embryology Flashcards
what happens during the first week of pregnancy?
- ovulation
- fertilisation
- implantation
what is a fertilised ovum called?
a zygote
what are the first cell divisions pre-embryo?
zygote > 2 cells > 8 cells > morula
what is a morula?
a solid mass of cells 4-6 days
what is a blastocyte?
a hollow ball of cells 6-10 days
- inner cell mass
- trophoblast
what does the early embryo have to secure?
its nutrient supply
what is the placenta?
- permeable barrier between embryo and mother, important for resources (not permeable to cells)
- the baby’s blood is replenished from the mother’s blood however the circulations DO NOT mix
what is the bilaminar embryo?
implanted trophoblast containing an embryo
- 10-12 days
- 2 cell layers
what is the bilaminar embryo?
implanted trophoblast containing an embryo
- 10-12 days
- 2 cell layers
what are the two layers of the bilaminar embryo?
- epiblast
- hypoblast
what does the epiblast layer of the bilaminar embryo do?
gives rise to embryonic ectoderm, mesoderm and endoderm
what does the hypoblast layer of the bilaminar embryo do?
participates in formation of the endoderm and extraembryonic (outwith embryo) mesoderm
what is the difference in the formations of identical twins vs fraternal twins?
in identical twins the trophoblast is fertilised by one sperm before dividing, whereas in fraternal twins, the trophoblast divides into two and are each fertilised by a different sperm
what is gastrulation?
an early developmental process in which an embryo transforms from a one-dimensional layer of epithelial cells (blastula) and reorganizes into a multilayered and multidimensional structure called the gastrula
describe the key points which occur during gastrultion
During gastrulation, the embryo develops:
- An axis (to become bilaterally symmetrical)- primitive streak
- The three embrionic cell layers
The key stage is formation of a groove, the primitive streak
what is the primitive streak?
the axis that the embryo develops during gastrulation
describe the involvement of the primitive streak?
Some ectodermal cells are induced to differentiate and migrate through the primitive streak, towards the hypoblast.
These new cells are the mesoderm. A “not so clear” interaction between the newly formed mesoderm and the hypoblast will form the endoderm.
what is the trilaminar embryo?
the mesodermal cells push through the primitive streak and spread out to form a third layer
what happens during weeks 3-8 of embryonic development?
organogenesis- the 3 basic germ cell layers form the major organs (CNS is one of the first to be developed)
how is the neural tube formed?
- neural groove appears in the center of the plate, dividing the future right and left sides of the embryo
- neural folds migrate toward the midline of the embryo, eventually fusing to form the neural tube beneath the overlying ectoderm
- cells at the dorsalmost portion of the neural tube become the neural crest cells
what are neural tube development defects?
spina bifida- neural groove persists
what is the neural groove important for?
development of the head
describe the steps in which the embryo takes shape
- trilaminar embryo front and back fold under midline
- embryo folds around the yolk sac and important organs eg heart, liver and lungs appear
what 3 cell types do all body cells come from?
ectoderm, mesoderm, endoderm
what cells does the ectoderm give rise to?
nervous system and epidermal skin cells
what cells does the endoderm give rise to?
digestive system and other internal organs
what cells does the mesoderm give rise to?
muscle cells and connective tissues
what are stem cells?
Stem cells are unspecialised cells (‘undifferentiated’) that can develop into more specialised cells
what are the characteristics of embryonic stem cells?
- pluripotent, meaning they can divide into more stem cells or can become any type of cell in the body- allows embryonic stem cells to be used to regenerate or repair diseased tissue and organs
- totipotent stem cells are in the inner cell mass and are present during the first few cell divisions post-fertilization and can form any of the different types of cells in the body
what are the characteristics of adult stem cells?
- multipotent- can form other cell types but have limited potency
- generally committed cell lines eg bone marrow stem cells
what does stem cell development involve?
genes and various signalling molecules
what are the three primary embryonic layers?
- ectoderm- outer covering
- mesoderm- middle
- endoderm- inner lining
what tissues are associated with ectoderm?
Skin
Mucous membranes of mouth, anus
Brain, spinal cord
Tooth ENAMEL
what tissues are associated with the mesoderm?
Most connective tissues
- Dermis, tendons, cartilage, bone
Muscle (most)
Blood vessels
Kidney and urinary system
Reproductive system
Serous membranes
what tissues are associated with the endoderm?
Alimentary canal (pharynx – rectum)
Respiratory system
Parts of urogenital system
what is the ectomesenchyme and what tissues are associated with it?
- ‘fourth’ layer, very relevant to dental studies.
gives rise to:
most of the peripheral nervous system: sensory and autonomic nerves
Melanocytes in skin
Adrenal medulla
Most of the mesenchyme in the head (muscles, connective tissues, most dental and periodontal tissues – except enamel)
Dentine, cementum, pulp, periodontal ligament, jaw bones. (next lecture)
what is a syndrome?
when theres multiple phenotypes/diseases- complex
what period of embryonic development has the greatest sensitivity?
week 3-12 (first trimester)
when do most developmental defects occur in embryonic development?
the first trimester (weeks 3-12)
what is the period of functional maturity of the embryo?
weeks 12-39
What cells form the yolk sac?
Hypoblast
