Anatomy and Physiology - Lymphatic System and Immunity Notes

Functions of the Lymphatic System
- Immunity: Resists infection and disease; involves all cells and tissues responsible for immune response.
- Maintenance of Blood Volume: Regulates normal blood volume and interstitial fluid composition.

Lymphocytes: Primary cells responsible for immune responses.
- Types of Responses:
- Invading pathogens (bacteria, viruses)
- Abnormal body cells (cancer, virus-infected)
- Foreign proteins (bacterial toxins)
- Lymph: Interstitial fluid that enters lymphatic vessels.
Lymphatic Vessels:
- Also called lymphatics.
- Begin in peripheral tissues, connecting to veins in the trunk.
Lymphoid Tissues and Organs:
- Primary Lymphoid Organs:
- Development and maturation of lymphocytes (e.g., red bone marrow, thymus).
- Secondary Lymphoid Organs:
- Activation and cloning of lymphocytes (e.g., lymph nodes, tonsils, spleen).

Lymphatic Capillaries:
- Different from blood capillaries:
- Closed at one end, larger diameter, thinner walls.
- Have overlapping endothelial cells acting as one-way valves.
- Permit entry of fluids, solutes, and foreign substances while preventing their return to intercellular space.
Collecting Vessels:
- Form lymphatic trunks leading to the thoracic duct or right lymphatic duct.
- Thoracic Duct: Collects lymph from body below diaphragm and left side above diaphragm; drains into the left subclavian vein.
- Right Lymphatic Duct: Collects lymph from the right side above diaphragm; drains into the right subclavian vein.
Lymphedema:
- Condition resulting from blockage of lymphatic drainage, leading to fluid accumulation and swelling, often seen in limbs.

Types of Lymphocytes:
- T Cells:
- 70-85% of all circulating lymphocytes, responsible for cell-mediated immunity.
- Cytotoxic T Cells: Directly attack infected or abnormal cells.
- Helper T Cells: Help activate other immune cells.
- Regulatory T Cells: Moderate immune response and maintain tolerance.
- Memory T Cells: Respond to antigens previously encountered.
B Cells:
- Differentiate into plasma cells to produce antibodies, responsible for humoral immunity.
NK Cells:
- Attack foreign, virus-infected, and cancer cells; involved in immune surveillance.

Lymphopoiesis: Production of lymphocytes.
- Involves red bone marrow and thymus.
- Lymphoid Stem Cells: Differentiate into T cells in the thymus and B cells/NK cells in the marrow.

Tissues:
- Lymphoid Nodules: Clustered lymphocytes; thrive in mucosal areas (e.g., MALT).
Tonsils: Large lymphoid masses in pharynx; inflammation called tonsillitis.
Lymph Nodes:
- Filters lymph fluid by removing pathogens; located in neck, groin, axillary regions.
Thymus:
- Organ producing hormones for T cell development; decreases in size with age.
Spleen:
- Largest lymphoid organ, filters blood, removes abnormal cells, stores iron, and initiates immune responses.

Innate (Non-Specific) Immunity:
- First line of defense against pathogens, includes physical barriers like skin, enzymes, and phagocytes.
Adaptive (Specific) Immunity:
- Developed over time, involving T cells and B cells, provides a specific immune response to pathogens.
Physical Barriers: Skin, mucous membranes, etc.
Phagocytes: Includes neutrophils, monocytes that engulf pathogens.
Inflammation and Fever: Localized responses that aid in infection control.

Antibodies (Immunoglobulins):
- Five classes (IgG, IgA, IgM, IgE, IgD), vary in structure and function.
- Neutralization: Binding to pathogens, preventing their effects.
- Opsonization: Coating pathogens for easier phagocytosis.
- Activation of the complement system: Enhances immune responses.

Allergies: Exaggerated immune responses to antigens (allergens).
- Immediate Hypersensitivity: Rapid response; allergens trigger IgE and mast cell degranulation leading to inflammation.
- Anaphylaxis: Severe systemic reaction requiring immediate intervention, can lead to shock.

Autoimmune Disorders: Immune system attacks self antigens, leading to conditions like rheumatoid arthritis and Type 1 diabetes.
End of Notes