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113 Cards in this Set
- Front
- Back
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What are some developmental challenges? |
1. Making the right number of cells 2. Acquiring distinct cellular identities 3. Translating tissue identity into tissue function |
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During what phase do developmental challenges typically occur? |
G1 phase |
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What is midblastula transition? |
is a stage during the blastula stage of embryonic development in which zygotic gene transcription is activated. three major characteristics of pre-MBT embryos
1. all of the embryonic cells undergo cell division at the same time. 2.Secondly, zygotic chromatin is condensed, hypo-acetylated and H3 methylated, ----indicating that most of the genes are in a repressed heterochromatic state. 3. embryos are observed to translate only maternally inherited mRNA, i.e. that mRNA which is present in the oocyte when it is fertilised. |
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What is the mRNA localized in different parts of the oocyte? |
so that as the embryo divides it is segregated into different cells.
----This segregation is thought to underlie much of the differentiation of cells that occurs after MBT. |
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What happens once MBT (mid blastula transition) has taken place? |
Once MBT has taken place, the embryo begins to transcribe its own DNA, cells become motile and cell division becomes asynchronous. Since the cells are now transcribing their own DNA, this stage is where differential expression of paternal genes is first observed.
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How are cell fates and tissue patterns aquired? |
1. Maternal determinants 2. Asymmetric cell divisions 3. Induction and cell-cell communication 4. Patterning fields of cells 5. Morphogenesis and organogenesis 6. Re-use of key signaling pathways |
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What is wnt8a? |
a ligand used in a signanling pathway to determine what is fixed -activates pathway that feeds into B-catenin -plays a role in formation of lib system ----evolutionary conserved -------used to be wingless and seperately int wingless+ ing= Wnt |
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When does the zygote start making their own protein? |
After a mid blastula transition |
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what might determinants change in genetically identical cells? |
what each identical cell may become |
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what is asymmetric cell divisions? |
An asymmetric cell division produces two daughter cellswith different cellular fates. This is in contrast to symmetriccell divisions which give rise to daughter cells of equivalent fate
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What is the spemann-mangold orgainzer? |
Experiement done in 1953 where they took dorsal tissue of a donor and put it on the ventral side of the host ---resulted in simease twins ---found that nervous system as derived from donor tissue |
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What is induction? |
When one group of cells is able to change the fate of another group of cells (usually mediated by secreted proteins) |
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what is the funtion of the organizer region?Where is it located? |
Dorsal side of embryo --in most mammals --has ability to change fate of other cells |
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What is patterning? |
establishing the regional tissues within an area |
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Notonly do tissue types (i.e. vertebra) have to be --1---, they also must be ---2--
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1. Induced 2. patterned |
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What occurs during morphogenesis |
Cells must often migrate large distances and tissues must often reorganize into complex shapes --structural changes that need to happen ---changes in where cells are located |
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What are the 4 main key signaling pathways during development? |
1. Wnt 2. BMP/TGFβ 3. FGG 4. Hedge hog |
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What is the Wnt pathway? What role does it play? |
1. Wnt ligandactivates a receptor leading to themovement of β catenininto the nucleus and transcription ----Plays a role in dorsal-ventral patterning, nervous system patterning, limb formation |
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What is the BMP/TGFβ pathway? |
-Diverse group of ligands (BMP, Nodal, Activin, TGF) that bind to ser/thr receptor kinases ---> Ultimately leads to theactivation of SMADswhich can act as transcription factors --> Involved in mesoderm and endodermformation and epidermis formation (inhibits nervous system development) |
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Which pathway is involved in mesoderm and endoderm formation? |
BMP/TGFβ
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What are the receptors in the BMP/TGFβ pathway? |
ser/thr receptor kinases |
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What if FGF? what does it activiate? |
fibroblast growth factor ---activates at typical tyrosine kinase receptor pathway ---Can lead to ras and MAPK activation, ultimately leading to transcriptional activation |
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What does the acronym LUBRICATING stand for? |
Ligands are released into the extracellular space
Upon Binding to their Receptor specific Interactions cause a Conformational change within the catalytic domain, this Activates the connected enzyme, phosphorylation generates Tethering sites where Intracellular effector proteins bind these further relay the signal to the Nucleus resulting in changes in Gene expression |
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What does FGF pathway involved with biologically? |
Involved in mesoderm formation,neural induction, limb patterning
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What is hedgehog signaling? |
1. ligandinhibits the patched receptor which inhibits the smoothened receptor (thereforehh activats smo) 2. Leads to the activation of Glitranscription factors 3. Expressed in the notochord and patterns the nervous system, somites, and gut; involved in limb patterning inhibits 1 receptor that inhibits another receptor **activates Smo and GLi transcription factors |
