Lymphatic and Immune System PowerPoint(1) (1)

Lymphatic System

Functions

• Draining excess interstitial fluid: The lymphatic system plays a crucial role in maintaining fluid balance within the body by draining the excess interstitial fluid that accumulates in tissues, thus preventing edema.

• Transporting dietary lipids and lipid-soluble vitamins: It facilitates the absorption of dietary lipids and the transport of lipid-soluble vitamins (A, D, E, K) from the digestive tract to the bloodstream, particularly via specialized vessels known as lacteals in the intestines.

• Facilitating the immune response: The lymphatic system is integral to the body's immune defenses, providing a network for the distribution and activation of immune cells, which helps in the identification and elimination of pathogens and foreign substances.

• Producing, maintaining, and distributing lymphocytes: The system is involved in the production of lymphocytes—critical components of the immune system—and maintains a distribution network that enables these cells to effectively respond to infections.

Parts of the Lymphatic System

Lymph

• Composition: Lymph is a clear fluid that resembles interstitial fluid, consisting mainly of water, electrolytes, and proteins. It is formed by the filtration of blood plasma through capillaries and contains lymphocytes and other immune system components.

Lymphatic Vessels

• Structure and Function: Lymphatic vessels resemble veins, with thinner walls and more valves to prevent backflow. They play a key role in transporting lymph to lymph nodes and ultimately to the venous system.

• Lymphatic Capillaries:

  • Characteristics: These are the smallest lymphatic vessels, blind-ended, and slightly larger than blood capillaries, allowing greater permeability, which facilitates the uptake of interstitial fluid, proteins, and pathogens.

  • Distribution: They are located throughout the body except in avascular tissues (e.g., cartilage), spleen, red bone marrow, and CNS.

  • Structure: Lymphatic capillaries allow one-way movement of fluid into the capillaries through overlapping endothelial cells, which act as mini-valves.

  • Lacteals: Specialized lymphatic capillaries located in the intestinal villi that are essential for lipid transport, specifically through chylomicrons during digestion.

Lymph Nodes

• Structure and Function:

  • Lymph nodes are small, bean-shaped structures (approximately 600 in human body) that filter lymph and are concentrated in regions like the neck, groin, and axilla. They contain immune cells like macrophages, T cells, and B cells that identify and neutralize pathogens and cancerous cells.

Flow through Lymph Nodes

• Pathway: Lymph enters through afferent lymphatics into the lymph node, passing through various compartments (cortex and medulla) for filtration, before exiting via efferent lymphatics. This sequential flow allows for effective immune surveillance as lymph passes from node to node in the lymphatic chain.

Major Lymphatic Structures

• Lymphatic Ducts:

  • Thoracic duct and Right lymphatic duct: These major lymphatic ducts collect lymph from different body regions (most from the thoracic duct) and return it to the venous circulation at the junction of the subclavian and internal jugular veins.

• Other Lymphoid Tissues and Organs: Include tonsils, thymus, spleen, and mucosa-associated lymphoid tissue (MALT), which is found throughout the gastrointestinal, respiratory, urinary, and reproductive tracts, providing localized immune responses.

Lymphadenitis and Lymphangitis

• Lymphadenitis: Refers to inflammation of lymph nodes, typically resulting in tenderness and swelling in the region near the site of infection or inflammation, often indicative of a localized immune response.

• Lymphangitis: Involves inflammation of lymphatic vessels, often appearing as reddish streaks on the skin, reflecting ongoing infection or inflammatory processes.

Types of Lymphatic Vessels

• Lymphatic vessels range from small capillaries to larger trunks and ducts. They contain valves that direct flow toward larger collecting vessels, known as trunks, before converging into the major ducts.

Characteristics of Lymph Flow

• Flow is Passive: The transport of lymph relies on passive mechanisms, similar to venous blood flow, aided by one-way valves, skeletal muscle contractions during physical movement, and the pressure changes associated with respiration. Any blockage can lead to lymphedema, characterized by localized swelling due to fluid accumulation.

Thymus

• The thymus is a primary lymphatic organ and endocrine gland critical for the maturation of T lymphocytes. It is particularly active during childhood and adolescence and gradually atrophies with age. The thymus provides an environment for T cells to mature and learn to distinguish between self and non-self antigens.

Spleen

• The spleen is the largest organ of the lymphatic system, involved in filtering blood as well as recycling iron from hemoglobin.

  • White Pulp: Contains lymphatic tissue rich in B and T lymphocytes, playing a crucial role in immune responses by producing antibodies and facilitating the activation of T cells.

  • Red Pulp: Responsible for the removal of aged or damaged red blood cells and serves as a storage reservoir for blood, releasing it during hemorrhagic events.

Mucosa-associated Lymphoid Tissue (MALT)

• MALT includes lymphoid nodules associated with mucosal surfaces, such as in the tonsils and Peyer’s patches in the small intestine. These structures play key roles in both the innate and adaptive immune responses within mucosal membranes, providing localized defense against pathogens.

Lymphocytes

• Types of Lymphocytes:

  • T Cells: Essential for cell-mediated immunity, targeting infected or cancerous cells.

  • B Cells (Plasma Cells): Responsible for humoral immunity by producing antibodies that neutralize pathogens and mark them for destruction.

  • Natural Killer Cells: A subset of lymphocytes that respond to viral infections and tumor cells without prior sensitization.

Immunity and Immune Responses

• Innate Immunity (Nonspecific): Provides immediate, non-specific protection against a wide array of pathogens through barriers and inflammatory responses.

• Acquired Immunity (Specific): Develops more slowly and relies on the adaptive immune response's ability to recognize specific foreign invaders, necessitating exposure to those antigens.

Immune Defense Mechanisms

• First Line of Defense: Involves physical barriers (skin and mucosal membranes) and chemical barriers (such as antimicrobial peptides in skin, acidic pH in gastric juices).

• Second Line of Defense: Involves cellular responses, particularly the action of phagocytes (neutrophils, eosinophils, macrophages) that engulf and destroy pathogens through phagocytosis.

Inflammatory Response

• An essential defensive mechanism against tissue injury characterized by redness, swelling, heat, and pain.

  • Stages:

    1. Vasodilation increases blood flow and capillary permeability, allowing immune cells to exit the bloodstream.

    2. Emigration of Phagocytes to the site of injury leads to the formation of pus and is essential for tissue repair.

Adaptive Immunity

• Characterized by specificity and memory. Requires previous exposure to an antigen to produce faster secondary immune responses upon subsequent exposures.

• Vaccination: Induces an immune response that generates memory cells, providing long-term immunity with minimal symptoms to the individual.

Immune Disorders

• Examples: Include congenital immunodeficiencies, autoimmune diseases (such as lupus, rheumatoid arthritis, and Type 1 Diabetes), and infections leading to acquired immunodeficiency syndrome (AIDS) from human immunodeficiency virus (HIV).

Autoimmune Diseases

• The immune system mistakenly attacks its own body tissues due to a failure to recognize self, influenced by genetic predispositions and environmental triggers, leading to chronic inflammation and damage to affected organs.

HIV and AIDS

• HIV specifically targets helper T cells (CD4+ T cells), leading to progressive immune deficiency. As HIV progresses and the immune system deteriorates, the individual becomes more susceptible to opportunistic infections. Advances in treatment can significantly improve life expectancy for those diagnosed with HIV.