The Lymphatic and Respiratory Systems: Comprehensive Study Notes

The Lymphatic System and Immunity

Overview of the Lymphatic System

• Two Main Components: The lymphatic vessels and lymphoid tissues/organs.

• Basic Functions:

  • Return excess interstitial fluid to the bloodstream.

  • Absorb dietary fats from the digestive tract (via lacteals).

  • Provide immune defense against pathogens.

Lymph and Lymphatic Circulation

• Lymph: The fluid transported by lymphatic vessels, derived from interstitial fluid.

• Characteristics:

  • Location: Found within lymphatic vessels and tissues.

  • Production: Formed as plasma leaks from capillaries into tissues, becoming interstitial fluid, then entering lymphatic capillaries.

  • Content: Contains water, proteins, lipids, and immune cells.

  • Movement: Enters lymphatic capillaries due to pressure gradients and one-way valves.

Lymphatic Vessels and Capillaries

• Structure: Thin-walled vessels with valves, similar to small veins but with more valves and thinner walls.

• Function: Collect and transport lymph toward the heart.

• Lymphatic Capillaries: Highly permeable, overlapping endothelial cells allow entry of fluid, proteins, and cells.

• Lacteals: Specialized lymphatic capillaries in the small intestine that absorb dietary fats.

Lymphatic Ducts and Drainage

• Thoracic Duct: Drains lymph from most of the body into the left subclavian vein.

• Right Lymphatic Duct: Drains lymph from the right upper limb, right side of head and thorax into the right subclavian vein.

• Cisterna Chyli: A dilated sac at the lower end of the thoracic duct, located in the abdomen; collects lymph from the lower limbs and intestines.

Lymphedema

• Definition: Swelling due to accumulation of lymph, often from obstruction or removal of lymphatic vessels.

• Causes: Surgical removal of lymph nodes, infection (e.g., filariasis), or trauma.

Lymphoid Tissue and Organs

• Lymphoid Tissue: Reticular connective tissue housing lymphocytes and other immune cells.

• Main Cell Types: Lymphocytes (B and T cells), macrophages, dendritic cells.

• MALT (Mucosa-Associated Lymphoid Tissue): Lymphoid tissue in mucosal linings (e.g., tonsils, Peyer's patches, appendix).

• Peyer's Patches: Aggregates of lymphoid tissue in the small intestine.

• Tonsils: Three main groups—pharyngeal (adenoids), palatine, and lingual—located in the pharynx and oral cavity.

• Appendix: Lymphoid organ attached to the cecum; involved in immune surveillance of the gut.

• Appendicitis: Inflammation of the appendix, which can lead to rupture and peritonitis.

Lymph Nodes, Spleen, and Thymus

• Lymph Nodes: Small, bean-shaped structures that filter lymph and house immune cells; located along lymphatic vessels.

• Spleen: Located in the upper left abdomen; filters blood, recycles old red blood cells, and mounts immune responses.

• Red Pulp vs. White Pulp: Red pulp filters blood and removes old erythrocytes; white pulp contains lymphocytes for immune function.

• Thymus: Located in the mediastinum; site of T cell maturation. Larger in children, shrinks with age.

Immunity and Immune Responses

• Three Lines of Defense:

  1. Surface barriers (skin, mucous membranes)

  2. Innate (nonspecific) immunity (cells, inflammation, complement)

  3. Adaptive (specific) immunity (B and T lymphocytes)

• Innate vs. Adaptive Immunity:

  • Innate: Rapid, nonspecific, no memory (e.g., phagocytes, NK cells, inflammation).

  • Adaptive: Slower, specific, memory (B and T cells, antibodies).

• Surface Barriers: Skin and mucosa prevent pathogen entry; pathogens may evade via enzymes or toxins.

• Immune Cells:

  • Agranulocytes: B and T lymphocytes (adaptive immunity), monocytes (become macrophages).

  • Granulocytes: Neutrophils, eosinophils, basophils (innate immunity).

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

  • Dendritic Cells: Antigen-presenting cells linking innate and adaptive immunity.

  • Macrophages: Phagocytose pathogens and present antigens.

• Complement System: Plasma proteins that enhance phagocytosis, inflammation, and cell lysis.

• Cytokines: Signaling proteins (e.g., interferons, interleukins) that regulate immune responses.

• Inflammation: Triggered by infection or injury; benefits include containment and destruction of pathogens. Four cardinal signs: redness, heat, swelling, pain. Anti-inflammatory drugs inhibit mediators of inflammation.

