bio chp#07

• Development


  The process by which an organism grows and matures from a single cell into a complex multicellular organism with specialized tissues and organs
• Development


  • It involves a series of coordinated and sequential events that begin with fertilization and continue throughout the life of an organism
  • It is a highly regulated process that is influenced by genetic and environmental factors
  • It requires the precise coordination of numerous cellular and molecular processes
• Growth


  An increase in size or number of cells, tissues, or organs, often resulting in an increase in overall mass
• Development


  The process by which an organism changes from a simple to a more complex structure, acquiring new structures and functions
• Fertilization


  1. Union of male and female gametes

  2. Formation of single cell called zygote
• Egg


  • Released from ovary in the form of secondary oocyte
  • Covered with zona pellucida
  • Fertilization takes place in proximal part of oviduct
• Sperm entering egg


  1. Sperm makes its way through the corona radiata

  2. Acrosomal enzymes digest a portion of zona pellucida

  3. Sperm binds to and fuses with oocyte plasma membrane

  4. Sperm nucleus enters cytoplasm of oocyte

  5. Cortical granules release enzymes; zona pellucida becomes fertilization membrane

  6. Sperm and egg pronuclei are enclosed in a nuclear envelope
• Cleavage


  Rapid cell division that occurs after fertilization, during which the zygote divides into smaller and smaller cells, each containing a copy of the genetic material from the original cell
• Holoblastic cleavage


  Cleavage occurs throughout the whole egg
• Meroblastic cleavage


  Cleavage is restricted to the blastodisc, the small amount of clear cytoplasm concentrated at one pole of the egg
• Types of eggs based on yolk distribution

  • Telolecithal (large amount of yolk concentrated at one end)
  • Centrolecithal (large, centrally located yolk surrounded by thin layer of cytoplasm)
  • Isolecithal (small amount of yolk evenly distributed)
• Morula


  Solid mass of blastomeres formed by cleavage of zygote
• Blastula


  Hollow, bubble-like structure that eventually implants in the uterine lining
• Gastrulation


  1. Formation of three germ layers: endoderm, mesoderm, and ectoderm

  2. Begins with formation of primitive streak and invagination of epiblast
• Germ layers and their derivatives

  • Ectoderm: skin, teeth, eyes, nervous system
  • Mesoderm: bones, muscles, heart, kidneys, blood vessels, reproductive system, dermis of skin
  • Endoderm: lining of digestive and respiratory tracts, liver, pancreas, bladder, thyroid gland
• Neurulation


  1. Formation of neural plate, neural grooves, and neural tube

  2. Neural crest cells form and migrate to give rise to various cell types
• Structures derived from neural crest cells

  • Cranial nerve ganglia
  • Adrenal medulla
  • Dorsal root ganglia
  • Melanocytes
  • Skeletal and connective tissue
  • Smooth muscle
  • Schwann cells
  • Enteric nervous system
• Organogenesis


  Process of organ formation in the developing embryo, beginning in the third week and continuing until the end of the eighth week
• Control of development


  • Involves interplay between genetic and environmental factors
  • Includes pattern formation, cell differentiation, and influence of environment on gene expression and cell differentiation
• Hammerling's experiment showed that the nucleus controls the information that determines the shape of the cap in Acetabularia
• The cytoplasmic gray crescent in frog eggs contains gene regulating substances that influence early development
• Separating the daughter cells of the first cleavage in frog eggs can result in the development of normal tadpole larvae
• The gray crescent is created when some pigments in the cytoplasm shift upward, leaving a crescent-shaped area
• During the first cleavage, the zygote divides vertically, and each daughter cell receives half of the crescent
• If the daughter cells are separated carefully, each of them develops into a normal tadpole larva
• Experiment conducted by Hans Spemann

  1. Altered the normal plane of the first cleavage

  2. One daughter cell received the entire gray crescent, while the other did not receive any crescent

  3. Daughter cell with the entire gray crescent developed into a complete tadpole larva

  4. Non-crescent daughter cell failed to develop properly
• Induction


  The process by which one type of embryonic tissue influences the development of another
• The proximity to the primary organizer determines the fate of cells, with those closest becoming endoderm, those farther away becoming mesoderm, and the farthest becoming ectoderm
• The notochord, acting as the primary organizer, played a vital role by releasing signaling molecules that guided neighboring cells to differentiate into neural tissue
• Primary organizers


  Regions that determine the basic body plan of the embryo
• Secondary organizers


  Develop later and are responsible for organizing specific regions of the embryo or promoting the differentiation of specific cell types
• The ZPA (zone of polarizing activity) in the developing limb bud of vertebrates is an example of a secondary organizer
• Pregnancy


  When a fertilized egg develops into a foetus within the mother's uterus
• Pregnancy


  1. Fertilization

  2. Zygote division and development

  3. Foetus formation
• Proper nourishment of the mother during the third trimester is essential for the rapid growth and development of the fetus, to support the mother's physiological changes, and to reduce the risk of delivery complications
• Three trimesters of human development

  • First trimester
  • Second trimester
  • Third trimester
• Trimester


  A period of approximately three months during pregnancy
• Identical twins


  Occur when a single fertilized egg splits into two embryos, with the same genetic material
• Fraternal twins


  Occur when two eggs are fertilized by two separate sperm, with different genetic material
• Placenta


  A temporary organ that develops during pregnancy and serves as the interface between the maternal and foetal circulatory systems