Introduce the general idea: human body need all kinds of nourishment during the life(such as water, inorganic acid, protein, glycolipin, microbian mineral, oxygen),blood cycle for digestion.

• 内容导入：人体在生命运动中需要各种营养（水、无机盐、蛋白质、糖类脂肪、维生物矿物质，氧气），其消化吸收需通过血液循环系统。