Download Development

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
the zygote
of cell divisions by
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 createdblastopore
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