Respiratory System Lecture Flashcards

Overview of the Respiratory System and Cellular Metabolism

• Aerobic Metabolism: The primary method by which cells obtain energy.     * Requires a constant supply of oxygen ($O_{2}$).     * Produces carbon dioxide ($CO_{2}$) as a byproduct.

• Gas Exchange and Transport:     * Oxygen is obtained from the atmospheric air through diffusion across exchange surfaces in the lungs.     * The blood functions as the transport medium:         * Carries $O_{2}$ from the lungs to peripheral tissues.         * Carries $CO_{2}$ from peripheral tissues back to the lungs.

Functions of the Respiratory System

• Extensive Surface Area: Provides a large area for gas exchange between the air and the circulating blood.

• Air Movement: Facilitates the movement of air to and from the exchange surfaces of the lungs.

• Protection: Safeguards respiratory surfaces from dehydration, temperature fluctuations, and various pathogens.

• Sound Production: Enables the production of sounds for communication.

• Olfactory Detection: Detects odors via olfactory receptors located in the nasal cavity.

Organization and Structure of the Respiratory System

• Upper Respiratory System: Includes the nose, nasal cavity, paranasal sinuses, and pharynx.

• Lower Respiratory System: Includes the larynx, trachea, bronchi, bronchioles, and alveoli.

• The Respiratory Tract:     * Conducting Portion: Extends from the nasal cavity to the larger bronchioles.     * Respiratory Portion: Includes the smallest respiratory bronchioles and the alveoli.

• Alveoli:     * Air-filled pockets within the lungs.     * The site where all gas exchange occurs.

The Respiratory Mucosa and Defense System

• Respiratory Mucosa: Lines the conducting portion of the system.     * Structure: Consists of an epithelium and an underlying areolar tissue layer known as the lamina propria.

• Lamina Propria Variations:     * Upper System, Trachea, and Bronchi: Contains mucous glands that discharge secretions onto the epithelial surface.     * Lower System (Conducting Portion): Contains smooth muscle cells that encircle the lumen of the bronchioles.

• Epithelial Structure by Region:     * Nasal Cavity and Superior Pharynx: Pseudostratified ciliated columnar epithelium with numerous mucous cells.     * Inferior Pharynx: Stratified squamous epithelium.     * Superior Lower Respiratory System: Pseudostratified ciliated columnar epithelium.     * Smaller Bronchioles: Cuboidal epithelium with scattered cilia.     * Alveolar Epithelium: Very delicate, simple squamous epithelium (exchange surfaces) with scattered specialized cells.

• Respiratory Defense System Mechanisms:     * Filtration: Large particles are removed in the nasal cavity.     * Mucus Production: Mucous cells and glands produce mucus to bathe exposed surfaces.     * Cilia: Sweep mucus, trapped debris, and microorganisms toward the pharynx for swallowing.     * Alveolar Macrophages: Engulf small particles that reach the deep lung tissue.

Anatomy of the Upper Respiratory System

• The Nose:     * Primary passageway for air entry through nostrils (nares).     * Nasal Vestibule: Space within the flexible tissues of the nose; contains nasal hairs to trap large particles.

• The Nasal Cavity:     * Nasal Septum: Divides the cavity into left and right sides; the anterior portion is hyaline cartilage.     * Olfactory Region: Superior portion providing the sense of smell.     * Conditioning: Mucus from paranasal sinuses and tears clean and moisten the cavity.

• Air Flow and Turbulence:     * Air flows from the vestibule to the choanae (openings).     * Passes through superior, middle, and inferior nasal meatuses (narrow passageways).     * Meatuses produce air turbulence to trap particles in mucus, warm/humidify air, and bring stimuli to olfactory receptors.

• The Palates:     * Hard Palate: Floor of the nasal cavity; separates nasal and oral cavities.     * Soft Palate: Posterior to the hard palate; divides the superior nasopharynx from the rest of the pharynx.

• Nasal Mucosa: Crucial for warming and humidifying air; mouth breathing bypasses this conditioning.

• Nosebleeds: Common due to extensive vascularization.

• The Pharynx: Shared chamber for digestive and respiratory systems.     * Nasopharynx: Superior portion; contains pharyngeal tonsil and auditory tube openings.     * Oropharynx: Connects directly to the oral cavity.     * Laryngopharynx: Inferior portion; between hyoid bone and entrance to larynx/esophagus.

