Subject - General Science
Chapter : Lymphatic System & Immunity

Lymphatic System

• The lymphatic system is composed of lymph vessels, lymph nodes, and organs. The functions of this system include the absorbtion 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 muscle 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.

Immunity

• 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 includes 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 transfusions, and diseases resulting from over-reaction (autoimmune, allergies) and under-reaction (AIDS).

General Defenses

Barriers to entry are the skin and mucous membranes:

• 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 the 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.

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

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.

Vaccination

Vaccination is a term derived from the Latin vacca (cow, after the cowpox material used by Edward Jenner in the first vaccination). A vaccine stimulates the antibody production and formation of memory cells without causing of the disease. Vaccines are made from killed pathogens or weakened strains that cause antibody production but not the disease. Recombinant DNA techniques can now be used to develop even safer vaccines. The immune system can develop long-term immunity to some diseases. Man can use this to develop vaccines, which produce induced immunity. Active immunity develops after an illness or vaccine. Vaccines are weakened (or killed) viruses or bacteria that prompt the development of antibodies.

Disorders of the Immune System

The immune system can overreact, causing allergies or autoimmune diseases. Likewise, a suppressed, absent, or destroyed immune system can also result in disease and death.

• Allergies : Allergies result from immune system hypersensitivity to weak antigens that do not cause an immune response in most people. Allergens, substances that cause allergies, include dust, molds, pollen, cat dander, certain foods, and some medicines (such as penicillin).

• Autoimmune diseases : The immune system usually distinguishes “self” from “nonself”. The immune system learns the difference between cells of the body and -foreign invaders. Autoimmune diseases result when the immune system attacks and destroys cells and tissues of the body. Juvenile diabetes, Grave’s disease, Multiple sclerosis, Systemic lupus erythematosus, and Rheumatoid arthritis are some of the autoimmune diseases.

• Myasthenia gravis : Myasthenia gravis (MG) is a muscle weakness caused by destruction of muscle-nerve connections. Multiple sclerosis (MS) is caused by antibodies attacking the myelin of nerve cells. Systemic lupus erythematosis (SLE) has the person forming a series of antibodies to their own tissues, such as kidneys (the leading cause of death in SLE patients) and the DNA in their own cellular nuclei. In systemic lupus erythematosus (SLE), the immune system attacks connective tissues and major organs of the body.

• Immuno deficiency diseases : Immunodeficiency diseases result from the lack or failure of one or more parts of the immune system. Affected individuals are susceptible to diseases that normally would not bother most people. Genetic disorders, Hodgkin’s disease, cancer chemotherapy, and radiation therapy can cause immunodeficiency diseases.

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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 the ‘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’.

Facts from N.C.E.R.T

• Ball and Socket Joints : The rounded end of one bone fits into the cavity (hollow space) of the other bone. Such a joint allows movements in all directions.

• Pivotal Joint : The joint where our neck joins, the head is a pivotal joint. It allows us to bend our head forward and backward and turn the head to our right or left.

• Hinge Joint : The elbow has a hinge joint that allows only a back and forth movement.

• Fixed Joint : There are some bones in our head that are joined together at some joints the bones cannot move at these joints. Such joints are called fixed joints.

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