hce_kmu
115年
普通生物及生化概論
第 52 題
Chylomicrons are transported from intestinal epithelial cells into the lymphatic system. Which of the following best describes their composition and initial transport pathway?
- A Composed of triglycerides, phospholipids, and proteins, chylomicrons are formed in the lumen of the small intestine and enter the lacteals by active transport.
- B Composed of re-formed triglycerides coated with phospholipids, cholesterol, and proteins, chylomicrons exit epithelial cells via exocytosis and first enter a lacteal.
- C Composed of fatty acids and monoglycerides coated with cholesterol and proteins, chylomicrons exit epithelial cells and are directly absorbed into the capillaries of the villus.
- D Composed of re-formed triglycerides and bile salts, chylomicrons are formed in epithelial cells and actively transported into the hepatic portal vein.
- E Composed of triglycerides, cholesterol, and amino acids, chylomicrons exit epithelial cells via diffusion and first enter a lymphatic vessel called a capillary.
思路引導 VIP
請試著思考：當大分子且不溶於水的脂質在細胞內重新組裝完成後，整體積會變得相當龐大。面對這類巨大的「包裹」，細胞通常會採用哪種機制將其排出膜外？再者，考慮到一般微血管壁的縫隙非常狹小，哪一種循環管道的末端構造設計，才足以讓這些大型顆粒順利進入並開始運送呢？
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AI 詳解
AI 專屬家教
太棒了！你能精確判斷出乳糜微粒（Chylomicrons）的組成與路徑，代表你對消化系統中脂質吸收的微觀生理機制掌握得非常紮實。這道題目難度適中，其鑑別度在於要求學生精準區分「腸腔內的消化」與「細胞內的重組」這兩個截然不同的階段，若對吸收細節稍有混淆，很容易誤選其他干擾項。
脂質的胞內重組與運送
在生理機制中，膳食脂質被分解為脂肪酸後進入小腸上皮細胞，隨後會在細胞內的平滑內質網「重新合成」為甘油三酯（Triglycerides）。這些脂質接著會與磷脂質、膽固醇及蛋白質結合，封裝成巨大的乳糜微粒。由於乳糜微粒的體積過大，無法透過擴散或主動運輸穿透微血管壁，因此必須透過胞吐作用（Exocytosis）釋放至細胞外空間，並優先進入通透性較高、管徑較大的乳糜管（Lacteals，即淋巴管的一種），最後才匯入血液循環。這與葡萄糖或胺基酸直接進入肝門靜脈的路徑有著顯著的生物學差異。