L8 Embryology Flashcards
Prior to gastrulation, embryonic cells are __?__
Pluripotent
Where does fertilisation take place?
Ampulla region of the oviduct
What is a ‘morula’?
The classic ball of 16 cells that forms as the fertilised zygote divides repeatedly.
What distinguishes a blastocyst from a morula?
Blastocyst contains a fluid sac of nutrients
The zygote divides into two __1__. Whilst the __2__ splits equally, the other contents of the cell do not - meaning one daughter cell will get more of certain factors than the other.
- blastomeres
2. nucleus
When the zygote contains 8 cells, the blastomeres undergo compaction. What is this process?
Compaction: flattening of blastomeres, maximising cell-cell contacts and forming tight junctions.
How does rotational cleavage occur in the zygote?
Each time the blastomeres divide they form a new cleavage plane
Why does the zygote need to form tight junctions?
To create a closed environment
Around day 5 the morula becomes a __?__
blastocyst
The outside of the blastocyst is made up of [1. polar/non-polar] cells (called __2__) and is called the __3__
- polar
- trophioblasts
- trophectoderm
The inside of the blastocyst is made up of [1. polar/non-polar] cells and is called the __2__. These internal cells form two layers: the __3__ and the __4__.
- non-polar
- inner cell mass (ICM)
- epiblast
- hypoblast
The __?__ is a fluid filled sac that develops within the blastocyst.
blastocoel
Around day __?__, the blastocoel begins to invades the uterine epithelium.
seven
At 8 days (when the blastocyst pentrates the uterine tissue), the trophoblasts of the trophectoderm differentiate into __1__ and __2__.
- cytotrophoblasts
2. syncytiotrophoblasts
Syncytiotrophoblasts do what?
Proliferate in uterine tissue as the blastocyst penetrates the wall of the uterus.
Around day 9 of gestation, a new cavity opens up adjacent to the epiblast. What is this cavity?
The amnionic cavity
What does the ectoderm give rise to?
- Epidermis
- Nervous system
- Pigment cells
What does the mesoderm give rise to?
- Gonads
- Bones
- Muscle
- Kidneys
- Heart
- Blood cells
- Most internal organs
What does the endoderm give rise to?
- Lining of gut
- Respiratory system
What is ‘pattern formation’?
embryology
The process by which a spatial and temporal pattern of cell activities is organised within the embryo.
Involves coordinated mechanisms of cellular communication.
e.g. axis specification, formation of germ layers
What is ‘induction’?
embryology
The process by which the presence of one tissue influences the development of others.
Certain tissues, especially in very young embryos, have the potential to direct the differentiation of adjacent cells.
What is ‘morphogenesis’?
embryology
The achievement of developmental diversity by formation of different structures from the same initial structure.
E.g. Gastrulation, neurulation, limb formation etc.
Juxtacrine (adjacent cells) or paracrine (nearby cells, but not touching) signalling leads to yes/no response. However, can also be variable as a result of modulation by interplay with other signals.
What is a morphogen?
A signalling molecule that forms an extracellular concentration gradient.
e.g. hedgehog, wingless, activin
Cells nearer the source of secretion are exposed to a higher concentration than those further away, affecting the way they develop and allowing differentiation/specialisation
In order for morphogenesis to occur, what characteristics must responding cells posses?
- competency to respond
- ability to detect inducing agent
- ability to quantify levels of inducing agent