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How are eggs make? |
1. Oogenesisstarts prenatally with the production of primary oocytes; about 1-2 million are produced 2. Primary oocyte starts meiosis I and stops in prophase I 3. Once menstuation starts, a few will continue meiosis I to produce a secondary oocyte and 1st polar body 4. The secondary oocyte starts meiosis II and stops in metaphase II (will continue only if fertilization happens) 5. Polar bodies will ultimately disintegratexN +JK?*-J8x |
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where are maternal determinants located |
the egg cytoplasm |
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What are the maternal determinants required for developing embryo |
1. Proteins- supply energy and amino acids 2. Ribosomes 3. mRNA- instruction for many proteins 4. Morphogenetic factors-FGF,nTGFβ, BMP, and Wntfamily members 5. Protective chemicals-abs, DNA repair enzymes |
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What protects the egg? |
zona pellucida consisting of glycoproteins
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What is going on in the uterus : Week 3( Day 14-21) |
--Multiple female hormones are involved: estrogen, progesterone, luteinizing hormone, follicle stimulating hormone
--- During mid-cycle, estrogen, LH and FSH peak, progesterone steadily increases -----Uterine lining at thickest point ---Positive and negative feedback results in these hormonal changes ---release of oocyte from follicle, entry into fallopian tube |
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Where does spematogenesis occur? |
in the seminiferous tubules of the male testes |
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What occurs during spermiogenesis? |
Duringspermiogenesis, the spermatid will then undergo structural changes(cytoskeleton and vesicular transport) to form mature spermatozoa --Thisoccurs throughout the life of the male |
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What is the tail of sperm made of? |
Centriole (MTOC) forms the flagella/axoneme (tail) made of microtubules
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Where are the acrosomal vesicles formed? |
the golgi |
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What is the function of acrosomal vesicles |
filled with enzymes to lyse egg |
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When is sperm able to fertilize? What occurs? |
when they enter the female genital tract. -acrosomal head is removed, cholesterol is reduced in membrane, increase in Ca and cAMP that aid in motility |
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What is the process of fertilization |
1. Egg releases chemoattractants that attract sperm 2. Sperm binds and passes through egg envelope 3. Acrosomal vesicles undergo exocytosis; this is required to penetrate the zona pellucida 4. Sperm and egg plasma membranes bind 5. Mechanisms to prevent polyspermy 6. Once sperm nucleus enters oocyte cytoplasm, the rest of the sperm cell desintegrates and the oocyte completes meosis II. The two nuclei then fuse |
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What are the mechanisms to prevent polyspermy? |
Release of intracellular Ca (sER) causes exocytosis of cortical granules (secretory vesicles containing enzymes that crosslink tyr residues between glycoproteins) making the zona pellucida impermeable to other sperm
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What is the first mitotitc divisions of the zygote called? |
cleavage |
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What are the two types of cleavage patterns in animals? |
holoblastic 2. meroblastic |
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What is holoblastic cleavage |
all of zygote divides completely (humans) |
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what is meroblastic cleavage |
a part of the zygote (yolky part) does not divide(fish) |
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What is a blastocyst |
It possesses an inner cell mass (ICM) which subsequently forms the embryo. Theouter layer of the blastocyst consists of cells collectively called the trophoblast. This layer surrounds the inner cell mass and a fluid-filled cavity known as the blastocoele. The trophoblast gives rise to the placenta |
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What happens after clevage? |
The embryo becomes a blastula, a hollow ball or disk |
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When and where does fertilization occur? |
In the fallopian tube (~Day 15-21) |
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What is the HCG |
human chorionic gonadotropin ---maintians the corpus luteum --> uterine lining maintained --negatively charged--> repel immune cells of mother -can cause morning sickness -detected in pregnancy tests |
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What is detected in pregnancy test? |
HCG (human chorionic gonadotropin) |
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When does the first cleavage division of the zygote occur? |
as it makes its way to the uterus |
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What are 3 types of endocytosis? |
1. Phagocytosis 2. Pinocytosis 3. Receptor mediated endocytosis |
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Steps of fertilizaion and cleavage |
1. Fertilization occurs inthe fallopian tube 2. The first cleavage division of the zygote occur as it makes its way to uterus 3. A blastocyst then forms 4. Upon implantation, blastocyst produces HCG |
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How is birth control effective in contraception? |
Many birth controls are estrogen andprogesterone based that prevent FSH production.
----Folliclestherefore don’t mature If fertilization does occur, follicularcells form corpus luteum which produces progesterone ---increase in Progesteronecauses the growth of uterine wall and blood vessels which prepares lining for implantation of blastocyst ***RU486(mifepristone) ->blocks progesterone receptors |
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What blocks progesteron receptors in birth control? |
RU486 |
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What is one of the first cell fate decisions?
