L4) Embryology 2 & Early pregnancy Flashcards
what is the embryonic period?
weeks 3 to 8
all major structures and systems are formed
why does the embryonic period have the greatest risk of major congenital malformation?
due to environmental exposure of drug therapy
how does the timing of the exposure dictate the consequences?
if pre-embryonic - lethal effects (pregnancy will not continue)
if embryonic
how does the timing of the exposure dictate the consequences?
if pre-embryonic period - not sensitive usually, high rate of lethality (pregnancy will not continue)
if embryonic period - greatest sensitivity, each organ system has its unique period of peak sensitivity
if fatal - decreasing sensitivity, period of functional maturation
the risk of functional development persists on what structure throughout pregnancy?
CNS
as it is the first to begin and last to finish development
what are the stages of early development?
fertilisation and implantation
gastrulation
neurulation
segmentation
folding
what is the result of early embryonic development?
foundations laid for the development of body systems
by placing sufficient cells of the right type in the right place
when does gastrulation occur?
in the third week of development
marks start of embryonic period
what occurs during gastrulation?
the bilaminar disc is converted to a trilaminar disc
forming three germ layers: endoderm, mesoderm, ectoderm
how does gastrulation occur?
primitive streak forms in caudal (tail) epiblast
leads to migration and invagination of epiblast cells at primitive node
why does gastrulation occur?
to ensure correct placement of precursor tissues
allowing subsequent morphogenesis to occur
how does a bilaminar disc differentiate into a trilaminar disc?
the epiblast persists → forms ectoderm
cells migrate and invaginate to displace the hypoblast → forms mesoderm
displaced hypoblast → endoderm
what are the derivatives of the endoderm?
internal structures
e.g.: epithelial lining of GI tract/respiratory tract
parenchyma of glands
what are the derivative of the mesoderm?
supporting tissues
e.g.: muscle, cartilage, bone, vascular system
what are the derivatives of the ectoderm?
organs & structures that maintain contact with the outside world
e.g.: nervous system (neurulation), epidermis
