Introduction to embryology Flashcards
Anatomical terms in embryology
Ventral (front) and dorsal (back)
Cranial (superior) and caudal (inferior)
Rostral (superior) and caudal (inferior)
What are Teratogens
Substances that may produce physical or functional defects in the human embryo or fetid after pregnant woman is exposed to the substance
Gametogenesis
Process that converts the PGCs into mature male and female gametes
What is spermatogenesis
PGCs from week 6 of development remain dormant until puberty
At puberty, the testes mature and the PGCs differentiate into spermatogonia
Spermatogonia then undergo meiosis
Then mature to spermatozoa
This is produced from puberty till death
What is oogenesis
PGCs undergo mitosis and differentiate into oogonia in ovaries
By 5th month of development, all oogonia begun mitosis and are primary oocytes
Primary oocytes remain dormant in mitotic arrest until puberty
When puberty starts, each month a primary oocyte will mature and continue meiosis but not finish it, becoming a secondary oocyte and is ovulated
Oocyte then gets fertilised and completes meiosis
What is ovulation
Process in which an oocyte is expulsed from the ovary onto its surface
After how long does oocyte lose its capacity to be fertilised
After 24 hours
What are the steps from fertilisation to blastocyst
Sperm penetrates oocyte, the nuclei swell within the zygote and are called male and female pronuclei
Within 24 hours of fertilisation, the zygote carry out a series of mitotic cell divisions to become a morula
Zygote splits into many daughter cells (blastomeres) but does not increase in size
What does compaction result in
Morula forms 2 groups of blastomere cells
1) inner cell mass (embryo blast)
2) trophoblast
What is embryoblast
Compact mass of cells at one end of the blastocyst
Give rise to the embryo
What is trophoblast
Cells at the periphery from an epithelium
Gives rise to the feral part of placenta
What happens on day 5
Blastocyst hatches from the zona pellucida (Thick transparent membrane surrounding it)
Blastocyst can now interact with the uterine endometrium
What happens at the end of week 1
Blastocyst adhered to uterine wall
Trophoblast at the embryonic pole of the embryo proliferates
Some of these cells lose their membrane and combine forming syncytiotrophoblast
The remaining trophoblast cells that line the wall of the blastocyst are now known as cytotrophoblast
The syncytiotrophoblast fully envelopes the blastocyst
What is the syncytium formed when trophoblast divides
Syncytiotrophoblast
What does the inner cell mass differentiate into
Two epithelial layers
1) epiblast
2) hypoblast
Which of the epithlial layers is dorsal and which is ventral
Epiblast is dorsal
Hypoblast is ventral
What is the amniotic cavity
Appears on the eighth day
Fluid starts to collect between the epiblast and the underlying cytotrophoblast
A layer of epiblast cells form a thin membrane that lines the cytotrophoblast and is called the amnion
How is primary yolk sac formed
Hypoblast cells proliferate and migrate into blastocyst cavity
Why is yolk sac important
Extraembryonic mesoderm that forms outer layer is importsnt site of haemstopoiesis in development
PGCs are first identified in the wall of yolk sac
What happened at the end of the second week
Definitive yolk sac no longer with remnants of primary yolk sac
The bilaminar embryonic disc, the yolk sac and the amniotic cavity are surrounded by the chrionic cavity
The embryonic disc is connected to the cytotrophoblast by the connecting stalk
What is ectopic pregnancy
Implantation of blastocyst into abnormal sites results in an ectopic pregnancy like Peritoneal cavity On the surface of the ovary Within the uterine tube Abnormal site within the uterus
What does gastrulation result in
3 primary germ layer -> foetal tissues
Bilaminar -> trilaminar. Embryonic disc
Establishment of major body axis
What does the appearance of the primitive streak in epiblast layer do
Has cranial and caudal end
Divides the embryo into right and left
The bilaminar/trilaminar disc also forms the dorsal-ventral axis
Migration of epiblast cells through the primitive streak form a layer called the endoderm that replaces hypoblast
Migration of more epiblast cells through the primitive streak forms the intraembryonic mesoderm
Remaining epiblast cells now ectoderm
What is the ectoderm
Germ layer that forms the covering of the body (skin) as well as the nervous systems
