Developmental Biology Overview - Anatomy & Physiology

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Introduction

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.

• Embryogenesis is driven by three cellular process:

1. Cell division and growth
   • Fertilisation produces a unicellular zygote which undergoes a series of mitotic divisions to eventually become a multicellular organism. Mitosis produces (i) growth by hyperplasia (ii) an increased number of cells for greater diversity of function, and thus more complex organism.
2. 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 gastrulation cells become pluripotent, meaning they can form several but not all cell types. Eventually, most cells terminally differentiate and can no longer form any other cell type.
3. 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).

Links

Alimentary

• Tooth Development
• Stomach Development
• Small Intestine Development
• Large Intestine Development
• Pancreas Development
• Peritoneal Cavity Development

Cardiorespiratory

• Heart Development
• Vascular Development

Endocrine

• Pituitary Gland Development
• Thyroid Gland Development
• Parathyroid Gland Development
• Adrenal Gland Development

Integumentary

• Skin Development
• Hair Development

Lymphoreticular

• Lymphatic Vessel Development
• Bone Marrow Development
• Bursa of Farbricus Development
• Thymus Development
• Lymph Node Development
• Spleen Development
• MALT Development
• Appendix Development
• Peyer's Patches Development

Musculoskeletal

• Bone and Cartilage Development

Reproductive

• Testicular Descent
• Fertilisation
• Blastocyst Development
• Implantation
• Sexual Differentiation
• Mammary Gland Development

Nervous System and Special Senses

• Central Nervous System Development

Urinary

• Kidneys and Urinary Tract Development

References

• Scott F. Gilbert Developmental Biology, 6th edition
• T.A.McGeady, P.J. Quinn, E.S.Fitzpatrick, M.T.Ryan Veterinary Embryology