Changes

#*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 a 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 [[Fertilisation, Implantation and Early Embryonic Development -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 [[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 a 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 [[Fertilisation, Implantation and Early Embryonic Development -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 [[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 [[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 [[Developmental Biology - Neurogenesis - Anatomy & Physiology|nervous system]] develops from ectoderm in the anterior part of the embryo, beginning with the formation of the neural plate. Some of the ectoderm will also develop into the [[Skin - Anatomy & Physiology#Origin of the epidermis|epidermis]] in response to signalling factors from elsewhere in the embryo; formation of the neural ectoderm is the default pathway. The neural plate develops into the [[CNS Development - Anatomy & Physiology|neural tube]], which is the precursor to the brain and spinal cord.

The [[Developmental Biology - Neurogenesis - Anatomy & Physiology|nervous system]] develops from ectoderm in the anterior part of the embryo, beginning with the formation of the neural plate. Some of the ectoderm will also develop into the [[Skin - Anatomy & Physiology#Origin of the epidermis|epidermis]] in response to signalling factors from elsewhere in the embryo; formation of the neural ectoderm is the default pathway. The neural plate develops into the [[CNS Development - Anatomy & Physiology|neural tube]], which is the precursor to the brain and spinal cord.

In the verterbrate embryo, the anterior of the embryo also begins to form into blocks of cells known as [[Developmental Biology - Somite Development - Anatomy & Physiology|somites]]. Somites are transient structures that will give rise to the vertebrae and ribs, the dermis of the dorsum, and the skeletal [[Developmental Biology - Muscle Development - Anatomy & Physiology|muscle]] of the body wall, back and limbs; they originate from the subsection of mesoderm known as [[Developmental Biology - Gastrulation - Anatomy & Physiology|paraxial mesoderm]].  

In the verterbrate embryo, the anterior of the embryo also begins to form into blocks of cells known as [[Developmental Biology - Somite Development - Anatomy & Physiology|somites]]. Somites are transient structures that will give rise to the vertebrae and ribs, the dermis of the dorsum, and the skeletal [[Developmental Biology - Muscle Development - Anatomy & Physiology|muscle]] of the body wall, back and limbs; they originate from the subsection of mesoderm known as [[Gastrulation - Anatomy & Physiology|paraxial mesoderm]].  

The mesoderm also gives rise to the [[Developmental Anatomy of the Kidneys and Urinary Tract - Anatomy & Physiology|urinary system]] and some parts of the reproductive system; these develop from intermediate mesoderm. The development of the male or female reproductive system is mediated by the [[Fertilisation, Implantation and Early Embryonic Development -Sexual Differentiation- Anatomy & Physiology|genetic sex]] of the embryo.

The mesoderm also gives rise to the [[Developmental Anatomy of the Kidneys and Urinary Tract - Anatomy & Physiology|urinary system]] and some parts of the reproductive system; these develop from intermediate mesoderm. The development of the male or female reproductive system is mediated by the [[Fertilisation, Implantation and Early Embryonic Development -Sexual Differentiation- Anatomy & Physiology|genetic sex]] of the embryo.