Composition of Lymph, Practice Problems and FAQs

Our body requires a constant supply of nutrients and removal of waste materials. This is done by the lymphatic system and blood vascular system. The delicate blood vessels that exist throughout the body are called capillaries. These capillaries are always present next to the body tissues. So the cells of the tissues are surrounded by the substances coming out of the capillaries. Can you tell what would be the substance which is coming out of the capillaries? We know that blood is flowing through capillaries and blood is composed of a liquid part called plasma and the formed elements like RBCs, WBCs and platelets.

Fig: Blood vessels

Just like a filter works, the liquid part, plasma along with WBCs oozes out from the capillaries, when the blood plasma reaches the intercellular spaces between the cells in a tissue. Now it is termed as ‘tissue fluid or interstitial fluid’.

The major function of this tissue fluid is to supply materials like nutrients, gases, and remove waste products with the cells. Hence this fluid contains water, dissolved minerals and WBCs. So what happens if the fluid keeps leaking out of the blood continuously? All the tissues in the body would swell with it and the blood vessels get emptied. Right? So there should be some alternative for this.

Here comes the role of the lymph vessel. Some of the tissue fluid gets reabsorbed into the blood capillaries but most of the tissue fluid enters the lymph vessels and once the interstitial fluid enters the lymph vessel, it is called lymph. Lymph has the same composition as that of the interstitial fluid. So what should be the composition of lymph? Let’s understand the composition of lymph in this article.

Fig: Interstitial fluid and lymph

Table of contents

• Lymph
• Composition of lymph
• Significance of lymph
• Practice Problems
• FAQs

Lymph

The colourless mobile liquid present in the lymphatic system, which contains water, ions, nutrients, hormones, proteins, and WBCs is called lymph.

Fig: Lymph vessel with lymph

Lymphatic system

An elaborate network of vessels, tissues and organs called the lymphatic system collects the lymph and drains it back to the subclavian veins in the circulatory system. The lymphatic system is composed of lymphoid organs, lymphatic vessels and lymph nodes. An important role of the tissue fluid is to keep the tissue cells moist.

Fig: Lymphatic system

Composition of lymph

The chemicals are constantly exchanged between the blood and its surroundings with the interstitial fluid. So the composition of lymph changes accordingly, because lymph originates from the interstitial fluid. Lymph from the intestine that has fatty acids and cholesterol (chylomicrons) which is milky white is called chyle. The major components of lymph are classified as follows:

• Lymph plasma
• Corpuscles

Lymph plasma

Lymph plasma is straw coloured and has the similar content as in blood plasma. The major difference is the presence of proteins in the blood plasma. Lymph plasma is composed of lesser amounts of calcium, few blood proteins and phosphorus, but it has high concentration of glucose. The natural antibodies called immunoglobulins are present in the lymph plasma. It is also the major component for the exchange of gases and nutrients between the blood and cells. Many organic and inorganic compounds are also found in the plasma.

Fig: Composition of plasma

Corpuscles

Corpuscles in lymph are composed of mainly leukocytes (WBC), which are amoeboid cells. Specialised lymphocytes that can elicit immune responses in the human body are also present here. But red blood cells and platelets are absent in the lymph.

Leukocytes (WBCs)

Lymph has many WBCs, but has more lymphocytes than the other types of WBCs like the monocytes. Lymphocytes are a type of WBCs that are involved in immune responses of the body. 20 - 40% of WBCs are lymphocytes. When lymph is in lymph capillaries, it lacks WBCs, but it receives them while passing through the lymph nodes. Lymph differs from blood in lacking RBCs, platelets and large plasma proteins. It has less power of clotting compared to blood.

Fig: Lymphocyte

Both T lymphocytes and B lymphocytes are present in the lymph and they are responsible for the antigen specific acquired immunity. Both the lymphocytes are produced in bone marrow.

Fig: Formation of T and B-lymphocytes

T- lymphocytes

The lymphocytes that are matured in the thymus are called T- lymphocytes or T cells. When they come in contact with an antigen, it will divide to form a clone of T lymphocytes. This clone is composed of a group of cells that are similar in structure, but having different functions. The different types of lymphocytes are as follows:

• Helper T cells or CD₄ or T₄ cells
• Killer or cytotoxic T cells or CD₈ or T₈ cells
• Suppressor T Cells
• T delayed hypersensitivity cells
• Memory T Cells

Fig: T-lymphocytes

B-lymphocytes

Bursa of Fabricius is the primary lymphoid organ in birds which is equivalent to the bone marrow of mammals. The lymphocytes that are matured in the bone marrow are called B-lymphocytes. The different types of B-lymphocytes are as follows:

• Plasma or effector cells
• Memory cells

Fig: Plasma cells

Macrophages

The type of WBCs which can engulf and digest the microorganisms and other foreign bodies in the human body are called macrophages. It is a type of antigen presenting cells. They have a long life span. Monocytes transform into macrophages with morphological and functional changes. They are strongly phagocytic to a wide variety of materials such as viable microorganisms, dead cells, cell debris etc.

