Respiration

Respiration Definition & Major Events

  • Respiration: Intake and use of oxygen (O2) to produce ATP, releasing and removing carbon dioxide (CO2).
  • Primary functions:
    • Supply O2 for oxidation of food to produce ATP.
    • Eliminate CO2, a poisonous byproduct of tissue oxidation.
  • Secondary functions:
    • Regulate blood pH via CO2 levels.
    • Body defense against microbes entering during inhalation.
    • Thermoregulation by releasing heat in expired air.
    • Metabolism in lung parenchyma.
  • Respiratory events:
    • Pulmonary ventilation (breathing): Air movement between lungs and surroundings.
    • External gas exchange: O2 and CO2 exchange between alveolar air and pulmonary capillaries.
    • Gas transportation: Distribution of O2 to cells and collection of CO2.
    • Internal gas exchange: Gas transfer between interstitial fluid and tissue cells.
    • Cellular respiration: O2 use for food breakdown, ATP formation, and CO2 release.

Anatomical Review of the Respiratory System

  • Gross structure: Starts at nostrils, ends at alveoli.
  • Upper Respiratory Tract (URT):
    • Nasal Cavity: Filters (hairs, mucus), warms, and moistens air.
    • Pharynx: Directs air/food, immune role (tonsils).
  • Lower Respiratory Tract (LRT):
    • Larynx: Protects trachea, produces sound (vocal cords).
    • Trachea: Transports air, protects via ciliated lining.
    • Bronchial Tree: Branches into smaller tubes, distributes air.
      • Ventilation and immunological functions (BALT).
    • Terminal bronchioles:
      • Gas exchange (alveoli, ducts, sacs).
      • Phagocytic action (macrophages).
    • Respiratory bronchioles: Convection and diffusion for gas exchange.
    • Respiratory Zone: Alveolar ducts, sacs, and alveoli for gas exchange.
    • Lungs:
      • Anchored to heart/trachea.
      • Covered in pleural sac (parietal/visceral pleura).
      • Elastic structure for easy inflation/deflation.
  • Functional divisions:
    • Air conducting zone: URT and LRT structures conveying air.
    • Transitional zone: Respiratory bronchioles/alveolar ducts, some gas exchange.
    • Respiratory zone: Alveoli ducts, sacs, and alveoli for primary gas exchange.

Pulmonary Ventilation (Breathing)

  • Involves inspiration and expiration.
  • Boyle’s Law: Volume and pressure are inversely related at constant temperature.
  • Inspiration (Inhalation):
    • Intake of tidal volume.
    • Muscles increase thoracic cavity volume, reducing pressure.
    • Air enters when PA > PL.
    • Mechanics:
      • Diaphragmatic muscles: Account for up to 80% of quiet breathing.
      • External intercostals: Cause rib movement.
      • Accessory muscles: Costal elevator, scalene, transverseus costarum, serratus dorsalis.
  • Expiration (Exhalation):
    • Expulsion of air when intrapulmonic pressure rises above atmospheric pressure.
    • Passive expiration: Elastic recoil forces (release of stretch, relaxation of muscles, compression release, surface tension).
    • Active expiration: Requires muscle contraction during stress or forced maneuvers.
      • Muscles: Internal intercostals, transversus thoracis, retractor costae, iliocostalis, abdominal wall muscles, serratus dorsalis.

Lung Volumes and Pressures

  • Lung volume changes via chest cavity volume changes.
  • Negative pressure aids blood/lymph flow and food aspiration.
  • Pressures:
    • Atmospheric pressure (PA): Constant.
    • Intra-pulmonic pressure (PL): Changes during breathing.
    • Pleural Pressure: Sub-atmospheric because the pleural space is closed and the lungs tend to collapse.
      • Pleural fluid: Lubricates, adheres pleura for force transmission, keeps lungs attached to chest wall.
    • Trans-pulmonary pressure (PT): PT = (PL – PP), net pressure across lung yielding to chest wall movements.
  • Respiratory cycles: Alternating volume/pressure changes during breathing.
  • Inflation and deflation: Vocal cords move apart, bronchi dilate, venous return increases during inflation.
    • Intrapulmonic pressure: Decreases during inspiration (-2 mm H2O), increases during expiration (+2 mm H2O).
    • Intrapleural pressure: -5 mm H2O at start of inspiration, -7.5 mm H2O at end. Always sub-atmospheric.
    • Transpulmonic pressure: Lowest at inspiration beginning, highest at end.

Surface Tension Properties of the Lungs

  • Alveoli act like soap bubbles; surface tension reduces volume, balanced by air pressure.
  • Laplace’s law: P = (2T/r); pressure increases as radius decreases.
  • Surfactant: Reduces surface tension; a lipoprotein complex (30% protein, 70% lipid).
    • Synthesis: Type II alveolar cells synthesize, store, and secrete surfactant.
    • Control: Glucocorticoids and thyroxin stimulate production.
    • Action: Reduces attractive forces between water molecules.