• Phagocyte Response: Phagocytes migrate to site, ingest pathogens, and present antigens.

• Fever: Elevated body temperature induced by pyrogens; controlled by the hypothalamus. Benefits: inhibits pathogens, enhances immune response. Risks: tissue damage at high temperatures.

Adaptive Immunity: Cell-Mediated and Humoral Responses

• Branches: Cell-mediated (T cells) and humoral (B cells/antibodies).

• Targets: Cell-mediated targets infected or abnormal cells; humoral targets extracellular pathogens.

• Antigens: Substances that elicit immune responses; self-antigens are normal body molecules, foreign antigens are from pathogens. Haptens are small molecules that become antigenic when attached to proteins.

• T Lymphocytes: Produced in bone marrow, mature in thymus. Selection ensures immunocompetence and self-tolerance.

• Major Histocompatibility Complex (MHC):

  • Class I: On all nucleated cells; present to cytotoxic T cells.

  • Class II: On antigen-presenting cells; present to helper T cells.

• T Cell Activation: Involves antigen presentation, clonal selection, and differentiation into effector and memory cells.

• Helper T Cells: Activate B cells, cytotoxic T cells, and macrophages.

• Cytotoxic T Cells: Destroy infected or abnormal cells; responsible for transplant rejection.

• B Lymphocytes: Produced and mature in bone marrow. Activation leads to plasma cells (antibody production) and memory cells.

• Immunoglobulins (Antibodies): Five classes—IgG, IgA, IgM, IgE, IgD—each with specific functions (e.g., neutralization, agglutination, complement activation).

• Immunological Memory: Memory cells enable faster, stronger secondary responses.

• Vaccination: Artificial exposure to antigens induces active immunity and memory cell formation.

• Active vs. Passive Immunity: Active (natural or artificial) involves memory cell production; passive (e.g., maternal antibodies, antiserum) does not.

• Immune Responses: Distinct responses to bacteria (antibody-mediated) and cancer cells (cell-mediated).

• Autoimmune Disorders: Immune system attacks self-tissues (e.g., type 1 diabetes, rheumatoid arthritis).

• HIV: Infects and destroys helper T cells, leading to immunodeficiency.

The Respiratory System

Overview and Functions

• Structures: Divided into upper (nose, nasal cavity, pharynx) and lower (larynx, trachea, bronchi, lungs) respiratory tracts.

• Functional Zones:

  • Conducting Zone: Air passageways (nose to terminal bronchioles).

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

• Respiration: The process of gas exchange; involves pulmonary ventilation, external respiration, transport of gases, and internal respiration.

• Functions: Gas exchange, pH regulation, voice production, olfaction, and protection.

Upper Respiratory Tract

• Nasal Cavity: Contains nasal conchae (superior, middle, inferior) that increase surface area and turbulence; olfactory mucosa for smell.

• Paranasal Sinuses: Four pairs—frontal, maxillary, ethmoid, sphenoid; lighten skull, warm and moisten air.

• Nasopharynx Structures: Soft palate/uvula (close nasopharynx during swallowing), pharyngeal tonsil (immune function), pharyngotympanic tube (equalizes ear pressure).

• Oropharynx Tonsils: Palatine and lingual tonsils; located at the back of the oral cavity and base of tongue.

• Epiglottis: Flap of cartilage that prevents food from entering the larynx during swallowing.

Lower Respiratory Tract

• Larynx: Made of three unpaired (thyroid, cricoid, epiglottis) and three paired (arytenoid, corniculate, cuneiform) cartilages. Contains vestibular (false vocal) and vocal (true vocal) folds for sound production; pitch and loudness depend on tension and force of air.

• Trachea: Supported by C-shaped cartilage rings (open posteriorly for esophageal expansion); lined by pseudostratified ciliated columnar epithelium for mucus transport. Carina marks the tracheal bifurcation.

• Bronchial Tree: Air passes from trachea → primary bronchi → secondary bronchi → tertiary bronchi → bronchioles → terminal bronchioles. Histological changes: decreasing cartilage, increasing smooth muscle, changing epithelium. Smooth muscle regulates airway diameter.

• Respiratory Zone: Includes respiratory bronchioles, alveolar ducts, alveoli. Type I alveolar cells (gas exchange), Type II cells (surfactant production), alveolar macrophages (defense). Respiratory membrane: alveolar epithelium, fused basement membrane, capillary endothelium. Oxygen diffuses into blood; CO2 diffuses into alveoli.

