Embryology - Part 1 Flashcards
What is compaction?
The development of a conceptus into a morula
What is the morula?
Post cleavage ball of cells from which the blastocyst is formed
What does the morula become when it differentiates? Describe this process.
The inner cells differ from those on the outside; forming a blastocyst.
What are the layers of the blastocyst?
Outer layer = trophoectoderm/trophoblast
Inner cell mass (undifferentiated)
Fluid filled cavity
What does the blastocyst do between the 6th and 10th day after fertilisation
The blastocyst hatches from the zona pellucida and implants into the uterine lining.
What does the inner cell mass become between the 6th and 10th day after fertilisation? What forms above and below these layers?
The inner cell mass becomes a bilayer disk composed of:
Hypoblast cells
Epiblast cells
Note: amniotic cavity forms in/above the epiblast around day 8
Yolk sac forms below hypoblast.
Which process converts this bilayer into a trilayer?
Gastrulation
What does gastrulation produce?
A trilaminar embryo consisting of the three germ cell layers:
Ectoderm
Mesoderm
Endoderm
When does gastrulation happen?
14-18 days after fertilisation
What happens to the epiblast cells?
They proliferate and differentiate to form mesoderm cells
Where do the mesoderm cells go?
They move between the epiblast and hypoblast cells
How is the endoderm made?
The mesoderm cells differentiate further to form the endoderm
What happens to the hypoblast cells and why?
They apoptose as they are replaced by the endoderm
What does the ectoderm give rise to?
Skin
CNS
(two largest organs)
What does the mesoderm give rise to?
Muscles Blood Skeleton Heart Kidney (think of everything that's really key for an athlete incl. peeing in a cup to check for doping)
What does the endoderm give rise to?
Gut
Lungs
Liver
(key organs for pharmacology?)
Which layer do other tissues come from?
A mixture of germ layers
What happens BEFORE gastrulation is complete?
Neurulation
What is neurulation guided by?
Neurulation i.e. the differentiation of the ectoderm into the CNS
Guided by: notochord in mesoderm
What initially forms in the ectoderm to prepare for CNS development?
Neural plate
Describe how the neural plate gives rise to the CNS
The neural plate folds inwards, forming a neural groove. The neural crests on either side come together and pinch off, forming the neural tube.
Neurulation and the fusion of the neural tube continues into which week?
3rd-4th week
What else happens in parallel to neurulation?
The precursors of other tissues are forming.
Give examples of precursor tissues forming at the cranial end
Cardiac
Vascular progenitors
Give examples of precursor tissues forming at the caudal end
Primordial germ cells form in the yolk sac at the caudal end
In which two directions does folding of the embryo occur?
Laterally
Anterior-Posterior direction
What does lateral fusion of the embryo actually fuse?
It fuses the ventral midline i.e. the chest and abdomen
Fuses gut tube
Forms main body cavities
What does anterior-posterior fusion of the embryo do?
Folds the primordial germ cells into the hind gut
Folds the heart progenitors under the head of embryo
What has happened by the 4th week?
Precursors of all internal tissues have been laid down
What development happens during the 5th to 8th week?
Elaboration of the tissues generated during the early weeks
Development of which organs happens during the second month?
Urogenital Cardiac Facial Lung Limb
What are the four cellular processes involved in embryological development?
Proliferation
Differentiation
Reorganisation
Apoptosis
