Lymphatic System

20.1 The Lymphatic System: Vessels, Lymph, and Lymph Nodes

The lymphatic system is a network of vessels, nodes, and organs that returns excess tissue fluid to the bloodstream and provides immune defense.

• Functions of Lymphatic Vessels: Return interstitial fluid and leaked plasma proteins to the blood, transport dietary fats, and facilitate immune responses.

• Structure and Distribution: Lymphatic vessels begin as blind-ended capillaries in tissues, merge into larger vessels, and eventually drain into the venous system.

• Lymph Transport: Lymph is moved by skeletal muscle contraction, pressure changes during breathing, and valves that prevent backflow.

20.2 Lymphoid Cells and Tissues

Lymphoid cells (lymphocytes, macrophages, dendritic cells) are found in lymphoid organs and connective tissues, providing immune surveillance and response.

• Basic Structure: Lymphoid tissue consists of reticular connective tissue with clusters of lymphocytes.

• Cellular Population: Includes B cells, T cells, macrophages, and dendritic cells.

• Diffuse vs. Follicular Tissue: Diffuse lymphoid tissue is scattered, while follicles are dense, spherical bodies often found in lymph nodes and spleen.

20.3 Lymph Nodes

Lymph nodes filter lymph and house lymphocytes, playing a crucial role in immune defense.

• Structure: Bean-shaped with a cortex (containing follicles) and medulla (containing medullary cords).

• Function: Filter lymph for pathogens and activate lymphocytes for immune response.

20.4 Spleen and Lymph Nodes: Comparison

The spleen and lymph nodes are major lymphoid organs with distinct structures and functions.

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

• Lymph Nodes: Filter lymph and initiate immune responses.

20.5 MALT (Mucosa-Associated Lymphoid Tissue)

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

• Definition: MALT is lymphoid tissue associated with mucous membranes throughout the body.

• Main Components: Tonsils, Peyer's patches (in the small intestine), and the appendix.

20.6 Thymus and T Lymphocyte Maturation

The thymus is the site of T lymphocyte maturation, essential for adaptive immunity.

• Structure: Bilobed organ in the mediastinum, prominent in children and atrophies with age.

• Function: Provides an environment for T cell maturation and selection.

Immune System: Innate and Adaptive Defenses

21.1 Surface Barriers

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

• Protective Functions: Physical barrier, secretion of antimicrobial substances, and trapping of microbes.

21.2 Innate Internal Defenses

Cells and chemicals provide a second line of defense when pathogens breach surface barriers.

• Phagocytes: Engulf and destroy pathogens (e.g., macrophages, neutrophils).

• Natural Killer (NK) Cells: Destroy infected or abnormal cells.

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

• Antimicrobial Proteins: Interferons and complement proteins enhance defense mechanisms.

• Fever: Elevated body temperature inhibits pathogen growth and enhances immune response.

21.3 Antigens and Adaptive Defenses

Antigens are substances that trigger adaptive immune responses, leading to the production of specific antibodies or activation of T cells.

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

• Antigenic Determinants: Specific regions of an antigen recognized by immune cells.

21.4 B and T Lymphocytes and Antigen-Presenting Cells

B and T lymphocytes are central to adaptive immunity, with antigen-presenting cells (APCs) facilitating their activation.

• B Cells: Produce antibodies and mediate humoral immunity.

• T Cells: Mediate cellular immunity, including helper, cytotoxic, and regulatory T cells.

• APCs: Include dendritic cells, macrophages, and B cells; present antigens to T cells.

• Immunocompetence and Self-Tolerance: Lymphocytes must recognize antigens and not react to self-antigens.

21.5 Antibodies and Humoral Immunity

Antibodies are proteins produced by B cells that target extracellular antigens.

• Antibody Structure: Y-shaped molecules with variable regions for antigen binding.

• Antibody Classes: IgG, IgM, IgA, IgD, IgE.

• Active vs. Passive Immunity: Active immunity results from exposure to antigen; passive immunity is acquired from another source (e.g., maternal antibodies).

21.6 Cellular Immunity and T Cells

T lymphocytes mediate cellular immunity by directly attacking infected or abnormal cells.

• Types of T Cells: Helper T cells (CD4+), cytotoxic T cells (CD8+), regulatory T cells.

• Functions: Coordinate immune response, kill infected cells, and regulate immune activity.

Respiratory System

22.1 Upper Respiratory System

The upper respiratory system warms, humidifies, and filters air before it reaches the lungs.

• Structures: Nose, paranasal sinuses, pharynx.

• Functions: Air filtration, humidification, and protection from pathogens.

22.2 Lower Respiratory System

The lower respiratory system conducts air to the lungs and facilitates gas exchange.

• Structures: Larynx, trachea, bronchi, bronchioles, alveoli.

• Conducting vs. Respiratory Zones: Conducting zone transports air; respiratory zone is where gas exchange occurs.

22.3 Pleural Cavities

Each lung is enclosed in its own pleural cavity, which reduces friction and aids lung expansion.

• Pleura: Double-layered membrane (parietal and visceral pleura) with pleural fluid in between.

22.4 Volume Changes and Pulmonary Ventilation

Changes in thoracic volume cause pressure changes that drive air movement.

• Boyle's Law: (Pressure and volume are inversely related at constant temperature.)

• Inspiration and Expiration: Diaphragm and intercostal muscles change thoracic volume, altering pressure to move air in and out.

• Lung Compliance and Elasticity: Affect the ease of lung expansion and recoil.

22.5 Measuring Respiratory Volumes and Capacities

Respiratory volumes and capacities are measured to assess lung function.

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

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

• Spirometry: Technique to measure lung volumes and capacities.

22.6 Gas Exchange

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

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

• Henry's Law: The amount of gas dissolved in a liquid is proportional to its partial pressure and solubility.

• External Respiration: Gas exchange between alveoli and blood.

• Internal Respiration: Gas exchange between blood and tissues.

22.7 Oxygen and Carbon Dioxide Transport

Oxygen is transported mainly by hemoglobin, while carbon dioxide is transported in three forms.

• Oxygen Transport: Most oxygen binds to hemoglobin; a small amount is dissolved in plasma.

• Carbon Dioxide Transport: Dissolved in plasma, bound to hemoglobin, or as bicarbonate ions ().

• Factors Affecting Oxygen Loading/Unloading: Temperature, pH, BPG, and .

22.8 Respiratory Centers in the Brain Stem

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

• Neural Control: Medullary and pontine centers control rhythm and depth of breathing.

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

• Influences: Emotions, voluntary control, and reflexes can modify breathing patterns.

22.9 Exercise and High Altitude

Exercise and high altitude require respiratory adjustments to meet increased oxygen demands or decreased oxygen availability.

• Exercise: Increases ventilation and oxygen delivery to tissues.

• High Altitude: Triggers acclimatization, including increased red blood cell production and ventilation.

22.10 Respiratory Diseases

Respiratory diseases are major causes of disability and death, affecting gas exchange and lung function.

• Chronic Bronchitis: Inflammation of bronchi, excessive mucus production.

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

• Asthma: Reversible airway constriction and inflammation.

• Tuberculosis: Infectious disease caused by Mycobacterium tuberculosis.

• Lung Cancer: Uncontrolled cell growth in lung tissue.