The Lymphatic and Immune System
Lymph is a clear, watery fluid that surrounds body cells and flows in a system of lymph vessels extending throughout the body. The term 'lymph' means clear spring water in Latin, perfectly describing this vital fluid that originates from blood as it filters out of tiny capillaries into spaces between cells.
Fluid Dynamics
From Blood to Lymph: The Journey
Interstitial fluid passes continuously into specialised thin-walled vessels called lymph capillaries, which are found at tissue spaces. Once the fluid enters these capillaries, it's called lymph instead of interstitial fluid.
The lymph passes through large lymphatic vessels and deposits of lymph tissues called lymph nodes, finally reaching large lymph vessels in the upper chest. These vessels then empty into the bloodstream, completing the circulation cycle.
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Three Essential Functions of the Lymphatic System
Drainage System
Transports needed proteins and fluid that have leaked out of blood capillaries back to the bloodstream via the veins.
Fat Absorption
Lymphatic vessels in the intestines absorb lipids (fats) from the small intestine and transport them to the bloodstream.
Immune Defence
Protects the body against foreign organisms such as bacteria and viruses through lymphocytes and monocytes.
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Lymph Capillaries and Vessels
Lymph Capillaries
Begin at the spaces around cells throughout the body. Like blood capillaries, they are thin-walled tubes that carry lymph from tissue spaces to larger lymph vessels.
Lymph Vessels
Have thicker walls than lymph capillaries and contain valves like veins, ensuring lymph flows only in one direction towards the thoracic cavity.
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Filtration
Lymph Nodes: The Body's Filters
Collections of stationary lymph tissue, called lymph nodes, are located along the path of lymph vessels. These masses of lymph tissue are surrounded by a fibrous connective tissue capsule.
Lymph Cell Production
Produce lymphocytes and other immune cells essential for fighting disease.
Filtration Function
Filter lymph and trap substances from inflammatory and cancerous lesions.
Macrophage Action
Special cells called macrophages engulf and destroy foreign substances through phagocytosis.
Antibody Production
Lymphocytes present in nodes produce antibodies to fight diseases.
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Major Lymphatic Ducts
Thoracic Duct
Drains the lower body and left chest. This is the larger of the two main lymphatic ducts.
Right Lymphatic Duct
Drains the right chest. Both ducts carry lymph into large veins in the neck where lymph merges with the blood system.
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The Spleen: A Multifunctional Organ
The spleen is located in the upper quadrant of the abdomen, adjacent to the stomach. This organ composed of lymph tissue performs several vital functions for the body.
01
Destruction of Old Erythrocytes
Macrophages destroy old red blood cells. Bilirubin is formed and added to the bloodstream through this haemolytic activity.
02
Filtration of Microorganisms
Filters out microorganisms and other foreign material from the blood, protecting the body from infection.
03
Activation of Lymphocytes
Filters out antigens from the blood. Activated lymphocytes produce antibodies and engulf antigens.
04
Storage of Blood
Stores blood components, especially platelets, for release when needed by the body.
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Thymus Gland
The Thymus: Guardian of Early Immunity
The thymus gland is a lymphatic organ located in the upper mediastinum between the lungs. During foetal life and childhood it is quite large, but it becomes smaller with age.
The thymus gland plays an important role in the body's ability to protect itself from disease (immunity), especially in foetal life and the early years of growth. It's crucial for developing T cell lymphocytes.
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Understanding Immunity
Immunity is the capacity to resist all types of organisms and toxins (poisons) that will damage tissues and organs. The body has multiple ways to achieve this protection.
Natural (Innate) Immunity
One's own genetic ability to fight off disease. This is the immunity we're born with, providing the first line of defence against pathogens.
Acquired Immunity
Immunity developed through exposure to antigens, either by having a disease or receiving vaccination. Can be active or passive.
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Types of Acquired Immunity
Active Immunity: Disease
Antibodies are made against foreign organisms and remain in the body to protect against subsequent infection.
Active Immunity: Vaccination
Receiving a vaccination containing a modified pathogen or toxin stimulates antibody production without having the disease.
Passive Immunity
Patient receives immune serum containing antibodies produced in another animal, such as antitoxins for snake bites or tetanus injections.
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Cell Types
B Cells and T Cells: The Immune Warriors
B Cells
Lymphocytes that transform into plasma cells and secrete antibodies. The B refers to the bursa of Fabricius, an organ in birds where B cell differentiation was first noted.
- Transform into plasma cells
- Secrete antibodies
- Part of humoral immunity
T Cells
Lymphocytes formed in the thymus gland that act directly on antigens to destroy them or produce chemicals toxic to antigens.
- Helper cells (T4 cells)
- Cytotoxic cells (T8 cells)
- Suppressor cells
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Cell-Mediated vs Humoral Immunity
Cell-Mediated Immunity
An immune response involving T cell lymphocytes where antigens are destroyed by direct action of cells. T cells directly kill foreign cells or produce chemicals like interferons and interleukins.
Humoral Immunity
Immune response in which B cells transform into plasma cells and secrete antibodies. These antibodies (immunoglobulins) such as IgA, IgD, IgE, IgG, and IgM circulate in body fluids.
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Key Immune System Components
Antibodies
Proteins produced by plasma cells that destroy antigens. Also called immunoglobulins or gamma globulins.
Macrophages
Large phagocytes found in lymph nodes and other tissues that engulf and destroy foreign substances.
Interferons
Antiviral proteins secreted by T cells that also stimulate macrophages to ingest bacteria.
Interleukins
Proteins that stimulate the growth of T cell lymphocytes and activate immune responses.
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Lymph Node Locations in the Body
Cervical Nodes
Lymph nodes in the neck region that filter lymph from the head and neck area.
