Respiratory Physiology (Day 1) Flashcards
Ventilation (breathing)
mechanical process that moves air into and out of the lungs
Where does gas exchange occur?
between blood and lungs
between blood and tissues
Cellular Respiration
oxygen utilization by tissues to make ATP
External respiration
ventilation and gas exchange in lungs
Internal respiration
oxygen utilization and gas exchange in tissues
Gas Exchange in Lungs
Occurs via diffusion
O2 concentration is higher in the lungs than in the blood, so O2 diffuses into blood.
CO2 concentration in the blood is higher than in the lungs, so CO2 diffuses out of blood.
Respiratory System Functions
GAS EXCHANGE between the atmosphere and the blood—brings in O2, eliminates CO2
Homeostatic REGULATION OF BODY PH—via selective retention vs excretion of CO2
PROTECTION from inhaled pathogens and irritating substances—via trapping & either expulsion or phagocytic destruction of potentially harmful substances, pathogens
VOCALIZATION—vibrations created by air passing over vocal cords
Conduction Zone
–>gets air to respiratory zone
trachea
primary bronchus
terminal bronchioles
Respiratory Zone
–> site of gas exchange
respiratory bronchioles
alveolar sacs
alveolus
What is the passage of inspired air?
nasal cavity
pharynx
larynx (through glottis and vocal cords)
trachea
R/L primary bronchi
Secondary bronchi
more branching
terminal bronchioles
respiratory zone (respiratory bronchioles)
terminal alveolar sacs
What does mucus do?
traps small particles
What do cilia do?
move small particles away from lungs by mucus
What is the structure of a lung lobule?
Each cluster of alveoli is surrounded by elastic fibers and a network of capillaries
Alveoli
Air sacs where gas exchange occurs
300 x 10^6 ; provide large surface area (760 ft^2) to increase diffusion rate
Each alveolus: one-cell layer thick
Form clusters at the ends of respiratory bronchioles
What are the two types of alveolar epithelial cells?
Type I: 95−97% total surface area where gas exchange occurs
Type II: secrete pulmonary surfactant and reabsorb sodium and water, preventing fluid buildup
Thoracic Cavity
- Contains the heart, trachea, esophagus, and thymus within the central mediastinum
- -> The lungs fill the rest of the cavity.
Pleura
parietal pleura: lines thoracic wall
visceral pleura: covers the lungs
normally pushed together, with a fluid-filled space between called the intrapleural space (pleural cavity).
diaphragm
a dome-shaped skeletal muscle of respiration that separates the thoracic and abdominal cavities
Physical aspects of ventilation
Air moves from higher to lower pressure.
Pressure differences between the two ends of the conducting zone occur due to changing lung volumes.
Compliance, elasticity, and surface tension are important physical properties of the lungs.
What are the types of pressure?
- Atmospheric pressure: pressure of air outside the body
- Intrapulmonary or intraalveolar pressure: pressure in the lungs
- Intrapleural pressure: pressure within the intrapleural space (between parietal and visceral pleura); contains thin layer of fluid to serve as a lubricant
Pressure differences when breathing
- Inspiration (inhalation): Intrapulmonary pressure Pressure atmospheric pressure (generally about +3mmHg)
Intrapleural Pressure
LESS than P(intrapulmonary) and P(atmospheric) in both inspiration and expiration
P(intrapulmonary) - P(intrapleural) = P(transpulmonary)
Keeps lungs against thoracic wall, allowing lungs to expand during inspiration
Pneumothorax
If the sealed pleural cavity is opened to the atmosphere, air flows in. The bond holding the lung to the chest wall is broken, and the lung collapses, creating a pneumothorax
(air in the thorax).
Boyle’s Law
↑ lung volume during inspiration ↓’s P(intrapulmonary) to Air flows in.
↓ lung volume during expiration –> P(intrapulmonary) > P(atmospheric) –> Air flows out.
Lung compliance
Lungs expand when stretched.
Defined as change in lung volume per change in transpulmonary pressure: ΔV/ΔP
Index of the ease with which the lungs expand under pressure—> high compliance: easily stretched
–> low compliance: requires more force, restrictive lung diseases (e.g. pulmonary fibrosis, surfactant deficiency)
Lung elasticity
Return to initial size after being stretched (recoil)
Lungs have elastin fibers.
