Early Embrology Flashcards
Describe the the development of primordial germ cells
Primordial germ cells develop from the wall of the yolk sac during the 2nd week of development, migrate into the embryo to the gonadal ridges, where they undero rapid mitotic divisions.
What is the difference of proliferation of primordial germs cells between the sexes
Oogina multiply rapidly until the 5th month reaching 7 million, then many undergo atresia
Spermatogenia continue to slowly proliferate from puberty throughout life
In the production of gametes how many meiotic cell divisions occur?
2 Diploid -> Haploid
What happens to the primodiary follicle before & after birth until puberty
In fetal life differentiate into primary oocyte, at birth enter prophase of first meiotic division & remain suspneded until puberty (suspended by oocyte maturation inhibitor OMI)
After puberty the primodiary follicle changes to primary follicle - how does he physiology change
primodiary follicle becomes surrounded in granulosa cells & ovarian connective tissue (theca folliculi)
The theca folliculi then divides into theca interna (vascualr/secretory) and theca externa (outer fibrous layer
When does fertilisation occur
12-24hours post ovulation
5 stages of fertilisation
1) Sperm activation & penetration of the corona radiata
2) Attachement & penetration of zona pellucida
3) Fusion of oocyte & sperm cell membrne
4) Completetion of meiosis in the oocyte & formation pronucli
5) Formation of the zygote
What is the name of the process sperm undergo to be capable of penetrating the ovvum? What happens?
Capacitation
Removal of glycoprotein & cholesterol of the acromsomal head frmo the secretions of he cervix/uterus
When come into contact with the corona radiata, they release the enzyme hyaluronidase
zona pellicuda -> reaction to prevent further sperm penetrating
What happens to the oocte on entry of the spermatzoa?
Second meitoic division, forming the mature ooytes and a second polar body.
The chromosomes of oocyte/sperm condense to form pronuclei -> then mix to form zygote
What is morula?
After mitotic division of the zygote, a 16 cell embro forms, each cell is called a blastomere, as each cell divisides the cells become smaller, they are all pluripotent.
Explain the anatomy of a blastocyst
Outer layer of cells: trophoblast
Inner cell mass
Blastocele inner cavity
How long after fertilisation is & where in the anatomy
1) 2 cell embryo
1) 30 hours middle of the tube
How long after fertilisation is & where in the anatomy
morula
3 days
junction of uterine tube & uterus
How long after fertilisation is & where in the anatomy
blastocyst
4-5 days
uterine lumen
During implantation
what is the name of the invading trophblast into maternal endometirum?
Syncytiotophoblast
During implantation the inner cell mass divides into 2 layers - what are these called
which layer a splits to form amniotic cavity
epiblast & hypoblast
epiblast splits to form amniotioc cavity
What is he primary yolk sac? What does it form from?
Fluid filled sac that is a source of nutrition for the embryp before the placenta is fully formed.
Forms from hypoblast -> bilaminar embryonic dis
At day 13 what does the cytotrophoblast form?
Primary chorionic villi which are finger like protrusions into the lacunae.
At day 13 describe the form of the embryo proper
The epiblast and hypoblast applied to each other (the bilaminar embryonic disc), the amniotic cavity above and yolk sac below the hypoblast.
At the end of the second week what does the syncytiothrophoblast produce? What is its role?
hCG, maintains the corpus lutem in the ovary which sustains the thickness of the endometrium
What is granulation?
Formation of 3 germ layers
Epiblast → ectoderm → mesoderm
Hypoblast → Endoderm
In general what tissues do each other layers form?
- Ectoderm
- Mesoderm
- Endoderm
Ectoderm: Epidermis and nervous system
Mesoderm:
Endoderm: Linning of GI and resp system
Mesoderm: Skeletal, connective tissue, muscle
How is the mesoderm layer produced?
End of the second week, a groove in the bilaminar embryonic disc called the primitive streak forms. Cells from the ectoderm migrate toward the streak and then detach from it and spread laterally beneath it forming the mesoderm. New layer lies between ectoderm and endoderm
The ectoderm and endoderm remain attached in 2 areas, the cloacal membrane and buccophargeal membrane.
What does the buccophargeal membrane form?
The oral cavity
What is the notochord? How does it develop and what is its significance?
Cells from the primitive streak migrate cranially towards the buccopharygeal membrane, creation the notochordal plate which forms folds to form a solid cylinder the notochord. This underlie the future neural tube
forms a longtiduninal axis for the embryo, and the centre nuclei polposi of intervertebral disc.
What is the importance of neural crest cells?
At the edges of the neural tube, where the neuroectroderm is continous wth the ectoderm, neural crest cells form - these detach from the neural tube and migrate from discrete structures
These contribute to the formation of autonomic ganglia, connective tissue, adrenal medulla, enteric ganglia, schwann cells, meninges, teeth.
What are the 3 segments of the mesoderm?
Paraxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm
What does the paraxial mesoderm from?
Skeletal muscle of trunk and limbs, skeleton (except skull) dermis and connective tissue
What are somites?
The paraxial mesoderm form paired blocks of tissue in the craniocaudal direction called somites, ranging up to a number of 42-44 pairs depending on the age of the embryo.
What 2 layers to the somites divide into?
Outer dermomyotome (connective tissue and skeletal muscle) Inner sclerotome (bone and cartilage)
Cells from the sclerotome surround the notochord and give rise to the vertebral column
The myoterms split into?
Dorsal epimeres and ventral hypomere.
Epimere → epaxial muscles/spine mucks
Hypomere → muscle of body wall
ventrolateral give buds off that give future limbs.
What does the lateral plate mesoderm form?
Serous membrane of the body, pleural/pericardium/peritoneum. Smooth muscle connection tissue
That in contact future body → parietal layer and that in contact with endodermal gut → visceral layer
What does the intermediate mesoderm form?
The urogenital tract
How is the yolk sac lost?
During the fourth week, lateral fold around the embryo the amniotic cavity pinches the the communication between the yolk sac and the gut → forms a narrowed communication the vitelline duct which is later lost.
4th week is all about the folding of the embryo.