Lungs and Pleurae

• Lobes: Right lung (3 lobes), left lung (2 lobes).

• Hilum: Entry/exit for bronchi, blood vessels, lymphatics, nerves.

• Bronchopulmonary Segments: Functionally independent regions supplied by tertiary bronchi.

• Pleurae: Double-layered serous membranes (parietal and visceral); pleural cavity contains serous fluid for lubrication and lung inflation.

Pulmonary Ventilation

• Definition: Movement of air into and out of the lungs.

• Phases: Inspiration and expiration.

• Boyle's Law: $P_1V_1 = P_2V_2$ (Pressure and volume are inversely related at constant temperature).

• Pressure Gradients: Atmospheric, intrapulmonary, and intrapleural pressures drive ventilation.

• Lung Inflation: Maintained by negative intrapleural pressure and surfactant.

• Muscles: Diaphragm and external intercostals for quiet inspiration; expiration is passive. Forced breathing uses accessory muscles.

• Airflow Determinants: Airway resistance, lung compliance, alveolar surface tension.

• Surfactant: Produced by Type II alveolar cells; reduces surface tension, preventing alveolar collapse.

• Compliance: Ease of lung expansion; decreased by fibrosis or low surfactant.

Pulmonary Volumes and Capacities

• Pulmonary Volumes:

  • Tidal Volume (TV): Air moved per breath (~500 mL).

  • Inspiratory Reserve Volume (IRV): Extra air inhaled after normal inspiration.

  • Expiratory Reserve Volume (ERV): Extra air exhaled after normal expiration.

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

• Capacities:

  • Vital Capacity (VC): $VC = TV + IRV + ERV$

  • Functional Residual Capacity (FRC): $FRC = ERV + RV$

• Minute Volume: $MV = TV \times \text{respiratory rate}$

• Alveolar Ventilation Rate: Volume of air reaching alveoli per minute.

• Anatomical Dead Space: Air in conducting zone not involved in gas exchange.

Gas Exchange and Transport

• Pulmonary Gas Exchange: Between alveoli and blood; tissue gas exchange is between blood and tissues.

• Partial Pressure: Pressure exerted by a single gas in a mixture; $P_{gas} = \text{fraction} \times \text{total pressure}$

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

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

• Gas Solubility: CO2 > O2 > N2 in water.

• Ventilation-Perfusion Matching: Ensures efficient gas exchange by matching airflow and blood flow.

• Oxygen Transport: 98.5% bound to hemoglobin (Hb), 1.5% dissolved in plasma. Oxyhemoglobin (HbO2) vs. deoxyhemoglobin (HHb).

• Percent Saturation: Proportion of Hb bound to O2; depends on PO2.

• Factors Affecting Hb-O2 Affinity: pH, temperature, PCO2, 2,3-BPG.

• CO2 Transport: Dissolved in plasma, as carbaminohemoglobin, or as bicarbonate (HCO3-).

• Bicarbonate Formation: $CO_2 + H_2O \rightarrow H_2CO_3 \rightarrow H^+ + HCO_3^-$

• Blood pH: Increased CO2 lowers pH (acidosis); decreased CO2 raises pH (alkalosis).

Ventilatory Control and Disorders

• Neural Control: Medullary respiratory centers (ventral and dorsal groups), pontine centers.

• Chemoreceptors: Central (medulla, sensitive to CO2/H+ in CSF), peripheral (carotid/aortic bodies, sensitive to O2, CO2, H+ in blood).

• Stimuli Affecting Breathing: Increased PCO2 or H+ increases rate/depth; decreased PO2 stimulates breathing if severe.

• Hyperventilation: Excessive ventilation; causes hypocapnia and respiratory alkalosis.

• Hypoventilation: Inadequate ventilation; causes hypoxemia, hypercapnia, and respiratory acidosis.

• Lung Diseases: Restrictive (reduced compliance, e.g., fibrosis) vs. obstructive (increased resistance, e.g., asthma).

Immunity Type	How Acquired	Memory Cells Produced?	Example
Active Natural	Infection/exposure	Yes	Chickenpox infection
Active Artificial	Vaccination	Yes	MMR vaccine
Passive Natural	Maternal antibodies	No	Placental IgG, breast milk IgA
Passive Artificial	Injection of antibodies	No	Antivenom, rabies immunoglobulin

Additional info: Some explanations and examples were expanded for clarity and completeness based on standard anatomy and physiology textbooks.