Lymphatic System

Overview of the Lymphatic System

The lymphatic system is a network of vessels, nodes, and organs that helps maintain fluid balance, defends against pathogens, and supports immune function. It includes lymphatic vessels, lymph, lymph nodes, and associated organs.

• Lymphatic vessels: Transport lymph fluid from tissues back to the bloodstream.

• Lymph: Clear fluid containing white blood cells, especially lymphocytes.

• Lymph nodes: Small, bean-shaped structures that filter lymph and house immune cells.

• Associated organs: Spleen, thymus, tonsils, and MALT (mucosa-associated lymphoid tissue).

Functions and Distribution of Lymphatic Vessels

• Fluid balance: Returns excess interstitial fluid to the bloodstream.

• Immune defense: Transports immune cells and filters pathogens.

• Absorption of fats: Lacteals in the small intestine absorb dietary lipids.

Example: Lymphatic vessels in the legs collect fluid that leaks from capillaries and return it to the circulatory system.

Lymphoid Cells and Tissues

Lymphoid cells are found in lymphoid organs and connective tissue throughout the body. These include lymphocytes (B cells and T cells), macrophages, and dendritic cells.

• B cells: Produce antibodies and mediate humoral immunity.

• T cells: Mediate cellular immunity and attack infected cells.

• Macrophages: Engulf and destroy pathogens.

• Follicular vs. diffuse lymphoid tissue: Follicular tissue contains densely packed lymphocytes; diffuse tissue is more loosely organized.

Lymph Nodes: Structure and Function

Lymph nodes filter lymph and house lymphocytes. They are key sites for immune surveillance and response.

• Structure: Cortex (outer region) contains follicles with germinal centers; medulla (inner region) contains medullary cords.

• Function: Filter lymph, trap pathogens, and activate immune responses.

Spleen and Lymph Nodes: Comparison

• Spleen: Filters blood, removes old red blood cells, and stores platelets.

• Lymph nodes: Filter lymph and initiate immune responses.

MALT (Mucosa-Associated Lymphoid Tissue)

MALT protects mucosal surfaces from pathogens. It includes tonsils, Peyer's patches, and the appendix.

• Function: Guards entryways against pathogens.

• Main components: Tonsils (pharyngeal, palatine, lingual), Peyer's patches (small intestine), appendix.

Thymus and T Lymphocyte Maturation

The thymus is the site of T lymphocyte maturation. It is most active during childhood and shrinks with age.

• Structure: Bilobed organ located in the mediastinum.

• Function: Educates and matures T cells for immune defense.

Immune System Defenses

Surface Barriers

Surface barriers, such as skin and mucous membranes, act as the first line of defense against pathogens.

• Physical barriers: Skin, mucous membranes.

• Chemical barriers: Secretions like sweat, saliva, and stomach acid.

Innate Internal Defenses

Cells and chemicals provide a second line of defense. These include phagocytes, natural killer cells, and inflammatory mediators.

• Phagocytosis: Macrophages and neutrophils engulf pathogens.

• Natural killer cells: Destroy infected or abnormal cells.

• Inflammation: Local response to injury or infection, characterized by redness, heat, swelling, and pain.

• Antimicrobial substances: Complement proteins, interferons.

Antigens and Adaptive Defenses

Antigens are substances that trigger adaptive immune responses. The adaptive system includes humoral (antibody-mediated) and cellular (T cell-mediated) immunity.

• Antigen: Any substance recognized as foreign by the immune system.

• Humoral immunity: B cells produce antibodies that neutralize pathogens.

• Cellular immunity: T cells attack infected or abnormal cells.

B and T Lymphocytes

B and T lymphocytes are central to adaptive immunity. B cells mature in bone marrow; T cells mature in the thymus.

• B cell function: Produce antibodies, mediate humoral immunity.

• T cell function: Directly attack infected cells, regulate immune responses.

• Antigen-presenting cells: Dendritic cells, macrophages, and B cells present antigens to T cells.

Antibodies and Humoral Immunity

Antibodies are proteins produced by B cells that target extracellular antigens. There are five main classes of antibodies.

