A&P2

Chapter 22: The Respiratory System

Functions of the Respiratory System

Primary Functions (Vital)

  • Intake Oxygen

  • Expel Carbon Dioxide (CO₂)

  • Help Maintain Acid-Base Balance

Secondary Functions (Non-vital)

  • Olfaction (sense of smell)

  • Speech (phonation)

  • Straining (e.g., coughing)

Respiratory and Cardiovascular Systems

Conducting Zone

  1. Pulmonary Ventilation (Breathing)

    • Inspiration: Air moves into the lungs from the atmosphere.

    • Expiration: Air moves out of the lungs into the atmosphere.

  2. External Respiration

    • Oxygen (O₂) diffuses from the lungs to the blood.

    • Carbon Dioxide (CO₂) diffuses from the blood to the lungs.

  3. Transport of Respiratory Gases

    • Cardiovascular System Role: Transports gases using blood as the transporting fluid.

    • O₂ is transported from the lungs to tissue cells.

    • CO₂ is transported from tissue cells to the lungs.

  4. Internal Respiration

    • O₂ diffuses from blood to tissue cells.

    • CO₂ diffuses from tissue cells to blood.

    • Cellular Respiration: Tissue cells utilize O₂ and produce CO₂.

Divisions of the Respiratory System

By Location

  1. Upper Respiratory Tract

    • Extends from the nasal/oral cavity through the pharynx (sometimes includes the larynx).

    • Functions: Warms, humidifies, and filters air.

      • Clinical Note: Humidification with Tracheal Tube.

  2. Lower Respiratory Tract

    • Extends from the larynx to the alveoli.

By Function

  1. Conducting Zone

    • Not directly involved in gas exchange (extends from the nose inferiorly to the terminal bronchioles).

  2. Respiratory Zone

    • Directly involved in gas exchange (extends from the respiratory bronchioles to alveoli).

Structure and Anatomy of the Conducting Zone

Nasal Cavity

  1. Skeletal Structure

    • Roof composed of sphenoid, ethmoid, frontal, and nasal bones.

    • Lateral walls contain 3 turbinates (conchae) on each side:

      • Superior Nasal Conchae (ethmoid)

      • Middle Nasal Conchae (ethmoid)

      • Inferior Nasal Concha (separate facial bone)

    • Conchae create turbulence and increase surface area for better air filtering.

  2. Septa and Palate

    • Nasal Septum: Made up of ethmoid bone, vomer, and septal cartilage.

    • Hard Palate: Composed of maxilla (anterior ¾) and palatine bone (posterior ¼).

  3. Respiratory Epithelium

    • Ciliated, pseudostratified columnar epithelial tissue that warms and humidifies incoming air, contains immune cells, proteins, and enzymes.

    • Goblet Cells: Produce mucus to trap debris.

    • Cilia: Move mucus towards throat for swallowing into an acidic stomach. Cilia activity decreases in cold weather, leading to congestion.

Pharynx Sections

  1. Nasopharynx (air only, contains:

    • Auditory (Eustachian) tube openings.

    • Adenoids (pharyngeal tonsils).

    • Soft palate and uvula swing up to close off nasopharynx during swallowing.

  2. Oropharynx (conducts air, liquid, and food):

    • Located posterior to mouth.

    • Houses lingual tonsils (base of the tongue) and palatine tonsils.

  3. Laryngopharynx (conducts air, liquid, and food):

    • Anteriorly opens into larynx, posteriorly into esophagus.

    • Epiglottis moves down to cover larynx during swallowing.

Lower Respiratory Tract

Larynx

  • Connection: Links pharynx to trachea.

  • Function: Produces sound.

  • Major Structures:

    1. Epiglottis: Flexible elastic cartilage covers airway during swallowing.

    2. Thyroid Cartilage: Known for prominence called "Adam's apple," more prominent in males.

    3. Cricoid Cartilage: Inferior ring of cartilage, only complete ring.

Trachea

  • Structure:

    • C-shaped hyaline cartilage rings: Incomplete, providing rigidity but allowing expansion.

    • Posteriorly joined by fibroelastic membrane that includes the trachealis muscle, which can contract during forced exhalation.

  • Carina: Cartilaginous ridge where primary bronchi branch; specialized nervous tissue here can induce violent coughing.

