Lymphatic System

Functions of the Lymphatic System

The lymphatic system is essential for fluid balance, immune defense, and fat absorption. It returns fluids leaked from blood vessels back to the blood and provides structural bases for the immune system.

• Fluid Recovery: Hydrostatic and colloid osmotic pressures at blood capillaries force fluid out and reabsorb most, but up to 3 L daily becomes interstitial fluid.

• Lymphatic Vessels: Collect excess protein-containing interstitial fluid and return it to the blood; also transport pathogens to lymph nodes.

• Fat Absorption: Lymphatic capillaries in the small intestine, called lacteals, absorb and transport digested fats as chyle.

• Immune Surveillance: Lymphoid organs and tissues provide sites for immune cell activation and proliferation.

Lymphatic Vessels and Capillaries

Lymphatic capillaries are blind-ended vessels, more permeable than blood capillaries, and absent from bones and teeth. In the brain, astrocytes form channels for lymphatic drainage.

• Larger Lymphatic Vessels: Capillaries drain into collecting vessels, which have thinner walls, more valves, and anastomoses than veins.

• Lymphatic Trunks and Ducts: Nine major trunks; right lymphatic duct drains right upper limb and right side of head/thorax, thoracic duct drains the rest.

• Cisterna Chyli: Enlarged sac at the start of thoracic duct in about half of individuals.

• Flow Mechanisms: Skeletal muscle milking, thoracic pressure changes, arterial pulse waves, and smooth muscle contractions promote lymph flow.

• Lymphedema: Insufficient lymph return causes localized edema, often due to tumors or surgical removal.

Lymphoid Cells and Tissues

Lymphoid cells include immune system cells (T and B lymphocytes, macrophages, dendritic cells) and reticular cells that form the stroma of lymphoid organs.

• T Cells: Manage immune response; some directly attack infected cells.

• B Cells: Produce plasma cells that secrete antibodies.

• Macrophages: Phagocytize foreign substances and activate T cells.

• Dendritic Cells: Capture and deliver antigens to lymph nodes.

• Reticular Cells: Produce reticular fibers for structural support.

Lymphoid Tissues and Organs

Lymphoid tissues house and provide activation sites for lymphocytes. They are composed of loose reticular connective tissue.

• Diffuse Lymphoid Tissue: Loose arrangement found in most organs.

• Lymphoid Follicles: Solid, spherical bodies with tightly packed cells.

Primary Lymphoid Organs

• Red Bone Marrow: B cell maturation.

• Thymus: T cell maturation; most active in childhood, lacks follicles, functions strictly in T cell maturation.

Secondary Lymphoid Organs

• Lymph Nodes: Cleanse lymph and house lymphocytes; act as filters and sites for immune activation.

• Spleen: Largest lymphoid organ; site for lymphocyte proliferation, immune surveillance, stores platelets and monocytes, removes aged RBCs.

• MALT (Mucosa-Associated Lymphoid Tissue): Includes tonsils, Peyer's patches, appendix; guards entryways against pathogens.

Lymph Node Structure and Function

• Cortex: Abundant dendritic cells.

• Medulla: Contains B cells, T cells, plasma cells.

• Lymph Sinuses: Macrophages reside on reticular fibers.

• Circulation: Lymph enters via afferent vessels, exits via efferent vessels.

• Buboes: Infected, swollen lymph nodes (e.g., bubonic plague).

Spleen Structure and Function

• White Pulp: Immune function.

• Red Pulp: Destruction of old RBCs and pathogens.

• Splenectomy: Surgical removal; spleen can regenerate in children.

MALT and Associated Structures

• Tonsils: Trap debris and bacteria; build immune memory.

• Peyer's Patches: Clusters in distal small intestine; generate memory lymphocytes.

• Appendix: Contains lymphoid follicles.

Immune System

Overview and Lines of Defense

The immune system provides resistance to disease-causing microorganisms. It is a functional system using molecules and immune cells, especially lymphocytes.

• First Line: Surface barriers (skin, mucosa).

• Second Line: Innate internal defenses (inflammation, phagocytes, NK cells).

• Third Line: Adaptive (specific) defense system (lymphocytes, antibodies).

Innate Immunity

• Surface Barriers: Keratinized epidermis, protective chemicals (acid, enzymes, mucin, defensins).

• Phagocytes: Neutrophils (abundant, die fighting), macrophages (voracious, derived from monocytes).

