Lymphatic System

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

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

• Lymphatic Vessels: Transport lymph, a fluid containing white blood cells, throughout the body.

• Lymph: Fluid derived from interstitial fluid that circulates through lymphatic vessels.

• Lymph Nodes: Small, bean-shaped structures that filter lymph and house lymphocytes.

• Functions: Returns excess tissue fluid to the bloodstream, absorbs fats from the digestive tract, and provides immune defense.

• Lymph Transport: Movement of lymph is aided by skeletal muscle contraction, respiratory movements, and valves preventing backflow.

Additional info: Lymphatic capillaries are highly permeable and allow the uptake of large molecules and particles.

20.2 Lymphoid Cells and Tissues

Lymphoid cells are found in lymphoid organs and connective tissue throughout the body. These cells are essential for immune responses.

• Lymphocytes: Main cells of the immune system, including B cells and T cells.

• Macrophages: Phagocytic cells that engulf pathogens and debris.

• Follicular vs. Diffuse Lymphoid Tissue: Follicular tissue contains densely packed lymphocytes, while diffuse tissue is less organized.

Additional info: Lymphoid organs include the spleen, thymus, tonsils, and MALT (mucosa-associated lymphoid tissue).

20.3 Lymph Nodes: Structure and Function

Lymph nodes filter lymph and are sites where immune responses are initiated.

• Structure: Consist of a capsule, cortex (with follicles), and medulla.

• Function: Remove pathogens and debris from lymph; house lymphocytes for immune surveillance.

20.4 Spleen and Lymph Nodes: Comparison

The spleen and lymph nodes are both lymphoid organs but have distinct roles.

• Spleen: Filters blood, removes 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.

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

• Function: Guards entryways to the body against pathogens.

20.6 Thymus and T Lymphocyte Maturation

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

• Structure: Located in the mediastinum, prominent in children.

• Function: T cells mature and become immunocompetent in the thymus.

Immune System

21.1 Surface Barriers: First Line of Defense

Surface barriers such as skin and mucous membranes prevent pathogens from entering the body.

• Physical Barriers: Skin, mucous membranes.

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

21.2 Innate Internal Defenses: Cells and Chemicals

Innate defenses include cells and chemicals that act as the second line of defense.

• Phagocytes: Neutrophils and macrophages engulf pathogens.

• Natural Killer Cells: Destroy infected or abnormal cells.

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

• Antimicrobial Proteins: Interferons and complement proteins.

21.3 Antigens and Adaptive Defenses

Antigens are substances that trigger adaptive immune responses.

• Antigen: Any substance that can provoke an immune response.

• Adaptive Defenses: Include humoral (antibody-mediated) and cellular (T cell-mediated) immunity.

21.4 B and T Lymphocytes and Antigen-Presenting Cells

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

• B Cells: Produce antibodies; mature in bone marrow.

• T Cells: Attack infected cells; mature in thymus.

• Antigen-Presenting Cells (APCs): Include dendritic cells, macrophages, and B cells.

21.5 Antibodies and Humoral Immunity

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

• Antibody Structure: Y-shaped proteins with variable and constant regions.

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

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

21.6 Cellular Immunity: T Cells

Cellular immunity involves T lymphocytes that target infected or abnormal cells.

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

• Functions: Directly kill infected cells, activate other immune cells.

Respiratory System

22.1 Upper Respiratory System: Warming, Humidifying, Filtering Air

The upper respiratory system prepares air for entry into the lungs by warming, humidifying, and filtering it.

• Structures: Nose, paranasal sinuses, pharynx.

• Protective Mechanisms: Mucus, cilia, and nasal hairs trap particles.

22.2 Lower Respiratory System: Conducting and Respiratory Zones

The lower respiratory system includes the larynx, trachea, bronchi, and lungs, divided into conducting and respiratory zones.

• Conducting Zone: Passages that transport air (larynx, trachea, bronchi).

• Respiratory Zone: Sites of gas exchange (respiratory bronchioles, alveoli).

22.3 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 and allows smooth movement of lungs.

22.4 Volume Changes and Air Movement

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

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

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

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

22.5 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 maximum inhalation.

• Spirometry: Technique to measure lung volumes and capacities.

22.6 Gas Exchange: Diffusion Between Blood, Lungs, and Tissues

Gas exchange occurs by diffusion, governed by Dalton's and Henry's laws.

• 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.

• External Respiration: Exchange of gases between alveoli and blood.

• Internal Respiration: Exchange of gases between blood and tissues.

22.7 Oxygen and Carbon Dioxide Transport

Oxygen is transported by hemoglobin, and carbon dioxide is carried in three forms.

• Oxygen Transport: Most oxygen binds to hemoglobin in red blood cells.

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

• Equation for Bicarbonate Formation:

• 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, with input from chemoreceptors and higher brain centers.

• Medullary Respiratory Centers: Control rhythm and rate of breathing.

• Chemoreceptors: Detect changes in blood CO2, O2, and pH.

22.9 Exercise and High Altitude: Respiratory Adjustments

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

• Hyperpnea: Increased ventilation in response to exercise.

• Acclimatization: Physiological adaptation to high altitude.

22.10 Respiratory Diseases

Respiratory diseases are major causes of disability and death worldwide.

• Chronic Bronchitis: Inflammation of bronchi, excessive 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 the lungs.