Development and Growth

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Development and Growth
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SoWhat do we know already?

• The events of early embryonic development are set
  in motion by two haploid cells coming together.
• Sperm (n)
• Egg (n)
• Gives us a zygote! (2n)

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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-a series of cell divisions by the zygote

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Prenatal Development

• Fertilized egg zygote
• Cleavage at approximately every 20 hrs
• 2, 4, 8, 16 cells
• Embryonic stages
• Morula stage
• migrating into the uterus by 3-4 days
• 16-32 cells
• Blastula stage about 1 week
• Cells rearrange to form a hollow ball

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Embryo Development
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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 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

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Development

• Cells act as sources of signaling molecules that
  influence other cells in their neighborhood.
• Pattern formation
• Each cell is exposed to a succession of signals.
  
• The signals are transient
• The cell has a memory to activate or repress
  specific genes

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Development

• Cells switch on different sets of genes according
  to their position and their history
• gene expression changes (transcription and
  translation)
• An original crude plan of structure is modified
  and filled in with progressively finer and more
  intricate detail
• by numerous communication vehicles

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Development

• A gene called sonic hedgehog
• it is a signaling protein responsible for
  organizing the pattern of the body it causes
  bipolar development of limbs and development of
  midline structures of the central nervous
  system--depending on what cell type receives the
  message
• mutations of this gene can cause a a single eye
  in the middle of a face and a rudimentary nose
  with a single nostril in drosophila