Respiratory

The Respiratory System (Chap 21)

Overview of Respiratory Processes

  • Respiration Definition: Refers to the physiological processes involving the exchange of gases, primarily oxygen (O2) and carbon dioxide (CO2), in humans.

  • Sequence of Events:

    • Pulmonary Ventilation (O2) →

    • External Respiration →

    • Transport of Respiratory Gases →

    • Internal Respiration.

  • The cycle is reversed when gases (CO2) are transported back to the lungs for exhalation.

PART I: Functional Anatomy of the Respiratory System

I. Upper Respiratory System

  • Functions:

    • Warms, humidifies, and filters air from the nose to the pharynx.

Learning Objectives

  • Describe the location, structure, and function of the following:

    • Nose

    • Paranasal sinuses

    • Pharynx

  • List and explain the protective mechanisms of the respiratory system.

The Nose and Paranasal Sinuses
Physiology (Functions)

  1. Conduct, moisten, warm, and clean incoming air.

  2. Serves as a resonating chamber for speech.

  3. Houses olfactory receptors for smell.

External Structures

  • Components: Bridge, tip, and nostrils (nares) shaped by bone and cartilage.

Internal Structures

  • Nasal Cavity:

    • Divided by the nasal septum.

    • Leads air to the nasopharynx.

    • Roof: Formed by the ethmoid and sphenoid bones.

    • Floor: Composed of hard palate (anterior) and soft palate (posterior), ending in the uvula (Cleft palate as a medical condition).

    • Lining:

    • Respiratory membrane (mucosa) containing pseudostratified ciliated columnar epithelial cells with goblet cells and mucus glands containing lysozymes (medical concern: rhinitis).

    • Nasal conchae: Superior, middle, and inferior with meatuses in-between.

  • Paranasal Sinuses:

    • Include maxillary, frontal, ethmoid, and sphenoid sinuses (medical concern: sinusitis).

II. The Pharynx

  • Commonly referred to as the "throat," divided into three regions:

  1. Nasopharynx

    • Contains pharyngeal tonsil (adenoids).

    • Hosts pharyngotympanic tubes (auditory tubes).

  2. Oropharynx

    • Contains fauces.

    • Contains palatine and lingual tonsils.

  3. Laryngopharynx

Lower Respiratory System

Learning Objectives

  • Distinguish between conducting and respiratory zone structures.

  • Describe the structure, function, and location of the larynx, trachea, and bronchi.

  • Describe the makeup of the respiratory membrane and relate structure to function.

  • Identify the organs forming the respiratory passageway(s) in descending order until reaching the alveoli.

Larynx (Voice Box)
Functions

  1. Provides an open airway.

  2. Functions as a switching mechanism to route food and water down the esophagus.

  3. Produces voice.

Structures

  1. Thyroid Cartilage: Contains laryngeal prominence (anterior "bump").

  2. Cricoid Cartilage: Provides greater posterior coverage.

  3. Glottis: Opening covered by the epiglottis.

  4. Vocal Folds (Vocal Cords):

    • Composed of connective tissue ligaments of elastin.

    • Involved in voice production.

    • Act as a sphincter valve to increase intra-abdominal pressure (e.g., Valsalva's maneuver for defecation and trunk stabilization during heavy lifting). (Medical concern: laryngitis).

Trachea (Windpipe)

  • Composed of C-shaped cartilage rings.

  • Mucosa: Protective lining of pseudostratified ciliated columnar epithelia with goblet cells.

Considerations

  1. Effects of smoking on ciliated cells (nicotine paralyzes cilia).

  2. Carina: Point of bifurcation rich in nerve endings; induces intense spastic coughing when stimulated (e.g., by food).

  3. Heimlich Maneuver: Utilizes trapped air in the lungs to expel foreign objects.

Bronchi and Subdivisions
Conducting Zone Structures

  • Bronchial Tree:

    • Primary bronchi: Right and Left (each presents a choking hazard due to small lumen size).

    • Secondary (Lobar) bronchi: 3 on the Right and 2 on the Left, servicing each lung lobe.

    • Tertiary bronchi: Subsequent smaller divisions.

    • Terminal Bronchioles: Less than 0.5 mm in diameter (size of pencil lead), with anatomical changes observed:

    • Less firm cartilage, more elastic fibers and smooth muscle (changing lumen diameter), and reduced mucus and cilia.

Respiratory Zone

  • Respiratory bronchioles transition to alveolar ducts, leading to alveolar sacs and individual alveoli essential for gas exchange.

