2Material to be covered (for Tri-C) Describe the events of each of the three stages of fertilization in an advanced vertebrate.Compare the cleavage patterns, describe the appearance of the blastula and indicate how gastrulation proceeds in primitive chordates, aquatic vertebrates and reptiles/birds/mammals.State the tissues produced by the three germ layers: endo-, meso- and ectoderm.Understand the developmental processes that occur during neuralation.Explain Haeckel’s “biogenic law”, ontogeny recapitulates phylogeny.
3Material to be covered (for Tri-C) Understand the importance of extra-embryonic membranes in terrestrial vertebrate development.Describe the characteristic events of each trimester of human pregnancy and of postnatal development.Use vertebrate models to understand embryonic development.Discussion and evaluation of bioethical issues related to embryology: cloning, stem cells and in vitro fertilization.Describe the ways that cells can signal each other.Differentiate between intracellular receptors and cell surfaces receptors.
4OutlineStages of DevelopmentCell Cleavage PatternsGastrulationDevelopmental Process During NeurulationHow Cells Communicate During DevelopmentEmbryonic Development-Vertebrate EvolutionExtraembryonic MembranesHuman TrimestersBirth and Postnatal Development
5Stages of Development Fertilization combination of gametes Cleavage series of extremely rapid mitotic divisionsGastrulationseries of extensive cell rearrangementNeuralationthe process where tissue forms a neural tubeOrganogenesisthe process where cells interact with one another and rearrange themselves to produce tissues and organsGametogenesisthe development of gametesoften not complete until the organism maturesvaries greatly within animal kingdomMaturityLarvae – pupae – adultmetamorphosis
6FertilizationPenetrationglycoprotein-digesting enzymes in acrosome of sperm headActivationevents initiated by sperm penetrationchromosomes in egg nucleus complete second meiotic divisiontriggers movement of egg cytoplasmsharp increase in metabolic activity
7Stages of DevelopmentNuclei fusionThe third stage of fertilization is fusion of the entering sperm nucleus with the haploid egg nucleus to form the diploid nucleus.
9Vertebrate Development Review Formation of blastulawater drawn into cell mass forming a hollow ball of cells - blastula or blastocystGastrulationsome cells of blastula push inward, forming a invaginated gastrulainvagination creates main axis of vertebrate bodyHas an animal pole and a vegetal poleAnimal pole end forms external tissuesVegetal pole form internal tissuesembryo now has three germ layers
10Vertebrate Development Review Neurulationzone of ectoderm thickens on dorsal surface of embryoneural tissue rolls and forms neural tubecell migrationvariety of cells migrate to form distant tissues
11Vertebrate Development Review Organogenesisbasic body plan establishedtissues develop into organsembryo will grow to be a hundred times larger
14Cell Cleavage Patterns Initial cell division, cleavage, is not accompanied by an increase in the overall size of the embryo.morula - mass of 32 cellsEach cell is a blastomere.eventually a blastula is formedThe pattern of cleavage is influenced by the presence of yolkAnimal Pole – small amount of yolkVegetal pole – large amount of yolk
15Cell Cleavage Patterns Primitive chordatesholoblastic cleavage - egg contains little or no yolk, and cleavage occurs throughout the whole eggAmphibians and advanced fishEggs contain much more cytoplasmic yolk in one hemisphere than the other.large cells containing a lot of yolk at one pole, and a concentrated mass of small cells with very little yolk at the other pole.
17Cell Cleavage Patterns Reptiles and birdseggs composed almost entirely of yolkcleavage only occurs in polar cytoplasmmeroblastic cleavageMammalscontain very little yolkholoblastic cleavageinner cell mass forms developing embryoouter sphere, trophoblast, enters endometrium
19Cell Cleavage Patterns BlastulaEach cell is in contact with a different set of neighboring cells.Interactions are a major factor influencing developmental fate.
