Control of Respiratory Function

Components of the Respiratory System
Ventilation
The movement of air between the atmosphere and the respiratory portion of the lungs
Perfusion
The flow of blood through the lungs
Diffusion
The transfer of gases between the air-filled spaces in the lungs and the blood
Structural Organization of the Respiratory System
Consists of the air passages and the lungs
Divided into two parts by function:
Conducting airways: through which air moves as it passes between the atmosphere and the lungs
Respiratory tissues of the lungs: where gas exchange takes place

Structures of the Conducting Airways
Nasal passages
Mouth and pharynx
Larynx
Trachea
Bronchi
Bronchioles
Ventilation
Depends on the conducting airways:
Nasopharynx and oropharynx
Larynx
Tracheobronchial tree
Function:
Moves air out of the lung but does not participate in gas exchange
Structure and Function of the Larynx
Structure
Connects the oropharynx with the trachea
Located in a strategic position between the upper airways and the lungs
Functions
Helping to produce speech
Protecting the lungs from substances other than air
Valsalva Maneuver
During elimination inhaled air is held in the lungs by a closed glottis
The intra-abdominal muscles contract and intra-abdominal and intrathoracic pressures rise
An increase in intrathoracic pressure decreases the return of blood to the heart, inciting circulatory reflexes
Tachycardia develops as compensation for the decrease in blood return to the heart
Upon termination, a short period of bradycardia occurs

Structures of the Lungs
Soft, spongy, cone-shaped organs located side by side in the chest cavity
Separated from each other by the mediastinum and its contents
divided into lobes (3 in the right lung, 2 in the left).
Apex: upper part of the lung; lies against the top of the thoracic cavity
Base: lower part of the lung; lies against the diaphragm
Composition of the Alveolar Structures
Type I alveolar cells
Flat squamous epithelial cells across which gas exchange takes place
Type II alveolar cells
Produce surfactant, a lipoprotein substance that decreases the surface tension in the alveoli and allows for greater ease of lung inflation
Lung Circulation
Pulmonary circulation
Arises from the pulmonary artery
Provides for the gas exchange function of the lungs
Bronchial circulation
Arises from the thoracic aorta
Supplies the lungs and other lung structures with oxygen
Distributes blood to the conducting airways
Warms and humidifies incoming air
Ventilation and Gas Exchange
Ventilation
The movement of gases into and out of the lungs
Inspiration
Air is drawn into the lungs as the respiratory muscles expand the chest cavity
Expiration
Air moves out of the lungs as the chest muscles recoil and the chest cavity becomes smaller
Respiratory Pressures
Intrapulmonary pressure or alveolar pressure
Pressure inside the airways and alveoli of the lungs
Intrapleural pressure
Pressure in the pleural cavity
Intrathoracic pressure
Pressure in the thoracic cavity
Lung Compliance
Lung compliance
(C) = (ΔV)/(ΔP)
The change in lung volume (ΔV) that can be accomplished with a given change in respiratory pressure (ΔP)
Airway Resistance
Airway Resistance
The volume of air that moves into and out of the air exchange portion of the lungs
Directly related to the pressure difference between the lungs and the atmosphere
Inversely related to the resistance the air encounters as it moves through the airways

Lung Volumes
Tidal volume (TV)
Amount of air that moves into and out of the lungs during a normal breath
Inspiratory reserve volume (IRV)
The maximum amount of air that can be inspired in excess of the normal TV
Lung Volumes (cont.)
Expiratory reserve volume (ERV)
Maximum amount of air that can be exhaled in excess of the normal TV
Residual volume
The air that remains in the lungs after forced respiration

Lung Capacities
Vital capacity: equals the IRV plus the TV plus the ERV
The amount of air that can be exhaled from the point of maximal inspiration
Inspiratory capacity: equals the TV plus the IRV
The amount of air a person can breathe in beginning at the normal expiratory level and distending the lungs to the maximal amount
Lung Capacities (cont.)
Functional residual capacity: the sum of the RV and ERV
The volume of air that remains in the lungs at the end of normal expiration
Total lung capacity: the sum of all the volumes in the lungs

Pulmonary Function Studies
Maximum voluntary ventilation
The volume of air a person can move into and out of the lungs during maximum effort lasting for 12 to 15 seconds
Forced expiratory vital capacity (FVC)
Involves full inspiration to total lung capacity followed by forceful maximal expiration.
Pulmonary Function Studies (cont.)
Forced expiratory volume (FEV)
The expiratory volume achieved in a given time period
Forced inspiratory vital flow (FIF)
The respiratory response during rapid maximal inspiration

Processes of Pulmonary Gas Exchange
Ventilation
The flow of gases into and out of the alveoli of the lungs
Perfusion
The flow of blood in the adjacent pulmonary capillaries
Diffusion
Transfer of gases between the alveoli and the pulmonary capillaries
Types of Air Movement in the lung
Bulk flow
Occurs in the conducting airways
Controlled by pressure differences between the mouth and that of airways in the lung
Diffusion
The movement of gases in the alveoli and across the alveolar capillary membrane
Types of Dead Space
Anatomic dead space
That contained in the conducting airways
Alveolar dead space
That contained in the respiratory portion of the lung
Physiologic dead space
The anatomic dead space plus alveolar dead space
Types of Shunts
Anatomic shunt
Blood moves from the venous to the arterial side of the circulation without moving through the lungs
Physiologic shunt
Mismatching of ventilation and perfusion with the lung
Results in insufficient ventilation to provide the oxygen needed to oxygenate the blood flowing through the alveolar capillaries
Factors Affecting Alveolar-Capillary Gas Exchange
Surface area available for diffusion
Thickness of the alveolar-capacity membrane
Partial pressure of alveolar gases
Solubility and molecular weight of the gas
Matching Ventilation and Perfusion
Required for exchange of gases between the air in the alveoli and the blood in pulmonary capillaries
Two factors interfere with the process:
Dead air space and shunt
The blood oxygen level reflects the mixing of blood from alveolar dead space and physiologic shunting areas as it moves into the pulmonary veins

Mechanisms of Carbon Dioxide Transport
Dissolved in carbon dioxide (10%)
Attached to hemoglobin (30%)
Bicarbonate (60%)
Acid-base balance is influenced by the amount of dissolved carbon dioxide and the bicarbonate level in the blood

Control of Breathing
Automatic regulation of ventilation
Controlled by input from two types of sensors or receptors:
Chemoreceptors: monitor blood levels of oxygen, carbon dioxide and adjust ventilation to meet the changing metabolic needs of the body
Lung receptors: monitor breathing patterns and lung function
Control of Breathing (cont.)
Voluntary regulation of ventilation
Integrates breathing with voluntary acts such as speaking, blowing, and singing
These acts, initiated by the motor and premotor cortex, cause a temporary suspension of automatic breathing

Mechanisms Involved in Dyspnea
Stimulation of lung receptors
Increased sensitivity to changes in ventilation perceived through central nervous system mechanisms
Reduced ventilatory capacity or breathing reserve
Stimulation of neural receptors in the muscle fibers of the intercostals and diaphragm and of receptors in the skeletal joints