Pregnancy is divided into ___trimesters
3; 3 month periods but doesnt give us info at what precise stage dev embryo is at.
What is happening during weeks 1-2
- Implantation; cell proliferation and migration
2. Zygote fertilization, morula, blastocyst, bilaminar disc,
There are no birth defects in:
in first two weeks of dev; usually defects you get are so severe that if you have it, the embryo is aborted.
What is going on during weeks 3-8
- Gastrulation- get third layer in dev trilaminar disc
- Organogenesis: Most organs initiated in this period
when is there the greatest vulnerability to birth defects
is during 4th-8th week of embryonic dev bc a lot of organs are forming during this period. AKA the first trimester.
When is the fetal period
3th month -9th month; growth and differentiation; birth defects less severe.
When is the gestational age
begins from the first day of last normal menstrual period. Adds 2 weeks to embryonic age.
When is embryonic age
begins at fertilization. Oocyte & sperm nuclei has fused. Happens 2 weeks after last menstrual period.
If no pregnancy thrives, ____degenerates
corpus luteum. Outer part of endometrium buds off and discharges
If pregnancy, it continues to produce estrogen and ___
What are the phases of the ovarian cycle
- menstrual phase (1-7)
- Proliferative phase
- Luteal phase
- Ischemic phase
What are the stages of getting pregnant
- Primary follicle that starts maturing
- Oocyte gets released to fallopian tube
- zygote gets formed and starts dividing.
- As it gets to uterus it forms a blastocyst in posterior wall of the uterus. (zona pellucida has already started disentregating)
how does a blastocyst get formed
2- cell stage, 4 cell stage, 8 cell stage –> morula –> blastocyst
Blastomeres mitotically divide but DO NOT:
what are trophoblasts
end up becoming supporting cells for dev embryo
For organism to survive, during dev, it needs to have supp structure. You can’t just have a trophoblast or just an ____. They are not viable on their own!
AS blastocyst gets to endometrium, the trophoblast attaches to endometrium and start to differentiate. The trophoblast gives rise to two structures:
- cytotrophoblast: surround the embryo
- syncytiotrophoblast: multinucleated mass of cells; produces the main protein we use in pregnancy tests and is responsible for producing human chorionic GnRH. (HcG)
What happens during second week?
Concerned primarily with the dev of the bilaminar germ disc.; 2 layers of trophoblast and you get two mesoderms.
Implantation is complete by the end of the ____week
At 2 weeks of embryonic dev you get get 2 layers of trophoblast in dev embryo:
- Epiblast/Amniotic Cavity: Layer towards amniotic cavity (top)
- Hypoblast: Layer towards exocoelomic cavity that later becomes yolk sac. (bottom)
What gives rise to supporting tissues?
What happens in third week>
development of the trilaminar germ disc (week of 3)
what is the start of morphogenesis
What do epiblasts and hypoblasts from bilaminar germ disc differentiate into
- Ectoderm; adjacent to embryonic cavity
- Endoderm: close to endoderm.
- Give rise to everything in body
what gives rise to embryo
2. umbilical vesicle (yolk sac)
What is the primitive streak
This is the first sign of gastrulation starting (how you get mesoderm); A double line that starts dev at caudal end of embryo at epiblast and starts lengthening. You cut embryo from top down and look at it from the side.
what is gastrulation
Organizing and differetiating the 3 germ layers. Get intraembryonic mesoderm in dev embryo.
After primitive streak gets to certain size it starts going to cranial end of embryo and get a ______. This is the are where all the cells start migrating to form the _____
primitive node; mesoderm
Epiblast is the layer that gives rise to all of the ____layers
From the top part of primitive node, cells that migrate into underlying layers, they migrate down and grow forward to prechordal plate. They keep to themselves and form a tube filling in the space between. This is called the _____
migration of mesenchymal cells from the primitive streak form _____ that organizes to form the ______ mesoderm. Most of the embryonic endoderm arises from the ______
mesoblast; intraembryonic; epiblast
What does the ectoderm give rise to
- internal ears
- neural crest cells
What does the endoderm give rise to
- epithelial lining of respiratory and digstive tract
- glands opening into the GI tract
- glandular cells of associated organs such as the liver and pancreas
What does the mesoderm give rise to
- skeletal muscle
- blood cells and lining of bv’s
- lining of body cavities
- ducts and organs of the reproductive and excretory systems.
