Embryology and Defects Flashcards
how does gestational timing differ with embryological timing?
Embryological timings are usually about 2 weeks less than the gestational time frames
GA uses LMP (2 weeks ahead/greater)
embryological age is the true foetal age
when does gestational timing starts from?
last menstrual period
which trimester has the most rapid weight gain in the foetus?
1st
what system is used to measure development of the embryo?
Carnegie stages
what is a blastocyst?
consists of a bilayer of epiblast and hypoblast
present at ~9-10 days
0.1 cm wide
give rise to all the tissues of the foetus
what is an embryo?
small developing conceptus present at ~5-6 weeks and is around 1cm wide.
what is a foetus?
after 8 weeks of development the conceptus can be referred to as the foetus (recognisable human)
developing conceptus
what is a conceptus?
anything derived from a fertilised egg
where are red blood cells produced in the embryo?
liver
what 4 process allow cells to reach embryological development?
o Proliferate
– in response to GF, receptor expression, cell survival
– all via para- or autocrine signalling.
o Move
– chemoattractants, cognate receptors, facilitated (via remodelling and proteases)
o Differentiate
– paracrine regulation, receptor expression, loss of proliferation.
o Cell loss
– PCD controlled by mainly paracrine factors.
what do the different signalling methods mean?
- paracrine
- autocrine
(- endocrine)
o Paracrine – to adjacent cells.
o Autocrine – to oneself.
- endocrine over long distances via vasculature but this does not occur in embryo development due to a lack vasculature
what is meant by concentration signalling?
the strongest signals are received by cells located closest to the source of the signalling molecules.
what is meant by a bud in development e.g limb bud?
If the source cells are at the tip, the highest levels of proliferation will remain at the tip and thus a “bud” will form towards the apex
With +ve stimuli and –ve stimuli, asymmetrical development
how does the formation of embryological structures depend on factors (to achieve their shapes etc)?
gradients of factors, combinations of factors, temporal changes in factors or responses to them.
what animal models are used to make sense of the complexity of the multiple influences driving embryology?
o Chick – limbs, mainly with wings.
o Fish – eyes.
o Mouse – knock-out or knock-in with tissue specificity.
our genes are similar to these animals
what are HOX genes?
group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals (AP) e.g. differences in the vertebrae, CNS divisions, patterns in the limbs.
what is HOX activation controlled by?
Activation of HOX is controlled by retinoic acid, a derivative of vitamin A.
HOX genes provide body plan of embryo
what does the conceptus start off as?
bilaminar disc inside a blastocyst
– comprised of an epiblast and a hypoblast layer
what is the result of gastrulation of the conceptus (day 14-18)?
3 layers created:
- ectoderm
- mesoderm
- endoderm
gastrulation is one of many complexes series of changes that occur to the blastocyst bilayer
where does gastrulation take place?
what happens in it?
occurs down the primitive streak
a. Epiblast cells migrate towards the centre.
b. Epiblasts then differentiate into the mesoderm cells and move down into the new mesoderm layer (between epi- and hypoblast)
c. The hypoblast cells apoptose and are replaced by endoderm cells (which has differentiated from mesoderm cells)
gastrulation is the process by which the blastula cells migrate and divide to form the 3 primary germ layers of the gastrula
(neurulation refers to the folding of the neural plate into the neural tube)
what does the endoderm develop into?
- lining of the organs
- becomes gut, liver, pancreas and lungs.
what does the mesoderm develop into?
muscles, kidneys, heart, blood and skeleton
MK-HBS
what does the ectoderm develop into?
skin and the CNS
what does the ectoderm proliferate into after gastrulation?
proliferates to form the neural plate i.e. CNS
(with no proliferation at the neural groove due to negative stimulation of notochord)
and the neural fold’s fold over and form the neural canal.