Human Anatomy and Physiology - N. I. Fedyukovich 2003

Cardiovascular System
Formation, Composition, and Properties of Lymph

The Lymphatic system is functionally closely linked to the Circulatory system and consists of capillaries, vessels, trunks (ducts), and nodes. As part of the internal environment, Lymph performs barrier, immune, excretory, and other Functions. Lymph drainage is driven by the same factors that govern venous return—namely, the suction effect of The Heart and Thorax, and Muscle activity.

The Mechanism of Lymph formation is based on filtration, diffusion, and osmosis, as well as the hydrostatic pressure gradient between capillary Blood and interstitial fluid. Among these factors, the permeability of lymphatic capillaries is of great importance. There are two pathways by which particles of various sizes cross the lymphatic Capillary Wall into the lumen: intercellular and transendothelial. The first pathway involves large particles (ranging from 10 nm to 10 µm) passing through intercellular clefts. The second pathway of transport into the lymphatic capillary is based on direct passage through the Cytoplasm of endothelial Cells via micropinocytic vesicles (pinocytosis). Both pathways operate simultaneously.

In addition to the hydrostatic pressure gradient between blood capillaries and Tissues, oncotic pressure plays a significant role in lymph formation. An increase in blood hydrostatic pressure promotes lymph formation, whereas an increase in blood oncotic pressure inhibits it. Fluid filtration from the blood occurs at the arterial end of the capillary, and the fluid then returns to the venous bed. This is due to the pressure difference between the arterial and venous ends of the capillary. The permeability of lymphatic capillary walls can vary depending on the functional state of the organ and METABOLISM/18.html">The Influence of certain substances such as histamine, Peptides, etc. It also depends on mechanical, chemical, neural, and humoral factors, and is therefore constantly changing.

Lymph is a colorless fluid that resembles Blood Plasma in composition. The total volume of lymph in The Human Body is 1500 ml; however, its content varies across different Organs depending on their function. For instance, there are 21–36 ml of lymph per 1 kg of Liver mass, 5–18 ml in the heart, 3–12 ml in the Spleen, and 2–3 ml in limb Muscles. The high lymph content in the liver is due to its role in transporting nutrients from the intestines.

In terms of composition, lymph differs from capillary filtrate and blood plasma. It contains the following anions (µg/100 ml):

Сl^- — 438, НСО₃^- — 48.0, H₂PO₄^- — 1.5; cations: Na⁺ — 524, К⁴⁺ — 9.8, Са²⁺ — 4.5, as well as various Enzymes. Lymphatic tissue stores Vitamins. Lymph also contains substances that promote faster blood clotting. The concentration of other substances corresponds to their content in blood plasma.