Bronchi Structure

  1. Primary Bronchi (R & L): One for each lung.

    • R primary bronchus is more vertical and wider, increasing likelihood of aspiration.

  2. Secondary (Lobar) Bronchi: One for each lobe of the lung (right lung has 3 lobes, left lung has 2 and a cardiac notch).

  3. Tertiary (Segmental) Bronchi: Smaller branches.

Mucociliary Escalator

  • Function: Clears debris by propelling mucus towards the pharynx for swallowing into the stomach.

Respiratory Zone Structure

  1. Respiratory Bronchiole

  2. Alveoli (singular: alveolus):

    • Structure: Simple squamous epithelium aligns with capillary endothelium, facilitating gas exchange due to fused basement membranes.

    • Gas Diffusion Processes:

      • Oxygen: From the more concentrated air in lungs to the blood.

      • Carbon Dioxide: From the more concentrated blood to the air in lungs.

  3. Alveolar Cells Types:

    1. Type 1 Alveolar Cells: Predominantly squamous epithelial cells (most abundant).

    2. Type 2 Alveolar Cells: Produce surfactant to decrease surface tension and prevent alveoli collapse; secrete antimicrobial proteins.

    3. Alveolar Macrophages: Consume pathogens and debris that evade other defenses.

Lung Characteristics

  • Each multilobed lung occupies its own pleural cavity.

  • Each lung has a superior apex, inferior base, and medial hilum, encased in pleural membranes.

Pleural Membranes

  • Functions:

    1. Reduce friction during breathing.

    2. Compartmentalize lungs to prevent spread of infection.

    3. Aid lung inflation by creating negative pressure in space between the layers due to serous fluid adhesion.

  • Potential Issues:

    • Pneumothorax: Air in the pleural cavity collapses lung.

    • Pleurisy: Inflamed pleura leading to pain with breath.

    • Pleural effusion: Fluid accumulation in the pleural space.

Boyle’s Law

  • Definition: If volume decreases, pressure increases; if volume increases, pressure decreases.

  • Air Movement: Air flows from areas of high pressure to low pressure.

Breathing Muscles

Diaphragm

  • Structure: Dome-shaped when relaxed, flattens upon contraction.

  • Action: Prime mover of inspiration.

  • Innervation: Phrenic nerves from cervical plexus (C3, C4, C5).

  • Mnemonic: C3, C4, C5 keeps the diaphragm alive.

Intercostal Muscles

  1. External Intercostals: Elevate rib cage, aiding inspiration.

  2. Internal Intercostals: Depress rib cage, aiding forced expiration.

Expiration Types

  • Resting Expiration: A passive process involving diaphragm relaxation and elastic recoil of the thoracic cavity.

  • Forced Expiration: Involves abdominal muscle contraction and internal intercostals pulling ribcage down and in.

Pressure Definitions

  • Atmospheric Pressure: Pressure of surrounding gases acting on the body.

  • Intrapulmonary Pressure (Intra-alveolar): Pressure within the lungs. Equalizes with atmospheric pressure (usually 760 mm Hg).

  • Intrapleural Pressure: Pressure in the potential space between visceral and parietal pleura (about -4 mm Hg, negative pressure aiding lung inflation).

Respiratory Volumes

  • Tidal Volume: About 500 mL (volume of air exchanged in normal breathing).

  • Inspiratory Reserve Volume: Extra volume inhaled beyond tidal volume.

  • Expiratory Reserve Volume: Extra volume exhaled beyond tidal volume.

  • Residual Volume: About 1200 mL remains after forced exhalation to keep alveoli open.

Spirometry Measurements

  • FVC: Forced Vital Capacity.

  • FEV1: Forced Expiratory Volume in the first second.

Pulmonary Diseases and Dead Space

Obstructive Pulmonary Diseases

  • Examples: Chronic Bronchitis, COPD.

  • Characteristics: Increased airway resistance, difficulty exhaling completely, hyperinflation of lungs, increased total lung capacity (TLC) and residual volume (RV), decreased FEV1.

Restrictive Pulmonary Diseases

  • Examples: Tuberculosis, exposure to asbestos.

  • Characteristics: Limited lung expansion, difficulty inhaling completely, decreased TLC and RV, may retain normal FEV1 percentage relative to volume.