Axillary Nodes
Lymph nodes in the armpit (under arm) that drain the upper limbs and chest wall.
Mediastinal Nodes
Lymph nodes in the area between the lungs in the thoracic (chest) cavity.
Inguinal Nodes
Lymph nodes in the groin region where the legs join the trunk of the body.
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Pathological Conditions
AIDS: Acquired Immunodeficiency Syndrome
Suppression or deficiency of the immune response caused by exposure to HIV (human immunodeficiency virus). A proper definition of AIDS now includes all HIV-infected people who have fewer than 200 CD4+ T cells, whilst healthy adults usually have 1,000 CD4+ T cells or more.
The infectious diseases associated with AIDS are often called opportunistic infections because the AIDS virus lowers resistance and allows opportunity for infection by bacteria and parasites that are easily contained by normal defences.
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Opportunistic Infections with AIDS
Candidiasis
Fungal infection affecting mucous membranes and skin.
Cryptococcus (Crypto)
Fungal infection that can affect the brain and lungs.
Cryptosporidiosis
Parasitic infection causing severe diarrhoea.
Cytomegalovirus (CMV)
Viral infection affecting multiple organs including eyes and digestive system.
Herpes Simplex
Viral infection causing painful sores and blisters.
Histoplasmosis (Histo)
Fungal infection primarily affecting the lungs.
Mycobacterium avium-intracellulare (MAI)
Bacterial infection affecting multiple organ systems.
Pneumocystis carinii pneumonia (PCP)
Severe lung infection, one of the most common AIDS-related illnesses.
Toxoplasmosis (Toxo)
Parasitic infection that can cause brain inflammation.
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Other Immune System Disorders
Hypersensitivity
Conditions in which the body reacts with an exaggerated immune response. The immune system produces tissue damage and disordered function rather than immunity.
Hypersplenism
A syndrome marked by enlargement of the spleen. Splenomegaly is often associated with destruction of blood cells resulting in anaemia, leukopaenia, and thrombocytopaenia.
Sarcoidosis
Inflammatory disease in which small nodules or tubercles form in lymph nodes and other organs throughout the body.
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Malignancies
Lymphoma: Malignant Tumours
Lymphoma refers to malignant tumours of lymph nodes and lymph tissue. There are many forms of lymphoma depending on the particular cell type and its degree of differentiation.
Hodgkin's Disease
Malignant tumour of lymph tissue in the spleen and lymph nodes, also called Hodgkin's lymphoma. Characterised by the presence of Reed-Sternberg cells.
Non-Hodgkin's Lymphoma
Types of this disease include lymphocytic lymphoma and histiocytic lymphoma. More diverse group of lymphomas with varying prognoses.
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Additional Pathological Conditions
Mononucleosis
Acute infectious disease with enlarged lymph nodes and increased numbers of lymphocytes and monocytes in the bloodstream. Often called the "kissing disease".
Thymoma
Malignant tumour of the thymus gland. Can affect immune function and may be associated with autoimmune disorders.
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Diagnostics
Clinical Procedures: Blood Tests
ELISA Test
Enzyme-linked immunosorbent assay. This test is used to screen blood for antibody to AIDS virus. A positive result indicates probable exposure to the virus and possibly that the virus is in the blood.
Western Blot
This test detects the presence of HIV (AIDS virus) in serum. Since false-positive results can occur with ELISA, this back-up test is used to confirm positive findings.
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Clinical Procedures: Imaging Studies
CT (CAT) Scan
Computed tomography (x-ray views in a transverse plane) is used to diagnose abnormalities of lymphoid organs such as lymph nodes, spleen, and thymus gland. Provides detailed cross-sectional images.
Lymphangiogram
Contrast medium is injected into lymph vessels in the foot, and x-rays are taken to show the path of lymph flow as it moves into the chest region. This test is often used in the staging and diagnosis of lymphoma.
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Essential Vocabulary: Anatomical Terms
Adenoids
Masses of lymph tissue in the nasopharynx that help fight infections entering through the nose and mouth.
Tonsils
Masses of lymph tissue in the back of the oropharynx that serve as the first line of defence against ingested pathogens.
Lymphoid Organs
Includes lymph nodes, spleen, and thymus gland—all essential components of the immune system.
Interstitial Fluid
Fluid in the spaces between cells that becomes lymph when it enters lymph capillaries.
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Essential Vocabulary: Immune Cells and Responses
Helper Cells
T cells that aid B cells in recognising antigens and stimulating antibody production; also called T4 cells. Critical for coordinating immune responses.
Cytotoxic Cells
T cells (killer cells) that directly kill foreign cells; also called T8 cells. Essential for eliminating infected or cancerous cells.
Suppressor Cells
T cell lymphocytes that inhibit the activity of B cell lymphocytes, helping to regulate immune responses and prevent overreaction.
Plasma Cell
A cell that secretes antibody and originates from B cell lymphocytes. The primary antibody-producing cells of the immune system.
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Essential Vocabulary: Medical Terms
Toxin
A poison; a protein produced by certain bacteria, animals, and plants that can cause disease or death.
Vaccination
Introduction of altered antigens (viruses or bacteria) to produce an immune response and protection against disease. The term comes from the Latin vacca, meaning cow.
Acquired Immunity
Formation of antibodies and lymphocytes after exposure to an antigen, providing long-term protection.
Natural Immunity
One's own genetic ability to fight off disease without prior exposure or vaccination.
Immune Response
The body's capacity to resist all types of organisms and toxins that can damage tissue and organs.
Immunoglobulins
Antibodies (gamma globulins) such as IgA, IgD, IgE, IgG, IgM that are secreted by plasma cells in humoral immunity.
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