Developmental Biology ZOL 320
Popular in Course
verified elite notetaker
verified elite notetaker
verified elite notetaker
verified elite notetaker
verified elite notetaker
verified elite notetaker
Popular in Animal Science
This 16 page Class Notes was uploaded by Marlon Brown on Saturday September 19, 2015. The Class Notes belongs to ZOL 320 at Michigan State University taught by Will Kopachik in Fall. Since its upload, it has received 73 views. For similar materials see /class/207230/zol-320-michigan-state-university in Animal Science at Michigan State University.
Reviews for Developmental Biology
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 09/19/15
ZOL 320 Unit 2 Fri 92311 III Stages of Spermatogenesis 0 The special anatomy ofthe testis swswmm o The types of cells E W gt gt gt gt 0 The genetic and immunological problems of sperm cell production 0 The hormonal regulation axis 0 Process takes two months hich cells would have a different genotype than the type B spermatogonial cell Primary spermatocytes Secondary spermatocytes Spermatids Spermatozoa gt E B C D above Secondary Spermatids and Spermatozoa A B C D Testis Anatomy Sertoli Cell Cytoplasm R esid ual budy 00 Results showing that cells in the seminiferous tubules are not normally exposed to the immune system 00 Sertoli cells form a blood barrier in the seminiferous tubules It s purpose is 0 To prevent immune cells which are involved in recognizing and killing genetically foreign cells from getting to the meiotic cells to In some other unknown way the Sertoli cells aid the development of meiotic cells in spermatogenesis 0 0 0 0 0 Gene expression problems to overcome during spermatogenesis gt 1 Cells nuclei genetically different will be made gt 2 Half of the cells nuclei will lack an 5 whereas the other half will lack a x Chromosome gt 3 Transcription cannot occur in the highly condensed chromatin during meiosis which takes months to accomplish A reason for a syncytial cell arrangement of spermatocytes is gt A A syncytium can make more gene products than can a single cell gt B The X or Y chromosome gene expression could be shared by all connected nuclei gt C The syncytial cells make tougher cell borders needed for resisting T cell invasion gt D Syncytial cells are better able to take up nutrients from the Sertoli cells You would expect to find relatively a lot of this type of control of gene expression during the later meiotic phases of spermatogenesis gt A Transcriptional control gt B Translational control gt C Long lasting mRNAs gt D A and B above gt E B and C above Mon 92611 IV Sperm Cell Structure 0 00 o 00 o 00 o 00 Sperm cell morphology is generated during Spermiogenesis from the spermatid differentiating into the spermatozoon The modification of a germ cell to form a mammalian sperm gt Acrosome Modified Golgi apparatus centriole flagellum axoneme and nucleus are most important gt The axoneme extends from the centriole gt This centriole will be later found in the oocyte and needed for cell division gt Mitochondria become modified in appearance Nuclcu Milod iundria I f l l V lolgi Lemrmle Aurosomal l lagcllum llagcllum V V V Axoneme Apparatus wmlc and gt grams Centriole Centriole Nucleus has histones replaced with Qrotamines specific to sperm to make an almost crystalline chromatin Different shapes of spermatozoa Ciliates move 10 X faster than protozoa with flagella 0 0 0 Microtubules connected by dynein bridges slide relative to each other 0 O Microtubule doublet and to move there are arms on the outer of the doublet called Dyenin motor proteins 0 o Sperm tail shows a corkscrew motion gt There is virtually no gliding at the cellular level It is a very high viscosity solution requiring a boring type of movement 0 0 PAGE 46 ON GAMETOGENESIS PPT 0 0 0 Too much testosterone stops spermatogenesis 0 0 Other aspects of the regulation of spermatogenesis gt A male may have seasonally high production of sperm eg during the rutting season Why have a season for it V Sperm can be stored V In primates there is a relationship between testis size to body mass and the sexual behavior of the species Bonobo chimps have large testes and high sexual activity V Males produce sperm throughout their life cycle Females produce oocytes for a limited time Oogenesis 00 I Stages of Oogenesis gt BackgroundPGCs multiply and migrate to ovary gt Only some survive to give rise to primary oocytes gt To become