Respiratory Physiology Flashcards
What is the role of the respiratory system in pH regulation?
- Removes CO2, which helps regulate H+ ion concentration (affects acidity).
- Increased CO2 leads to increased H+ ions (more acidic environment)
What are the functions of the respiratory system? (6 points)
- Provides oxygen to tissues for metabolism
- Removes carbon dioxide and regulates pH
- Endocrine functions (activates angiotensin II)
- Immunological functions (clears irritants, pathogens)
- Voice production
- Water loss and heat elimination
How does the respiratory system contribute to immune defense?
- Clears irritants and potential pathogens (bacteria, viruses).
- Alveolar macrophages engulf foreign particles
List the components of the respiratory system involved in ventilation.
- Nasal passages
- Pharynx
- Larynx
- Trachea
- Right and left bronchi
- Bronchioles
- Alveoli
How is pleural pressure generated?
- The pleural cavity, containing intrapleural fluid, creates a pressure lower than atmospheric pressure.
- When the diaphragm contracts, it pulls the parietal pleura, expanding the lungs and decreasing pleural pressure.
Why is intrapleural pressure lower than atmospheric pressure?
The lungs are always stretched to some degree due to the pressure difference, which keeps them from collapsing.
How does intrapleural pressure help lung expansion?
A lower intrapleural pressure compared to intra-alveolar pressure allows the lungs to expand as the thoracic cavity enlarges.
What changes occur in alveolar pressure during inspiration?
During inspiration, intra-alveolar pressure < atmospheric pressure, = air to flow into lungs.
What is the relationship between alveolar pressure and atmospheric pressure during expiration?
During expiration, intra-alveolar pressure > atmospheric pressure = push air out of the lungs.
How is a negative alveolar pressure created during inspiration?
- Diaphragm contracts
- This expands the thoracic cavity
- Which decreases intra-alveolar pressure below atmospheric pressure = draw air in
How is a positive alveolar pressure created during expiration?
- Diaphragm relaxes
- Decreases the thoracic cavity volume
- This increases intra-alveolar pressure above atmospheric pressure = push air out.
What are the pressures involved in ventilation?
- Atmospheric pressure: 760 mmHg (at sea level)
- Intra-alveolar pressure: varies with ventilation
- Intrapleural pressure: 756 mmHg (lower than atmospheric)
How does air move in and out of the lungs?
Air moves according to pressure gradients; air flows from areas of higher pressure to areas of lower pressure.
What happens to the pleural pressure during inspiration?
Diaphragm contract = pleural pressure dec. & thoracic cavity expands
What role does the diaphragm play in ventilation?
During inspiration = diaphragm contract = inc. thoracic cavity vol.
During expiration = diaphragm relax = reduce thoracic cavity vol.
How do intercostal muscles contribute to ventilation?
- Ext intercostal muscles elevate ribs during inspiration = inc. thoracic cavity vol.
- int. intercostal muscles help during forced expiration
What is the relationship between the pleural cavity and lung expansion?
Pleural cavity contains fluid that allows lung to expand & contract w/o friction as pleural layers slide over e/o
What is the function of alveoli in gas exchange?
Alveoli provide a large SA for O2 and CO2 exchange b/w air and blood in capillaries.
How does gas exchange occur in the alveoli?
Diffusion
O2 move from alveoli into blood
CO2 move from blood into alveoli
What is the importance of surfactant in the alveoli?
Reduce tension = prevent alveoli from collapsing & ensure efficient gas exchange
What is the role of the pleura in lung function?
Visceral pleura covers lungs
Parietal pleura lines the thoracic cavity.
The pleural cavity b/w helps reduce friction and help in lung expansion.
How does the pleural pressure prevent lung collapse?
Negative pleural pressure (below atm pressure) keeps lung partially inflated = prevent collapse
How does pleural effusion affect lung function?
Pleural effusion = fluid in pleural cavity (>50mL)
affect lung expansion & reduce gas exchange efficiency
What is pneumothorax, and how does it affect the lungs?
Air enters pleural cavity
Cause lung to collapse bc of loss of -ve pleural pressure
How does airway resistance affect airflow?
Inc. resistance (e.g. bronchoconstriction) dec. air flow
Dec. resistance (e.g. bronchodilation) inc. air flow
What is the function of the conducting zone of the respiratory system?
