PHASES OF EMBRYONIC DEVELOPMENT 2

Somatic Cells

Found in all body tissues except gonads.

Somatic Cells

Contain diploid numbers of chromosomes (2N)

Somatic Cells

Replacement of dead cells

Somatic Cells

Reproduce by mitotic division

Somatic Cells

Responsible for formation of different system and organ

myoplast

muscular system have ___ for contraction and relaxation .

neurons

nervous system have ___ for transmission of impulses.

secretory cells

digestive system have_____ for secretion of enzymes

for digestion.

osteoplasts

bones have ____ which make hardening of bone.

Germ Cells

Found only in gonads (testes & ovary)

Germ Cells

Contain haploid number of chromosomes (1N)

Germ Cells

Reproduce by meiotic division (meiosis).

Germ Cells

Function : Formation of gametes (male & female)

PRIMORDIAL GERM CELLS

Appears in the wall of the endodermal layer of the yolk sac due to their

large size and high content of alkaline phosphatase , and migrate by

amoeboid movement toward the hind gut epithelium and then through

dorsal mesentery reach to the primordia of the gonads

PRIMORDIAL GERM CELLS

Become recognizable at 24 days post-fertilization

PRIMORDIAL GERM CELLS

Invading the genital ridges in the 6th week of development.

Fertilization

activates egg & brings together the nuclei of the egg and sperm.

Cleavage

partitions the zygote into many smaller cells.

Gastrulation

rearranges the blastula to form a three- layered embryo with a primitive gut, the archenteron.

Organogenesis

the process by which the organs in the animal body form from the three embryonic germ layers.

Blastula

a hollow sphere of cells (128 cells) formed by cleavage of the morula

Blastula

contains the blastocoel that is fluid-filled

blastopore

the place where gastrulation begins.

Gastrula

transformation of the blastula into an embryo possessing 3 germ

layers, ectoderm, mesoderm, endoderm

Morula

solid mass of 16-64 cells formed by cleavage.