a large oocyte ready for fertilization takes time follicle cells help gt Strategy is to have stopping points in meiosis 00 Continuious vs Discontinuous Oogenesis gt Continuous Oogenesis With immortal oogonia ii Ex Frog seasonal increase in oogonia gt Discontinuous Oogenesis All oogonia become oocytes once early in embryogenesis no new ones made it Ex Humans 00 General points about oogenesis gt Egg is nonmotile relatively large cell gt Cytoplasm usually is nonuniform gt Can be continuous or discontinuous gt Meiotic divisions are not equal and frequently delayed 00 II Egg Cell Structure gt Classified by yolk gt Isolecithal little or no yolk Ex Humans mammals gt Meseolpethal a lot of yolk in a gradient Ex Frog gt Telolecithial much more yolk Ex Chicken Reptiles gt Yolk affects cleavage patterns next slide Wed September 28 2011 0 LOOK AT SEA URCHIN EGG STRCUTURE I SpermEgg Interactions gt Sperm and egg meet and match gt sperm nucleus usually fuses with egg gt Egg is activated gt Sperm and egg pronuclei fuse o The sea urchin sequence of fertilization up to fusion of plasma membranes 0 ICC method to show the acrosome bindin protein is now on the outer plasma membrane gt Bindin will be the sperm protein and binds to the ventral envelope Actin polymerization contributes the extension of the acrosomal process Preparation for fusion and cortical granule reaction The formation of the fertilization envelope makes a mechanical block to polyspermy The vitelline envelope or membrane is partially peeled away to show the plasma membrane underneath Time span for the formation of the fertilization envelope is about one minute Cortical granules store materials used for prevention of polyspermy during fertilization Egg Contents gt More of everything in somatic cell mitochondria other organelles gt Masked untranslated but stored mRNA gt Sometimes yolk gt Sometimes morphogenetic cytoplasmic determinants distributed in the yolk gt Sometimes protein proteins like lysozymes o Vitellogenesis in the frog gt Is the period of yolk formation and deposition gt Vitellogenin is the yolk precursor molecule made in the liver gt Broken down into phosvitin and lipovitellin in Oocyte gt No yolk in eutherian mammals o RNAs in Oocytes ampbrush gt Masked mRNA Under translational control gt Ribosomal RNA Genes are uniquely and selectively increased in numbers 500 fold 0 0 0 0 0 O 0 O 0 O 0 O 0 O 0 O 0 O 0 0 0 00 o 00 0 0 0 0 0 0 III Regulation of OogenesisOvulation in the frog gt Functions of MPF gt Releases Diplotene meiosis I arrest gt Phosphorylate nuclear lamines so germinal vesicle breaks down gt Causes chromosomes to condense further gt Cause progression to next arrest point Metaphase II Cyclin protein levels peak before Cytokinesis in a study of surf clams Cyclins are found MPF is made of two proteins gt Protein kinase adds Phosphate to other proteins called P34 cdc2 gene product gt Plus the regulatory cyclin gt Without cyclin the kinase has no activity gt What level of ene exression control is this Protein Activation Control gt More complex but only three new hormones Estrogen LH Luteinizing Hormonemammal specific and FSH Chorionic Fri September 30 2011 o 00 Mammalian sequence of fertilization Fertilization occurs in the ampulla region of the oviduct Note ovary position and potential problems with ovulation The ovulated mammalian oocyte is surrounded by a protein layer the zona pellucida and a layer of follicle cells Secondary oocyte is ovulated with cumulus cells Follicle cells Mouse Fertilization Sequence iL Main pts i Late acrosome rx 4 Species recognition at the Zona Pellucida The three fibrous glycoproteins of the zona pellucida are crosslinked to make it strong Experiment to show that addition of soluble glycosylated ZP3 can inhibit the binding of sperm to the zona pellucida of eggs 4L Main pt Sperm bind to ZP3 glycoprotein The soluble ZP 3 protein blocks sperm binding because 4L A It causes an acrosome reaction to occur in the sperm il B In high amounts it interrupts assembly of the ZP3 to ZP2 linkage 4 C It occupies the ZP3 binding site on the sperm 4 D It is like an ECM in that sperm stop moving when they stick to it V V VV V V V 00 11 Fusion of membranes and cortical reaction gt In sea urchins bindin plays a role in fusion whereas in the mouse another protein fertilin does this V Seconds after fusion a depolarization occurs across the sea urchin membrane Depolarized