Changes

Perhaps quite remarkably, all animals follow the same developmental "plan" - until the latter stages of development, it is difficult to tell a human embryo from a chicken embryo. This suggests an evolutionary programme for cell development.

Perhaps quite remarkably, all animals follow the same developmental "plan" - until the latter stages of development, it is difficult to tell a human embryo from a chicken embryo. This suggests an evolutionary programme for cell development.

*Embryogenesis is driven by three cellular process:

Embryogenesis is driven by three cellular process:

#'''Cell division and growth'''

#'''Cell division and growth'''

#*Fertilisation produces a unicellular zygote which undergoes a series of mitotic divisions to eventually become a multicellular organism known as a [[Blastocyst Embryonic Development - Anatomy & Physiology|blastocyst]]. Mitosis produces (i) growth by hyperplasia (ii) an increased number of cells for greater diversity of function, and thus more a complex organism. The first differentiation of cells creates trophoblasts that contain molecules that adhere to the endometrium during [[Implantation - Anatomy & Physiology|implantation]]. The extent of cellular growth and division and the [[Implantation - Anatomy & Physiology|timing]] of implantation varies between species.  

#:Fertilisation produces a unicellular zygote which undergoes a series of mitotic divisions to eventually become a multicellular organism known as a [[Blastocyst Embryonic Development - Anatomy & Physiology|blastocyst]]. Mitosis produces (i) growth by hyperplasia (ii) an increased number of cells for greater diversity of function, and thus more a complex organism. The first differentiation of cells creates trophoblasts that contain molecules that adhere to the endometrium during [[Implantation - Anatomy & Physiology|implantation]]. The extent of cellular growth and division and the [[Implantation - Anatomy & Physiology|timing]] of implantation varies between species.  

#'''Cell differentiation'''

#'''Cell differentiation'''

#*As embryogenesis progresses, cells become specialised in structure and function. Regulation of gene expression allows different proteins to be expressed in some cells, allowing tissue differentiation even though all cells contain the same DNA. At the blastomere stage (16 cells) cells are '''totipotent''', meaning they have the capacity to form every adult cell type. As the embryo progresses and enters [[Gastrulation - Anatomy & Physiology|gastrulation]] cells become '''pluripotent''', meaning they can form several but not all cell types. Gastrulation is the process of forming the three germ layers; ectoderm, mesoderm and endoderm. Eventually, most cells terminally differentiate and can no longer form any other cell type.   

#:As embryogenesis progresses, cells become specialised in structure and function. Regulation of gene expression allows different proteins to be expressed in some cells, allowing tissue differentiation even though all cells contain the same DNA. At the blastomere stage (16 cells) cells are '''totipotent''', meaning they have the capacity to form every adult cell type. As the embryo progresses and enters [[Gastrulation - Anatomy & Physiology|gastrulation]] cells become '''pluripotent''', meaning they can form several but not all cell types. Gastrulation is the process of forming the three germ layers; ectoderm, mesoderm and endoderm. Eventually, most cells terminally differentiate and can no longer form any other cell type.   

#'''Morphogenesis'''

#'''Morphogenesis'''

#*During embryogenesis two cell types exist; mesenchymal and epithelial. Mesenchymal cells are single cells or loosely linked to other cells and irregularly shaped. Epithelial cells are tightly attached to each other or a membrane and have a regular shape (cuboidal or columnar).

#:During embryogenesis two cell types exist; mesenchymal and epithelial. Mesenchymal cells are single cells or loosely linked to other cells and irregularly shaped. Epithelial cells are tightly attached to each other or a membrane and have a regular shape (cuboidal or columnar).

==The Development of Anatomical Structures==

==The Development of Anatomical Structures==

[[Category:Developmental Biology]]

[[Category:Developmental Biology]]