Blood Plasma and Tissue Fluid | 血浆与组织液

📚 Blood Plasma and Tissue Fluid | 血浆与组织液

Blood plasma is the pale yellow liquid component of blood in which blood cells are suspended. Tissue fluid is the extracellular fluid that surrounds cells in tissues. In A-level Biology, understanding how plasma forms tissue fluid is essential for explaining transport between blood and cells.

血浆是血液中淡黄色的液体部分，血细胞悬浮其中。组织液是包围组织细胞的细胞外液。在 A-level 生物中，理解血浆如何形成组织液是解释血液与细胞之间运输的基础。

1. The Internal Environment: Why Plasma and Tissue Fluid Matter | 内环境：血浆和组织液为何重要

Blood plasma carries nutrients, hormones, waste products and proteins around the body. Tissue fluid acts as the immediate environment for cells, allowing oxygen, glucose and other solutes to diffuse between blood and cells.

血浆在体内运输营养物质、激素、废物和蛋白质。组织液是细胞的直接环境，使氧气、葡萄糖和其他溶质能够在血液与细胞之间扩散。

The formation and drainage of tissue fluid maintain a stable internal environment. If the balance between filtration and reabsorption is disturbed, fluid can accumulate and cause swelling.

组织液的生成和引流维持了稳定的内环境。如果滤过和重吸收之间的平衡被打破，液体会积聚并引起肿胀。

2. Composition of Blood Plasma | 血浆的组成

Plasma is about 90% water, which acts as a solvent. Dissolved in it are plasma proteins such as albumin, globulins and fibrinogen, as well as glucose, amino acids, fatty acids, ions and dissolved gases.

血浆约 90% 是水，水作为溶剂。溶解在其中的物质包括白蛋白、球蛋白和纤维蛋白原等血浆蛋白，以及葡萄糖、氨基酸、脂肪酸、离子和溶解气体。

Important ions include Na⁺, K⁺, Ca²⁺, Cl⁻ and HCO₃⁻. Urea, hormones and dissolved CO₂ are also transported in plasma. Plasma proteins are particularly important because they are too large to pass easily through healthy capillary pores.

重要的离子包括 Na⁺、K⁺、Ca²⁺、Cl⁻ 和 HCO₃⁻。尿素、激素和溶解的 CO₂ 也在血浆中运输。血浆蛋白尤为重要，因为它们体积较大，难以通过健康的毛细血管孔。

The presence of plasma proteins lowers the water potential of plasma and creates an osmotic pull that draws water back into capillaries. Albumin is the main protein responsible for maintaining this plasma osmotic pressure.

血浆蛋白的存在降低了血浆的水势，产生一种渗透吸引力，将水拉回毛细血管。白蛋白是维持血浆渗透压的主要蛋白质。

3. Capillary Structure and Exchange Surfaces | 毛细血管结构与交换表面

Capillaries have walls made of a single layer of flattened endothelial cells resting on a basement membrane. Narrow pores between and within these cells make the wall leaky enough for water and small solutes, but not normally for large proteins or blood cells.

毛细血管壁由单层扁平内皮细胞和基底膜组成。细胞之间和细胞内的狭窄孔隙使管壁具有通透性，允许水和小分子溶质通过，但正常情况下不允许大分子蛋白质和血细胞通过。

The thin capillary wall minimises the diffusion distance, while the narrow lumen slows blood flow. These features allow efficient exchange between plasma and tissue fluid in capillary beds.

薄薄的毛细血管壁使扩散距离最小化，而狭窄的管腔减慢了血流速度。这些特点使血浆与组织液在毛细血管床中能够高效交换。

4. Formation of Tissue Fluid by Ultrafiltration | 组织液经超滤形成

At the arterial end of a capillary, the hydrostatic pressure of the blood is higher than the opposing pressures from tissue fluid and plasma proteins. This net outward pressure forces water and small solutes through the capillary pores, a process called ultraf

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