Because the lungs are stuck to the thoracic wall, they are always under elastic tension.
Tension increases during inspiration and is reduced by elastic recoil during expiration.
Surface Tension
“force holding fluid molecules together in an air-fluid interface… due to strong attractive force of H bonds between H2O molecules”
Resists distension, promotes collapse of alveolar space
Exerted by fluid secreted on the alveoli
Fluid is absorbed by active transport of Na+ and secreted by active transport of Cl-
–> any imbalance between these can result in viscous fluid that is difficult to clear –> raises the pressure of the alveolar air as it acts to collapse the alveolus
Ex. People with cystic fibrosis have a genetic defect that causes such an imbalance of fluid absorption and secretion
Law of Laplace
Pressure is DIRECTLY proportional to surface tension and INVERSELY proportional to radius of alveolus.
Small alveoli would be at greater risk of collapse without surfactant.
Surfactant
SURFACE ACTIVE AGENT
Secreted by type II alveolar cells
Consists of hydrophobic protein and phospholipids
REDUCES surface tension between water molecules by reducing the number of hydrogen bonds between water molecules
More concentrated as alveoli get smaller during expiration to equalize pressure.
Prevents collapse
Allows a residual volume of air to remain in lungs
Respiratory Distress Syndrome
Production of surfactant begins late in fetal life, so premature babies have higher risk for alveolar collapse–respiratory distress syndrome (RDS)
–> treated with surfactant
Similar problem may occur in adults with septic shock
–↓ lung compliance, ↓ surfactant—acute respiratory distress syndrome (ARDS); NOT treatable with surfactant
Muscles of Inspiration: Sternocleidomastoid, Scalenes
used for forced inspiration
Muscles of Inspiration: External Intercostals
raises rib cage during inspiration
Muscles of Inspiration: Parasternal intercostals
works w/external intercostals
Muscles of Inspiration: Diaphragm
contracts in inspiration - lowers –> enlarging thoracic cavity
relaxes in expiration - raises –> thoracic cavity smaller
Muscles of Expiration: Internal Intercostals
lowers rib cage during forced expiration
Muscles of Expiration: External Abdominal Obliques, Internal Abdominal Oblique, Transversus Abdominus, Rectus Abdominus
abdoominal muscles are also used in forced expiration
Quiet Expiration
occurs with the relaxation of the inspiratory muscles (PASSIVE)
Inspiration
Volume of thoracic cavity (and lungs) increases vertically when diaphragm contracts (flattens) and laterally when parasternal and external intercostals raise the ribs.
–Thoracic & lung volume increase –> intrapulmonary pressure decreases –> air in
–occurs when alveolar pressure decreases
- thoracic cage expands outwards
- diaphragm drops down- contracts and flattens
- -> both of these lead to increased thoracic volume and decreased thoracic (alveolar) pressure
Expiration
Volume of thoracic cavity (and lungs) decreases vertically when diaphragm relaxes (dome) and laterally when external and parasternal intercostals relax for quiet expiration or internal intercostals contract in forced expiration to lower the ribs.
–Thoracic & lung volume decrease –> intrapulmonary pressure increases –> air out
Regulation of Ventilation
Unlike cardiac muscle, skeletal muscles are NOT spontaneously active, so they must be stimulated by nerve signals.
Rhythmic pattern of contraction & relaxation of breathing muscles arises from a neural network of spontaneously discharging motor neurons from:
- CEREBRAL CORTEX (voluntary breathing)
- MEDULLA OBLONGATA and PONS (Involuntary breathing)
Motor neurons– innervate diaphragm/other breathing muscles; regulated by descending neurons from the brainstem (Medulla & Pons).
Control of Breathing: Medulla
Two rhythmicity centers: excitatory inspiratory neurons vs neurons which inhibit those inspiratory neurons—intrinsic rhythmicity, but influenced by other factors.
1) Involuntary breathing (e.g. at rest)
- intrinsic to medulla
2) Voluntary (“forced,” e.g. exercise)
- input from cerebral cortex
Control of Breathing: Pons
Two resp control centers:
1) apneustic (stimulates inspiratory neurons in medulla)
2) pneumotaxic (antagonizes apneustic to inhibit inspiration)
