It's actually a subsystem of both the circulatory and immune system.

它其實是循環系統和免疫系統的子系統。

The major purpose of the circulatory system is to bring oxygen and nutrients to body tissues and remove wastes.

循環系統的主要作用是將氧氣和營養物質輸送到身體組織中，並清除廢物。

This exchange happens in the smallest blood vessels called the capillaries.

這種物質交換最小的微血管中進行。

Blood plasma containing nutrients moves out of capillaries at the arterial end of capillary beds, while tissue fluid containing wastes re-absorbs back in at the venous end.

含有營養物質的血漿從微血管床的動脈端流出，而含有廢物的組織液在靜脈端被重新吸收。

However, not all of the fluid is drawn back to the bloodstream at this point.

然而，此時並非所有的液體都重新回到血液中。

About 15% of it is left in the tissues and would cause swelling if accumulated.

約有 15% 殘留在組織內，持續積聚會引起腫脹。

This is where the lymphatic system comes into play. It picks up the excess fluid and returns it to the circulatory system.

此時，淋巴系統就會發揮作用。它會吸收多餘的液體，使其重返循環系統。

Unlike the blood circulatory system, which is a closed loop, the lymphatic system is a one-direction, open-ended network of vessels.

淋巴系統與血液循環系統不同，它是單向、開放式的血管網絡。

Lymphatic vessels begin as lymphatic capillaries made of overlapping endothelial cells.

淋巴管起源於淋巴微管，由管壁內皮細胞重疊而成。

The overlapping flaps function as a one-way valve.

這些重疊的小瓣膜如同單向閥。

When fluid accumulates in the tissue, interstitial pressure increases, pushing the flaps inward, opening the gaps between cells, allowing fluid to flow in.

當液體在組織中堆積時，間隙壓力增加並向內推擠瓣膜，打開細胞間的間隙，讓液體流入。

As pressure inside the capillary increases, the endothelial cells are pressed outward, closing the gaps, thus preventing backflow.

隨著微血管內的壓力增加，內皮細胞被向外推擠，間隙閉合，從而防止回流。

Unlike blood capillaries, the gaps in lymphatic capillaries are so large that they allow bacteria, immune cells, such as macrophages, and other large particles to enter.

淋巴微管與微血管不同，它的間隙很大，足以讓細菌、免疫細胞(如巨噬細胞)和其他大顆粒進入。

This makes the lymphatic system a useful way for large particles to reach the bloodstream.

這使淋巴系統成為大顆粒進入血液的有效途徑。

It is used, for example, for dietary fat absorption in the intestine.

舉例來說，它有助於腸道中膳食脂肪的吸收。

Once inside lymphatic vessels, the recovered fluid is called lymph.

一旦進入淋巴管，回收的液體就稱為淋巴液。

Lymph flow is enabled by the same forces that facilitate blood flow in the veins.

促進淋巴液流動和促進靜脈血液流動的力量一樣。

It goes from lymphatic capillaries to larger and larger lymphatic vessels and eventually drains into the bloodstream via the subclavian veins.

它從淋巴微管進入越來越大的淋巴管，最終通過鎖骨下靜脈流入血液中。

On the way, it passes through a number of lymph nodes, which serve as filters, cleansing the fluid before it reaches the bloodstream.

在此過程中，它會經過許多充當過濾器的淋巴結，在流入血液前完成淨化。

Lymph nodes are small bean-shaped structures scattered throughout the lymphatic network.

淋巴結是散佈在淋巴網絡中的小型豆狀結構。

They are most prominent in the areas where the vessels converge.

它們主要分布於血管匯集處。

Lymph nodes contain macrophages and dendritic cells that directly swallow up any pathogens, such as bacteria or viruses, that may have been taken up from an infected tissue.

淋巴結內含有巨噬細胞和樹突狀細胞，它們可以直接吞噬感染組織中的病原體，如細菌或病毒。

They also contain lymphocytes: T-cells and B-cells, which are involved in adaptive immune response, a process that produces activated lymphocytes and antibodies specific to the invading pathogen.

它們也含有淋巴細胞：T 細胞和 B 細胞，主要負責適應性免疫反應，促進淋巴細胞和入侵病原體的抗體的活化。

These are then carried by the lymph to the bloodstream to be distributed wherever they are needed.

它們通過淋巴進入血液中，然後被分配到需要它們的地方。

The lymphatic system also includes lymphoid organs.

淋巴系統也包括淋巴器官。

Primary lymphoid organs, the thymus and bone marrow, are the sites of lymphocyte production, maturation and selection.

初级淋巴器官，包括胸腺和骨髓，為淋巴細胞生成、發育和篩選的地方。

Selection is the process in which lymphocytes learn to distinguish between self and non-self, so they can recognize and destroy pathogens without attacking the body's own cells.

篩選是淋巴細胞學會區分「自我」和「非我」的過程，這樣它們才能在不攻擊自身細胞的情況下有效辨識並摧毀病原體。

Mature lymphocytes then leave the primary for the secondary lymphoid organs, the lymph nodes, spleen, and lymphoid nodules, where they encounter pathogens and become activated.

接著，成熟的淋巴細胞離開初級淋巴器官，進入次級淋巴器官、淋巴結、脾臟和淋巴小結，並於遇到病原體時活化。