UPSC Biology Lymphatic System and Immunity Lymphatic System and Immunity

Lymphatic System and Immunity

Category : UPSC

Lymphatic System and Immunity



The Lymphatic System

  • The lymphatic system is composed of lymph vessels, lymph nodes, and organs. The functions of this system include the absorption of excess fluid and its return to the blood stream, absorption of fat (in the villi of the small intestine) and the immune system function.


  • Lymph vessels are closely associated with the circulatory system vessels. Larger lymph vessels are similar to veins. Lymph capillaries are scatted throughout the body. Contraction of skeletal muscles causes movement of the lymph fluid through valves.




  • Lymph organs include the bone marrow, lymph nodes, spleen, and thymus.


  • Bone marrow contains tissue that produces lymphocytes. B-lymphocytes (B-cells) mature in the bone marrow.


  • T-lymphocytes (T-cells) mature in the thymus gland.


  • Other blood cells such as monocytes and leukocytes are produced in the bone marrow.


  • Lymph nodes are areas of concentrated lymphocytes and macrophages along the lymphatic veins.


  • The spleen is similar to the lymph node except that it is larger and filled with blood.


  • The spleen serves as a reservoir for blood, and filters of purifies the blood and lymph fluid that flows through it.


  • If the spleen is damaged or removed, the individual is more susceptible to infections.


  • The thymus secretes a hormone, thyroxin, that causes pre-T-cells to mature (in the thymus) into T-cells.



  • Immunity is the body’s capability to repel foreign substances and cells.


  • The nonspecific responses are the first line of defense.


  • Highly specific responses are the second line of defense and are tailored to an individual threat.


  • The immune response included both specific and nonspecific components. Nonspecific responses block the entry and spread of disease-causing agents.


  • Antibody-mediated and cell-mediated responses are two types of specific response.


  • The immune system is associated with defense against disease-causing agents, problems in transplants and blood transfusion, and diseases resulting from over-reaction (autoimmune, allergies) and under-reaction (AIDS).


(A) General Defenses


Barriers to entry are the skin and mucous membranes.


  1. The skin is a passive barrier to infectious agents such as bacteria and viruses. The organisms living on the skin surface are unable to penetrate layers of dead skin at the surface. Tears and saliva secrete enzymes that breakdown bacterial cell walls. Skin glands secrete chemicals that retard the growth of bacteria.


  1. Mucus membrane lining the respiratory, digestive, urinary, and reproductive tracts secrete mucus that forms another barrier. Physical barriers are the first line of defense.


  1. When microorganisms penetrate skin or epithelium lining respiratory, digestive or urinary tracts, inflammation results. Damaged cells release chemical signals such as histamine that increase capillary blood flow into the affected area (causing the areas to become heated and reddened). The heat makes the environment unfavorable for microbes, promotes healing, raises mobility of white blood cells, and increases the metabolic rate of nearby cells. Capillaries pass fluid into intestinal areas, causing the infected/injured area to swell.


  1. Clotting factors trigger formation of many small blood clots. Finally, monocytes (a type of white blood cell) clean up dead microbes, cells, and debris.


  1. If this is not enough to stop the invaders, the complement system and immune response act.


  1. Protective proteins that are produced in the liver include the complement system of proteins. The complement system proteins bind to a bacterium and open pores in its membrane through which fluids and salt move, swelling and bursting the cell. The complement system directly kills microbes, supplements inflammatory response. It complements the actions of the immune system. Complement proteins are made in the liver and become active in a sequence ( activates ). The final five proteins form a membrane-attack complex (MAC) that embeds itself into the plasma membrane of the attacker.


  1. Salts enter the invader, facilitating water to cross the membrane, swelling and bursting the microbe. Complement also functions in the immune response by tagging the outer surface of invaders for attack by phagocytes.


(B) Specific Defenses

  • The immune system also generates specific responses to specific invaders.


  • The immune system is more effective than the nonspecific methods, and has a memory component that improves response time when an invader of the same type (or species) is again encountered.


  • Immunity results from the production of antibodies specific to a given antigen (antibody-generators, located on the surface of an invader).


  • Antibodies bind to the antigens on invaders and kill or inactivate them in several ways.


  • Most antibodies are themselves proteins or are a mix of protein and polysaccharides. Antigen’s can be any molecule that causes antibody production.


Lymphocytes: White blood cells known as lymphocytes arise from mitosis of stem cells in the bone marrow. Some lymphocytes migrate to the thymus and become T cell that circulate in the blood and are associated with the lymph nodes and spleen.


B cells remain in the bone marrow develop before moving into the circulatory and lymph systems. B cells produce antibodies.