Conducting zone = trachea to terminal bronchioles
Tpt air to lungs but does not participate in gas exchange
What is the respiratory zone?
Resp. zone = resp bronchioles to alveolar sacs
where gas exchange occurs in lungs
How does the autonomic nervous system regulate airway diameter?
Sympathetic stimulation = bronchodilation
parasympathetic stimulation = bronchoconstriction
What happens to alveolar pressure at the end of inspiration and expiration?
At the end of inspiration & expiration:
Alveolar pressure = atm pressure
How is alveolar ventilation calculated?
Alveolar Ventilation = (Tidal Volume – Dead Space) × Breaths per minute
What are the key components involved in ventilation and gas exchange by diffusion?
- Fresh air reaching the alveoli
- Effective diffusion of air across the alveolar-capillary barrier
- Efficient removal of CO2 from the lungs
What factors influence effective oxygenation and CO2 removal in the lungs?
- Ventilation : sufficient air reaching alveoli
- Perfusion : sufficient blood flow to alveoli
- Diffusion : efficient gas exchange across alveolar-capillary barrier
How does partial pressure drive the diffusion of O2 and CO2?
- Gas diffuses from areas of high partial pressure to low partial pressure until equalized.
E.g. O2 moves from alveoli (high O2 pressure) to capillary blood (low O2 pressure).
What is partial pressure and how is it calculated for O2 in the air?
Partial pressure is the pressure a gas exerts in a mixture, proportional to its percentage.
Partial pressure = % of O2 in air x total air pressure
E.g. Partial pressure = 0.21 (21% of air is O2) x 760 mm Hg (total air pressure at sea level)
How does CO2 diffuse from capillaries to the alveoli?
CO2 moves from capillaries (high CO2 partial pressure) to alveoli (low CO2 partial pressure), driven by the pressure gradient.
What influences the rate of gas transfer across the alveolar membrane?
- Partial pressure differences
- Thickness of the alveolar-capillary barrier
- Surface area for diffusion
How does exercise affect the rate of gas diffusion across the alveoli?
Exercise = more alveoli open = inc. the surface area for diffusion and the rate of gas exchange.
Why does the diffusion of gases stop once partial pressures are equalized?
Diffusion only occurs when there is a difference in partial pressure.
Once equalized, no further movement occurs.
What are the main barriers to gas diffusion in the alveoli?
- Alveolar epithelium
- Capillary endothelium
- Basement membranes
How does surface area affect gas exchange in the lungs?
Larger surface area allows more gas to diffuse across the alveolar membrane
What happens if the surface area for diffusion is reduced, such as in emphysema?
Emphysema : lung dz that results from damage to walls of alveoli
reduced SA limits the amt of gas exchange, leading to poor oxygenation of blood
How does the rate of blood flow through the alveoli affect gas exchange?
Blood flow must allow sufficient time for gases to diffuse & equilibrate across the alveolar membrane
What happens when blood flow to an alveolus ceases?What happens when blood flow to an alveolus ceases?
Gas exchange stops, as blood is no longer available to transport O2 and CO2 (e.g., in pulmonary embolism).
How does gravity affect the perfusion of the lungs?
Blood flow is greater at the base of the lungs due to gravity, with less perfusion at the apex
What are the characteristics of pulmonary circulation?
Low pressure, high volume system that always receives 100% of cardiac output
How does the low-pressure nature of pulmonary circulation affect gas exchange?
Low pressure allows blood to flow more slowly, giving gases time to exchange across the alveolar membrane
What is the difference between pulmonary and systemic circulation in terms of pressure?
Pulmonary artery pressure: ~25/15 mmHg
Systemic artery pressure: ~120/80 mmHg
How do ventilation and perfusion ratios vary between the apex and base of the lungs?
Apex: more ventilation, less perfusion
Base: more perfusion, less ventilation
What are the local controls to match airflow and blood flow of the lung (large air-flow / small blood flow)?
i.e. apex of lungs
- Areas with more O2 (i.e. apex of lungs) = pulmonary arteriolar smooth muscle relax = dilation of local blood vessels = dec. vascular resistance = inc. bld flow to these areas
- Areas with low CO2 (i.e. apex of lungs) = inc. contraction of local-airway smooth muscle = constriction of local airways = inc. airway resistance = dec. airflow to these areas
What is tidal volume (TV)?
