk sac
How does the primitive yolk sac becomes definite yolk sac.
What is the fate of the primitive yolk sac
When will the 2 yolk sacs completely lose contact
The hypotrophoblast undergoes a second wave of proliferation to form a new membrane to push the primitive yolk sac away.
The primitive yolk sac eventually degrade into several vesicles
By the end of second week
At the end of second week, what suspends the yolk sac and the amnion
Connecting stalk.
During the embryonic period, what is formed by the movement of the epiblast .
What is the axis it is growing along and from where to where.
Which end does it elongate
What is formed by the proliferation at an end
It also forms a depression, what is it called
Primitive streak
Cranial-Causadal axis
It elongate at the causadal end
It forms the primitive node at the cranial end
Primitive Pit
What is gestrulation
It is the migration of cells
How is the 3 germ layers formed
The epiblast ingress along the primitive streak to displace some of the hypoblast cells to form the endoderm
Some epiblast ingress to the space between the endoderm and the epiblast, and becomes the mesoderm
The pre-existing epiblast becomes the ectoderm
What will the mesoderm becomes after migation
To future oropharyngeal membrane
–> Cranial mesoderm
Moving slightly lateral from midline
–>Paraxial mesoderm
—-> Form somite in the future
Moving to a more caudal part
–>Intermediate mesoderm
—-> Form Urogenital mesoderm
Move laterally from caudal end of Pirmitive streak
–> Lateral plate mesoderm
A mesoderm is split into 2 layers. Name the mesoderm, the stuff splitting that and the spilted layers
Lateral plate mesoderm’
Coelomic vesicle
Somatic mesoderm and Splanchnic mesoderm
What are the fate of somatic and splanchnic mesoderm
They will grow and eventually meet the extraembryonic mesoderm
Where the somatic mesoderm develops into body walls
The splanchnic mesoderm forms body cavity and lining of internal organs
Where is the notochordal process happening and what is it about.
Some cells ingress and go downwards to between ectoderm and endoderm in the central midline from the primitive node and pit (Notochordal process)
Name the 2 sites that the ecoderm and endoderm are fused
The oropharyngeal membrane (future mouth) and the cloacal membrane (future anus)
What is the prechordal mesoderm
The first group of mesoderm that arrives at oropharyngeal membrane
What happens after the notochordal process (day 17)
The cells are the central undergoes apoptosis and make it hollow
At day 18, what is formed at the base of notochordal chord
Notochordal plate (opening at the base of notochordal chord)
At day 19, what will happen
the notochordal process and the endoderm fuses and degenerate to form a connection between the amnionic cavity and the yolk sac.
Note that as the ectoderm is the precursor of nervous system while the endoderm is the precursor of GI tract, the canal formed is alos called neuroenteric canal
What is the fate of the remnant of the notochord
nucleus pulposus of interverbral disc
What body parts are derived from the ecoderm
The outerlining, which includes the epidermis
And the nervous system
What body parts does the endoderm forms
Majority of epithelial linings of the body, most have connections with external world
GI tract, respiratory tract, urethra
What body parts are formed by the mesoderm
Bones, muscles, bone marrow, blood, blood vessel,lympathic vessel, internal reproductive organ, kidney and epithelial linings of body cavities ( pleural and peritoneal linings)
What is neurulation
Both the notochord and prechordal mesoderm are able to induce part of the ectoderm to become a neural plate.
The notochord then further induces the neural plate invaginates along its central axis to form a longitudinal median neural groove, which has neural folds on each side.
So this is the neural fold, and this is the neural groove.
Eventually the neural groove will deepen more and completely detach from the ectoderm above to form the neural tube.
What are the derivatives of the neural tube
- Sensory and postganglionic
portions of PNS - Adrenal medulla
- Melanocytes of the skin
- Connective tissues of the head
What wil somite be divided into
medial part (Sclerotome): Vertbebrate and ribs
Middle part (Myotome): skeletal muscle
Lateral part (dermatome): Dermis of skin
Where does somite grows
Along neural tube
What are the derivatives of endoderm and how are they formed
- At week 3-4, it grows rapidly and foldsa around the yolk sac (cranial-caudal fold) to become a cylindral form
–> Internalizing the endoderm and is iniitated by the rapid growth of somite and lateral plate mesoderm)
During further development, endoderm gives rise to pharyngeal pouches, epithelial
lining of the lung buds and trachea, liver, gallbladder, and pancreas
What is the origin of gametes and where are they formed.
What is the time and where will they migrate to
Primordial Germ Cell (PGC) in epiblast at 2nd week
They will migrate to the wall of YOLK SAC
After migrating to yolk sac, where will the PGC move (4-6 weeeks)
It will migrate to the wall of gut tube and then dorsal body wall
Most populate at the level of gonads.
In male gametogenesis, when will the PGC remain dormant till
From 6th week to puberty
What are the phases of Sperm development
PGC derives into Spermatogonia
Spermatogonia grows and increase in size to form primary spermatocyte
Primary spermatocyte undergoes meiosis I to form secondary spermatocyte
Secondary spermatocyte undergoes meiosis II to form spermatid
Spermatid undergoes Spermiogenesis to form spermatozoa
What does spermiogenensis involve
Adding acrosome
Condensation of nucleus
Forming head neck tail
Shedding most cytoplasm as Residual Body
What is the path of PGCs before birth
PGC differientates to form Oogonia
Oogonia and some PGC enters prophase of meiosis I to become primary oocyte (Around month 7 most oogonia are converted)
At this stage there is a flat follicular epithelial cell surrounding the primary oocyte
Newborn babies will have primordial follicles (flat epithelial cell surrounding primary oocyte)
What will happen to the oocyte during puberty
It develops into the primary follicle which has cuboidal follicular cell and well-developed ZOna pellucida
The connective tissue of ovary also becomes more organised
It then complete first meiosis to form secondary follicle.
At the secondary follicle, the Secondary oocyte has the first meiosis completed and a follicular antrium is found within the follicle
At last, a Graafian Follicle forms, which has a large space inside
The secondary oocyte is locked at metaphaseII 3h before ovulation