  • Respiratory Membrane: Composed of simple squamous epithelial cells with macrophages.

    • Macrophages fulfill a patrol function against invaders or debris due to reduced mucus or cilia.

    • Surfactant: Secreted by some alveolar cells; decreases surface tension to prevent alveolar wall collapse.

    • Capillaries: Form a rich blood supply to facilitate gas exchange (O2 into blood, CO₂ into lungs).

Gross Structure of the Lungs

  1. Paired Lungs:

    • Left lung: 2 lobes.

    • Right lung: 3 lobes (superior, middle, inferior).

  2. Anatomical Features:

    • Apex, base, costal surface, and cardiac notch (notable on the left side).

    • Spongy elastic lung tissue termed stroma surrounds air structures (bronchial tubes and alveolar sacs).

    • Hilum: Indentation where vessels and bronchial tubes enter and exit.

  3. Blood Supply and Innervation:

    • Lung tissue (stroma) supplied by systemic circulation while pulmonary circuit afferently supplies alveolar capillaries, carrying all flow from the heart's right side.

    • Sympathetic innervation induces bronchodilation; parasympathetic induces bronchoconstriction.

  4. Pleurae:

    • Parietal pleura covers thoracic cavity walls; visceral pleura covers lung surface.

    • Pleural cavity contains a serous fluid layer (pleural fluid) for lubrication, aiding in lung inflation/deflation via surface tension.

    • Conditions:

    • Pleural Effusion: Excess pleural fluid causing inflation problems.

    • Pleurisy: Inflamed pleurae causing painful friction during respiration, common in smokers or pneumonia cases.

PART II: Respiratory Physiology

IV. Volume and Pressure Dynamics
Learning Objectives

  • Explain pressures involved in atmospheric, intrapulmonary, and intrapleural scenarios.

  • Connect Boyle's Law to inspiration and expiration events.

  • Assess respiratory muscle and lung elastic roles in air volume changes.

  • Describe physical factors influencing pulmonary ventilation.

Pressure Relationships in the Thoracic Cavity

  1. Air molecules create atmospheric pressure through movement, resulting in a pressure of 760 mm Hg at sea level.

  2. Intrapulmonary Pressure (Ppul):

    • Differentiates by either rising (exhalation) or lowering (inhalation) to match atmospheric pressure.

  3. Intrapleural Pressure (Pip):

    • Slightly lower pressure than intrapulmonary due to the adhesive forces between visceral and parietal pleura, aiding lung expansion and keeping them filled with air.

  4. Atelectasis (Collapsed Lung):

    • Occurs when obstructing the respiratory bronchiole restricts alveolar sac inflation, potentially due to conditions like pneumonia.

    • Pneumothorax: Occurs when intrapleural air entry eliminates negative pressure needed for lung inflation, leading to collapse.

Pulmonary Ventilation and Boyle's Law

  • Boyle's Law: Inverse relationship where decreasing container volume increases pressure; increasing container volume decreases pressure.

  • Inspiration: Thoracic cavity enlarges, causing pressure drop and air influx.

    • Diaphragm contracts (flattens).

    • If a larger breath is necessary, external intercostal muscles assist in elevating the chest.

  • Expiration: Thoracic cavity reduces volume, raising pressure and facilitating air outflow.

    • Diaphragm relaxes and abdominal organs rebound upward.

    • In forced expiration, abdominal and internal intercostal muscles help contract the chest further.

Physical Factors Influencing Ventilation

  1. Lumen Diameter of Bronchioles: Determines airflow.

    • Irritants may trigger parasympathetic responses (bronchoconstriction) or release histamines during severe allergic reactions.

    • Asthma-associated bronchiole spasms can be fatal.

    • Epinephrine causes bronchodilation (reaction with β2 receptors on muscle cells).

  2. Alveolar Surface Tension:

    • Surfactant is critical to prevent moisture surfaces from collapsing.

    • Infant Respiratory Distress Syndrome (IRDS) occurs in newborns with inadequate surfactant production, impairing gas diffusion.

    • ARDS: Similar adult conditions leading to gas exchange issues, notably after drowning or inhalation of superheated air.

  3. Lung Compliance: Refers to lung stretchability, which diminishes with age, damage (fibrosis), or genetic conditions.

Measuring Respiratory Volumes and Capacities
Learning Objectives

  • Explain various lung volumes and capacities.