Volume of air entering or exiting the lungs during a normal breath (usually ~500 mL)
What are the local controls to match airflow and blood flow of the lung (small air-flow / large blood flow)?
i.e. base of the lungs
- Areas with less O2 (i.e. base of lung) = inc contraction of local pulmonary arteriolar smooth muscle = constriction of local bld vessels = inc. vascular resistance = dec. bld flow
- areas with high CO2 (i.e. base of lungs) = relaxation of local airway smooth muscle = dilation of local airways = dec. airway resistance = inc airflow
What is inspiratory reserve volume (IRV)?
The additional air that can be inhaled with a maximum effort after a normal tidal inhalation
What is expiratory reserve volume (ERV)?
The additional air that can be exhaled with a maximum effort after a normal tidal exhalation
What is residual volume (RV)?
The volume of air remaining in the lungs after a maximal expiration (~1.2 L in men)
What factors can change lung volume measurements?
Factors like activity level, age, size, and physical fitness can alter tidal volume, IRV, ERV, and RV
What is vital capacity (VC)?
The total amount of air that can be exhaled after a maximal inhalation (TV + IRV + ERV).
How does physical activity affect tidal volume?
Tidal volume increases during exercise as the body demands more oxygen and removes more CO2
What is minute ventilation, and how is it calculated?
- Minute ventilation = Tidal volume (TV) × Respiratory rate
- Represents total volume of air moved into and out of the lungs per minute.
What is alveolar ventilation?
- Volume of air that reaches the alveoli and participates in gas exchange per minute
- Alveolar Ventilation = (TV – Dead Space) × Respiratory Rate
How is ventilation controlled?
Controlled by central and peripheral chemoreceptors –> respond to changes in CO2, O2, and pH levels
What are central chemoreceptors, and how do they control breathing?
- Central chemoreceptors located in the medulla
- Detect changes in CO2 levels in cerebrospinal fluid, inc respiratory rate when CO2 rises.
How do peripheral chemoreceptors contribute to the control of respiration?
- Peripheral chemoreceptors located in the carotid and aortic bodies
- Detect changes in O2 and H+ levels = triggering inc in ventilation when O2 drops or H+ increases.
What is the main respiratory regulator?
pCO2 is the main regulator of respiration, primarily affecting central chemoreceptors
How does pO2 affect respiration? (peripheral chemoreceptors)
Peripheral chemoreceptors respond to pO2 levels, but are only triggered when arterial pO2 drops below 60 mmHg.
What happens to CO2 in the blood during gas transport
CO2 is transported in three forms:
- Dissolved CO2 (~7%)
- Bound to hemoglobin (~23%)
- bicarbonate ions (HCO3-, ~70%)
What is the chloride shift, and why is it important in CO2 transport?
The chloride shift exchanges bicarbonate ions (HCO3-) with chloride ions (Cl-) to maintain electrical neutrality during CO2 transport
Cl- shift exchanges ions (HCO3-) with Cl- = maintain electrical neutrality during CO2 tpt
How does H+ affect breathing?
Increased H+ concentration (due to rising CO2) lowers blood pH = stimulates central and peripheral chemoreceptors to inc respiration
How does hyperventilation affect blood pH?
Hyperventilation lowers CO2 levels, which reduces H+ concentration and inc. blood pH (causing alkalosis).
How does alveolar area affect gas diffusion?
- Larger alveolar area increases surface area for gas exchange = improve diffusion
- Reduced alveolar area (e.g., in emphysema) dec diffusion efficiency
How does membrane thickness affect gas diffusion?
- Thicker alveolar-capillary membranes (e.g., fibrosis, edema) slow down diffusion
- Normal membrane thickness (~0.5 µm) allows rapid diffusion of O2 and CO2
What happens to gas diffusion at high altitudes?
Reduced atmospheric pressure = dec the partial pressure of O2 = less O2 diffusion across the alveolar membrane
How does abnormal thickening of the alveolar-capillary barrier affect diffusion?
Conditions like pulmonary fibrosis or edema increase barrier thickness = slow gas diffusion.
What is lung compliance?
- Lung compliance refers to how easily the lungs and chest wall expand in response to pressure changes
- Compliance = Change in lung volume / Change in pressure (ΔV/ΔP)
How does elastic recoil affect lung compliance?
