The heart, blood vessels, blood cells, skeleton, kidneys, spleen, and muscles are all tissues or organs that arise from what primary germ layer?
A - The mesoderm
B - The ectoderm
C - The inner cell mass or ICM
D - The endoderm
E - The epiblast
Answer: A - The mesoderm
The ECTODERM will form the nervous system, the epithelial cells of the mammary glands, the lens of the eyes, hair, pigment cells and the epidermis of the skin. The MESODERM will form skeletal muscle, smooth muscle, the heart, blood vessels, blood cells, kidney, spleen, fat cells, the skeleton, most connective tissues and most of the urogenital system. The ENDODERM will form the entire epithelial lining of the gastrointestinal tract, as well as the liver, pancreas, gall bladder, thyroid, the epithelial lining of the trachea and the respiratory surface of the lungs.