The zang-fu organs refer to both the zang organs and fu organs. Delicacy means weakness, liability to attack and tenderness. The physique here refers to the configuration of the human body such as the limbs, skeleton, musculature, essence, blood and body fluid. Qi refers to Physiological functional activities, such as lung qi, spleenqi and kidney qi. Delicacy of the Zang-fu organs and underdevelopment of the physique and qi mean that, during the childhood, the morphological development and the physiological functions are immature and imperfect, and that the development and functions of the viscera are insufficient. Since the physical substances of the body pertain to yin and the functional activities of the body pertain to yang, doctors in the ancient times summarized the physiological characteristics of the infants as underdeveloped yin and yang.

The idea that the viscera of the infants are delicate and the body of the infants is underdeveloped is characterized by delicacy of the muscles and skin, loose striae, insufficient qi and blood, weak lung and spleen, insufficient kidney qi, timid will and fragile bones and muscles. For instance, from birth to the infancy, the infants are marked by big head, thin neck, longer upper portion and shorter lower portion. Within the period of one year and a half, the infants are prominent for metopism, thin and soft skin, loose muscular interstitial striae, yellowish and thin hair, liability to sweat during sleep, short voice in crying and instantaneous changes in emotions. The functions of both the five zang organs and six fu organs are underdeveloped, especially the lung, the spleen and the kidney.
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source:http://www.tcmadvisory.com/tcm.asp