Anatomy and Mechanics of the Larynx

• The Glottis: Slit-like opening between vocal cords; air flows from pharynx to larynx through it.

• Unpaired Laryngeal Cartilages:     1. Thyroid Cartilage: Hyaline cartilage; forms anterior and lateral walls; features the laryngeal prominence (Adam’s apple).     2. Cricoid Cartilage: Hyaline cartilage; forms posterior portion; articulates with arytenoid cartilages.     3. Epiglottis: Elastic cartilage; covers the glottis during swallowing to prevent food/liquid entry.

• Paired Laryngeal Cartilages: Arytenoid, Corniculate, and Cuneiform (all hyaline).     * Arytenoid and Corniculate cartilages function in opening/closing the glottis and sound production.

• Ligaments and Folds:     * Vestibular Ligaments: Lie within vestibular folds; protect delicate vocal folds.     * Vocal Ligaments: Covered by vocal folds (vocal cords); involved in sound production.

• Sound Production Mechanisms:     * Phonation: Sound production at the larynx via air vibrating vocal folds.     * Articulation: Sound modification by tongues, teeth, and lips.     * Pitch Control: Voluntary muscles reposition arytenoid cartilages to alter vocal fold tension.

• Laryngeal Muscles:     * Neck and pharynx muscles stabilize the larynx.     * Intrinsic muscles control fold tension and glottis movement.

The Trachea and Bronchial Tree

• Trachea (Windpipe):     * Extends from cricoid cartilage to the mediastinum.     * Contains $15$ to $20$ C-shaped tracheal cartilages to stiffen walls.     * Discontinuous at the esophagus to allow for swallowing distortion.     * Trachealis Muscle: Connects the ends of the tracheal cartilages.

• Bronchial Tree Structure:     * Carina: Ridge separating the right and left main bronchi.     * Main Bronchi: Branch into lobar bronchi (supply lobes), then segmental bronchi (supply bronchopulmonary segments).     * Segments: Right lung has $10$; Left lung has $8$ or $9$.

• Bronchial Composition: Walls contain progressively less cartilage and more smooth muscle as they branch.

• Bronchitis: Inflammation/constriction of bronchi due to infection.

Bronchioles and Alveoli

• Bronchioles: Lack cartilage; dominated by smooth muscle.     * Segmental bronchi branch into multiple bronchioles, then into roughly $6500$ terminal bronchioles.

• Autonomic Control:     * Bronchodilation: Sympathetic activation; increases luminal diameter and reduces resistance.     * Bronchoconstriction: Parasympathetic activation or histamine release; reduces diameter.     * Asthma: Excessive smooth muscle stimulation causing severe bronchoconstriction.

• Alveolar Structure:     * Respiratory bronchioles connect to alveoli via alveolar ducts ending in alveolar sacs.     * Pneumocytes Type I: Thin simple squamous epithelium; site of gas exchange.     * Pneumocytes Type II: Produce surfactant.     * Surfactant: Oily secretion of phospholipids and proteins; reduces surface tension to prevent alveolar collapse.     * Respiratory Distress Syndrome: Alveolar collapse due to inadequate surfactant.

• Blood Air Barrier: Consists of alveolar cell layer, capillary endothelial layer, and fused basement membrane.     * Exchange is efficient because distance is short and gases ($O_{2}$, $CO_{2}$) are small and lipid-soluble.     * Pneumonia: Inflammation causing fluid leakage into alveoli, compromising the barrier.

Gross Anatomy and Blood Supply of the Lungs

• Lung Characteristics:     * Left Lung: Two lobes (Superior, Inferior); separated by oblique fissure; features the cardiac notch; longer than the right.     * Right Lung: Three lobes (Superior, Middle, Inferior); separated by horizontal and oblique fissures; wider; displaced upward by the liver.

• Hilum: Entry/exit point for pulmonary vessels, nerves, and lymphatics.

• Root: Dense connective tissue anchoring the lung to the mediastinum.

• Trabeculae and Septa: Fibrous partitions dividing lobes into pulmonary lobules.

• Blood Supply:     * Pulmonary Arteries: Carry deoxygenated blood to exchange surfaces.     * Pulmonary Veins: Carry oxygen-rich blood to the left atrium.     * Bronchial Arteries: Provide oxygen and nutrients to conducting passageways.

• Pulmonary Embolism: Blockage of a pulmonary artery branch stopping flow to lobules.

