What is the difference between the gestational age and post-fertilisation?
- Gestational age starts from the first day of the last period;
- post-fertilisation is 2 weeks less than gestational age -> makes a difference at the beginning of the pregnancy, but not really at the end of the pregnancy.
What are the main size gains that occur in each trimester?
Last 2 trimesters are for growth of foetus, but first trimester is for development
What are the carnegie stages of human development?
What occurs in the first trimester?
How are the carnegie stages broken up into weeks of pregnancy?
What is the difference between a blastocyst, embryo and foetus?
Red area is the liver as the RBC are produced in the liver in the embryo as there is no bone marrow, yolk is used for nutrition -> very translucent. Embryo is baby up to week 8, foetus is baby for rest of pregnancy
What is a conceptus?
Everything produced from a fertilized egg
What is an embryo?
Cells that give rise to everything at the beginning not just the baby -> terms are used in 2 different ways; baby up to week 8 of development OR for the first week then whole conceptus is embryo, after blastocyst differentiation, then only baby tissue is foetus
Why does cell proliferation occur?
Changes in response to ‘growth factors’
Changes in receptor expression
May be due to changes in cell survival
All paracrine or autocrine regulation
Why do cells move?
Chemo-attractants (local production, paracrine effects), cognate receptors (expressed on target cells) -> needs facilitation, requiring change in tissue structures; remodelling of tissues (ECM) and proteases and inhibitors need to be produced and activated
What are the steps of differentiation that occur in foetus?
Necessary in target cells
Loss of proliferation
Not necessarily in embryo or fetus
Cells can differentiate and proliferate at the same time
How does cell loss occur in foetus?
Apoptosis -> regulated cell death, controlled by paracrine factors mainly
How can concentration of paracrine stimulus affect regulation of cells?
Some cells exposed to different regulators and different concentrations, which by working together can bring out how cells behave -> occurs in 3D (shown here in different planes) and looks like a limb bud (occurs in embryo proliferation)
How can different regulators work together in the embryo?
How do genetic factors regulate development?
Controlled by signals from genes.
Complex gene interactions occur throughout development to form a normal fetus.
Hox genes, with retinoic acid controlling activation of Hox genes
What does embryonic development need?
Gradients of factors
Combinations of factors
Temporal changes in factors or responses to them
What is the bilaminar disc (~9d PF)?
Epiblast (yellow) and hypoblasts (blue) -> circular disc cut in the middle
What is gastrulation?
Becomes more elongated -> Gastrulation is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a trilaminar ("three-layered") structure known as the gastrula. These three germ layers are known as the ectoderm, mesoderm, and endoderm.
How is the germ layer formed?
Proliferating and differentiating to form mesoderm cells, which move towards the hypoblast -> forming the germ layers; hypoblast is bumping into mesoderm cells which then undergo another differentiation stage, forming the endoderm, with hypoblast being lost via apoptosis
What does gastrulation result in?
Epiblast becomes ectoderm, mesoderm is in the middle, endoderm is where the hypoblast was
What do the 3 germ layers become?
NB: very few tissues are of one specific type -> skin is both ectoderm and mesoderm
What is neurulation?
Occurs at the same time as gastrulation -> can see the primitive streak;
Neurulation refers to the folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube.
The embryo at this stage is termed the neurula.
Notochord (acts as negative regulator, not allowing certain things to happen) formed from mesoderm, and upper epiblast layer is turning into neural plate which forms the CNS.
Proliferation cells, grow and meet in the middle forming the neural tube which will then become the CNS. Skin overlies the CNS, which explains why some neuroblastomas can affect the skin as well as the NS, as they have the same embryological origin.
By day 21, 3D embryo is developing, with mesoderm becoming more dimensional
How does the body cavity close?
Umbilical cord is a gap in the body wall, where the yolk was
How does the embryo fold head to tail?
What occurs in the 2nd month of development?
Faces developing, hands developing, eyes developing from an early stage; apoptosis used to remove webbing in between fingers and remove our tail
When do each of the systems develop?
How does the CNS develop?
Brain development occurs in 2 separate halves -> with fusion of tissues and elaboration occurs -> neuropores then fuse to give a complete tube that is the CNS
What is spina bifida?
Twin/two spines, with 2 areas of tissue -> bulges of tissue and depending where they are and what is in them decides the problems that it is going to cause -> above the point is normal;
Incidence of 1-2 per 1000 pregnancies;
Surgery can help anatomical but not functional problems and folic acid (need to take it earlier to have enough reserve for baby) can prevent it, primary problem is failure to complete neurulation and problem is present within 4 weeks of fertilisation
How is spina bifida caused?
A gap is left where the fusion would have occurred -> posterior neural chord hasn't closed properly
What are the types of spina bifida?
Occulta has a patch of hair, with vertebra not being formed properly; in meningocele is a bulge of CSF; myelomeningocele includes neural tissue and CSF -> development of bones of spine are controlled by neural tissue, which means it doesn't cut off the neural tissue in spina bifida