Lecture 49 Flashcards
What are the stages in parturition and what occurs?
Parturition (childbirth) occurs roughly from 38-40 weeks of development, the first stage is cervix dilation to allow fetal head through, contractions andruptureing of the fetal membranes and lasts from 7-12 hours. The second stage is the contractions for birth of the baby and lasts 20-50 minutes. The third stage is the detachment of the placenta (15 minutes), contractions close the materrnal arteries which supplied it to prevent haemorrages.
What are the three germ cell layers? What is the overall goal?
The three germ cell layers are the endoderm, mesoderm and ectoderm. These will develop all of the tissues which make up our body.
What is the specificity of the cells in the morula and blastocyst?
Initially the cells in the morula are totipotent (can give rise to all cell types, including placenta). By 5 days the blastocyst has formed and has 2 types of cell, the trophoblast will form the placenta, the inner cell mass will form the embryo, this means the inner cells are pluripotent (all cell type can be formed except placenta, these are the embyronic stem cells).
What cell layers are in the embryonic disc? What is gastrulation and what does it lead to?
The epiblast and hypoblast make up the embryonic disc. The epiblast is bordered by the amniotic cavity and the hypoblast is bordered by the yolk sack. Gastrulation is the formation of three germ cell layers from the two layered structur, the cells in this have a defined future (specialising). Development involves cell division, differentiation and migration and also programmed cell death (apoptosis).
How and when does gastrulation occur?
Gastrulation occurs at about 3 weeks, this is done via the formation of the primitive streak (the site of which acts as a basic body plan, the posterior end will be the rear.) at one end of the epiblast (ectoderm), this is a cut which allows cells to migrate down into it and form both the endoderm (replaces hypoblast) and the mesoderm.
What is embryonic folding and what structures do each layer end up becoming?
The embryo will fuse at the midline during embryonic folding, the ectoderm is therefore the outermost, the mesoderm is the middle and the endoderm the inner (some yolk sack was lost. The ectoderm therefore forms the epidermis(skin) as well as the brain and spinal cord, nerve cells and some bones of the skull and face. The endoderm will form the gut tube and the mesoderm will form the muscle, connective.
What is neurulation, what are the steps? What parts are formed and what
Neurulation is the process of forming a tube from a piece of ectoderm, the steps are 1. rises up at the edges to form neural folds,2. these then converge together inwards (neural plate) and 3. they fuse together in the top middle to form a tube. The anterior portion of this tube forms the brain, the posterior region of the neural tube forms the spinal cord. If the tube fails to close at either end it will lead to problems of formation at whichever part is that end.
What are the parts of the mesoderm?
The mesoderm has an intermediate component (kidney/gonads, below paraxial), paraxial mesoderm (bone, skeletal muscle, endothelial cells, dermis and tendons, neural tube) and the lateral mesoderm (circulatory system and body wall, Borders ectoderm furthest from neural tube).
What are the stages of embryo to fetus? (Past 4 weeks).
By 5 weeks we see budding of limbs, by week 6 we see eyes/ears forming, by week 7 we see hands and fingers forming, week 8 we see external genitalia, at week 9 its a fetus and all major organs have started to form.
What is considered premature birth and is this is a problem? What are some examples of problems with development?
Premature birth is anything 3 weeks or more before due date of 38-40 weeks, its normally fine but if extreme (22-26 weeks) complications can occur easily. Processes can go wrong if the germ cell layers do not form properly (not enough can lead to missing parts if not death, too many can lead to tissues where you wouldn’t expect them in large amounts), gene mutations vs environmental effects can occur.