Pulmonary Surfactant: Functions and Pathophysiology

  • Functions:
    • Reduces surface tension, easing inflation.
    • Increases compliance; keeps alveoli open.
    • Contributes to elastic recoil via apoproteins and Ca2+.
    • Stabilizes alveoli expansion and shrinking.
    • Prevents fluid accumulation and keeps airways dry.
    • Emulsifies small particles for phagocytosis.
  • Pathophysiology: Lack of surfactant leads to:
    • Stiff lung (difficult elastic recoil).
    • Pulmonary edema (fluid accumulation).
    • Atelectasis (lung collapse).

Pulmonary and Total Compliance of Respiratory System

  • Pulmonary Compliance (PC): Lung distensibility; change in volume per change in pressure.
  • Total compliance: Lung + chest wall compliance.
  • Factors:
    • Lung tissue elasticity.
    • Surface tension forces.
    • Blood amount in lungs.
  • Factors altering PC:
    • Lung fibrosis (decreases PC).
    • Pulmonary congestion (decreases PC).
    • Pulmonary edema (decreases PC).
    • Alveolar collapse (decreases PC).
    • Lung consolidation (decreases PC).

Work of Breathing and Breath Sounds

  • Work of Breathing: Work by muscles during respiration.
    • Compliance work: To expand lungs against elastic forces.
    • Tissue resistance work: To overcome viscosity of structures.
    • Airways resistance work: To overcome resistance in airways.
      • P = [V8ηl/πr4]
      • Rairways = P/V
  • Breath Sounds:
    • Bronchial: Larynx and large bronchi; loud during inspiration.
    • Vesicular: Alveoli branching; quiet, wispy.
    • Bronchovesicular: Full inspiratory phase with shortened expiratory phase.

Pulmonary Volumes and Capacities

  • Pulmonary Volumes are the lungs capacity to handle airflow while breathing under different conditions.
    • Resting Tidal Volume (Vt): Volume of air exchanged during quiet breathing.
    • Inspiratory reserve volume (IRV): Extra volume inspired above normal Vt.
    • Expiratory reserve volume (ERV): Extra volume expired by forceful expiration.
    • Residual volume (RV): Air remaining after forceful expiration.
    • Total lung volume = Vt+ IRV + ERV + RV
  • Pulmonary Capacities are Lung Volumes with combined properties.
    • Inspiratory capacity (IC): Vt + IRV. Air inspired from normal expiration to maximum.
    • Functional residual capacity (FRC): RV + ERV. Air in lungs after normal tidal expiration.
    • Vital capacity (VC): IRV + Vt + ERV. Air expired after maximal inspiration/expiration.
    • Total lung capacity (TLC): VC + RV. Maximum lung volume after maximal inspiration.
  • Limitations of spirometry: Does not measure O2/CO2 exchange details.
    • Modern Methods:
      • Gas composition.
      • Gas partial pressures.

Tidal volume, Alveolar and Dead space Ventilation

  • Distribution of Tidal Volume
    • Alveolar ventilation: Fraction of tidal volume involved in gas exchange.
    • Dead space ventilation: Fraction of tidal volume not involved in gas exchange.
      • Composition remains that of inspired air
  • Lung Ventilation: Ultimate function of pulmonary ventilation is ventilation
    • Alveolar Ventilation: Rate new air reaching functional zone (alveoli ducts, alveolar sacs, alveoli).
      • Slow and deep breaths allow process of translocation and diffusion of gases into the alveoli.
    • Respiratory Minute Volume:
      • Total volume of air moved into/out of respiratory passages per minute.
      • Types: Inhaled/Exhaled
      • Minute Volume = Alveolar (effective) ventilation + dead space (wasted) ventilation.
      • Tidal volume varies inversely with respiratory rate.

Respiratory Dead Space & Rate of Alveolar Ventilation

  • Dead Space Volume: Air that does not reach respiratory zones.
    • Anatomical dead space: Conducting zone volume from nares to terminal bronchioles.
      • Morphological Anatomical Dead Space.
      • Functional Anatomical (Series) Dead Space.
    • Alveolar Dead Space:
      • Inspired are, mixes in alveoli spaces without perfusion.
    • Physiological (Total) Dead Space.
      • Volume of inspired air that does not take part in gas exchange.
      • Alveolar dead space = Physiological dead space – Anatomical dead space
  • Rate of Alveolar Ventilation
    • Minute alveolar ventilation = (Tidal volume- minute – Anatomical Dead Space).
    • Va- = f(Vt –VD-anatomical)
  • Respiratory Dead Space: Volume of air wasted' to ventilate the lungs of fresh air
    • Respiratory dead space ventilation increases with breathing rate.

Functions of Dead Space Ventilation

  • Dead space make up of URT- nose, pharynx, larynx, trachea and bronchioles, play role in gas exchange.
  • Functions:
    • Distribution of O2-rich air to alveoli and CO2-rich air to the outside.
    • Warming inspired air.
    • Elimination of foreign particles.
      • Cough reflex vs Sneeze reflex.
    • Humidification:
      • Increases relative PO2.
    • Phonation or voice production:
      • Epiglottis. Vocal cords.