  1. Antibody-mediated (humeral) immunity is regulated by B cells and the antibodies they produce. Cell-mediated immunity is controlled by T cells.


  1. Antibody-mediated reactions defend against invading viruses and bacteria. Cell-mediated immunity concerns cells in the body that have been infected by viruses and bacteria, protect against parasites, function, protozoans, and also kill cancerous body cells.


Antibody-mediated immunity :


(i)   antigen detection


(ii)   activation of helps T cells


(iii)  antibody production by B cells


Each stage is directed by a specific cell type.


  • Microphages : Macrophages are white blood cells that continually search for foreign (nonself) antigenic molecules, viruses, or microbes. When found, the macrophages engulfs and destroys them. Small fragments of the antigen are displayed on the outer surface of the macrophages plasma membrane.


  • Helper T Cells : Helper T cells are macrophages that become activated when they encounter the antigens now displayed on the macrophages surface. Activated T cells identify and activate B cells.


  • B Cells: B cells divide forming plasma cells and B memory cells. Plasma cells make and release between 2000 and 20,000 antibody molecules per second into the blood for the next four or five days. B memory cells live for months or years, and are part of the immune memory system.


  • Antibodies : Antibodies bind to specific antigens in a lock-and-key fashion, forming an antigen-antibody complex. Antibodies are a type of protein molecule known as immunoglobulin’s: lgG, lgA, lgD, lgE and lgM.


Antibodies are Y-shaped molecules composed of two identical long polypeptide (Heavy or H chains) and two identical short polypepticles (Light or L chains). Function of antibodies includes:


      (i)   Recognition and binding to antigens

      (ii)   Inactivation of the antigens


A unique antigenic determinant recognizes and binds to a site on the antigen, leading to the destruction of the antigen in several ways. The ends of the Y are the antigen combining site that is different for each antigen.


Helper T cell activate B cell that produce antibodies. Suppressor T cells slow down and stop the immune response of B and T cells, serving as an off switch for the immune system. Cytotoxic (or killer) T cells destroy body cell infected with a virus or bacteria Memory T cells remain in the a virus or bacteria. Memory T cells remain in the body awaiting the reintroduction of the antigens.


A cell infected with a virus will display viral antigens on its plasma membrane. Killer T cells recognize the viral antigens and attach to that cell’s plasma membrane. The T cells secrete proteins that punch holes in the infected cell’s plasma membrane. The infected cell’s cytoplasm leaks out, the cell dies, and is removed by phagocytes. Killer T cells may also bind to cells of transplanted organs.


The immune system is the major component of this defense. Lymphocytes, monocytes, lymph organs, and lymph vessels make up the system. The immune system is able to distinguish self from non-self. Antigens are chemicals on the surface of a cell. All cells have these. The immune system checks cells and identifies them as “self” or “non-self’. Antibodies are proteins produced by certain lymphocytes in response to a specific antigen. B-lymphocytes and T-lymphocytes produce the antibodies. B-lymphocytes become plasma cells which then generate antibodies. T-lymphocytes attack cells which bear antigens they recognize. They also mediate the immune response.


Blood Types, Rh, and Antibodies

There are 30 or more known antigens on the surface of blood cells. These form the blood groups of blood types. In a transfusion, the blood groups of the recipient and donor should match.


It improperly matched, the recipient’s immune system will produce antibodies causing clotting of the transfused cells, blocking circulation through capillaries and producing serious or even fatal results. Individuals with blood type ‘A’ have the A antigen on the surface of their red blood cells, and antibodies to type B blood in their plasma. People with blood type ‘B’ have the B antigen on their blood cells and antibodies against type A in their plasma.


Individuals with type ‘AB’ blood produce have antigens for A and B on their cell surfaces and no antibodies for either blood type A or B in their plasma. Type O individuals have no antigens on their red blood cells but antigens on their red blood cells but antigens of both A and B are in their plasma. People with type AB blood can receive blood of any type, so it is called as Universal Receptor.


 Those with type O blood can donate to anyone. So it is called as Universal Donor. Hemolytic disease of the newborn (HDN) results from Rh incompatibility between an Rh mother and blood from the fetus enters the mother’s system during birth, causing her to produce Rh antibodies. The first child is usually not affected, however subsequent fetuses will cause a massive secondary reaction of the material immune system.


To prevent HDN, Rh- mothers are given an Rh antibody during the first pregnancy with an R+ fetus and all subsequent Rh+ fetuses.


Organ Transplants and Antibodies

Success of organ transplants and skin grafts requires a matching of histocompatibility antigens that occur on all cells in the body.