  • Identify insights provided by pulmonary function tests.

Respiratory Capacities and Volumes

  • Normal Values Assigned:

    1. Tidal Volume (TV): Approx. 500 ml; volume inhaled/exhaled at rest.

    2. Inspiratory Reserve Volume (IRV): Approx. 3100 ml; forced inhalation above TV.

    3. Expiratory Reserve Volume (ERV): Approx. 1200 ml; forced exhalation beyond TV.

    4. Residual Volume (RV): Approx. 1200 ml; unexchanged air remaining post-forced expiration.

Example of Respiratory Capacities

  • Vital Capacity (VC):

    • Formula: VC=IRV+TV+ERVVC = IRV + TV + ERV (FVC: forced vital capacity).

    • Patient's directive: "Take a deep breath, and forcibly exhale as quickly as possible."

    • FVC less than normal indicates restrictive air diseases, such as asthma/pulmonary fibrosis.

  • FEV1: Volume exhaled in the first second of FVC, ideally around 80% of total VC. Deviations may indicate air retention issues (COPD, etc.).

Gases Exchanged by Diffusion
Learning Objectives

  • Compare atmospheric and alveolar air compositions and the reasons behind differences.

Atmospheric vs Alveolar Air Composition

  • Total Atmospheric Pressure: 760 mm Hg.

    • Portion attributed to Nitrogen (N2): 80% or 597 mm Hg.

    • Humans do not metabolize nitrogen from air, focusing on its food-based derivation.

    • Portion attributed to Oxygen (O2): 20% or 160 mm Hg.

    • Portion attributed to Carbon Dioxide (CO2): <1% or 0.3 mm Hg.

Partial Pressures**

  • Atmospheric Pressure:

    • PO₂: 160 mm Hg

    • PCO₂: 0.3 mm Hg

  • Alveolar Pressure:

    • PO₂: 104 mm Hg

    • PCO₂: 40 mm Hg

  • Pulmonary Arteries:

    • PO₂: ≤40 mm Hg

    • PCO₂: 45 mm Hg

  • Systemic Veins:

    • PO₂: 40 mm Hg

    • PCO₂: 45 mm Hg

  • Tissue Cells:

    • PO₂: 40 mm Hg

    • PCO₂: 45 mm Hg

  • Pulmonary Vein:

    • PO₂: 100 mm Hg

    • PCO₂: 40 mm Hg

  • Systemic Arteries:

    • PO₂: 100 mm Hg

    • PCO₂: 40 mm Hg

Factors Affecting External Respiration

  • Diffusion Issues:

    • Surface Area Reduction: Decreases gas exchange (e.g., emphysema destruction of alveolar walls).

    • Edema: From pneumonia or pulmonary edema due to heart failure increases barrier thickness affecting gas exchange.

  • Solutions for Poor Diffusion:

    1. Maintaining a consistent oxygen diffusion gradient across membranes.

    2. Employing Low-Flow Oxygen Supplementation:

    • Nasal cannula connected to an oxygen supply.

    1. Implementing Hyperbaric Therapy:

    • Enclosing a patient in a chamber with pure O2, raising pressure to 3-4 atmospheres, yielding PO₂s of 2000-3000 mm Hg.

  • For example, assists in,

    • Displacing CO from hemoglobin in cases of carbon monoxide poisoning (CO binds to hemoglobin).

    • Aiding hypoxic tissue from gangrene or poor healing scars from diabetes.

    • Increased phagocytosis and epithelialization to promote healing.

  • Cautions:

    • Hyperbaric oxygen exposure is limited to prevent nerve damage from oxotoxicity.

    • Risk of blindness from oxygen therapy in infants due to optic nerve vulnerabilities.

Transport of Respiratory Gases in Blood

  1. Oxygen Transport:

    • 98% of O2 from pulmonary capillaries carried by hemoglobin as oxyhemoglobin (HbO₂).

    • 2% of O2 is found dissolved in plasma; common fingertip monitor data reveals oxyhemoglobin saturation statistics.

    • Hemoglobin saturation of 98% correlates to PO₂ of ~100 mm Hg, whereas saturation of 95% is reached at PO₂ of ~75 mm Hg.

    • Saturation falls below 90% (PO₂ < 60 mm Hg) signals hypoxic drive which triggers increased respiration rates.

    • Falling below 75% (PO₂ < 40 mm Hg) can lead to tissue hypoxia due to insufficient O2.