20GastrulationCertain groups of cells invaginate and involute from the surface of the blastula during gastrulation.By the end of gastrulation, embryonic cells have rearranged into three primary germ layers:ectodermmesodermendoderm
21GastrulationGastrulation in primitive chordatessurface of blastula invaginates into the blastocoeleventually inward-moving wall pushes up against the opposite side of the blastulaproduces embryo with two cell layers:outer ectoderminner endodermmesoderm forms later between the ectoderm and endoderm
25GastrulationGastrulation in reptiles, birds, mammalsno yolk separates two sides of embryolower cell layer differentiates into endoderm and upper layer into ectoderm without cell movementprimitive streak
27Developmental Processes During Neurulation Tissue differentiation begins with the formation of the notochord and the hollow dorsal nerve cord.neurulationAfter the notochord has been laid down, ectodermal cells above the notochord invaginate, forming the neural groove down the long axis of the embryo.edges move toward each other and fuse creating neural tube
29Developmental Processes During Neurulation On either side of the developing notochord, segmented blocks of mesoderm tissue called somites form.Ultimately, somites give rise to muscles, vertebrae, and connective tissues.Mesoderm in the head region remains connected as somitomeres and form striated muscles of the face, jaws, and throat.
30Developmental Processes During Neurulation Neural crestEdges of neural groove pinch off and form the neural crest.Nearby clusters of ectodermal cells thicken into placodes.Gill chamberSome of the neural crest cells form cartilaginous bars between the embryonic pharyngeal slits.forms efficient pump
31Developmental Processes During Neurulation Elaboration of the nervous systemSome neural crest cells migrate ventrally toward the notochord and form sensory neurons in the dorsal root ganglia.others become specialized Schwann cells
32How Cells Communicate During Development Inductions between the three primary tissue types are referred to as primary inductions.Inductions between tissues that have already been differentiated are called secondary inductions.
33How Cells Communicate During Development Nature of development decisionsSome cells become determined early in development.At some stage, every cell’s fate becomes fixed (commitment).not irreversible, but rarely reverses under normal conditions
34Embryonic Development - Vertebrate Evolution Ontogeny recapitulates phylogenyEmbryological development (ontogeny) involves the same progression of changes that have occurred during evolution (phylogeny).Homework (due by wednesday) find out if this makes any sense. (turnitin.com)Do you agree or disagree with this statement? Why?Does science agree with this statement? Why?
36Extraembryonic Membranes Fluid-filled amniotic membrane: an adaptation to terrestrial lifeamniotic membrane an extraembryonic membraneExtraembryonic membranes, later to become fetal membranes, include the amnion, chorion, yolk sac, and allantois.
38First TrimesterFirst trimesterfourth week - organ developmentorganogenesismost women not yet aware of pregnancyFetal Alcohol Syndrome
39First TrimesterSecond month - morphogenesislimbs assume adult shapemajor organs become evidentembryo is about one inch in lengthThird month - completion of developmentnow referred to as fetusnervous system and sense organs developall major organs established
40Second and Third Trimesters Second trimester - growthbone formation occurscovered with fine hair (lanugo)by the end of the sixth month, baby is one foot in lengthThird trimester - pace of growth acceleratesweight of fetus more than doublesmost major nerve tracts formed within brainby end, fetus is able to survive on own
41Birth and Postnatal Development Uterus releases prostaglandinsbegin uterine contractions, but then sensory feedback from the uterus stimulates the release of oxytocin from the mother’s pituitary glandrate of contraction increases to one contraction every two or three minutesstrong contractions, aided by the mother’s pushing, expels the fetus
42Birth and Postnatal Development NursingMilk production, lactation, occurs in the alveoli of mammary glands when they are stimulated by prolactin.milk secreted in alveolar ducts which are surrounded by smooth muscle and lead to the nipplefirst milk produced after birth called colostrum - rich in maternal antibodiesMilk synthesis begins about three days following birth.
43Birth and Postnatal Development Babies typically double their birth weight within a few months.Neuron production occurs for six months.allometric growth