Respiration: 2/24

UNIT 4: RESPIRATION

• Dr. John Redden

• Physiology and Neurobiology

• University of Connecticut

Learning Objectives

• LECTURE ROADMAP

  • Respiratory Anatomy

  • Histology/Microanatomy

  • Blood Pressure/Volume Relationships During Ventilation

  • Gas Exchange

  • Control of Breathing

RESPIRATORY SYSTEM ANATOMY

UPPER RESPIRATORY SYSTEM

• Entry Point Into Respiratory Tract

  • Air entering the body must be:

    • Filtered

    • Warmed

    • Humidified

LOWER RESPIRATORY ANATOMY

• Components:

  • Larynx

  • Tracheal cartilages

  • Right lung & Left lung

  • Primary & Secondary bronchi

  • Trachea

  • Pulmonary arteries & veins

  • Alveoli & Alveolar ducts

  • Smooth muscle in bronchioles

  • Capillaries

LUNGS

• Right Lung:

  • 3 Lobes (3 Secondary Bronchi)

• Left Lung:

  • 2 Lobes (2 Secondary Bronchi)

PLEURAL MEMBRANE

• Types:

  • Visceral Pleura (Surface of Lung)

  • Parietal Pleura (Thoracic Wall)

  • Function:

    • Contains pleural cavity (Pleural space) allowing for lung expansion during respiration

FUNCTIONAL: CONDUCTING ZONE

• Respiratory Passages Include:

  • Primary bronchi, Secondary bronchi, Tertiary bronchi (1 bronchioles < 1mm), Terminal bronchioles (6500 potential pathways)

• Epithelium Types:

  • Pseudostratified epithelia

  • Stratified epithelia

  • Cuboidal epithelial layers

  • Cartilage present in Trachea

  • Smooth muscle found in bronchioles

EPITHELIA LINE CONDUCTING ZONE

• Types of Epithelium:

  • Inferior Pharynx: Stratified Epithelium

  • Nasopharynx, Pharynx & Lower Respiratory Tract: Pseudostratified Columnar Epithelium

MUCOUS ESCALATOR

• Function:

  • Traps dust/pathogens, humidifies air

  • Cilia move mucus and debris upward toward the pharynx

  • Not found in bronchioles/alveoli (local alveolar macrophages instead)

RESPIRATORY ZONE

• **Components: **

  • Respiratory bronchioles, Alveolar ducts, Alveolar sacs

• Cell Types in Alveoli:

  • Type I Cells: Squamous epithelium for gas exchange

  • Type II Cells: Secrete surfactant (chemical to reduce surface tension)

GAS EXCHANGE

• Occurs across:

  • Alveolar wall

  • Capillary wall (fused basal lamina)

• Properties:

  • Large surface area facilitates easy diffusion of CO2 and O2 due to their lipid solubility

SURFACTANT REGULATES SURFACE TENSION

• Type I epithelia are over 90% of alveoli for gas exchange

• Surfactant is crucial as water creates surface tension risking alveolar collapse

• Surface Tension Influence:

  • Too much makes lung inflation difficult, especially at lower volumes

  • Too little means no recoil leading to airway closure during expiration

TYPE II CELLS SECRETE SURFACTANT

• Surfactant lowers surface tension thus preventing small alveoli from collapsing into larger ones

• Clinical Relevance:

  • Respiratory Distress Syndrome: surfactant deficiency leads to instability and collapse of alveoli

ANATOMY FACILITATES VENTILATION

• Ventilation Process:

  • Move air in and out through Boyle’s law (closed system)

  • Inspiration:

    • Increase thoracic volume, decrease lung pressure

  • Expiration:

    • Decrease thoracic volume, increase lung pressure

RESPIRATORY MUSCLES

INSPIRATORY MUSCLES

• Diaphragm (contracted)

• External intercostals

• Accessory muscles: Pectoralis minor, Scalene, SCM

EXPIRATORY MUSCLES

• Diaphragm (relaxed)

• Internal intercostals

• Abdominal muscles (during forced expiration)

RESPIRATORY PRESSURES

• Components:

  • Atmospheric pressure

  • Intrapleural pressure

  • Intrapulmonary pressure (intra-alveolar pressure)

• Mechanics:

  • Diaphragm and inspiratory intercostals contract to create a pressure gradient

  • Leads to lung expansion and airflow into alveoli

  • Diaphragm relaxing/stopping leads to thorax recoiling, expelling air

PNEUMOTHORAX

• Loss of intrapleural pressure due to trauma/lung damage

• Normally, negative pressure in pleural cavity prevents lung collapse

PULMONARY VENTILATION

• Gas flow impacted by resistance in air passages

  • Physiologically:

    • Parasympathetic impact: constriction

    • Sympathetic impact: dilation

  • Highest resistance occurs in bronchioles

  • Bronchodilation & Bronchoconstriction deal with airway resistance

DEAD SPACES

• Gas exchange only occurs in specific lung regions:

  • Anatomical Dead Space:

    • Air in non-respiratory parts (conducting zone)

  • Physiological Dead Space:

    • Failure of respiratory zones for gas exchange, increased with aging

ALVEOLAR VENTILATION

• Measurement:

  • Components:

    • VD (dead space), VT (tidal volume), VA (alveolar ventilation)

  • Involves gas diffusion in lungs among O2 and CO2 transportation

GAS LAWS

PARTIAL PRESSURES

• Gas diffusion is dependent on partial pressure gradients

• Factors Determining Partial Pressure:

  • Concentration of gas

  • Barometric pressure

  • Normal Air Composition:

    • Mostly nitrogen and oxygen, negligible CO2

HENRY’S LAW

• At constant temperature, gas in solution is proportional to partial pressure

• Implications of altitude change on gas behavior in the body

GAS EXCHANGE IN ALVEOLI / TISSUES

• Pressure Values:

  • Air: Po₂ = 160 mmHg, Pco₂ = 0.3 mmHg

  • Alveoli: Po₂ = 100 mmHg, Pco₂ = 40 mmHg

  • Tissue: Po₂ < 40 mmHg, Pco₂ > 46 mmHg

• Transport pathways between pulmonary arteries, veins, and tissues are essential for respiration

CONCENTRATION & SOLUBILITY

• Increased concentrations enhance solubility (O2 binds to Hb)

• Important Note: CO2 is ~24 times more soluble than O2, allowing rapid diffusion and signaling for respiration

BLOOD BUFFER SYSTEM

• Functionality:

  • Donates and accepts H+ to maintain acid-base balance via bicarbonate buffering system

  • Impacts of hyperventilation/hypoventilation on pH, achieving acid-alkaline balance (pH 7.35 - 7.45)

VENTILATION – PERFUSION COUPLING

• Concepts:

  • Gas reaching an alveolus (ventilation)

  • Blood flow in capillaries (perfusion)

  • V/Q ratio is usually matched for optimal function in a healthy person

CONTROL OF BREATHING

PATTERN GENERATOR

• Functionality:

  • Rhythmic output of CNS to respiratory muscles located in the brainstem

CARDIORESPIRATORY INTEGRATION

• Hypoxia triggers increased respiration and heart rates via peripheral chemoreceptors

RESPIRATORY RHYTHM

• Established by the Pre-Bötzinger complex in the medulla (an inspiratory pacemaker)

• Modulated activity affects only inspiratory muscles

DORSAL RESPIRATORY GROUP

• Primarily sensory input, mostly inspiratory neurons

• Projects to other respiratory centers (Ventral & Pontine) and spinal motorneurons

CROSS-PERFUSION & CHEMORECEPTORS

• Presence in CNS for CO2 monitoring (specifically H+)

• Significance in respiratory control mechanisms

RETROTRAPEZOID NUCLEUS (RTN)

• Located in the medulla, controls the chemical drive to breathe by processing CO2 levels

ONDINE'S CURSE

• Congenital hypoventilation syndrome due to lack of transcription factor (Phox2b) in RTN, disrupting respiratory control

PONTINE RESPIRATORY GROUP

• Facilitates transition between inspiration and respiration phases, promoting effective expiration.