2.19 Intercellular Fluid and Lymph

The lymphatic system includes lymph, lymphocytes, lymphatic vessels, lymph nodes, tonsils, spleen, and thymus gland. About one-sixth of the body consists of spaces between the cells, which collectively are called the interstitium. The fluid in these spaces is the interstitial fluid or intercellular fluid. Lymph is the fluid that enters the lymphatic capillaries.

Definition

Intercellular Fluid (Interstitial Fluid): The fluid in the spaces between cells (interstitium) is called intercellular fluid or interstitial fluid. It is derived by filtration and diffusion from the capillaries.

Lymph: The tissue fluid that has entered the lymphatic capillaries is called lymph. It passes through the lymphatic vessels back to the blood.

Interstitium: The spaces between the cells are collectively called the interstitium. About one-sixth of the body consists of these spaces.

Main Idea

• Intercellular fluid = fluid between cells; derived from blood capillaries
• Lymph = intercellular fluid that enters lymphatic capillaries
• Composition = intercellular fluid is similar to plasma but with less protein
• Lymph = contains more white blood cells, especially lymphocytes
• Function = transport of water, electrolytes, nutrients, gases, and wastes
• Difference = lymph has more lymphocytes and can be high in fats (chyle)

Core Concept

• Interstitium = spaces between cells
• Intercellular fluid = fluid in interstitium
• Lymph = fluid in lymphatic vessels
• Formation = filtration and diffusion from capillaries
• Composition = similar to plasma; less protein
• Lymph = more white blood cells; especially lymphocytes
• Function = transport; exchange; immunity
• Comparison = lymph has more lymphocytes; can be high in fats

Detailed Explanation

Interstitial Fluid

Formation: - The fluid in the interstitium is derived by filtration and diffusion from the capillaries.

• Interstitial fluid contains almost the same constituents as plasma.
• Except for much lower concentrations of proteins.
• Proteins do not pass outward through the walls of the capillaries with ease.

• Allows rapid transport of water molecules, electrolytes, nutrients, cellular excreta, oxygen, carbon dioxide, etc.
• Materials are exchanged between the blood and interstitial fluid and between the interstitial fluid and the body cells.
• In other words, to get from the blood to body cells or vice versa, materials must pass through the interstitial fluid.

Comparison of the Composition of Interstitial Fluid and Lymph

The composition of intercellular fluid is primarily water, along with electrolytes, sugars, salts, acids, hormones, neurotransmitters, and cell wall products.

The tissue fluid that has entered the lymphatic capillaries is called lymph and passes through the lymphatic vessels back to the blood.

• Solutes such as ions, nutrients, gases, and some proteins
• Hormones
• Enzymes
• Waste products

As lymph moves through the lymphatic system, it accumulates more white blood cells (lymphocytes) and proteins.

Table of Differences Between Intercellular Fluid and Lymph

Intermediate Level

Intercellular Fluid vs Lymph

Formation of Intercellular Fluid

• Blood flows through capillaries.
• Hydrostatic pressure forces fluid out of capillaries.
• Fluid enters the interstitium.
• Fluid becomes intercellular fluid.
• Materials are exchanged between blood and cells.
• Most fluid returns to capillaries.
• Some fluid enters lymphatic capillaries.
• Fluid becomes lymph.

Composition of Intercellular Fluid

Composition of Lymph

Function of Intercellular Fluid

Function of Lymph

Formula / Mathematical Form

Net Filtration: Net Filtration = (P_c + π_i) - (P_i + π_c)

• P_c = capillary hydrostatic pressure
• π_i = interstitial fluid colloid osmotic pressure
• P_i = interstitial fluid hydrostatic pressure
• π_c = plasma colloid osmotic pressure