Pleural Cavities and Respiratory Physiology

• Pleura: Serous membrane with two layers.     * Parietal Pleura: Lines the inner thoracic wall.     * Visceral Pleura: Covers the outer lung surface.     * Pleural Fluid: Lubricates the space between layers.

• Respiration Processes:     1. External Respiration: Exchange of gases with the external environment.         * Steps: Pulmonary ventilation, gas diffusion, and transport.     2. Internal Respiration: Uptake of $O_{2}$ and release of $CO_{2}$ by cells (cellular respiration).

• Abnormal States:     * Hypoxia: Low tissue oxygen levels.     * Anoxia: Complete lack of oxygen in tissues.

Mechanics of Pulmonary Ventilation

• Boyle’s Law: Defines pressure-volume relationship: $P = 1/V$.     * External pressure forces molecules closer together; volume change creates pressure change.

• Pressure and Airflow: Air flows from higher pressure to lower pressure.

• Respiratory Cycle: Consists of one inspiration and one expiration.

• Respiratory Muscles:     * Primary: Diaphragm (provides $75\%$ of normal air movement) and External Intercostals ($25\%$).     * Accessory Inhalation: Sternocleidomastoid, scalenes, pectoralis minor, serratus anterior.     * Accessory Exhalation: Internal intercostals, transversus thoracis, abdominal muscles.

• Breathing Patterns:     * Quiet Breathing (Eupnea): Active inhalation, passive exhalation.         * Diaphragmatic (Deep): Dominated by diaphragm.         * Costal (Shallow): Dominated by rib cage.     * Forced Breathing (Hyperpnea): Active inhalation and exhalation involving accessory muscles.

• Elastic Rebound: Recoil of tissues during relaxation that returns the thoracic cage to its original position.

Pressure Variations and Lung Compliance

• Atmospheric Pressure: Standard is $1\,atm = 760\,mm\,Hg$.

• Intrapulmonary Pressure: Intra-alveolar pressure.     * Relaxed breathing differential: $-1\,mm\,Hg$ (inhalation) to $+1\,mm\,Hg$ (exhalation).     * Maximum capacity straining: $-30\,mm\,Hg$ to $+100\,mm\,Hg$.

• Intrapleural Pressure: Pressure in the space between pleurae; averages $-4\,mm\,Hg$ (reaches $-18\,mm\,Hg$ during powerful inhalation).     * Creates the Respiratory Pump assisting venous return.

• Pneumothorax: Air entering the pleural cavity leading to atelectasis (collapsed lung).

• Compliance: Measure of lung expandability.     * Affected by connective tissue, surfactant, and thoracic cage mobility.

Respiratory Rates, Volumes, and Capacities

• Tidal Volume ($V_{T}$): Air moved in/out per breath.

• Respiratory Rate: Number of breaths per minute.

• Respiratory Minute Volume ($V_{E}$): $V_{E} = \text{Respiratory Rate} \times V_{T}$.

• Pulmonary Function Tests: Measured via spirometer.

• Specific Volumes and Capacities:     * Expiratory Reserve Volume (ERV): Extra air exhalable after normal breath.     * Residual Volume: Air remaining after maximal exhalation.     * Inspiratory Reserve Volume (IRV): Extra air inhalable after normal breath.     * Inspiratory Capacity: $V_{T} + IRV$.     * Functional Residual Capacity (FRC): $ERV + \text{Residual Volume}$.     * Vital Capacity: $ERV + V_{T} + IRV$.     * Total Lung Capacity: $\text{Vital Capacity} + \text{Residual Volume}$.

Principles of Gas Exchange and Diffusion

• Dalton’s Law: Each gas in a mixture contributes to total pressure proportional to its abundance.

• Partial Pressures ($P$) in Atmosphere ($760\,mm\,Hg$):     * $N_{2}$: $78.6\% \approx 597\,mm\,Hg$.     * $O_{2}$: $20.9\% \approx 159\,mm\,Hg$.     * $H_{2}O$: $0.5\% \approx 3.7\,mm\,Hg$.     * $CO_{2}$: $0.04\% \approx 0.3\,mm\,Hg$.

• Henry’s Law: Amount of gas in solution is proportional to its partial pressure and solubility.     * Solubility: $CO_{2}$ is highly soluble; $O_{2}$ is less; $N_{2}$ is very limited.