• Phagocytosis Steps:

  1. Phagocyte binds particle.

  2. Particle enclosed in phagosome.

  3. Phagosome fuses with lysosome (phagolysosome).

  4. Opsonization: Pathogens coated with opsonins (complement proteins or antibodies) for easier phagocytosis.

• NK Cells: Kill cancer and virus-infected cells by inducing apoptosis.

• Inflammation: Triggered by injury; signs include redness, heat, swelling, pain.

• Inflammation Stages: Chemical release (histamine), vasodilation, increased permeability, phagocyte mobilization (leukocytosis, margination, diapedesis, chemotaxis).

• Pus: Mixture of dead neutrophils, tissue cells, pathogens.

• Antimicrobial Proteins: Interferons (IFNs) and complement proteins.

• Fever: Systemic response to infection; increases body temperature.

Adaptive Immunity

Adaptive immunity is specific, systemic, and has memory. It targets and eliminates pathogens and abnormal cells.

• Humoral Immunity: Antibody-mediated; antibodies produced by B cells circulate in body fluids.

• Cellular Immunity: T cells act directly or indirectly against target cells.

Antigens

• Definition: Substances that provoke an immune response; not normally found in the body.

• Complete Antigens: Have immunogenicity and reactivity.

• Haptens: Incomplete antigens; small molecules that become immunogenic when combined with proteins.

• Antigenic Determinants: Parts of antigen that antibodies bind to.

• Self-Antigens: MHC proteins; display self or foreign peptides.

Cells of Adaptive Immunity

• B Cells: Provide humoral immunity.

• T Cells: Provide cellular immunity.

• Antigen-Presenting Cells (APCs): Dendritic cells, macrophages, B cells; present antigens to T cells.

Lymphocyte Development and Activation

• Origin: Both B and T cells originate in red bone marrow.

• Maturation: Occurs in primary lymphoid organs; involves immunocompetence and self-tolerance.

• Seeding: Immunocompetent but naive cells colonize secondary lymphoid organs.

• Activation: Encounter with antigen triggers proliferation and differentiation into effector and memory cells.

T Cell Education

• Positive Selection: Ensures T cells recognize self MHC proteins.

• Negative Selection: Ensures T cells do not react to self antigens; those that do are destroyed (clonal deletion).

Humoral Immunity

• Primary Response: Lag period 3-6 days; peak antibody levels in 10 days.

• Secondary Response: Faster, stronger due to memory cells.

• Active Immunity: B cells encounter antigens and produce antibodies (naturally or artificially acquired).

• Passive Immunity: Ready-made antibodies introduced (e.g., antivenom).

• Antibody Mechanisms: PLAN: Precipitation, Lysis (via complement), Agglutination, Neutralization.

Cellular Immunity

• T Cells: CD4 (helper, regulatory), CD8 (cytotoxic).

• MHC Proteins: Present antigens to T cells; required for activation.

• Activation: Two-step process: antigen binding and co-stimulation.

• Cytokines: Chemical messengers that regulate immune responses.

• Helper T Cells: Activate B and T cells, secrete cytokines, amplify innate defenses.

• Cytotoxic T Cells: Directly attack and kill infected or abnormal cells.

• Regulatory T Cells: Dampen immune response, prevent autoimmunity.

Immune Disorders

• Immunodeficiency: SCID, Hodgkin's lymphoma, AIDS.

• Autoimmune Diseases: Rheumatoid arthritis, myasthenia gravis, multiple sclerosis, Graves' disease, type 1 diabetes, SLE, glomerulonephritis.

• Hypersensitivities: Allergies (immediate), anaphylactic shock, delayed hypersensitivity (e.g., contact dermatitis).

Respiratory System

Functions and Anatomy

The respiratory system is responsible for gas exchange, olfaction, and speech. It consists of upper and lower respiratory tracts.

• Upper Respiratory Tract: Nose, sinuses, pharynx.

• Lower Respiratory Tract: Larynx, trachea, bronchi, lungs.

Nose and Paranasal Sinuses

• Functions: Airway, moistens/warms air, filters, resonating chamber, olfactory receptors.

• Nasal Cavity: Lined with mucosa, vibrissae filter particles, conchae increase surface area.

• Paranasal Sinuses: Lighten skull, warm/moisten air, secrete mucus.

Pharynx

• Regions: Nasopharynx (airway), oropharynx (food/air), laryngopharynx (food/air).

• Tonsils: Palatine, lingual, pharyngeal, tubal.

Larynx

• Functions: Open airway, routes air/food, voice production.

• Cartilages: Nine total; eight hyaline, one elastic (epiglottis).