membranes are unable to fuse in this fast block to poyspermy Mechanism of action Ca storage 4L Calcium release spreading across cytoplasm triggers the cortical granule reaction 4L Due to the fluorescence you can see where the sperm fusion takes place Evidence for Ca mediation of the cortical granule reaction 4L Adding Ca to unfertilized egg triggers it The ionophore A23187 allows Ca to enter the cytoplasm 4 Binding up Ca with a chelator like EDTA will eliminate it gt Pronuclear fusion Formation of the zygote nucleus DNA blue tubulin green 0 Egg Cell Activation gt Metabolic and gene expression changes gt What happens after fusion of the sperm with the egg 0 Interceluar activation events occurring after fusion in sea urchins V V V 0 0 0 spam blnding Andcor nal9quot 0 35 ca l nmuhrmu l m mmwmmt araLLvar 5 mm rim r 5 u v A 00 w o v 11 Cytoplasmic Rearrangements also needed Cortical rotation would be expected to be sensitive Parthenogenesis Activation and fertilization of an egg without male genes Occurs naturally in insects amphibians lizards not mammals Sometimes alternates with sexual reproduction heterogamy Incomplete or during produces diploid eggs Polar bodies used as sperm Germ cells undergo rather than meiosis In gynogenetic species male sperm is necessary to activate egg but does not contribute DNA to offspring VV err trek Mon October 3 2011 Cleavage and Blastulation Cleavage Stages gt Very rapid mitosis and cytokinesis in oviparous species gt Cell cycle can lack and phases gt No net growth uses endogenous egg cytoplasm Wed October 5 2011 Gastrulation 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O o 0 0 0 0 Formation and arrangement of major germ layers gt Ectoderm mesoderm endoderm a triploblastic embryo Establishment of the major axes of the body Axes of the body gt DorsalVentral gt AnteriorPosterior CranialRostralCaudal gt LeftRight MedialLateral Two classes of bilateral animals begin their developmental differences in gastrulation gt Protostomes All invertebrates except echinoderms and a few other phyla the mouth forms at or near the blastopore region gt Deuterostomes Echinoderms plus chordates the mouth is the second opening to form about 180 degrees from the blastopore the anal opening forms near or at the blastopore region Intercalation two types Radical and Mediolateral The six types of morphogenetic movement are used to varying extent in different organisms gt Invagination Involution Ingression Delamination Epiboly and Intercalation For instance sea urchin gastrulation uses ingression and invagination a lot but in frog gastrulation involution and intercalation is used more than ingression Later in the frog is a prominent mechanism There are different ways to accomplish the similar tasks I The anatomical process of gastrulation gt Formation of first two cell layers by invagination in Amphioxus a primitive chordate Ingression and invagination in sea urchin gastrulation Ingression by bottle cells They shortly form mesenchyme which makes the spicules of the skeleton Fate map a method to label and trace where cells end up gt In many frog species prospective mesoderm is on the outer surface gt In Xenopus however most of the prospective mesoderm cells are already inside the blastula Vital Dye Staining of Amphibian Embryos for fate mapping Vogt 1925 Main point outer cells move in forming a line of cells along the A P axis cells closest to blastopore move farthest to the future mouth area Frog fate maps 0 0 Label and know for exam II Try labeling ectoderm blue mesoderm red endoderm yellow 0 Bottle cell invagination to form the blastopore in frogs gt IMZ Band of outer cells at a latitude of the lower edge of the gray crescent o Holtfreter s experiment 1944 with bottle cells shows that they are invasive but stick together 0 Xenopus Early Dorsal Blastopore Lip gt IMZ involuting marginal zone cell movement at dorsal lip gt Involution rolling around an edge 0 Vegetal Rotation occurs just prior to bottle cell formation gt The prospective Pharyngeal Endoderm is first to move up from the vegetal endoderm to be the leading cells moving along the blastocoel upper wall 0 Pharyngeal endoderm and bottle cells pull the later involuting cells along in the developing A P axis 0 Which cells take a short cut to get inside 0 Convergent Extension of IMZ mesoderm pulls bottle cells and endoderm into the archenteron 0 Cell movement to the blastopore is circumferential 