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Questions and Answers
What is the structure of lymphatic vessels compared to veins?
What is the structure of lymphatic vessels compared to veins?
Which layer of lymphatic vessels contains smooth muscle and elastic fibers?
Which layer of lymphatic vessels contains smooth muscle and elastic fibers?
What prevents backflow in the lymphatic vessels?
What prevents backflow in the lymphatic vessels?
Which lymphatic trunk drains lymph from the lower body regions?
Which lymphatic trunk drains lymph from the lower body regions?
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What is the primary function of lymphatic collecting ducts?
What is the primary function of lymphatic collecting ducts?
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Where does the thoracic duct drain lymph?
Where does the thoracic duct drain lymph?
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What initiates the formation of lymph?
What initiates the formation of lymph?
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What distinguishes the right lymphatic duct from the thoracic duct?
What distinguishes the right lymphatic duct from the thoracic duct?
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What is one of the primary functions of the lymphatic system?
What is one of the primary functions of the lymphatic system?
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Which component of the lymphatic system is responsible for absorbing lipids?
Which component of the lymphatic system is responsible for absorbing lipids?
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What term is used to describe the network of vessels in the lymphatic system?
What term is used to describe the network of vessels in the lymphatic system?
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What is the correct sequence of lymphatic pathways?
What is the correct sequence of lymphatic pathways?
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What structural feature distinguishes lymphatic capillaries from blood capillaries?
What structural feature distinguishes lymphatic capillaries from blood capillaries?
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What role does the immune system play within the lymphatic system?
What role does the immune system play within the lymphatic system?
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Which of the following best describes lymph?
Which of the following best describes lymph?
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How are lymphatic capillaries structurally adapted to their function?
How are lymphatic capillaries structurally adapted to their function?
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What component is primarily excluded from tissue fluid that is found in blood plasma?
What component is primarily excluded from tissue fluid that is found in blood plasma?
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What is the consequence of the filtration from the plasma exceeding reabsorption?
What is the consequence of the filtration from the plasma exceeding reabsorption?
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How does muscle activity contribute to lymphatic flow?
How does muscle activity contribute to lymphatic flow?
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What role do lymphatic capillaries play in the lymphatic system?
What role do lymphatic capillaries play in the lymphatic system?
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What prevents the backflow of lymph in the lymphatic vessels?
What prevents the backflow of lymph in the lymphatic vessels?
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What effect does the respiratory process have on lymphatic flow?
What effect does the respiratory process have on lymphatic flow?
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What can lead to the accumulation of excess tissue fluid or edema?
What can lead to the accumulation of excess tissue fluid or edema?
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What is the primary function of lymph as it flows through lymphatic vessels?
What is the primary function of lymph as it flows through lymphatic vessels?
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Study Notes
Lymphatic System and Immunity
- The lymphatic system is a network of cells and biochemicals that travel in lymphatic vessels.
- This system contains vessels that help circulate fluids.
- It's closely related to the cardiovascular system.
- Its three primary functions include: transporting excess interstitial fluid back to the bloodstream; absorbing lipids from the digestive system and transferring them to the bloodstream; and defending the body against disease.
- "Immune system" refers to the lymphatic system's role in protecting the body from diseases and providing immunity to future infections.
Lymphatic System Overview
- The lymphatic system is a collection of cells and biochemicals that travel in lymphatic vessels.
- The lymphatic system contains a network of vessels that assist in circulating fluids.
- It is closely associated with the cardiovascular system.
- The lymphatic system has three main functions:
- Transport of interstitial fluid: excess interstitial fluid is transported away from the interstitial spaces and returned to the bloodstream.
- Absorption of dietary fats: lipids absorbed from the digestive system are transported to the bloodstream, accomplished by lymphatic capillaries called lacteals.
- Defense against diseases: Protects the body from diseases and allows for survival in a world containing other organisms.
Lymphatic Pathways
- Lymphatic capillaries feed into lymphatic vessels, which lead to lymph nodes, then larger lymphatic vessels, lymphatic trunks, and finally lymphatic collecting ducts.
- Lymphatic collecting ducts empty into subclavian veins in the thorax.
Lymphatic Capillaries
- Lymphatic capillaries are microscopic, closed-ended tubes.
- They form networks that are parallel to blood capillaries throughout the body.
- Thin-walled
- Walls are formed from simple squamous epithelium
- Interstitial fluid enters lymphatic capillaries and becomes lymph.
- Lymphatic capillaries merge into lymphatic vessels.
Lymphatic Vessels
- Lymphatic vessels are similar in structure to veins but thinner.
- They consist of three layers: an inner endothelial lining, a middle layer of smooth muscle and elastic fibers, and an outer layer of connective tissue.
- Semilunar valves allow one-way flow within the vessels.
- Larger vessels lead to lymph nodes, then to lymphatic trunks.
Lymphatic Trunks and Collecting Ducts
- Lymphatic trunks drain lymph from specific regions of the body (e.g., lumbar, intestinal, intercostal, bronchomediastinal, subclavian, jugular).
