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 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

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 4th week of human development

–Neurulation (nervous system) is underway

–Gastrulation is complete

Embryo Development

By the 5th week of human development

–Limb buds are present

–Organs start to form

Fetal Development

By the 10th week of human development

–Intestines are located in the abdomen

–Fingernail development

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

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