☆蛋白质的生理价值 ☆蛋白质中大致含有16%的氮 ·氮的总平衡：摄入大致等于排出 ·氮的正平衡：摄入大于排出 ·氮的负平衡：摄入小于排出 ☆蛋白质的生理价值（1-100) 氮的体内保留量/氮的摄入量X100
☆蛋白质的生理价值 ☆蛋白质中大致含有16%的氮 • 氮的总平衡：摄入大致等于排出 • 氮的正平衡：摄入大于排出 • 氮的负平衡：摄入小于排出 ☆蛋白质的生理价值（1-100） 氮的体内保留量/氮的摄入量X100
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Intracellular protein 内源性蛋白质 消化道吸收的蛋白质 Dietary protein Amno acids 生成氨基酸， NH 和其他生物活性物质 Carbon skeletons Biosynthesis of amino acids nucleotides,and biological amines Carbameyl phosphate a-Keto acids Aspartate- arginino- Urea Citric succinate cyele acid CO:+HO shunt of cyele 十ATP citric acid cycle 燃料分子 Oxaloacetate Urea (nitrogen excretion product) 合成尿素 Glucose (synthesized in 糖异生 gluconeogenesis)
糖异生 燃料分子 合成尿素 生成氨基酸， 和其他生物活性物质 内源性蛋白质 消化道吸收的蛋白质
a .11 -Chief colls pepeinogen) Stomach (eecretes gastrin) Pancreas (b) Exocrine cells of pancreas Ro ramui Collecting duet mal Small Villus Intestinal m时c0a (abeorbs amino acids】 胃，胰脏和小肠的蛋白酶(Proteinase)将蛋白质分解成许 多小的片断，暴露出许多末端，然后在肽酶(Peptidase) 的作用下进一步分解为氨基酸
胃，胰脏和小肠的蛋白酶（Proteinase）将蛋白质分解成许 多小的片断，暴露出许多末端，然后在肽酶（Peptidase） 的作用下进一步分解为氨基酸
Proteins Are Degraded to Amino Acids Dietary protein is a vital source of amino acids.Proteins ingested in the diet are digested into amino acids or small peptides that can be absorbed by the intestine and transported in the blood. Another source of amino acids is the degradation of defective or unneeded cellular proteins
Proteins Are Degraded to Amino Acids • Dietary protein is a vital source of amino acids. Proteins ingested in the diet are digested into amino acids or small peptides that can be absorbed by the intestine and transported in the blood. Another source of amino acids is the degradation of defective or unneeded cellular proteins