0 Animal pole epiboly through cell division 0 Cells labeled with black dots are those undergoing cell division in this autoradiograph of a gastrula section v What are the black dots Where is the most cell division gt 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Animal pole epiboly through intercalationshown and cell flattening not shown gt The thicker early multicell layer st 8 becomes a thinner twocell layer later st 115 II Cellcell associations 9 99 How do cells form the germ layers in the correct locations gt 1 What are the adhesive molecules involved gt 2 Could cell adhesion changes create the pattern Cell sorting experiments like these show that a reasonable mimic of the embryonic arrangement of cells forms by some mechanism Bottle cell invagination to form the blastopore in frogs gt Marginal Zone a band of outer cells at a latitude of the lower edge of the gray crescent What is known gt Fibronectin plays a role in gastrulation cell movements gt Immunofluorescence experiments show that fibronectin is produced from cells on the animal pole side of the blastocoel gt That is just a correlation How could we disable fibronectin to prove it has a necessary functional role Exogastrula f forms after disrupting fibronectin to cell connections with RGD peptide Cadherins are involved in embryonic cell adhesion o 99 o 99 o 99 o 99 o 99 9 9 9 9 9 9 9 9 9 9 9 9 0 0 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 Note the binding of catenins to cadherin Protocadherins do not have binding to beta catenin Betacatenin is a protein that can move to the nucleus and activate transcription factors Protocadherins initiate convergent extension lateral intercalation gt Not expressed in head mesenchyme which do not intercalate protocadherin protein location shown in dark blueblack gt Different forms expressed in segmental plate and notochord which do intercalate but do so separately from each other Holtfreter s hypothesis gt 1 Cells have affinity for similar cells gt 2 Dissimilar cells will form separate clusters if mixed Selective affinity could explain cell clustering of germ layers The Importance of NCadherin in Separation of Neural and Epidermal Ectoderm gt Ncadherin blocked Cells are mixed together here gt Normal Cadherins present gt Loss of Ncadherin done by injection into one of two blastomeres Main points Different types of cells if mixed together will sort out into cell masses of one cell type Typically the final sorting is roughly similar to that of the normal embryo s cell types There are some general adhesive proteins present and functional and some celltype specific adhesive proteins gt Is this enough to explain the sorting What explains the order of the layers ectodermmesodermendoderm outside to inside Steinberg s 1970 differential adhesion hypothesis gt Cells differ in adhesive strength and those with the strongest adhesion move to the middle What is the minimum requirement for sorting out gt A Must have different adhesion molecules in different cells gt B Need different adhesion strengths in different cells gt C Movement of cells is required gt D A and B above gt E B and C above Some think that mechanical forces compression and stretching influence development What might be a mechanism for it gt A Cells destined to die are usually torn apart or simply squashed gt B A cell when compressed removes cell adhesion molecules from its surface so it can slip out gt C Stressing pulling or pushing on an adhesion protein causes a signal to be sent back to the nucleus gt D Cells are mostly water an incompressible fluid so they are wrong cells cannot be compressed or stressed by mechanical force Fri October 14 2011 Experimental Analysis of Gastrulation and Neurulation The search for the organizer 9 9 99 O gt VV VV V VV gt gt What are the cell signals and mechanisms used to coordinate the complex events of gastrulation and neuralation What organizes the embryo When is the prospective potency ie what a cell can become determined ie restricted and fixed to its prospective fate ie what a cell will form What is a test for determination Transplant to new location and see if the tissue differentiates according to what is expected of the old or new location Indeterminant regulative development in early gastrula means the fate was not determined Determinant development in late gastrula means the fate was determined What is the first frog tissue to