5 - Respiration Flashcards
What are the two main components of respiration
Gas exchange between the blood and external environment (lungs to and from atmosphere)
Internal respiration – diffusion of O₂ and CO₂ between capillaries and body cells
What structures are included in the upper airway and what are their functions
Nasal cavity, pharynx, and larynx
They filter, warm, and humidify incoming air
What structures are included in the lower airway and what is their main function
Trachea, bronchi, bronchioles, and alveoli
They conduct air to the lungs and allow for gas exchange in the alveoli
What happens during inspiration (breathing in)
Diaphragm contracts and flattens
External intercostal muscles contract, lifting ribs
Thoracic volume increases → pressure decreases → air flows in
What happens during expiration (breathing out)
Diaphragm relaxes and domes
Intercostal muscles relax, ribs fall
Thoracic volume decreases → pressure increases → air flows out
What is Boyle’s Law and how does it relate to ventilation
At constant temperature, pressure and volume are inversely related (P₁V₁ = P₂V₂)
As lung volume increases, pressure decreases, allowing air to enter
Define Tidal Volume (TV)
Volume of air breathed in or out during normal quiet breathing (~500 mL)
What is Inspiratory Reserve Volume (IRV)
Extra volume of air that can be inhaled after a normal inhalation
What is Expiratory Reserve Volume (ERV)
Extra volume of air that can be forcefully exhaled after a normal expiration
What is Residual Volume (RV)
Volume of air remaining in lungs after the most forceful expiration
Define Inspiratory Capacity and Functional Residual Capacity
IC = TV + IRV
FRC = ERV + RV
What are the key thoracic pressures involved in breathing (4)
Atmospheric pressure (~760 mmHg)
Intrapulmonary pressure (inside alveoli)
Intrapleural pressure (in pleural space – always negative)
Transpulmonary pressure = intrapulmonary – intrapleural
How do pressure changes allow for inspiration and expiration
Inspiration: Intrapulmonary < Atmospheric → air in
Expiration: Intrapulmonary > Atmospheric → air out
How is airway diameter regulated
Smooth muscle in bronchioles
Sympathetic NS → bronchodilation (β₂ receptors)
Parasympathetic NS → bronchoconstriction
What is asthma and how does it affect the airways
Chronic inflammation causes airway narrowing, excess mucus, and bronchospasms
Increases airway resistance and reduces oxygen exchange
What affects airway resistance
Airway diameter (↓ in asthma/COPD → ↑ resistance)
What is lung compliance
Ease of lung expansion
↓ in fibrosis (stiff)
↑ in emphysema (floppy)
What does breathing work overcome
Airway resistance + elastic/stretching forces
What is surface tension in alveoli
Force from fluid lining alveoli, can cause collapse
What is the role of surfactant
Reduces surface tension, prevents collapse, ↑ lung compliance; made by type II alveolar cells
Where does gas exchange occur
Across alveolar-capillary membrane via diffusion
What drives diffusion of O₂ and CO₂
Partial pressure gradients
Henry’s Law
Gas dissolves ∝ partial pressure & solubility
Fick’s Law
Diffusion ∝ surface area × gradient / thickness
Graham’s Law
Diffusion ∝ solubility / √molecular weight
How is CO₂ transported in blood
10% dissolved
30% bound to Hb
60% as bicarbonate (HCO₃⁻)
What is the role of the bicarbonate buffer system
Regulates blood pH (7.35–7.45) via:
CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻
What is the Haldane effect
Deoxygenated Hb can carry more CO₂
What does spirometry measure
TV, FVC, FEV₁, FEV₁/FVC ratio
What does a low FEV₁/FVC ratio indicate
Obstructive disease (e.g., asthma, COPD)
What pattern is seen in restrictive disease
↓ FVC, normal/increased FEV₁/FVC ratio (e.g., fibrosis)
How is oxygen transported in blood
98.5% bound to Hb, 1.5% dissolved in plasma
What is the Bohr effect
↑ CO₂, H⁺, or temp → curve shifts right → O₂ released more easily to tissues
What brain areas control ventilation
Medulla (DRG & VRG) and Pons
What do chemoreceptors monitor
Central (medulla): CO₂ and pH (via CSF)
Peripheral (carotid/aortic bodies): ↓ O₂, ↑ CO₂, ↓ pH
What’s the issue at high altitudes
↓ PO₂ → hypoxia
Altitude acclimation - How does the body respond short-term
Hyperventilation to bring in more O₂
What is EPO and how does it help altitude acclimatisation
Erythropoietin is a hormone from kidneys
Increases RBC production → ↑ Hb → better O₂ carrying
What are long-term adaptations to altitude
↑ 2,3-BPG → Hb releases O₂ more easily
↑ Capillary density
↑ Mitochondrial enzymes
