Goodhead Lauren K, MacMillan Frances M
School of Physiology, Pharmacology, and Neuroscience, University of Bristol, Bristol, United Kingdom
School of Physiology, Pharmacology, and Neuroscience, University of Bristol, Bristol, United Kingdom.
Adv Physiol Educ. 2017 Jun 1;41(2):298-305. doi: 10.1152/advan.00083.2016.
Since the discovery of the composition and structure of the mammalian cell membrane, biologists have had a clearer understanding of how substances enter and exit the cell's interior. The selectively permeable nature of the cell membrane allows the movement of some solutes and prevents the movement of others. This has important consequences for cell volume and the integrity of the cell and, as a result, is of utmost clinical importance, for example in the administration of isotonic intravenous infusions. The concepts of osmolarity and tonicity are often confused by students as impermeant isosmotic solutes such as NaCl are also isotonic; however, isosmotic solutes such as urea are actually hypotonic due to the permeant nature of the membrane. By placing red blood cells in solutions of differing osmolarities and tonicities, this experiment demonstrates the effects of osmosis and the resultant changes in cell volume. Using hemoglobin standard solutions, where known concentrations of hemoglobin are produced, the proportion of hemolysis and the effect of this on resultant hematocrit can be estimated. No change in cell volume occurs in isotonic NaCl, and, by placing blood cells in hypotonic NaCl, incomplete hemolysis occurs. By changing the bathing solution to either distilled water or isosmotic urea, complete hemolysis occurs due to their hypotonic effects. With the use of animal blood in this practical, students gain useful experience in handling tissue fluids and calculating dilutions and can appreciate the science behind clinical scenarios.
自从发现哺乳动物细胞膜的组成和结构以来，生物学家对物质如何进出细胞内部有了更清晰的认识。细胞膜的选择性渗透性质允许一些溶质移动，同时阻止其他溶质移动。这对细胞体积和细胞完整性有重要影响，因此在临床上极为重要，例如在静脉输注等渗溶液时。渗透压和张力的概念常常让学生感到困惑，因为像氯化钠这样的非渗透性等渗溶质也是等张的；然而，像尿素这样的等渗溶质实际上是低渗的，因为细胞膜对其具有通透性。通过将红细胞置于不同渗透压和张力的溶液中，本实验展示了渗透作用的效果以及细胞体积随之发生的变化。使用血红蛋白标准溶液（可产生已知浓度的血红蛋白），可以估算溶血比例及其对最终血细胞比容的影响。在等渗氯化钠溶液中细胞体积无变化，而将血细胞置于低渗氯化钠溶液中会发生不完全溶血。通过将浴液换成蒸馏水或等渗尿素，由于它们的低渗作用会发生完全溶血。在本实验中使用动物血液，学生能获得处理组织液和计算稀释度的有益经验，并能理解临床情况背后的科学原理。