exhibit determinant development 4L These cells might be special because they start development and all the rest might depend on them and will be organized by them it A theory of development is implied SpemannMangold Organizer Experiment 1924 Main pointThe had organizing ability This effect was called Primary Embryonic Induction 4L Dorsal lip cells form chordamesoderm derivedtissues i But most of that secondary axis is induced in the surrounding host cells Is secondary axis formation in frogs similar to twinning in mammals Why or gt why not What do you think the analogous part to the dorsal lip in avian and mammal development would be gt II Induction and Competence general requirements Induction A tissue interaction causing differentiation of neighboring cells gt Inducer sends a signal Responder changes because of signal Responder s ability to be induced could be as simple as having the receptor for the signal Induction and competence are shown in eye development transplant experiments 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 There are numerous species of fish living in caves that have evolved eyeless Propose two ways for eyeless and tests of the hypothesis Electrical impulses stimulate neurotransmitter release at target cell Signals travel via the bloodstream act far from site of synthesis Ligand amp receptor are transmembrane proteins on neighboring cells Ligand is produced and acts locally Evidence for diffusible signals not cellcell contacts gt Induction of neural plate by chordamesoderm can occur across a barrier that allows diffusion but not cellcell contact Neural Structures induced in Presumptive Ectoderm by Newt Dorsal Lip Tissue Separated From the Ectoderm by a Nucleopore Filter Concentrationdependent effects of activin TGFB familyshow that the amount of a morphogen determines what the cell response will be Activin is a polypeptide that induces ventral mesoderm best blood and muscle Are morphogens distributed in a gradient gt Pattern formation in the French Flag model for diffusible molecules invented by Lewis Wolpert gt Main point In this theory depends on amount received Release of activin diffusing out from a source in center causes different mesodermrelated genes express depending on the distance from the center gt But no morphogens have yet been shown to form a gradient Two es of ind tio 4i Inducer causes change in responder among a number of potential fates 4L Particular change cannot occur without a particular inducer lj l ligilf iii F x is eirimii i39 39 all Inducer simply allows change but does not cause it Four classes of polypeptide paracrine factors are involved as morphogens gt 1 TGFbeta class eg activin BMP4 and othersVg1 gt 2 FGF class eg FGFs gt 3 WNT class eg WNTs gt 4 New class unrelated to each other and to the first three AL Noggin chordin follistatin Summary of the main points about induction in gastrulation An inducer cell sends out morphogen to which a competence cell responds The morphogen is a paracrine diffusible ligand Induction is instructive The morphogen probably is distributed in a gradient The morphogen concentration a cell encounters determines cell response Morphogens are usually polypeptides four classes VVVVVV III Molecular mechanisms of induction How can proteins and genes involved in induction found gt Use bioassay make transplants and check for ability to form second axis or prevent an axis formation gt Find a rich source of morphogen tissues or clones and test them in a bioassay for formation or inhibition of axes gt Injection of sense strand or antisense strand RNA Rich sources of the organizer activity were sought leading to some odd associations gt i Guinea pig bone marrow had high activity for inducing somites and nephric tubules snake kidney induced hindbrain and otic vesicle Even dyes or high pH could induce Testing possible genes for effects on axis formation gt Inject sense mRNA of candidate gene which induce another axis gt Inject antisense RNA to mRNA of candidate gene which inhibit axis Threei d t39 eref d z of the marginal zone cells by the vegetal cells from the organizer r from the chordamesoderm this is the same as primary embryonic induction There are four major morphogen signals Ventral mesoderm signals Dorsal mesoderm signals Organizer signals Neural differentiation signals 9 Mesoderm Induction The first induction of mesoderm and the organizer Mesoderm induction begins