Development and Growth

Embryology So…meiosis gives us gametes which unite through fertilization to form a fertilized zygote. Now what?

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

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

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

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.

Examples:

3 Stages

Stage 1: Morula: Solid ball of cells Cells grow more numerous while their size decreases

Stage 2: Blastula: Cell division keeps going and the cells begin to form a hollow fluid filled ball

Embryo Development

Stage 3: Embryo Development Gastrula- cells on one side of the blastula move inward and form a two layered embryo opening is created- blastopore

Embryo Development The 2 nd 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

Embryo Development The endoderm differentiates into –digestive tract –lungs –bladder The mesoderm differentiates into –skeleton –skeletal muscle –connective tissue

Embryo Development The ectoderm differentiates into –skin –hair –brain –spinal cord

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

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

Fetal Development By the 10 th week of human development –Intestines are located in the abdomen –Fingernail development

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

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