Fig: Formation of macrophage

Lymph borne antigens are digested by the macrophages. Hence macrophages act as a frontline immune defence in the lymph. The macrophages that capture the lymph borne pathogens are called subcapsular sinus macrophages and they are present in the lymph node.

Fig: Macrophage engulfing the pathogen

Other components of lymph in humans

Apart from the above components, lymph possess the below mentioned components:

• Carbohydrates
• Lymphocytes
• Creatinine
• Water – 94%
• Urea
• Chlorides
• Enzymes
• Proteins – Albumin, globulin, and fibrinogen
• Non-protein nitrogenous substances

Significance of lymph

The major significances of lymph are as follows:

• The body cells are kept moist.
• It acts as a middle man and transports oxygen, hormones and nutrients to the tissues cells.
• Removal of metabolic wastes from the tissue cells to the venous blood.
• Transportation of antibodies and lymphocytes to the blood.
• Maintaining the composition of the tissue fluid and the blood volume.
• Lymphatic vessels like lacteal absorb the fatty acids, glycerols and fat soluble vitamins (A, D, E and K) from the small intestine.

Fig: Lacteal

• Invasion of microbes and foregin substances inside the lymph vessel are prevented.

Practice Problems

1. Find out the incorrect statement about the lymph.

1. The colourless liquid present in the lymphatic system
2. Composed of ions, nutrients, hormones, proteins, RBCs and WBCs
3. Once the interstitial fluid enters the lymph vessel, it is called lymph
4. An elaborate network of vessels called the lymphatic system collects this fluid and drains it back to the veins

Solution: Some of the tissue fluid gets reabsorbed into the blood capillaries but most of the tissue fluid enters the lymph vessels and forms the lymph. Lymph has the same composition as that of the interstitial fluid. The colourless liquid present in the lymphatic system, which contains water, ions, nutrients, hormones, proteins, and WBCs is called lymph. An elaborate network of vessels, tissues, and organs called the lymphatic system collects this fluid and drains it back to the subclavian veins in the circulatory system. The lymphatic system is composed of lymphatic vessels, lymphoid organs and lymph nodes. An important role of the tissue fluid is to keep the tissue cells moist. Lymph differs from blood in lacking RBCs, platelets and some plasma proteins. Hence the correct option is b.

2. Which of the following are the components of a lymph?

1. Leukocytes
2. Macrophages
3. Lymph plasma
4. All the above

Solution: The colourless liquid present in the lymphatic system, which contains water, ions, nutrients, hormones, proteins, and WBCs is called lymph. The major components of lymph are classified as lymph plasma and corpuscles. Lymph plasma has the similar content as that of the blood plasma. The major difference is the presence of some large proteins in the blood plasma. Corpuscles in lymph are composed of mainly leukocytes (WBC), which are amoeboid cells. Hence the correct option is d.

3. In which of the following components of the lymph contains the proteins called globulins?

1. Lymph plasma
2. Leukocytes
3. Macrophages
4. All the above

Solution: Lymph plasma has the similar composition as that of the blood plasma. The major difference is the presence of some large proteins in the blood plasma. Lymph plasma is composed of lesser amounts of calcium, few blood proteins and phosphorus, but it has high concentration of glucose. The natural antibodies called immunoglobulins are present in lymph plasma. It is also the major component for the exchange of gases and nutrients between the blood and cells. Many organic and inorganic compounds are also found in the lymph plasma. Hence the correct option is a.

4. Which is the major leukocyte present in the lymph?

1. Monocytes
2. Lymphocytes
3. Neutrophils
4. Basophils

Solution: Lymph has many WBCs, but has more lymphocytes than the other types of WBCs like the monocytes. Lymphocytes are a type of WBCs that are involved in immune responses of the body. 20 - 40% of WBCs are lymphocytes. Lymph differs from blood in lacking RBCs, platelets and large plasma proteins. It has less power of clotting compared to the blood. Both T lymphocytes and B lymphocytes are present in the lymph and they are responsible for the antigen specific acquired immunity. Hence the correct option is b.

FAQs

1. What are the differences between lymph and blood?

Answer: The major differences between lymph and blood are as follows:

2. Why are RBCs not present in lymph?

Answer: Red blood cells do not have the amoeboid character just like the white blood cells. So RBCs can not ooze out through the capillaries. Hence RBCs are not present in the fluid tissue or the lymph.

3. What is lymphocytosis?

Answer: The lymphatic disease caused by the high amount of lymphocyte count is called lymphocytosis. The causes of this disease are infection, blood cancer, lymphoma etc.

4. What is the average amount of lymph present in the human body?

Answer: A human with 65 kg of body weight contains approximately 12 litres of interstitial fluid. He produces 8 – 12 litres of lymph per day. From this 4 – 8 litres of lymph is reabsorbed by the lymph nodes and the remaining 4 litres is returned to blood circulation through the efferent lymphatic vessels and ducts.