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Intercellular fluid is the fluid between cells.
• 2. Interstitium is the space between cells.
• 3. Intercellular fluid is derived from capillaries.
• 4. Intercellular fluid is similar to plasma but with less protein.
• 5. Lymph is the fluid in lymphatic vessels.
• 6. Lymph is derived from intercellular fluid.
• 7. Lymph contains more white blood cells (lymphocytes).
• 8. Lymph can be high in fats (chyle).
• 9. Intercellular fluid functions in transport and exchange.
• 10. Lymph functions in transport, immunity, and fat absorption.
• 11. About one-sixth of the body is interstitium.
• 12. Proteins do not pass easily through capillary walls.
• 13. Materials must pass through intercellular fluid to reach cells.
• 14. Lymph nodes filter lymph.
• 15. Lymph returns fluid to the blood.

Remember

• - Intercellular fluid = fluid between cells
• - Interstitium = space between cells
• - Lymph = fluid in lymphatic vessels
• - Formation = filtration and diffusion from capillaries
• - Composition = similar to plasma; less protein
• - Lymph = more white blood cells; especially lymphocytes
• - Function = transport; exchange; immunity
• - Comparison = lymph has more lymphocytes; can be high in fats
• - About one-sixth = of body is interstitium
• - Proteins = do not pass easily through capillary walls
• - Materials = must pass through intercellular fluid to reach cells
• - Lymph nodes = filter lymph

Common Mistakes

• 1. Confusing intercellular fluid and lymph — Intercellular fluid is between cells; lymph is in lymphatic vessels.
• 2. Thinking intercellular fluid has more protein than plasma — It has less protein.
• 3. Forgetting that lymph has more lymphocytes — Lymph has significantly more white blood cells.
• 4. Mixing up the origins — Intercellular fluid is from capillaries; lymph is from intercellular fluid.
• 5. Thinking red blood cells are normally in lymph — Red blood cells are absent in lymph.
• 6. Believing lymph and intercellular fluid are the same — They are related but different.
• 7. Mixing up the functions — Intercellular fluid: exchange; lymph: transport and immunity.
• 8. Forgetting the role of the lymphatic system — It returns fluid to the blood.
• 9. Confusing chyle with lymph — Chyle is lymph from the digestive system; it is high in fats.
• 10. Thinking proteins pass easily through capillary walls — Proteins do not pass easily.

Quick Revision

The lymphatic system includes lymph, lymphocytes, lymphatic vessels, lymph nodes, tonsils, spleen, and thymus gland. About one-sixth of the body consists of spaces between cells, collectively called the interstitium. The fluid in these spaces is the interstitial fluid or intercellular fluid. Intercellular fluid is derived by filtration and diffusion from the capillaries. It contains almost the same constituents as plasma except for much lower concentrations of proteins. Intercellular fluid allows rapid transport of water, electrolytes, nutrients, cellular excreta, oxygen, and carbon dioxide. Materials are exchanged between the blood and interstitial fluid and between the interstitial fluid and body cells. Lymph is the tissue fluid that has entered the lymphatic capillaries. In addition to water, lymph contains solutes such as ions, nutrients, gases, and some proteins, hormones, enzymes, and waste products. As lymph moves through the lymphatic system, it accumulates more white blood cells (lymphocytes) and proteins. The major differences between intercellular fluid and lymph are that lymph has significantly higher white blood cells, particularly lymphocytes, and can be high in fats (chyle) from the digestive system.

60-Second Revision

• Intercellular fluid = fluid between cells
• Interstitium = space between cells
• Lymph = fluid in lymphatic vessels
• Formation = filtration and diffusion from capillaries
• Composition = similar to plasma; less protein
• Lymph = more white blood cells; especially lymphocytes
• Function = transport; exchange; immunity
• Comparison = lymph has more lymphocytes; can be high in fats
• About one-sixth = of body is interstitium
• Proteins = do not pass easily through capillary walls
• Materials = must pass through intercellular fluid to reach cells
• Warning: Intercellular fluid is between cells; lymph is in lymphatic vessels

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