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. (turnitin.com)
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