Dead Space Types

  1. Anatomical Dead Space: Normal volume (~150 mL) in conducting zones, warms, humidifies, cleans air; no gas exchange occurs.

  2. Alveolar Dead Space: Collapsed or obstructed alveoli; not normal; increases total dead space, decreases gas exchange.

Gas Exchange by Diffusion

Dalton’s Law

  • Definition: The total pressure of a gas mixture is the sum of the partial pressures of its individual gases.

    • Example: Partial pressure of O₂ + Partial pressure of nitrogen = Total pressure.

Henry’s Law

  • Definition: Gas diffuses into a liquid in proportion to its partial pressure; higher partial pressure means more diffusion.

  • Solubility of Gases: Nitrogen is less soluble than O₂ and CO₂.

Clinical Application

  • Hyperbaric Oxygen Chamber: Increases O₂ partial pressure, enhancing blood absorption.

Types of Respiration

Internal Respiration

  • Occurs in capillaries of tissues:

    • Blood has higher O₂ partial pressure than tissue, facilitating O₂ diffusion from blood to tissues.

    • Tissues have higher CO₂ partial pressure than blood, facilitating CO₂ diffusion from tissues to blood.

External Respiration

  • Occurs in the alveoli of lungs:

    • Air has higher O₂ partial pressure compared to blood, facilitating O₂ diffusion from air into blood.

    • Blood has higher CO₂ partial pressure than air, facilitating CO₂ diffusion from blood into air.

Oxyhemoglobin Dissociation Curve

  • Shape: S-shaped curve due to changes in hemoglobin conformation.

  • Implications: Indicates how O₂ saturation in hemoglobin varies between lungs and tissues based on partial pressure of O₂.

Factors Influencing Dissociation Curve

Shifts in the Curve

  1. Shift to the Left: Hemoglobin holds O₂ more tightly (less release)

    • Causes: Decreased temperature, decreased CO₂, increased pH.

  2. Shift to the Right: Hemoglobin releases O₂ more easily.

    • Causes: Increased temperature, increased CO₂, decreased pH.

    • Relevant in active tissues requiring more O₂.

Carbon Dioxide Transport Mechanisms

  1. Bound to hemoglobin (about 20%).

  2. Dissolved directly in plasma (about 10%).

  3. As bicarbonate ions in plasma (about 70%).

Respiratory Control

Brain Stem Centers

  • Medulla: Generates and modifies breathing rhythm.

    • Ventral Respiratory Group (VRG): Can be suppressed by substances like alcohol/morphine, ceasing breath.

    • Dorsal Respiratory Group (DRG).

  • Pons: Smooths respiratory pattern via pontine respiratory centers.

Autonomic Innervation

  • Sympathetic Nervous System: Dilates bronchioles.

  • Parasympathetic Nervous System: Constricts bronchioles.

Breathing Patterns

  • Eupnea: Normal breathing (12-16 breaths/min).

  • Hyperventilation: Leads to hypocapnia (low CO₂); breathing into a paper bag helps recycle CO₂.

  • Apnea: Cessation of breathing, often related to low CO₂ levels.

Control of Respiration

  • Key Stimulus: Carbon Dioxide (most powerful stimulant for breathing):

    • Accumulation (hypercapnia) makes blood more acidic, triggering chemoreceptors to increase respiratory rate and depth.

    • Oxygen levels are not primary control in healthy individuals but can influence respiration under pathological conditions with very low levels.

Special Topic: Acid-Base Balance

  • Normal Blood pH: 7.35 to 7.45; sensitive yet vital range.

  • Alkalosis: Blood pH increases; less acidic.

  • Acidosis: Blood pH decreases; more acidic.

Physiological Buffers

  • Chemical Buffers: Immediate response.

  • Respiratory System: Modifies respiration within minutes.

  • Renal System: Slow to respond (around 24 hours), secreting H+ ions and absorbing bicarbonate during acidosis, and the reverse in alkalosis.

References

  • Marieb, E. N. & Hoehn, K. (2019). Human Anatomy & Physiology, 11th Edition. Pearson.

  • Marieb, E. N. & Smith, L. A. (2019). Human Anatomy & Physiology Laboratory Manual, 12th Edition. Pearson.

  • Additional references and resources as noted throughout the transcript.