with cortical rotation Rotation allows betacatenin to be activated on future dorsal side Nieuwkoop center Signals from the Nieuwkoop center induce the organizer dorsal mesoderm Overlap area induces SpemannMangold organizer in adjacent marginal zone just below the gray crescent mRNA testing of a candidate molecule used in induction Normal embryo One dorsal lip Typical results of a partial secondary axis formed by excess or ventral expression of goosecoid or siamois 4 Main Point The results indicate that these play a role in mesoderm induction 9 VVVVVVVElkVVVV VVV gt Growth factors with mesodermal induction activity arise in the endoderm and diffuse from it B Dorsal Induction V V VV V V Morphogens from the organizer diffuse out to induce the dorsal side structures Noggin chordin foistatin three independent and unrelated polypeptides act redundantly Why have three molecules do the same job Inducers expressed in organizer is Main Point Three are in the right place at the right time Noggin effects on dorsal structures depend on dose iL Too Little Noggin A belly tissue it Too Much Noggin A head tissue Dorsalventral axis formation all Bone morphogenic protein 4 BMP4 5L Initially found throughout prospective mesoderm and ectoderm It ventralizes mesoderm and induces ectoderm to become skin epithelium 4L BM P4 action must be blocked if dorsal structures are to be formed aii Noggin chordin foistatin all do that they block BM P4 action all How do they block BMP4 Noggin and Chordin directly bind to BMP4 outside of the cells Follistatin blocks the BM P4 receptor on the cells C Neural Plate Induction VV VVVV V Not the type of induction we once thought it was Isolated cells form neural cells so their default pathway is to form the neural plate not be induced to form it They become competent to form neural tissue even in the bastua stage What causes them to not form neural tissue It s another role for BMP and Wnt gradients establish dorsalventral and anteriorposterior axes Early or more anterior chordamesoderm tend to induce anterior neural plate and other anterior structures Anterior to posterior regional specificity of induction Jin Anterior structures are formed by low levels of Wnt and BMP inhibition ll Posterior structures are formed through Wnt gradient induces posterior structures Retinoic acid Vitamin A precursor induces more posterior structures Fibroblast growth factors FGFs are needed for Wnt to act on cells Avian Mammalian Gastrulation and Neuralation Avian developmental anatomy has been covered extensively in the lab Here 9 99 o 99 o 9 we will concentrate on cellular mechanisms and genes Frog vs Chick Nieuwkoop center gt Asymmetry leading to Koller s sickle formation occurs in the marginal zone Chick Dorsalventral Axis Formation Same Genes as for frog gt Nieuwkoop center Koller s Sickle it Bcatenin TGFB specifically VGl gt Organizer Hensen s Node 4L Chordin and new ones Shh and nodal which are all BMP blockers it But FGFs are needed too for neural induction quotScatter Factor is a primitive streak protein gt Protein secreted by streak cells 4 Causes degradation of basal lamina Interferes with Cadherins Both functions allow ingression of individual cells into the blastocoel Mammalian gastrulation and neuralation Developmental Anatomy Neuralation Early ectoderm derivatives Primary neuralation First of two types it Ectoderm thickens to form neural plate 4 Plate folds and edges curl inwards as neural folds all Folds fuse to form neural tube Primary Neuralation Stages 4L Formation of neural plate 4 Shaping of neural plate ll Bending to form neural groove 4 Closure of groove to form neural tube Formation and Shaping of Neural Plate 4E The ectoderm over the chordamesoderm forms the neural plate bordered by prospective neural crest Folding bending of neural plate il Folding depends on formation of hinge points of two types Closing of the neural tube Cell shape changes in the neural plate hinge points Cadherins expression differences may in part explain the separation of neural plate from epidermis ll It is thought that the appearance of Ncadherin allows plate cells to sort away from epidermal cells without it while allowing neural folds to stick to each other during closure Neuropore closure defects Spina Bifida and Anencephaly EV V VV V V VVV V V Propose a theory to explain these epidemiological correlations with neural tube closure problems le In 3rd world