Comprehensive Guide to Respiratory Physiology: Functions, Mechanisms, and Regulation
Functions of the Respiratory System
- Regulation of blood pH
- Protection against microbes
- Making sounds used for speaking
Gas Exchange and Transport
Alveolar Sac
Function: Production of surfactant
Anatomical Dead Space
Structure NOT included: Respiratory bronchiole
Inhalation/Inspiration
Cause: Flattening (downward movement) of the diaphragm
Intrapleural Pressure
Normal state: Lower than alveolar pressure
Pressure Gradient
Effect on inhalation/inspiration: Increased pressure gradient from the atmosphere to the alveoli increases air flow into the alveoli
Transpulmonary Pressure
Effect on inhalation/inspiration: Increased transpulmonary pressure normally results in inhalation/inspiration
Pulmonary Surfactant
Effect: Increases the compliance of the lungs
Oxygen Transport
Form of oxygen in arterial blood: Bound to hemoglobin
Factor increasing oxygen binding to hemoglobin: Increased plasma PO2
Demonstration by oxygen-hemoglobin dissociation curve: At normal resting systemic arterial PO2, hemoglobin is almost 100% saturated with oxygen
Factor decreasing oxygen binding affinity of hemoglobin: Increased temperature of the blood
Carbon Dioxide Transport
Reaction catalyzed by carbonic anhydrase: H2O and CO2
Form of carbon transported to lungs: Dissolved HCO3-
Description of chloride shift: In the tissues, chloride enters red blood cells in exchange for bicarbonate ions
Effect of hypoventilation: Levels of blood H+ ions increase
Effect of hyperventilation: Decreased alveolar PCO2 and increased alveolar PO2
Respiratory Control
Neural Control
Action potentials in inspiratory center: Result in action potentials in the sympathetic nerves to the diaphragm, causing contraction of the muscle and an increase in the volume of the thoracic cage
Chloride Shift
Exchange of ions: Chloride ions for bicarbonate through tissue capillaries
Carbon Dioxide Transport
Majority of carbon dioxide transported in blood: Bicarbonate ion
Chemoreceptors
Location of peripheral chemoreceptors: Aortic and carotid bodies
Primary drive to breathe: Increased PCO2
Stimulation by inspiratory neurons: Phrenic nerve
Limits on lung stretching: Hering-Breuer reflex
Respiratory System Disorders
Function NOT performed by respiratory system: Regulation of body fluid
Gas Exchange in the Lungs
Site of initial gas exchange: Respiratory bronchioles
Physical Principles of Respiration
Boyle’s Law
Relationship described: Pressure exerted by a fixed number of gas molecules and the volume at some constant temperature
Elastic Recoil of the Lungs
Effect: Opposes expansion of the lungs
Lung Compliance
Effect of abnormally low lung compliance: Person must work harder than a normal person to inspire the same amount of air
Respiratory Diseases
Disease resulting from excessive airway constriction: Asthma
Lung Volumes and Capacities
Vital capacity: Sum of tidal volume, inspiratory reserve volume, and expiratory reserve volume
Anatomical dead space: Volume of conducting airways (about 150mL) not capable of exchanging gases with the blood
Gas Laws
Dalton’s Law
Statement: In a mixture of gases, the total pressure is the sum of the pressures of the individual gases, and the pressure each gas exerts is independent of the pressure the other gases exert
Ventilation-Perfusion Inequality
Effect of decreased alveolar PO2: Local vasoconstriction to decrease blood flow to the affected alveolus
Stimulus increasing blood flow through pulmonary capillary bed: Increased PO2 in the alveoli
Oxygen Transport in Blood
Form of most oxygen carried by blood: Bound to iron
Amount of oxygen leaving hemoglobin in tissues at rest: Approximately 25%
Effect of rapidly metabolizing tissues: Decreased affinity of hemoglobin for O2
Condition resulting in a shift from right to left in the Hb/O2 saturation curve: Blood flowing in capillaries to the alveoli
Carbon Dioxide Transport in Blood
Most effective mode of carbon dioxide transport: As bicarbonate
Molecule NOT bound by hemoglobin: Carbonic acid
Respiratory Control
Central Chemoreceptors
Location: Medulla
Stimulus: H+
Chemoreceptors NOT Regulating Respiration
Location: Heart ventricles
Chemoreceptors Regulating Respiration: Aortic bodies, Carotid bodies, Brain medulla