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Embryo, when applied to mammals, is the term given to the developing organism from fertilisation to birth. Developmental biology, or embryology, is the study of the embryo as it transforms from a unicellular zygote to a multicellular, mulitsystemed organism which in some cases, is ready to function autonomously. Developmental biology is of interest to vets in understanding why organs and systems are the way they are, but also in understanding genetic disease and applying cell based therapy to treat loss or damage to tissue.

Embryo, when applied to mammals, is the term given to the developing organism from fertilisation to birth. Developmental biology, or embryology, is the study of the embryo as it transforms from a unicellular zygote to a multicellular, mulitsystemed organism which in some cases, is ready to function autonomously. Developmental biology is of interest to vets in understanding why organs and systems are the way they are, but also in understanding genetic disease and applying cell based therapy to treat loss or damage to tissue.

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 cells.

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 [[Fertilisation, Implantation and Early Embryonic Development -Embryonic Development of the Blastocyst- Anatomy & Physiology|blastocyst]]. Mitosis produces (i) growth by hyperplasia (ii) an increased number of cells for greater diversity of function, and thus more complex organism. The first differentiation of cells includes trophoblasts that contain adhesion molecules to adhere to the endometrium during [[Developmental Biology - Implantation - Anatomy & Physiology|implantation]]. The extent of cellular growth and division and the time taken for implantation differs between [[Fertilisation, Implantation and Early Embryonic Development -Implantation- Anatomy & Physiology|species]].  

#*Fertilisation produces a unicellular zygote which undergoes a series of mitotic divisions to eventually become a multicellular organism known as a [[Fertilisation, Implantation and Early Embryonic Development -Embryonic Development of the Blastocyst- Anatomy & Physiology|blastocyst]]. Mitosis produces:

(i) growth by hyperplasia  

(ii) an increased number of cells for greater diversity of function, and thus more complex organism.  

The first differentiation of cells creates trophoblasts that contain molecules that adhere to the endometrium during [[Developmental Biology - Implantation - Anatomy & Physiology|implantation]]. The extent of cellular growth and division and the timing of implantation varies between [[Fertilisation, Implantation and Early Embryonic Development -Implantation- Anatomy & Physiology|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 different tissues to exists despite all cells containing 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 [[Developmental Biology - 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 [[Developmental Biology - 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 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==