Relationship Between Tissue Fluid and Lymph

The blood contains cells bathed in a liquid known as plasma. The plasma that leaks out from the blood is referred to as the tissue fluid. The tissue fluid is very similar to blood. However, it contains less amount of protein molecules and no red blood cells. The hydrostatic pressure at the arteriole level of blood capillaries pushes fluid out from the blood into the extracellular space of tissues and organs. Nutrients such as glucose and amino acids as well as oxygen are pushed out from the blood into the tissue fluid. These nutrients are taken up by cells in the tissue. Most of the fluid is taken up to the capillaries at their venule end. The rest of the fluid is collected by the lymphatic system. The lymph is similar to the tissue fluid. This is the relationship between tissue fluid and lymph.

Key Areas Covered

1. What is Tissue Fluid
      – Definition, Formation, Function
2. What is Lymph
      – Definition, Formation, Function
3. What are the similarities between Tissue Fluid and Lymph
      – Outline of Common Features
4. What is the difference between Tissue Fluid and Lymph
      – Comparison of Key Differences

Key Terms: Arteriole End, Blood Capillaries, Hydrostatic Pressure, Interstitial Fluid, Lymph, Lymphatic Capillaries, Plasma, Tissue Fluid, Venule End

What is Tissue Fluid

The tissue fluid is the extracellular fluid that bathes and surrounds the tissue cells of multicellular animals. It arrives via blood capillaries and is removed via the lymphatic vessels. The tissue fluid is also called the interstitial fluid. The high hydrostatic pressure of blood at the arteriole end of the capillary allows the fluid to push out from the capillaries. Glucose, fatty acids, nucleic acids, amino acids, salts, minerals, and water in the blood are pushed out through capillaries into the tissue fluid and are uptaken by cells in the tissue. Tissue fluid is composed of 40% water. Neither red blood cells nor large proteins leave the blood at capillaries. However, white blood cells can migrate into the tissue fluid. After losing fluid at the capillaries, the hydrostatic pressure is low at the venule end of the capillary and the solute concentration is high. Therefore, fluid drains back into the capillary along with the metabolic wastes such as urea and carbon dioxide at their venule ends. About 90% of the fluid leaked out from blood is taken back and the remaining 10% is taken back by the lymphatic system as lymph. The formation of tissue fluid and lymph is shown in figure 1.

Figure 1: Tissue Fluid and Lymph

What is Lymph

The lymph is an alkaline fluid, which is originated from the tissue fluid. The main function of lymph is to clear metabolic wastes and infectious organisms. Typically, lymph contains glucose, proteins, fats, salts, and water. But the composition of lymph varies depending on the origination. The lymph of legs and arms are clear and have a similar composition to tissue fluid. At the intestine, lymph mixes with fats to form the chyle. The scattered network of lymphatic capillaries within tissues collects the remaining tissue fluid, which is not uptaken at the venule and of the blood capillaries. Lymphatic capillaries are porous, tiny tubules. The pressure inside the lymphatic capillaries is lower than that of blood capillaries and tissue fluid. Therefore, fluids in the blood capillaries tend to migrate into lymphatic capillaries via the tissue fluid. Small lymphatic capillaries join together to form larger lymphatic vessels. The lymph from legs, intestine and other organs, left arm, and the left side of head and neck is collected to the thoracic duct. The lymph of the right arm and right side of the head and neck is collected by the right lymphatic duct. The thoracic duct and the right lymphatic duct drain their collections into left and right brachiocephalic veins respectively. While flowing, bacteria and cancer cells are filtered through lymph nodes. The lymph capillaries in the tissue space are shown in figure 2.

Figure 2: Lymph Capillaries in the Tissue Space

Similarities Between Tissue Fluid and Lymph

• Tissue fluid and lymph originate from plasma.
• Tissue fluid and lymph are typically colorless.
• Both tissue fluid and lymph often comprise a similar composition.
• The flow of tissue fluid and lymph occur due to the muscular contractions in the body.
• Both tissue fluid and lymph are collected back and pushed back into the circulation.
• Both tissue fluid and lymph are involved in maintaining the fluid balance of the body.
• Both tissue fluid and lymph ensure the removal of metabolic wastes.

Difference Between Tissue Fluid and Lymph

Definition

Tissue Fluid: Tissue fluid is the extracellular fluid, bathing cells in the tissues, arriving into the blood capillaries, and being removed by the lymphatic system

Lymph: Lymph is a colorless fluid, containing white blood cells, bathing tissues, and draining out through the lymphatic system into the circulation.

Location

Tissue Fluid: Tissue fluid is found in the spaces between cells in tissues.

Lymph: Lymph is found inside the lymphatic vessels.

Role

Tissue Fluid: Tissue fluid ensures the supply of materials, nutrients, oxygen into the cells in tissues and organs, and removal of metabolic wastes from tissues.

Lymph: Lymph is involved in the removal of metabolic wastes and infectious organisms from tissues.

Cells

Tissue Fluid: Tissue fluid may comprise phagocytes.

Lymph: Lymph may comprise lymphocytes.

Fats

Tissue Fluid: Tissue fluid does not contain fat.

Lymph: Lymph contains fats absorbed from lacteals in the intestine.

Conclusion

Tissue fluid can be considered as the leaked plasma, which leaves blood capillaries due to the hydrostatic pressure of blood. Tissue fluid ensures the supply of nutrients, oxygen, and hormones into the cells in tissues. Most of the tissue fluid returns to the circulation along with metabolic wastes such as carbon dioxide and urea. The remaining tissue fluid in the tissue spaces forms lymph. The lymphatic system collects and pushes lymph into the circulation. The lymphatic system plays a vital role in immunity of the animal. This is the relationship between tissue fluid and lymph.

Image Courtesy:

1. “Anatomy and physiology of animals The formulation of tissue fluid and lymph from blood” By  Sunshine Connelly at English Wikibooks – Transferred from en.wikibooks to Commons by Adrignola (CC BY 3.0) via Commons Wikimedia
2. “2202 Lymphatic Capillaries” By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia

Reference:

1. “Transport in Mammals .” S-cool, the revision website. N.p., n.d. Web. Available here. 29 June 2017. 
2. “What is a Lymph? – Definition & Anatomy.” Study.com. N.p., n.d. Web. Available here. 29 June 2017.