Development and Growth

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Development and Growth
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Embryology

• Someiosis gives us gametes which unite through
  fertilization to form a fertilized zygote. Now
  what?

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9 months later.

• A baby is born with a complete body structure,
  both inside and out. How do we get there?

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We must look at the early stages of

• embryology (study of dev. embryos) as these early
  stages set up the body for the rest of the
  pregnancy

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Definitions

• Development- a series of events that give rise to
  a full grown organism
• Embryo- a multicellular organism in the early
  stages of development
• Differentiation- a series of changes that
  transforms unspecialized embryonic cells into
  specialized cells, tissues, and organs.
• Cleavage- series of cell divisions by the zygote

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After fertilization.

• Zygote begins a series of cell divisions called
  cleavage
• Cleavage occurs every 20 hours. To produce more
  cells that decrease in size until all cells are
  the size they will be of the adult.

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Examples
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3 Stages
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Stage 1

• Morula
• Solid ball of cells
• Cells grow more numerous while their size
  decreases

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Stage 2

• Blastula
• Cell division keeps going and the cells begin to
  form a hollow fluid filled ball

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Embryo Development
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Stage 3 Embryo Development

• Gastrula- cells on one side of the blastula move
  inward and form a two layered embryo
• opening is created- blastopore

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Embryo Development

• The 2nd week of human development Gastrulation
• early in development, a gut is created through an
  intucking of cells from the exterior of the
  embryo into the interior
• It results in 3 basic germ layers
• Ectoderm
• Mesoderm
• Endoderm

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Embryo Development

• The endoderm differentiates into
• digestive tract
• lungs
• bladder
• The mesoderm differentiates into
• skeleton
• skeletal muscle
• connective tissue

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Embryo Development

• The ectoderm differentiates into
• skin
• hair
• brain
• spinal cord

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Embryo Development

• By the 4th week of human development
• Neurulation (nervous system) is underway
• Gastrulation is complete

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Embryo Development

• By the 5th week of human development
• Limb buds are present
• Organs start to form

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Fetal Development

• By the 10th week of human development
• Intestines are located in the abdomen
• Fingernail development

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Fetal Development

• By the 15th week of human development
• Fetus is very recognizable
• While internal organs continue to grow and
  mature, the external appearance is very human-like

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Fetal Development

• By the 38th week of human development
• Baby has reached full term and is ready to exit
  the uterus for the real world