  2. Scenarios of Hypoxia:

    • Anemic Hypoxia: Due to insufficient hemoglobin or red blood cells quantity.

    • Ischemic Hypoxia: Due to systemic blockages or localized thrombus/emboli.

    • Hypoxemic Hypoxia: Arterial PO₂ drop, typically resulting from diffusion impairments in lungs.

    • During exertion, O2 saturation in veins can drop to 25% (PO₂ ~15 mm Hg), as increased capillary time compensates to maintain arterial PO₂ close to 100 mm Hg.

  3. Factors Enhancing Oxygen Release:

    • Increased CO₂, elevated temperature, and reduced pH (acidosis); enhancing O₂ release from hemoglobin.

    • Hemoglobin disassociation curve shifts right under these conditions, facilitating oxygen delivery to tissues.

Carbon Dioxide Transport

  1. Forms of Transport:

    • 10% dissolved in plasma.

    • 20% bound to hemoglobin.

    • 70% transported as bicarbonate (HCO₃).

  2. Normal Arterial PCO₂: Approximately 40 mm Hg (range: 35-45 mm Hg); abnormal levels noted as hypocapnia (<35 mm Hg) and hypercapnia (>45 mm Hg).

  3. Carbonic Acid Formation: CO₂ interacts with water producing carbonic acid which dissociates into hydrogen ions and bicarbonate ions.

  4. Diagrams: Illustrate loading and unloading of O₂ and CO₂ across tissues and pulmonary structures, highlighting the chloride shift mechanism.

VIII. Neural Control of Breathing
Learning Objectives

  • Explain the neural regulation of respiration-related processes.

  • Compare influences of arterial pH, partial pressures of O₂ and CO₂, lung reflexes, volition, and emotions on respiratory rates.

Neural Mechanisms

  1. Normal respiration rates are set by the medulla oblongata, disseminating signals via phrenic nerves and intercostal nerves.

Factors Influencing Respiratory Rates

  1. Detected Changes: Chemoreceptors in the aortic arch and carotid arteries trigger respiratory adjustments.

    • Increase in PCO₂, PO₂, and [H] (hydrogen ion concentration affecting pH) stimulate increased respiration rate and depth.

  2. Apnea: The absence of breathing, potentially voluntary for brief times.

    • CO₂ levels surge as respiratory function decreases, leading to hypercapnia (elevated CO₂) affecting respiration rate.

  3. Respiration Rate Increase:

    • A rise of 5 mm in PCO₂ can lead to a 100% increase in respiratory rate, while PO₂ would need to drop below 60 mm Hg to invoke an urgent need to breathe (hypoxic drive).

  4. Hyperventilation: Elevated respiratory rate (above normal) resulting in hypocapnia (below normal PCO₂).

    • Causes may include emotional excitement or high-altitude exposure, potentially leading to side effects like dizziness or fainting due to rapid CO₂ depletion.

IX. Respiratory Adjustments during Exercise and High Altitudes
Learning Objective

  • Distinguish hyperpnea during exercise from hyperventilation.

Hyperpnea

  • Increased respiration (>normal) to meet enhanced metabolic demands during physical activities (e.g., exercise or fever) without causing hypocapnia or pH imbalances.

X. Lung Diseases
Learning Objective

  • Compare chronic bronchitis, emphysema, asthma, tuberculosis, and lung cancer's causes and consequences.

Chronic Obstructive Pulmonary Disease (COPD)

  1. Irreversible lung disease characterized by progressively destructive processes leading to trapped air and compromised air expulsion.

  2. Symptoms:

    • Dyspnea: Difficulty breathing associated with a sensation of air hunger.

    • Frequent coughing and susceptibility to pulmonary infections.

    • Potential progression to respiratory failure due to insufficient ventilation, resulting in hypercapnia (elevated CO₂), acidosis (high H+ levels), and hypoxemia (low O₂).

  3. Causes Include:

    • Chronic bronchitis involving thickened mucus and inflamed bronchiole tubes.

    • Emphysema resulting in expanded air pockets due to alveolar wall destruction.

    • Significant history of smoking contributes to approximately 80% incidence rate; however, chronic bronchitis is increasingly observed among uncontrolled asthma patients.

  4. Asthma: Characterized by intermittent bronchospasm that obstructs inflamed respiratory bronchioles, necessitating daily management through corticosteroids and emergency bronchodilators (e.g., epinephrine during attacks).

    • Failure to manage asthma effectively may lead to chronic bronchitis and COPD.