• Classes: IgG, IgM, IgA, IgE, IgD.

• Function: Neutralize toxins, opsonize pathogens, activate complement.

Equation:

Cellular Immunity and T Cells

T lymphocytes mediate cellular immunity by attacking infected or abnormal cells. Different types of T cells have specialized roles.

• Helper T cells (CD4+): Activate other immune cells.

• Cytotoxic T cells (CD8+): Destroy infected cells.

• Regulatory T cells: Suppress immune responses to prevent autoimmunity.

Respiratory System

Upper Respiratory System

The upper respiratory system warms, humidifies, and filters air. It includes the nose, paranasal sinuses, and pharynx.

• Nose: Filters and humidifies air.

• Paranasal sinuses: Lighten the skull and produce mucus.

• Pharynx: Passageway for air and food.

Lower Respiratory System

The lower respiratory system conducts air to the lungs and facilitates gas exchange. It includes the larynx, trachea, bronchi, and lungs.

• Larynx: Voice production and airway protection.

• Trachea: Windpipe; conducts air to bronchi.

• Bronchi: Branch into smaller airways within the lungs.

• Lungs: Main organs of respiration.

Pleural Cavities

Each lung is housed in its own pleural cavity, which reduces friction during breathing.

• Pleura: Double-layered membrane surrounding each lung.

• Pleural fluid: Lubricates lung movement.

Volume Changes and Air Movement

Changes in thoracic volume cause pressure changes, which drive air movement in and out of the lungs.

• Boyle's Law: Pressure and volume are inversely related.

Equation:

• Inspiration: Diaphragm contracts, thoracic volume increases, pressure decreases, air flows in.

• Expiration: Diaphragm relaxes, thoracic volume decreases, pressure increases, air flows out.

Measuring Respiratory Volumes and Capacities

Respiratory volumes and capacities are measured to assess lung function.

• Tidal volume (TV): Volume of air inhaled or exhaled in a normal breath.

• Vital capacity (VC): Maximum amount of air exhaled after a maximal inhalation.

• Functional residual capacity (FRC): Volume of air remaining in lungs after normal exhalation.

Gas Exchange

Gases are exchanged between the blood, lungs, and tissues by diffusion.

• Dalton's Law: Total pressure of a mixture of gases is the sum of the partial pressures of each gas.

• Henry's Law: Amount of gas dissolved in a liquid is proportional to its partial pressure.

Equation:

Oxygen and Carbon Dioxide Transport

Oxygen is transported by hemoglobin; carbon dioxide is transported in three forms: dissolved in plasma, as bicarbonate ions, and bound to hemoglobin.

• Oxygen loading/unloading: Influenced by temperature, pH, BPG, and .

• Carbon dioxide transport: Majority as bicarbonate () via the following reaction:

Equation:

Respiratory Centers and Regulation

Respiratory centers in the brain stem regulate breathing, integrating input from chemoreceptors and higher brain centers.

• Medullary respiratory centers: Control rhythm and rate of breathing.

• Chemoreceptors: Monitor blood levels of CO2, O2, and pH.

Exercise, Altitude, and Respiratory Adjustments

Exercise and high altitude require adjustments in respiratory function to meet increased oxygen demands and adapt to lower oxygen availability.

• Hyperventilation: Increased breathing rate during exercise.

• Acclimatization: Physiological adaptation to high altitude.

Respiratory Diseases

Chronic respiratory diseases are major causes of disability and death. Common conditions include chronic bronchitis, emphysema, asthma, tuberculosis, and lung cancer.

• Chronic bronchitis: Inflammation of bronchi, excess mucus production.

• Emphysema: Destruction of alveolar walls, reduced gas exchange.

• Asthma: Airway inflammation and constriction.

• Tuberculosis: Bacterial infection of the lungs.

• Lung cancer: Uncontrolled growth of abnormal cells in lung tissue.

Summary Table: Key Lymphatic and Respiratory Structures

Additional info: Academic context and definitions have been expanded for clarity and completeness. Equations and table entries are inferred from standard Anatomy & Physiology curriculum.