rural areas babies born in the spring have the highest rates it Fifty years ago it was 10 times higher in Ireland than in the USA it There is a 1500 incidence of closure problems now in the USA What does folic acid do is Forms a coenzyme tetrahydrofolate used for biosynthesis especially of Purines A and G and T DNA precursors 4L If DNA synthesis occurs throughout the embryo why would Neuropore closure be particularly sensitive Secondary Neurulation a second way to form a neural tube 4L This process occurs in the abdomen caudal to the pelvis and tail it Cavitation Process of forming a space by hollowing out a block of cells LeftRight Axis Formation is a paracrine protein controls leftright specific genes Activates leftspecific and blocks rightspecific genes 4i Activin expression on right blocks shh and induces Snail Snail is a right side specific transcription factor 41s on left induces Pitx2 and nodal 4L Pitx2 transcription factor and nodal paracrine protein are leftspecific Nodal and Pitx2 expression on the left side Increase in nodal after SHH application Normal and Kartagener s syndrome axoneme L Gene that codes for dynein also affects laterality of the heart all V V V VV V Relatively more growth on one side leads to a bending of the column This could be one side of a heart tube for instance Placenta Formation Placenta Formation 4 Major Points gt 1 Between birds or reptiles and mammals extraembryonic membranes are similar by Homology all The amnion and chorion which make the embryonic part of the placenta as well as the yolk sac and allantois in eutherian mammals evolved from the amniotic egg membranes 39L The formation of the yolk sac and allantois would be difficult to explain as Analogous structures no yolk and no need for nitrogenous waste storage gt 2 The advantages of having a placenta are substantial o No need for yolk mother provides nutrients gas and waste exchange Internal Protected Environment V V V V V VS V On the other hand the problems of formation are substantial too A rich blood supply must be established and later severed without excess bleeding It must prevent a Genetically Different embryo from being recognized and rejected by the maternal immune system Sobering statistics on maternal mortality the risk of the mother dying within 24 hours of childbirth Mainly due to postpartum bleeding and sepsis The placenta is made of embryonic and endometrial cells Cytotrophoblast Cells contact the endometrium and soon form a second outer layer of unusual cells Syrtiotrophoblast syncytial large invasive cells burrow in and make spaces in which maternal blood will pool sinuses or trophoblastic lacunae Chorion is the extraembryonic mesoderm plus cytotrophoblast plus the syncytiotrophoblast Sinuses will attract blood vessels from the decidua the maternal portion of the placenta and from extraembryonic mesoderm Chorionic villus formation establishes the region where maternal and fetal blood will be able to exchange oxygen hemoglobin differences will be discussed later carbon dioxide nutrients water and removal of wastes ammonia early and urea later Blood supplies do not mix except for brief times during villi formation and during birth and then only in limited amounts The body stalk contains the umbilical artert poorly oxygenated blood and umbilical vein well oxygenated blood forms from extraembryonic mesoderm The allantois forms from endoderm as an outpocketing of the gut but is non functional in mammals Why form it ill Later primordial germ cells migrate along it The allantois forms from endoderm as an outpocketing of the gut but is non functional in mammals Why form it Later primordial germ cells migrate along it err wasth all Maternalfetal interactions There are multiple functions of the placenta 4L Gasses nutrients wastes water are exchanged ilk Supports pregnancy through luteotropin formationFor early part when corpus luteum is maintained then E and P are made from placenta 4L Prevents maternal immune system rejection Harmful agents that pass across a placenta 4L Gasses Carbon monoxide ll Viruses rubella polio measles HIV and others that is most cross i Protozoa Toxopasma gondii affects brain and eye development all Almost all bacteria do not syphilis excepted wily Drugs alcohol sedatives thalidomide analgesics nicotine heroin cocaine etcthat is most drugs pass 4L In summary Assume it
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'