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Vertebrate Development

Chapter 51

From Biology

Raven & Johnson 7th Ed.

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Outline

• Stages of Development• Cell Cleavage Patterns (focus on mammalian)

• Gastrulation• Developmental Process During Neurulation• How Cells Communicate During Development• Embryonic Development-Vertebrate Evolution• Extraembryonic Membranes• Human Trimesters• Birth and Postnatal Development

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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

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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.

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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

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Terminology of Stages of Development

ZYGOTE

GASTRULA

BLASTULA (BLASTOCYST IN MAMMALS)

MORULA SOLID BALL

EMBRYO

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Cell Cleavage Patterns(only need to know yellow vocab here)

• 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.

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Holoblastic Cleavage

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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

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Meroblastic Cleavage

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Cell Cleavage Patterns

• Blastula– Each cell is in contact with a different set

of neighboring cells. Induction; ie: eye formation Cell signals (chemical messengers)

regulate gene transcription in neighboring cells.

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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

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Gastrulation

• Gastrulation in primitive chordates– surface of blastula invaginates into the

blastocoel eventually inward-moving wall pushes up

against the opposite side of the blastulaproduces embryo with two cell layers:

outer ectoderm inner endoderm mesoderm forms later between the

ectoderm and endoderm

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Gastrulation in a Lancet (a non-vertebrate chordate)

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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

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Mammalian Gastrulation

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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

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Mammalian Neural Tube Formation

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INDUCTIONFORMATION OF THE EYE (pg 1093 Fig 51.16)

• 1. Optic vesicle grows from embryonic brain, which induces…

• 2. Lens vesicle forms from ectodermal cells, which induces…

• 3. Optic vesicle to round into optic cup (most of eyeball)

**Induction is based on genes turning on. It is influenced by where the cell is (and what chemical messengers it contacts).

• 4. Lens vesicle separates from ectoderm• 5. Inner layer of optic cup becomes retina• 6. Lens becomes transparent

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Developmental Processes During Neurulation

• On either side of the developing notochord, segmented blocks of mesoderm tissue called somites form (segmentation).

– 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.

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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• How is this related to stem cell research

(embryonic/ adult stem cells)?

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Lining ofrespiratory

tract

Lining ofdigestive

tract

PancreasOuter covering

of internalorgans

Lining ofthoracic andabdominal

cavities

Vessels

Dermis

Epidermis, skin,hair, epithelium,inner ear, lens

of eye

Circulatorysystem

SomitesGonads

Integu-ments

Kidney

Gastrula

Blastula

Zygote

Majorglands

Endoderm

Pharynx

Ectoderm

Mesoderm

Gill arches,sensory ganglia,Schwann cells,adrenal medulla

Heart

Skeleton

Neuralcrest

Notochord

Segmentedmuscles

Dorsalnervecord

Chordates Vertebrates

Liver

Blood

Brain,spinal cord,spinal

nerves

Fig 51.17

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• Go to Active Board Interactive

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Embryonic Development - Vertebrate Evolution

• Ontogeny recapitulates phylogeny– Embryological development (ontogeny)

involves the same progression of changes that have occurred during evolution (phylogeny).

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Vertebrate Embryonic Development

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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.

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Extraembryonic Membranes

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First Trimester

• First trimester– fourth week - organ development

organogenesismost women not yet aware of

pregnancy Fetal Alcohol Syndrome

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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

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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

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Birth and Postnatal Development

• Uterus releases prostaglandins– begin uterine contractions, but then

sensory feedback (positive) 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

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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.

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Birth and Postnatal Development

• Postnatal development– Babies typically double their birth weight

within a few months.– Neuron production occurs for six months.– allometric growth

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Summary

• 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

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