- Greater lung recoil (e.g., in fibrosis) dec. compliance = make lungs stiffer and harder to inflate
- Lower lung recoil (e.g., in emphysema) inc. compliance = lungs easy to inflate but harder to empty.
What role does surface tension play in lung compliance?
Surface tension in the alveoli creates inward pressure = reduce compliance = harder for the lungs to expand
What is the function of surfactant in the lungs?
Surfactant dec. surface tension in the alveoli = prevent collapse & improve lung compliance
How does the absence of surfactant affect lung function?
Lack of surfactant (e.g., in premature babies) causes alveolar collapse = leads to respiratory distress syndrome
How does surfactant contribute to alveolar stability at low lung volumes?
Surfactant lowers surface tension more in smaller alveoli = equalise pressure (with larger alveoli) = preventing collapse
What is alveolar interdependence?
Refers to the mechanical support alveoli provide each other to prevent collapse = maintaining alveolar stability
What factors affect airway resistance?
- Airway diameter (narrower airways increase resistance).
- Lung volume (lower volume increases resistance).
- Mucus accumulation.
- Bronchoconstriction (e.g., in asthma)
How does bronchoconstriction affect airway resistance?
Constriction of bronchioles (e.g., due to irritants or asthma) narrows the airways = inc. resistance = make breathing difficult
What is spirometry, and what does it measure?
Spirometry is a test that measures lung volumes and airflow rates. It is used to assess conditions like asthma and COPD
How do sympathetic and parasympathetic nerves affect airway resistance?
Sympathetic stimulation: bronchodilation = reducing resistance
Parasympathetic stimulation: bronchoconstriction = inc resistance
What does FEV1/FVC represent in spirometry?
FEV1: forced expiratory volume in 1 second after a full inspiration
FVC: forced vital capacity, or the total air expired forcefully
FEV1/FVC < 0.8 may indicate airway narrowing (e.g. asthma)
How is oxygen transported in the blood?
- 98% of oxygen is tpted bound to hemoglobin (Hb).
- 1-2% dissolved in plasma
How is carbon dioxide transported in the blood?
- 70% as bicarbonate (HCO3-)
- 23% bound to proteins, including hemoglobin (as carbamino compounds)
- 7% dissolved in plasma
What factors affect hemoglobin’s affinity for oxygen?
- pH (Bohr effect)
- temperature
- levels of 2,3-DPG
Lower pH, higher temperature, and higher 2,3-DPG levels dec. affinity = promote O2 release to tissues
What is the oxygen-hemoglobin dissociation curve?
- The curve shows the rs b/w partial pressure of O2 (PO2) & hemoglobin saturation
- Has a sigmoidal shape, with a plateau in the lungs and a steep slope in tissues
How does the oxygen-hemoglobin curve shift during exercise?
- During exercise, the curve shifts to the right - - indicates reduced hemoglobin affinity for O2 = facilitates O2 release to tissues
What is the Bohr effect?
Describes how lower pH (higher H+ concentration) dec. hemoglobin’s affinity for O2 = enhance O2 release to tissues
How does temperature affect the oxygen-hemoglobin dissociation curve?
inc. temperature dec. hemoglobin’s affinity for O2 = shift the curve to the right and promoting O2 release
How does 2,3-DPG affect oxygen transport?
2,3-DPG dec. hemoglobin’s affinity for O2 = facilitates O2 release to tissues
esp during hypoxia/exercise
How does exercise affect O2 and CO2 balance in the body?
Inc. oxygen dd and CO2 production = body inc. ventilation & blood flow to match metabolic needs
What happens to CO2 levels during exercise?
CO2 levels inc = ventilation inc to remove excess CO2 & maintain acid-base balance
How does the body maintain acid-base balance during exercise?
Inc. ventilation removes CO2 = reducing H+ conc. & helping to maintain blood pH
How does oxygen delivery to tissues change during exercise?
- Oxygen delivery inc. due to inc. cardiac output
- more efficient hemoglobin oxygen release (due to lower affinity) + enhanced tissue perfusion
What is the chloride shift, and how does it relate to CO2 transport?
Cl- shift exchanges bicarbonate (HCO3-) with chloride (Cl-) in RBCs = maintain electrical neutrality during CO2 tpt
What is the normal PO2 and PCO2 in alveolar air?
PO2: 102 mm Hg
PCO2: 40 mm Hg