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to become embryonic vs extraembryonic |
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What are the parts of the early blastocyst |
Trophoblast cells- on the outside ---secrete luteotropin to maintian corpus luteum--> maintain high progesteron ---contain Na+/K+-ATPase to pump sodium ions into cavity ---will become the placenta Inner cell mass- on the outside ---This will form all embryonic tissues |
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Where are the 3 germ layers determined? |
In the blastocyst |
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What are the 3 germ layers? |
1. Ectoderm-epidermis and nervous system 2. Endoderm- digestive and respiratory systems 3. Mesoderm- muscle/cartilage/bone/blood vessels/connective tissue |
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How are the 3 germ layers formed |
--intially most of the embryo is ectoderm --Maternal determinants make endoderm --Endoderm (FGF and TGFβ) induces mesoderm from ectoderm --Dorsal vs ventral is also determined (Wnt) |
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what are bmps |
-Bone morphogenetic protein ------a group of growth factors also known as cytokines and as metabologens |
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How does the organizer induce a seconday axis |
BMP inhibitors |
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What is the function of BMP inhibitors in the 3 germ layers? |
---BMP inhibits brain development; BMP is throughout embryo
---BMP inhibitors are therefore required to induce neural tissue ----BMP inhibitors are present in theOrganizer -------This is how the Organizer inducesa secondary axis |
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What is the organizer? |
dorsal tissue in all vertebrates that induces the nervous system but does not itself contribute to neural tissue; differentiates into notochord |
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What does the organizer differentiates into? |
the notochord |
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What is the notochord? |
a flexible rod made out of a material similar to cartilage
---- The most commonly cited functions are as a site of muscle attachment, vertebral precursor, and as a midline tissue that provides signals to the surrounding tissue during development |
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What are SMADs? |
are intracellular proteins that transduce extracellular signals from transforming growth factor beta ligands to the nucleus where they activate downstream gene transcription
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Where can you find blastocyst? |
inside of blastula |
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What are trophoblasts? |
are cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta. They are formed during the first stage of pregnancy and are the first cells to differentiate from the fertilized egg.
***play a huge role in progesterone production |
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What does the ectoderm give rise to? |
epidermis and nervous system |
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What does the mesoderm give rise to? |
1. muscle 2. cartilage 3. bone 4. blood vessels 5. connective tissue |
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What does the endoderm give rise to? |
digestive and respiratory systems |
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What is the funciton of the fate map |
label cells and see where they end up. Does not indicate commitment ----every cell has a fate, though there is some plasticity |
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Where is the destination of the ectoderm germ layer according to the fate map? |
ventral: epidermis dorsal: nervous system |
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Where is the destination of the endoderm germ layer according to the fate map?
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Ventral: liver dorsal: digestive system |
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Where is the destination of the mesoderm germ layer according to the fate map?
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Ventral: blood Lateral: heart and muscle Dorsal: notochord |
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What is gastrulation? When does it occur? |
Week 4 is the process of morphogenesis that transforms the blastula fate map into an embryonic axis with 3 germ layers ***gastrulating- the process of making stomach; gastrointestines |
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What are amniotes? |
an any animal that has amniotic fluid ---embryos develop in embryonic fluid |
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What is the node? |
the organizer in humans |
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What occurs during gastrulation in amniotes? |
1. a primitive streak forms through which future mesoderm and endoderm cells migrate; the organizer(called the node) is at the anterior tip of the streak ---those that migrate deepest will be endoderm ---Result: mesoderm in between the ectoderm and endoderm 2. shape changes form found to being long ---happens bc cells all move to midline ---cells are polarized -->flatten so they move (convergent extension) ---if Tho & rac are messed up cells won't flatten |
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What is a primitive streak? |
is a structure that forms in the blastula during the early stages of embryonic development. It forms on the dorsal (back) face of the developing embryo, toward the caudal or posterior end.
