Mechanics of Breathing Flashcards
Four main functions of the respiratory system
- Exchange of gasses between the atmosphere and blood
- Homeostatic regulation of blood pH
- Protection from inhaled pathogens and irritating substances
- Speech/vocalization
Pressure gradient
Fluid flows from regions of high pressure to low pressure
Upper respiratory system
Nasal cavity, pharynx, down to top of trachea
Lower respiratory system
Trachea down through diaphragm
What does it mean to condition air in the upper respiratory system?
Warm, humidify, filter using nose hairs
Resistance to air flow is caused by?
Inappropriate bronchoconstriction and presents as wheezing. Smooth muscle surrounds the bronchioles to allow for changes in air resistance.
Thoracic cavity
Region of the chest housing the lungs. Lungs are sealed within the TC. The TC helps maintain appropriate pressure gradients. Each lung exists within its own membrane - pleural sac.
Bronchioles branch several times until they terminate in a cluster of?
Alveoli
Factors that affect airway resistance
- length of the system (which is constant)
- viscosity of air (changes slightly with humidity and altitude)
- diameter of upper airways (physical obstructions, mediated by mucus)
- diameter of bronchioles
What mediates bronchoconstriction?
parasympathetic neurons, histamine, leukotrienes
What mediates bronchodilation?
Carbon dioxide, epi
What surrounds a cluster of alveoli?
Elastic fibers and a network of capillaries
Two types of alveolar cells
Type I - gas exchange
Type II - secretes surfactant
Alveolar macrophage
Ingests foreign material
Pathway of oxygen from alveolar air space to RBC
- Alveolar air space
- Alveolar epithelium (covered in surfactant)
- “Fused basement membranes” tiniest space between basement membranes
- Capillary endothelium
- Plasma
- RBC
Upper airway mucus
Ciliated epithelium lines the upper airway/trachea secreting mucus from submucosal glands
Mucus traps inhaled particles and sits atop a watery saline layer that allows cilia to push mucus toward the pharynx (upwards)
Submucosal glands are made up of goblet cells which secretariat mucous
Cilia have a beating motion to clear pathogens. CF patients have thicker mucus which prevents this beating action.
What solution thins the mucous of the airway and how is it formed?
A saline layer sits atop the layer of respiratory epithelial cells. I
Chloride ions move into the epithelial cell from the ECF via secondary active transport. They then travel down their concentration gradient out of the epithelial cell to the lumen of airway via anion channels (CFTR).
Sodium ions follow through junctions between cells. Movement of ions into the lumen draws water through junctions between cells to form the saline layer.
Why does air move into the lungs when the thoracic cavity expands?
Volume increases so intrapleural pressure decreases forming a pressure gradient/negative pressure in the thoracic cavity so air flows down the pressure gradient into the lungs
How does altitude affect the partial pressure of oxygen?
Decreases
The % of oxygen in the air remains the same, but the amount we’re able to breathe decreases.
During inspiration, the diaphragm ________.
Contracts and flattens increasing the volume of the thoracic cavity
During expiration, the diaphragm ________.
Relaxes, decreasing the volume of the thoracic cavity
Pleural fluid
Fluid that keeps the lung adhered to the chest wall
What happens to the lungs during a pneumothorax?
Air flows into the pleural cavity, lung is no longer stuck to the chest wall, lung collapses
Surfactant
A fatty substance that reduces the surface tension of a liquid. Without surfactant, water-water interactions would make it harder to expand the alveolus.
Secreted by type II alveolar cells
Surrounds alveoli and aids in alveoli expansion especially when lung volume is low
Stale air in the respiratory system
After exhalation, 150 mL of stale air is left in the airway. This stale air is pushed down with the next inhalation in addition to fresh air. Fresh (Po2 = 150 mm Hg) and stale (Po2 = 100 mm Hg) mix. This leads to the Po2 of the alveoli being much lower than that of air.
Maximum alveolar partial pressure of oxygen
100 mm hg
How do changes in alveolar ventilation (volume/min) affect alveolar partial pressure of oxygen?
Decreasing ventilation decreases alveolar partial pressure of oxygen and vice versa to a maximum of 100 mm Hg
How does minute ventilation (L/min) change with exercise?
Exercise —> higher minute ventilation
How does arterial oxygen change with with exercise?
Stays the same - 100 mm Hg, max
How does arterial CO2 change with exercise?
Decreases with exercise
How does arterial pH change with oxygen consumption/exercise?
PH decreases (becomes more acidic) with more exercise
Breathing rate is governed by which gas in the body?
CO2
Very big changes in oxygen change breathing rate
Patients with lung disease for a long time will eventually switch over to using oxygen as a breathing rate signal because they’ve been in an oxygen-deprived state for a while