Alveolocapillary Transfer of Gases

  • External gas exchange, O2 and CO2 is exchanged between alveoli and pulmonary capillaries, oxygen diffuses from the alveolar air into the blood and CO2 diffuses out of the blood into the alveolar air. the gas exchange, the composition of atmospheric and expired air differ. Most of the CO2 is carried to the lungs in plasma as bicarbonate ions -.
  • Structure of respiratory membrane:
    • Respiratory bronchiole, alveolar ducts, atria, alveoli, membrane is composed of capillary blood.
      • Fluid lining inside of alveoli: thin alveolar fluid layer lining the inside surface of alveoli composed of surfactant.
      • Alveolar epithelium: thin epithelial cells (type I and II pneumocytes and macrophages).
      • Alveolar epithelial basement membrane:.
      • Narrow interstitial space.
      • Capillary Basement membrane: which anchors the capillary endothelial cells to the lung parenchyma
      • Capillary Endothelial membrane: composed of a single layer of endothelial cells
  • Mechanism of gas exchange
    • Exchange of respiratory gases between the alveolar air and the pulmonary capillary blood occurs by simple diffusion governed by Fick's law.
    • Fick's Law: R = -(dC/dx)(T0/ MW)A

Functional Adaptations of Alveolocapillary Membrane

  • Respiratory membrane adapted to maximize net diffusion and rate for gas exchange, structure includes:
    • Short diffusion distance of between 0.2-0.6 m
    • Large surface area provided by 300 x 106 alveoli amounting to 1m2 per kg of body weight or surface area of diffusion.
    • Steep partial pressure gradients oxygen and carbon dixoide through efficient ventilation, high perfussion rate for blood in sheaths and humidificaitin process.
    • High membrane permeability in the lipid bilayer of the membrane for O2/CO2 through the nasal epithelum.
  • Abnormality of Gas exchange: conditions with Alveolocapillary affects respiration.
    • Thickening of the respiratory membrane: Inflammation and increase in distance dx increases diminishing has exchange efficiency.
    • Fluid infilitration: pulmonary oedema increases tickness in thickness in membrane causing diffucsion efficieny to diminish as O2,O2 cannot diffuse will through water.
    • Pulmonary emphysema: reduction in surface area causing dramatic gas exchange fall.
    • Pneumonia: any damage to lung tissues causes flow obstruceion.

Transportation of O2/CO2

  • Transfer of gases between humidified air in lungs to tissues employs two process
    • Diffusion transports over short distqnces depending on O2 and CO2 partial pressures.
    • Blood circulation, the two gasses are transported in different ways, one which may include:
  • Oxygen Transportation in Blood:
    • Circa 2.5% is transported through in blood plasma using dissolved form which represents 0.17 mls of O2 per dL of blood.
      • Arterial blood = 95 mm of Hg$$
    • In combination with Hb typically most fo the oxygen 97.5% is transported in Hb to form oxyhemoglobin representing 5.0ml per dL of blood.
    • The Oxyhemoglobin Dissociation Curve is the amount of O2 transported in association with Hb PO2 dissolved and O2 unloaded in capillaries and PO2 plot using the % saturation of Hb shape. Oxygen is bound to the haemoglobin at different conditions denonating partial pressure oxygen between the pulmonary capillaries, which maintains favor by the Hb.
      • Factors include shifts of of temperature, pressure increase for CO2, Decrease in PH 2,3-Diphosphoglycerated (DPG).
      • Tissue increase and low pH levels cause O2-Hb dissociation to change direction and to the right cause greater yield of O2.
      • Decrease in low O2 levels causes H
        Transport of Oxygen and Oxygen-Haemoglobin Dissociation Curve

Transport of Capillaries and Carbon Dioxide

  • Mechanism: Solubility of the ability to form carbonic acid in water allows transport in four different ways for CO2.
    • Hydrogen ions HCO380-90% CO2+water (use carbonic anydrase) which results in H+formation transfer called humburger shift.
    • Carbamino haemoglobin:
      5-10% of CO2 = haemoglobin.
    • Carbamino compounds:
      5-10% CO2 plasma protein is formed.
    • Physically dissolved:
      Solulibiry is directlly in a Henry's Law where very minamilistic O2 values increase.
  • Carbon dixodie-hemoglobin dissociation curve: Total CO2 made up of all aspects of the system are transported using what is known as the Haldane affect which is an integration of O2 and CO2 depending what they are doing on different functional groups.
    • Haldane Effective: Increase O2 concentration will displace and release more CO2 so that it can be ventilated away
    • Bohr Model: Influenced for the oxygen is dependent on high or low high in tissue releasing from Hb and low level causing favors in transportation of body.
      Both facilitate regulation for Hb for transport for O2 and CO2 in the transport system.

Internal Gas Exchange O2

  • Oxygen Exchange: Tissues O2 moves from isf or ISF by metoblizing cells to transfer energy by oxidative