- most of the cardiovascular system
Gastrulation begins at ____end with formation of _____ ____ in epiblast, but the cranial end begins to differentiate first causing the embryo to develop ______
caudal (anterior); primitive streak; cephalocaudally
notochordal process lengthens by migration of cells from the ____ ____. As the notchordal process elongates, the ___ ___ shortens. At the end of the 3rd week the notochordal process is transformed into the notochord
primitive node; primitiive streak
prechordal plate and cloacal membrane are the only two areas that stay ______. No mesoderm here. They end up disentragating forming the mouth and anus. Prechordal plate Forms the ____ membrane
The notochordal processes and adjacement mesoderm indude the _____to form the neural ____
ectoderm; plate (the primordium of the CNS)
Thickened area on top of notochord =
when folds start growing together they form a hollow tube that initially contains 1 layer of cells and dissociates from ectoderm which was on the top. Now, neural crest cells detach and migrate to underlying _____
what is the seq of events that happen during the third week
neural plate –>neural folds–> edges dont go into tube formation, they detach and lay underneath the ectoderm –> neural tube –> neural crest cells–> give rise to CNS, and PNS
All most all CT from head and neck region and pigment cells come from _____ ____
process of formation of nervous system is called
During 3rd week start with gastrulation to get mesoderm in between. Then get formation of notochord then start neuralation. Cells detach and form neural crest cells which become brain and ____
As neural crest cells are forming cells in ____ also start to proliferate. Somites are bulges you see on dev embryo and can estimate at what dev stage the embryo is
Anterior forms _____. The forebrain is the ____. The midbrain is the ____ and the hindbrain is called the ____Lower parts give rise to___
brain; prosencephalon; mesencephalon; rhombencephalon
ventral would be towards _____ ____. Amiotic cavity would be towards dorsal side.
first area to express morphogenic protein is the :
What happens from 4th to 8th week
When a lot of our structures develop. Flat embryo starts folding (extends forward from top and bottom part)
septum transversum, primordial heart, pericardial coelom, and oropharyngeal membrane move onto the ___ surface of the embryo. Part of the umbilical vesicle is incorporated into the embryo as the ____
Neural crest gets feedback from local cells such as :
Heart forms above the head, but due to ______ folding the bow gets located ventrally; its above the prechordal plate but as it folds (orapharngeal plate)
Fusion of neural folds start in the middle and start going upward and downward. You get specific structures induced by ____ which gives rise to muscles and skeletal muscles. But the folds havnt fused together. You have an open neural tube. These two areas are called the ______ (head region) and the neuropore
Structures follow the folds. Amniotic cavity covers most of the ____. Part of the yolk sac gets incorporated to inner parts of embryo which gives rise to _____cavity and thorax
What happens closer the the 4th week?
As the embryo folds, you see structures forming below the brain crosses in dev embryo which are impt and are called branchial arches
what do pharyngeal arches give rise to fish? What about humans?
gills; dev maxilla, mandible
major parts of eye and retina come directly from:
telencephalon gives rise to
Umbilical vessel gives rise to :
Initially there are 3 areas in anterior part of the brain:
The rest form the spinal cord.
- forebrain ( prosencephalon)
- midbrain (mesencephalon)
- hindbrain (rhombencephalon)
The cavity forms the ventricles
The forebrain (prosencephalon) forms the ____ and ______ which forms the walls of the cerebral hemispheres and the thalamus and make up the ____ ventricles and _____ ventricle. The midbrain (mesencephalon) forms the ______. The hindbrain (rhombencephalon) makes up the ______ and _____ which makes the pons and _____ and medulla
telencephalon; diencephalon lateral; third cerebral aquduct metencephalon; myelencephalon cerebellum (met)
_________of hindbrain are impt because it dictates the antero posterior identity of the dev brain and the embryo.