-- The presence of the primitive streak will establish bilateral symmetry, determine the site of gastrulation and initiate germ layer formation |
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What happens the the 1st epithelial cells that go through primative streak |
-Change shape -can stick to thinks -stop expressing cadherin |
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What could be wrong if cells wont flatten? |
There may be an issue with Rho or Rac |
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when do miscarriages typically occur |
During gastrulation |
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How does the cytoskeleton play a role in morphogenesis |
it is unknown |
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For tissues to have the proper“morph”, they need to acquire ______ -________ (layers, asymmetries, etc)
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complex organizations
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What is convergent extension? |
cell polarization andintercalation mediated by rho and rac;required for the elongation of the bodyaxis
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What is the epithelial to mesenchymal transition |
activationof snail TFs that downregulate cadherins and other adhesive molecules
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What are the key embryonic structures after gastrulation? |
Ectoderm; forms neural plate Mesoderm; notochord, somites -----notochord; important signaling tissue at the midline ---somites; future muscle and cartilage ---lateral mesoderm; future heart Endoderm; forms the gut |
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What is secreted from the hedgehog |
the notochord |
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What is the function of the notochord? |
a key embyonic structure that secreates hedgehog to pattern all the germ layers ---in adults, will have no funciton |
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What are the somites? |
small mesodermal tissue balls lateral to the notochord that will form muscle and segmented structures of the vertebrae |
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What is patterned by the notochord? |
Dermatome; skin myotome; muscle sclerotome; vertebrae and rib cartilage |
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Where are the somites in relation for the notochord? |
lateral |
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in adults the notochord becomes a part of the? |
vertebrae |
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the amoung ____1-__ results in different brain tissue in a concentration dependent manner |
hedge hog |
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What is organogensis? |
is the process by which the ectoderm, endoderm, and mesoderm develop into the internal organs of the organism. This process can be studied using both embryos and organoids.
---Internal organs initiate development in humans within the 3rd to 8th weeks in utero |
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Where does the gut form from? |
the endoderm, the cells that migrate deepest during gastrulation -->it then forms a gut tube --> differentiation along the A/P axis with distinct morphogenetic events for each organ |
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What is 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.
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What occurs during neuralation? |
1. Neural plate forms 2. Neural fold formation (cell shape changes) 3. Induction formt he notochord and the epidermis (shh and BMP4) ---once neural tube form come off epitheilum migrate away 4. AP patterning (hox TFs) 5. EMT in neural crest cells and their migration 6. Placodes-epithelial thickenings that will become sensory organs |
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What are placodes? |
epithelial thickenings that will become sensory organs ---do not go in neural tube; gives rise to cranial nerves etc |
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what do neural crest cells turn out to be? |
touch receptors |
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What are the regional identities of the germ layers after patterning the AP axis |
Ectoderm; forebrain vs spinal cord Mesoderm: thoracic vs lumbar vertebrae Endoderm: stomach vs intestine |
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What is homeobox? |
any of a class of closely similar sequences that occur in various genes and are involved in regulating embryonic development in a wide range of species.
---Hox genes are required ----cause homeotic transformations |
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What is required for homeobox ? |
hox genes |
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What is going on with the embryo by week 5 (day 28-35) |
1. Accumulation of heart cells --begin to contract --divide into chambers --major blood vessels form 2. Digestive system forms --kidneys and liver --intestines and appendix 3. Nerual tube forms --connects brain to spinal cord --closes by the end of the week tail forms |
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At what week does the nerual tube form |
by week 5 |
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When does limb development beging? |
starts week 7 |
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When does limbs present with hands and feet? |
at week 7 --webbed --wrist movements possible --webbing recedes (apoptosis) |
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What is going on in weeks 6-7? |
Limb development -hedgehog is expressed it the limb(zone of polarizing activity) -plays a role in limb patterning ----need a lot of polarzation ---limb presents with hands and feet at week 7 **webbed **wrist movements possible ** webbing recedes (apoptosis) ****other players include FGFs and BMPs |
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describe polarization in limb development |
a lot of patterning dorsal side --proximal to distal -anterior/posterior |
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How is apoptosis regulated |
by levels of BMP and FGF --differences in regulatory sequences have been characterized ---determines abundance |
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What is happening by the end of week 14 (1st trimester)? |
most embryonic regions are established and patterned
--still requires further refinement and much more growth ---head to rump is 3 inches |
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What are some types of prenatal screening? Non-invasive and invasive |
1. Nuchal translucency scan 2. Blood test (non invasive ---Quad test ------AFP-(alpha -fetoprotein made by fetus) **high levels: spinal defects; **low levels: c. somal abnormalities ------hCG (human chorionic gonadotropin) **made by placenta ------Estriol (made by fetus and placenta) ------Inhibin A ( made by placenta ---APP-A (pregnancy associated plasma protein A ****low levels indicate risk for genetic defects 3. Invasive test ---amniocentesis- a needle takes a sample of amniotic flud ---chorionic villus sampling-a needle takes a smple of the placenta |
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What is a nuchal translucency scan? |
-for Down’s syndrome (week 11-14)
-extra fluid in transnuchal fold |
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What is the going on in weeks 35-40? |
-All organs are fully formed -Pre term= < 37 weeks Full term =37-42 weeks fetus is 17-19 inches |
