Embryology Flashcards
What occurs within the first week of embryology
Ovulation
Fertilisation
Implantation
Roughly when does implantation occur
5 1/2 - 6 days
What is a zygote
A fertilised ovum
What is a morula
A mass of cells resulting from division or a fertilised ovum
What is a blastocyst
A hollow ball of cells:
-Inner cell mass
-Trophoblast
What is the purpose of the placenta
A way to transfer nutrients and waste to and from the mother
When might a baby and mother’s circulatory system interact
During birth
Is the placental barrier permeable
Yes to most molecules but not cells
What is an embryological difference between identical and fraternal twins after implantation
Fraternal twins each have a placenta while identical twins share a placenta
When does the implanted trophoblast contain a bilaminar embryo
10-12 days
What layers does the bilaminar embryo have
Epiblast layer
Hypoblast layer
What does the epiblast layer give rise to
Embryonic ectoderm
Mesoderm
Endoderm
Mesendoderm?
What does the hypoblast layer participate in
Formation of endoderm and extraembryonic mesoderm
What does the embryo develop during gastrulation
An axis (becomes bilaterally symmetrical)
The three embrionic cell layers
What is the key stage of gastrulation
Formation of a groove, the primitive streak
What does organogenesis mean
Generating an organ
What forms the mesoderm
Ectodermal cells induced to differentiate and migrate through the primitive streak towards the hypoblast
What forms the third layer to form the trilaminar embryo
The mesodermal cells push through the primitive streak and spread out to form a third layer
What is one of the first organs to be formed
Central nervous system
What is developing muscle called
Somite
When is the neural groove evident
19,20 days when the embryo is about 2mm long
What is the order of development of the central nervous system
Neural fold
Neural groove
Neural tube
Dorsal root ganglion
What defects are associated with the neural groove
Spina bifida -non closer of neural groove lack of formation of the neural tube
When do the cells become a foetus
Week 9 as there is development of organs
Why is the neural crest also known as ‘ectomesenchyme’
Derived from ectoderm but has the characteristics of mesenchyme
Approx how long is the embryo at 7 weeks
27mm
What length is the fetus at weeks 9,14,20
44mm
120mm
185mm
Where do all body cells originate from
3 cell types:
-Ectoderm: outer covering
-Mesoderm: middle
-Endoderm: inner lining
When does the face start to form
Week 4-7 via migration of cells from posterior to anterior region
Which stem cells are totipotent
Embryonic inner cell mass - capable of giving rise to any cell type
Which embryonic stem cells are pluripotent
Cells in the 3 germ layers
What does stem cell development involve
Genes and various signalling molecules
What does the ectoderm compose
Skin
TOOTH ENAMEL
Mucous membranes of mouth,anus
Brain, spinal chord
What structures are made of mesoderm
Most connective tissues
-Dermis, tendons, cartilage, bone
Muscle (most)
Blood vessels
Kidney and urinary system
Reproductive system
Serous membranes
What does the endoderm make up
Alimentary canal (pharynx - rectum)
Respiratory system
Parts of urogenitakl system
What is the ‘fourth’ primary embryonic layer
Ectomesenchyme
What does the ectomesenchyme give rise to
Most of the peripheral nervous system: sensory + autonomic
Melanocytes
Adrenal medulla
Most of the mesenchyme in the head
Dentine, cementum, pulp, periodontal ligament, jaw bones
When is the period of greatest sensitivity for development in utero
First trimester: weeks 3-12
When do teeth begin to form in utero
week 6-7
When are primary teeth fully formed
Around week 9
