Dr. Khayati Santram
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Three Germ layers 


Three Germ Layers

An embryonic disc is made up of three germ layers. The name of these three embryonic gem layers are ectoderm, endoderm and mesoderm. This three germinal layer disc is formed during third week of intrauterine life. After fertilization cleavage take place in which eight cell stage is converted into sixteen cell stage called morula.


Then, formation of blastocyst take place. This blastocyst differentiate into inner cell mass and outer cell mass. Outer cell mass is known as trophoblast.


During implantation this trophoblast penetrates to uterine epithelium and differentiates into cytotrophoblast & syncytiotrophoblast.


During 2nd week of development , few cells of inner cell mass become flatten  and form primitive endoderm. The remaining cell of inner cell mass become columnar & form primitive ectoderm.


Few cells of primitive ectoderm multiplies and form primitive streak. These primitive streak cells migrated between ectoderm & endoderm & form intraembryonic mesoderm. The cells of trophoblast multiply and form extraembryonic mesoderm.


Cavities developed in extraembryonic mesoderm and form extraembryonic coelom which differentiates into somatopleuric and splanchnopleuric layer.


3 Germ Layers details

1. Ectoderm: The ectoderm is the outermost of the three germ layers. It gives rise to the skin, hair, nails, and the nervous system, including the brain and spinal cord. Read in detail about ectoderm

2. Mesoderm: The mesoderm is the middle of the three germ layers. It gives rise to the muscles, bones, cartilage, and connective tissue, as well as the circulatory system, including the heart and blood vessels. The mesoderm also gives rise to the kidneys, adrenal glands, and reproductive organs. Read in detail about Mesoderm

3. Endoderm: The endoderm is the innermost of the three germ layers. It gives rise to the lining of the gastrointestinal tract, the liver, pancreas, and the respiratory system, including the lungs. The endoderm also gives rise to the thyroid gland and the bladder. More about Endoderm

Additionally, it is important to note that during embryonic development, the three germ layers interact with each other and form various structures such as the notochord, which provides structural support for the developing embryo and also gives rise to the vertebral column. The ectoderm and mesoderm also form the neural crest, which gives rise to several important structures such as the cranial and spinal nerves and adrenal medulla.


It is also important to note that the three germ layers interact with each other throughout the lifespan of an organism. For example, the ectoderm and mesoderm interact to form the dermis and epidermis of the skin, while the mesoderm and endoderm interact to form the lining of the digestive tract and the organs within it.


In the study of anatomy and physiology, medical students will learn how the three germ layers interact with each other to form the various tissues and organs in the body, and how these tissues and organs interact with each other to maintain homeostasis, or balance, within the body. Understanding the three germ layers is essential for medical students, as it lays the foundation for understanding the complex processes that occur within the human body. It helps medical students understand how the various organs and tissues interact with each other and how disruptions in these interactions can lead to disease.


In addition to anatomy and physiology, the three germ layers also have important implications for medical treatments and procedures. For example, knowledge of the ectoderm and its derivatives can help in the treatment of skin conditions, while knowledge of the mesoderm and its derivatives can aid in the treatment of musculoskeletal and cardiovascular conditions. Understanding the endoderm and its derivatives is important for the treatment of digestive, respiratory, and endocrine conditions.

In conclusion, the three germ layers are a fundamental concept in the study of anatomy, physiology, and medicine. Medical students must have a thorough understanding of the three germ layers in order to fully understand the complexity of the human body and to provide effective medical care to their patients.