- Lymphatic trunks drain into lymphatic collecting ducts
- There are two major collecting ducts: the thoracic duct and right lymphatic duct.
- The thoracic duct is larger and wider, draining most of the body, entering the left subclavian vein.
- The right lymphatic duct is smaller and drains the right side of the upper body and the right upper arm and enters the right subclavian vein
Lymph Nodes
- Lymph nodes are usually bean-shaped and less than 2.5 cm long.
- They are located along lymphatic vessels and filter pathogens from lymph.
- They contain lymphocytes that attack viruses, bacteria, and parasites.
- Macrophages engulf foreign substances, damaged cells, and cellular debris.
- Lymph nodes are grouped or chained along lymphatic vessels throughout the body; major locations include cervical, axillary, supratrochlear, inguinal, pelvic, and thoracic cavities.
- Lymph nodes are not found in the central nervous system.
Lymph Node Structure
- Lymph nodes have an outer capsule and internal structures, including afferent lymphatic vessels (carrying lymph into the node), efferent lymphatic vessels (carrying lymph out of the node), subcapsular sinus, trabeculae, medulla, and lymphatic sinuses.
- Specialized cells (macrophages and lymphocytes) within these structures filter lymph
Lymphatic Tissues and Lymphatic Organs
- Lymphatic tissue has several cell types, including lymphocytes and macrophages.
- Mucosa-associated lymphoid tissue (MALT) is unencapsulated lymphatic tissue found in the digestive, respiratory, urinary, and reproductive tracts (e.g. tonsils, appendix, and Peyer's patches).
- Peyer's patches are lymphatic nodules found in the ileum (part of the small intestine).
- Lymphatic organs consist of encapsulated lymphatic tissue (e.g., lymph nodes, thymus, and spleen).
Thymus
- A soft, bilobed gland located in the mediastinum.
- Lobules that have lymphocytes coming from progenitor cells in the red bone marrow.
- In active, cells are called thymocytes. Some mature in the T-lymphocytes, leaving the thymus and providing immunity.
- Hormones (thymosins) present in the thymus aid in T-cell maturation.
- Larger in infants and children shrinks at puberty, becoming smaller in adults.
Spleen
- The spleen is the largest lymphatic organ, located in the upper left portion of the abdominal cavity.
- It resembles a large lymph node.
- It contains venous sinuses filled with blood.
- Two main regions:
- White pulp: Contains lymphocytes and macrophages.
- Red pulp: Contains red blood cells, and many macrophages.
- Filters blood, breaks down worn-out red blood cells, and macrophages engulf foreign debris.
- Lymphocytes defend the body against infections.
Immunity: Body Defenses Against Infection
- The lymphatic system protects the body against pathogens (disease-causing agents).
- Pathogens can be bacteria, viruses, protozoa, and fungi.
- The presence of pathogens in the body, if unchecked, can lead to infection.
Types of Immune Mechanisms
- Immunity is the body's ability to prevent pathogen entry or destroy pathogens.
- Immune mechanisms include innate (nonspecific) and adaptive (specific) defenses.
- Innate defenses are general defenses against many types of pathogens.
- Adaptive defenses are more specific and precise, targeting specific pathogens or antigens.
Innate (Nonspecific) Defenses
- Species resistance: resistance to diseases that affect other species.
- Mechanical barriers (first line of defense): unbroken skin and mucous membranes prevent pathogen entry.
- Inflammation (second line of defense): local response to injury or infection; it is a process that walls off the site of the infection and inhibits the spread of infection. It involves redness, swelling, heat, and pain (due to vasodilation and increased capillary permeability)
- Chemical barriers (second line of defense): enzymes and other chemicals in body fluids that provide a chemical barrier to pathogens (e.g., lysozyme, interferons, defensins, and complement proteins).
- Natural Killer (NK) cells (second line of defense): defend against viruses and cancer cells and act against cell membranes by releasing perforins.
- Phagocytosis removes foreign particles from the lymph, spleen, liver, and bone marrow.
Adaptive (Specific) Defenses
- The third line of defense is based on the ability to distinguish molecules that are part of the body from those that are not (antigens).
- Lymphocytes and macrophages carry out adaptive responses.
- Types of adaptive defenses:
- Cellular immune response (T cells): T cells provide cellular defense by attacking infected or cancerous cells directly.
- Humoral immune response (B cells) : B cells produce antibodies, which are proteins that combat a pathogen, and are transported in body fluids.
Antigens
- Antigens trigger an immune response.
- Antigens are located on the surface of the lymphocytes.
- They can be proteins, polysaccharides, glycoproteins, or glycolipids.
- Antigens can evoke an immune response if they are combined with a large molecule in the body.
Lymphocyte Origins
- Lymphocytes are produced throughout life, beginning in fetal development.
- Red bone marrow releases unspecialized lymphocytes into the blood.
- Half of these unspecialized lymphocytes settle in the thymus, specialize, and become T cells.