• Vocal Folds: True and false vocal cords; pitch and loudness determined by tension and airflow.

• Laryngitis: Inflammation of vocal folds.

Trachea

• Layers: Mucosa (goblet cells), submucosa (seromucous glands), adventitia (CT).

• Trachealis: Smooth muscle.

• Smoking: Destroys cilia; recovery possible after cessation.

• Heimlich Maneuver: Expels airway obstructions.

Bronchi and Subdivisions

• Bronchial Tree: 23 generations; conducting zone gives rise to respiratory zone.

• Epithelium: Thins, cilia/goblet cells sparse, smooth muscle increases.

• Alveoli: 300 million; site of gas exchange; surrounded by elastic fibers and capillaries.

• Respiratory Membrane: Thin, allows efficient gas exchange; surfactant reduces surface tension.

Lungs

• Structure: Apex, base, hilum, lobes (right: 3, left: 2), bronchopulmonary segments, lobules.

• Blood Supply: Pulmonary arteries (deoxygenated), pulmonary veins (oxygenated), bronchial arteries (systemic).

• Pleurae: Parietal and visceral layers; pleurisy and pleural effusion are disorders.

Pulmonary Ventilation

Pulmonary ventilation (breathing) consists of inspiration and expiration. Volume changes cause pressure changes, driving air movement.

• Boyle's Law: Relationship between pressure and volume of a gas:

• Inspiration: Diaphragm and intercostal muscles contract, increasing thoracic volume.

• Expiration: Muscles relax, thoracic volume decreases.

• Compliance: Ease of lung expansion; decreased in fibrosis, increased in emphysema.

• Surfactant: Reduces alveolar surface tension; deficiency causes infant respiratory distress syndrome.

Pulmonary Volumes and Capacities

• Tidal Volume (TV): Air moved per breath.

• Inspiratory Reserve Volume (IRV): Air forcibly inspired beyond TV.

• Expiratory Reserve Volume (ERV): Air forcibly expired beyond TV.

• Residual Volume (RV): Air remaining after maximal expiration.

• Capacities: Combinations of volumes (e.g., Inspiratory Capacity = TV + IRV).

Pulmonary Function Tests

• Spirometry: Measures FVC, FEV1; distinguishes obstructive vs. restrictive diseases.

• Dead Space: Anatomical and alveolar; total dead space affects alveolar ventilation.

Gas Exchange

• Pulmonary Gas Exchange: Diffusion between lungs and blood.

• Tissue Gas Exchange: Diffusion between blood and tissues.

• Dalton's Law: Total pressure is sum of partial pressures:

• Henry's Law: Gas dissolves in liquid proportional to partial pressure and solubility.

• Ventilation-Perfusion Coupling: Synchronizes air flow and blood flow.

Oxygen Transport

• 98.5% Bound to Hemoglobin: Each Hb has four polypeptide chains.

• Bohr Effect: Reduced affinity of Hb for O2 with falling pH and rising PCO2.

Carbon Dioxide Transport

• Dissolved in Plasma: 7-10%

• Bound to Hemoglobin: ~20%

• As Bicarbonate: ~70%; bicarbonate buffer system resists pH changes.

• Haldane Effect: Amount of CO2 transported is affected by PO2.

Hypoxia

• Types: Anemic, ischemic, histotoxic, hypoxemic.

• Carbon Monoxide Poisoning: Leading cause of death from fire.

Neural Control of Breathing

• Medullary Respiratory Centers: VRG (rhythm generation), DRG (integration).

• Pontine Centers: Modify VRG activity.

• Chemical Factors: PCO2 is strongest influence; hyperventilation can result from anxiety.

• Higher Brain Centers: Hypothalamic, limbic, cortical controls.

• Pulmonary Irritant Reflexes: Respond to dust, mucous, etc.

Respiratory Disorders

• Dyspnea: Labored breathing.

• Emphysema: Permanent enlargement of alveoli.

• Asthma: Coughing, wheezing, chest tightness.

• Tuberculosis: Infectious disease caused by bacteria.

• Lung Cancer: Leading cause of cancer death; most cases due to smoking.

• Sleep Apnea: Temporary cessation of breathing during sleep; obstructive and central types.

• Cystic Fibrosis: Most common lethal genetic disease in North America.

Summary Table: Lymphatic and Immune System Cells

Summary Table: Pulmonary Volumes and Capacities

Additional info: Academic context and expanded explanations were added to clarify mechanisms, cell types, and physiological processes. Tables were inferred and constructed for clarity and exam preparation.