Chromosome 6 contains a cluster of genes known as the human leukocyte antigen complex (HLA) that are critical to the outcome of such procedures. The array of HLA alleles on either copy of our chromosome 6 is known as a haplotype.


The large number of alleles involved mean no two individuals, even in a family, will have the same identical haplotype.


Identical twins have a 100% HLA match. The best matches are going to occur within a family. The preference order for transplants is identical twin > sibling > parent > unrelated donor.


Chances of an unrelated donor matching the recipient range between 1 in 100,000-200,000. Matches across racial or ethnic lines are often more difficult. When HLA types are matched survival of transplanted organs dramatically increases.


Body Defenses

The specialized cells which deal with germs and forcing particles by eating them up are called ‘phagocytes’ (phagein ‘to eat’; cyte ‘cell’). They are present in all tissues but are particularly concentrated in liver, spleen and bone marrow.


  • Monocyte in the blood are the circulating counterparts of these cells.


  • Specific acquired immunity can be categorized into two groups: humeral immunity and cellular immunity


  • Lymphoid organs produce lymphocytes. These organs include principally bone marrow, thymus, lymph, nodes, spleen and some ‘patches’ in the wall of the small intestine.


  • The two types of lymphocytes — B lymphocytes concerned with humeral immunity, and T lymphocytes concerned with cellular immunity


  • Antibody production takes place in Numeral immunity. It is triggered by a protein called the antigen. It is the plasma cells which manufacture antibodies specific for the antigen presented.


  • Theories which spring to explain the synthesis of specific antibodies — ‘in structure’ and selective theories. Instructive thrones postulate that all plasma cells are alike, it is the antigen that directs the plasma cells to manufacture a specific protein (antibody)


  • Selective theories originally proposed by Busnet, assume that there are as many types of B cells as the antigens


Antibodies are proteins belonging to a class called ‘gamma globulins’ or immunoglobulin’s.


Hepatitis Vaccine - Three doses are required: the interval between the first and second dose being one month, and that between the second and third being six months.


Oral typhoid vaccine is available in the form of capsule under the brand name ‘Typhorla’.


Blood: The Vital Fluid

Blood looks like a homogenous red fluid to the uncover edge. But when spread into a thin layer, it is found to be a suspension of different type of cells in a liquid called ‘plasma’. Most of the cells are faint yellow and without a nucleus. A dense accumulation of these cells is responsible for the red colour of the blood. These cells are called ‘erythrocytes’ or red blood cells. These are also another two types of cells - the ‘leucocytes’ or white blood cells and ‘thrombocytes’ or platelets.


Plasma - is a straw coloured liquid, about 90 percent of which is water. The chief salt dissolved in plasma is sodium chloride, or common table salt. The salinity of plasma is one-third that of sea water.


  • Fibrinogen is a protein which is essential for clotting of blood, another protein globulins aid in the defense mechanisms of the body.


  • Red Blood Cells:- are the most numerous of the blood cells, they neither have a nucleus nor mitochondria, RBC are a reddish coloured protein containing iron.


  • It is hemoglobin which makes it possible to deliver oxygen to tissue which need it.


The normal quantity of hemoglobin present in blood in 12-15 g in every 100 ml of blood. A decrease in this quantity is called ‘anemia’.


  • The nucleus membrane of the roof of the mouth (palate) is the best region to access the quantity of hemoglobin.


  • The average life span of a red cell is about four months. They are produced in the hollow of the bones (bone marrow).


  • White Blood Cells - WBC are far less numerous than the RBC, the ratio being one white cell every 600 red cells. They are slightly larger than the red cells and differ in three aspect - first, they have nuclei, secondly, they do not contain hemoglobin, and are therefore nearly colourless, finally, some white cells can move and engulf particles or bacteria the process in called phagocytosis.


      WBCare further subdivided in five groups.


(1) Neutrophils

(2) Eosinophills

(3) Basophils

(4) Lymphocytes

(5) Monocytes


Platelets are much smaller than red or white blood cells and are devoid of nuclei. They check the bleeding from an injury (hemostasis: haime blood; stages ‘standing’ Platelets contribute to this process of hemostasis by liberating a chemical called ‘sesolonies’.


  • A, B, AB and O are the four blood groups. The classification is based on the type of substance present on the surface of red blood cells.


Lungs: The Life Linke

The bronchial tree consists of larynx, trachea, bronchus lung, right lung.


Alveoli - is a cluster of thin walled air sacs which end in tiny air cells. It is covered with a tracery of capillaries. A men has about 600 million alveoli.


  • Oxygen move from the alveoli into the blood and carbon dioxide move out of the capillaries to entre the alveoli.    

Other Topics

NCERT Summary - Lymphatic System and Immunity

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