- The other half differentiate in the red bone marrow and become B cells.
T Cells and the Cellular Immune Response
- T cells require activation before responding to antigens.
- Antigen-presenting cells (APCs) display processed antigens on their surface.
- When a T cell encounters an APC displaying a matching antigen, it becomes activated and can respond.
- T cells produce cytokines that enhance cellular responses to antigens.
- Types of T cells include helper T cells, cytotoxic T cells, memory T cells, and regulatory T cells
MHC Proteins (Major Histocompatibility Complexes)
- MHC proteins act as antigen-presenting cells (APCs) for certain T cell types.
- Class I MHC proteins are found on the surface of all nucleated cells, and display processed antigens.
- Class II MHC proteins are found on certain cell types (like macrophages and B cells) and display processed antigens.
- Foreign (non-self) antigens trigger an immune response from cytotoxic T cells.
Cytokines
- Cytokines are protein messengers produced by cells in the immune response.
- Some cytokines regulate the immune response and aid in other aspects of the immune response regulation
B Cells and the Humoral Immune Response
- B cells can be activated when antigen targets their receptors.
- Cytokines released from helper T cells further activate B cells.
- Activated B cells divide to create clones of identical cells: Memory B cells; providing future immunity, and plasma cells, which produce antibodies.
- Antibodies circulate in the blood and bind to foreign antigens to identify them for elimination.
Antibody Molecules
- Antibodies are globular proteins that make up the gamma globulin portion of plasma proteins (also called immunoglobulins).
- Antibodies have a specific structure consisting of two heavy chains and two light chains.
- Different regions of antibodies function in different ways (e.g., antigen-binding sites, variable regions, constant regions).
- Major classes of antibodies (immunoglobulins) are IgG, IgA, IgM, IgD, and IgE, each with specific roles in the immune response.
Antibody Activities
- Antibodies fight pathogens in several ways, including direct attack (agglutination, precipitation, and neutralization); activation of complement; or localized changes (inflammation).
Immune Responses (Primary and Secondary)
- Primary immune response: the initial response to an antigen, takes days for antibodies to be produced. Memory B cells are formed during this response.
- Secondary immune response: subsequent exposure to the same antigen; response is quicker and greater due to the presence of memory cells, resulting in a faster production of higher antibody concentrations.
Practical Classification of Immunity
- Immunity is classified based on how it is acquired (naturally or artificially) or on whether it is temporary or permanent (passive or active).
- Natural immunity: obtained though contracting the disease.
- Passive immunity: involves antibodies obtained via a different method (e.g. from mother to fetus or infants).
Hypersensitivity Reactions
- Hypersensitivity is an exaggerated immune response to non-harmful antigens (allergens).
- Hypersensitivity can result in allergies and other pathological effects
- Four types of hypersensitivity reactions:
- Type I (immediate hypersensitivity): rapid reaction to allergens; involves IgE antibodies, mast cells, and histamine release.
- Type II (antibody-dependent cytotoxic hypersensitivity): antibodies bind to specific cells; phagocytosis and complement-mediated cell damage or lysis.
- Type III (immune complex hypersensitivity): antigen-antibody complexes deposit in tissues, promoting inflammation and tissue damage.
- Type IV (delayed-type hypersensitivity): cell-mediated response; involves T cells and macrophages, causing inflammation and tissue damage; often delayed in action (takes days)
Transplantation and Tissue Rejection
- Transplantation involves transferring tissues or organs between individuals.
- Recipient's immune response recognizes donor tissue as foreign causing rejection reaction.
- Types of grafts:
- Autografts (from the individual's own tissue, often not rejected)
- Isografts (from an identical twin)
- Allografts (from a different individual of the same species)
- Xenografts (from a different species)
- Immunosuppressive drugs or treatments prevent the rejection reaction to transplanted tissue/organs
Autoimmunity
- In autoimmunity, the immune system attacks its own body tissues or organs.
- Immune system fails to discriminate between "self" and "non-self".
- The body produces antibodies (autoantibodies) that attack its own tissues/organs.
- Cytotoxic T cells can also attack own tissues or organs
- Many autoimmune disorders exist, each affecting different types of cells.
Immunity Breakdown: HIV/AIDS
- HIV (Human Immunodeficiency Virus): a virus that breaks down the immune system
- It may lay dormant for years before progressing to AIDS (acquired immune deficiency syndrome).
- Opportunistic infections often occur when the immune system declines.
- HIV initially targets macrophages and Helper T cells, then later Cytotoxic T cells.
- Without the immune system, the body can no longer effectively respond or defend against pathogens, cancers, etc leading to death.
Life-Span Changes
- Immune function declines with age, as the thymus shrinks, and the strength of certain immune responses decreases.
- Higher risk of infection, cancer.
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Description
Test your knowledge about the structure and function of the lymphatic system. This quiz covers topics such as lymphatic vessels, ducts, and the system's role in immune function and lipid absorption. See how well you understand the connections within the lymphatic pathways.