• Plasma Partial Pressures (Pulmonary Vein):     * $PCO_{2} = 40\,mm\,Hg$.     * $PO_{2} = 100\,mm\,Hg$.     * $PN_{2} = 573\,mm\,Hg$.

• Efficiency Factors: Substantial pressure gradients, short distances, lipid solubility of gases, large surface area, and coordinated blood/airflow.

Gas Transport and Hemoglobin Dynamics

• Oxygen Transport:     * Oxygen binds to iron ions in hemoglobin ($Hb$) to form oxyhemoglobin ($HbO_{2}$).     * Each RBC has about $280$ million $Hb$ molecules, each binding up to four $O_{2}$ molecules.

• Oxygen-Hemoglobin Saturation Curve:     * Relates percentage of heme units bound to $O_{2}$ to the $PO_{2}$.     * Curve is S-shaped because each bound $O_{2}$ makes the next easier to bind.

• Factors Affecting Hemoglobin Saturation:     * pH (Bohr Effect): Lower pH (more acidic) shifts the curve to the right, releasing more oxygen.     * Temperature: Higher temperature shifts the curve right, releasing more oxygen.     * 2,3-bisphosphoglycerate (BPG): Produced by RBC glycolysis; higher BPG induces more oxygen release.

• Fetal Hemoglobin: Has a higher affinity for $O_{2}$ than adult $Hb$, allowing the fetus to extract oxygen from maternal blood.

• Carbon Monoxide (CO): Binds much more strongly to $Hb$ than $O_{2}$, leading to poisoning.

Carbon Dioxide Transport

• Transport Methods:     1. Bicarbonate Ions ($70\%$): $CO_{2} + H_{2}O \rightarrow H_{2}CO_{3} \rightarrow H^{+} + HCO_{3}^{-}$ via carbonic anhydrase.         * Chloride Shift: $HCO_{3}^{-}$ moves into plasma while $Cl^{-}$ moves into the RBC.     2. Carbaminohemoglobin ($23\%$): $CO_{2}$ bound to protein portions of hemoglobin.     3. Dissolved in Plasma ($7\%$): Transported as gas molecules.

Control and Regulation of Respiration

• Local Regulation:     * Arteriole/Capillary Response: High $PCO_{2}$ relaxes smooth muscle to increase blood flow.     * Ventilation-to-Perfusion Ratio (V/Q): Coordinates blood flow to alveoli with airflow.

• Brain Respiratory Centers:     * Medulla Oblongata: Contains rhythmicity centers.         * Dorsal Respiratory Group (DRG): Inspiratory center; active in quiet and forced breathing.         * Ventral Respiratory Group (VRG): Inspiratory and expiratory centers; functions only in forced breathing.     * Pons:         * Apneustic Center: Stimulates the DRG (depth of respiration).         * Pneumotaxic Center: Inhibits the apneustic center; regulates rate and promotes exhalation.

• Sensory Input and Reflexes:     * Chemoreceptors: Monitor $PCO_{2}$, $PO_{2}$, and pH in blood (carotid/aortic bodies) and CSF.         * Hypercapnia: Elevated arterial $PCO_{2}$ (hypoventilation) increases rate/depth.         * Hypocapnia: Low $PCO_{2}$ (hyperventilation) decreases rate.     * Baroreceptors: If blood pressure falls, respiratory rate increases.     * Hering-Breuer Reflexes: Inflation reflex (prevents overexpansion) and Deflation reflex (inhibits expiration/stimulates inspiration during deflation).     * Protective Reflexes: Sneezing, coughing, and laryngeal spasms triggered by irritants.     * Apnea: Suspended respiration often followed by forceful expulsion of air.

Development and Aging of the Respiratory System

• Changes at Birth:     * Before birth: Lungs are collapsed and fluid-filled.     * During delivery: Placental loss causes $PO_{2}$ drop and $PCO_{2}$ rise.     * First breath: Overcomes surface tension to inflate bronchial tree; causes pressure drop that pulls blood into pulmonary circuit, closing the foramen ovale and ductus arteriosus.

• Aging-Related Effects:     * Deterioration of elastic tissue lowering vital capacity.     * Arthritic changes restricting chest wall movement.     * Emphysema: Extent depends on exposure to irritants (e.g., smoke) in individuals over $50$.

• Coordination: Homeostasis requires the integration of the respiratory and cardiovascular systems to manage lung perfusion, cardiac output, and gas exchange efficiency.