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Vertebrate Development

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Presentation on theme: "Vertebrate Development"— Presentation transcript:

1 Vertebrate Development
Chapter 51

2 Material 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.

3 Material 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.

4 Outline Stages of Development Cell Cleavage Patterns Gastrulation Developmental Process During Neurulation How Cells Communicate During Development Embryonic Development-Vertebrate Evolution Extraembryonic Membranes Human Trimesters Birth and Postnatal Development

5 Stages of Development Fertilization combination of gametes Cleavage
series of extremely rapid mitotic divisions Gastrulation series of extensive cell rearrangement Neuralation the process where tissue forms a neural tube Organogenesis the process where cells interact with one another and rearrange themselves to produce tissues and organs Gametogenesis the development of gametes often not complete until the organism matures varies greatly within animal kingdom Maturity Larvae – pupae – adult metamorphosis

6 Fertilization Penetration glycoprotein-digesting enzymes in acrosome of sperm head Activation events initiated by sperm penetration chromosomes in egg nucleus complete second meiotic division triggers movement of egg cytoplasm sharp increase in metabolic activity

7 Stages of Development Nuclei fusion The third stage of fertilization is fusion of the entering sperm nucleus with the haploid egg nucleus to form the diploid nucleus.

8 Mammalian Reproductive Cells

9 Vertebrate Development Review
Formation of blastula water drawn into cell mass forming a hollow ball of cells - blastula or blastocyst Gastrulation some cells of blastula push inward, forming a invaginated gastrula invagination creates main axis of vertebrate body Has an animal pole and a vegetal pole Animal pole end forms external tissues Vegetal pole form internal tissues embryo now has three germ layers

10 Vertebrate Development Review
Neurulation zone of ectoderm thickens on dorsal surface of embryo neural tissue rolls and forms neural tube cell migration variety of cells migrate to form distant tissues

11 Vertebrate Development Review
Organogenesis basic body plan established tissues develop into organs embryo will grow to be a hundred times larger

12 Vertebrate Development

13 Vertebrate Development

14 Cell Cleavage Patterns
Initial cell division, cleavage, is not accompanied by an increase in the overall size of the embryo. morula - mass of 32 cells Each cell is a blastomere. eventually a blastula is formed The pattern of cleavage is influenced by the presence of yolk Animal Pole – small amount of yolk Vegetal pole – large amount of yolk

15 Cell Cleavage Patterns
Primitive chordates holoblastic cleavage - egg contains little or no yolk, and cleavage occurs throughout the whole egg Amphibians and advanced fish Eggs 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.

16 Holoblastic Cleavage

17 Cell Cleavage Patterns
Reptiles and birds eggs composed almost entirely of yolk cleavage only occurs in polar cytoplasm meroblastic cleavage Mammals contain very little yolk holoblastic cleavage inner cell mass forms developing embryo outer sphere, trophoblast, enters endometrium

18 Meroblastic Cleavage

19 Cell Cleavage Patterns
Blastula Each cell is in contact with a different set of neighboring cells. Interactions are a major factor influencing developmental fate.

20 Gastrulation Certain 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: ectoderm mesoderm endoderm

21 Gastrulation Gastrulation in primitive chordates surface of blastula invaginates into the blastocoel eventually inward-moving wall pushes up against the opposite side of the blastula produces embryo with two cell layers: outer ectoderm inner endoderm mesoderm forms later between the ectoderm and endoderm

22 Gastrulation in a Lancet

23 Gastrulation Gastrulation in most aquatic vertebrates Yolk-laden cells of the vegetal pole are fewer and much larger than the yolk-free cells of the animal pole.

24 Frog Gastrulation

25 Gastrulation Gastrulation in reptiles, birds, mammals no yolk separates two sides of embryo lower cell layer differentiates into endoderm and upper layer into ectoderm without cell movement primitive streak

26 Mammalian Gastrulation

27 Developmental Processes During Neurulation
Tissue differentiation begins with the formation of the notochord and the hollow dorsal nerve cord. neurulation After 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

28 Mammalian Neural Tube Formation

29 Developmental 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.

30 Developmental Processes During Neurulation
Neural crest Edges of neural groove pinch off and form the neural crest. Nearby clusters of ectodermal cells thicken into placodes. Gill chamber Some of the neural crest cells form cartilaginous bars between the embryonic pharyngeal slits. forms efficient pump

31 Developmental Processes During Neurulation
Elaboration of the nervous system Some neural crest cells migrate ventrally toward the notochord and form sensory neurons in the dorsal root ganglia. others become specialized Schwann cells

32 How 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.

33 How Cells Communicate During Development
Nature of development decisions Some cells become determined early in development. At some stage, every cell’s fate becomes fixed (commitment). not irreversible, but rarely reverses under normal conditions

34 Embryonic Development - Vertebrate Evolution
Ontogeny recapitulates phylogeny Embryological 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. ( Do you agree or disagree with this statement? Why? Does science agree with this statement? Why?

35 Vertebrate Embryonic Development

36 Extraembryonic Membranes
Fluid-filled amniotic membrane: an adaptation to terrestrial life amniotic membrane an extraembryonic membrane Extraembryonic membranes, later to become fetal membranes, include the amnion, chorion, yolk sac, and allantois.

37 Extraembryonic Membranes

38 First Trimester First trimester fourth week - organ development organogenesis most women not yet aware of pregnancy Fetal Alcohol Syndrome

39 First Trimester Second month - morphogenesis limbs assume adult shape major organs become evident embryo is about one inch in length Third month - completion of development now referred to as fetus nervous system and sense organs develop all major organs established

40 Second and Third Trimesters
Second trimester - growth bone formation occurs covered with fine hair (lanugo) by the end of the sixth month, baby is one foot in length Third trimester - pace of growth accelerates weight of fetus more than doubles most major nerve tracts formed within brain by end, fetus is able to survive on own

41 Birth and Postnatal Development
Uterus releases prostaglandins begin uterine contractions, but then sensory feedback from the uterus stimulates the release of oxytocin from the mother’s pituitary gland rate of contraction increases to one contraction every two or three minutes strong contractions, aided by the mother’s pushing, expels the fetus

42 Birth and Postnatal Development
Nursing Milk 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 nipple first milk produced after birth called colostrum - rich in maternal antibodies Milk synthesis begins about three days following birth.

43 Birth and Postnatal Development
Babies typically double their birth weight within a few months. Neuron production occurs for six months. allometric growth


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