Respiratory Physiology Flashcards
Functions of respiratory system
Gas exchange Acid-base balance Thermoregulation Immune function Vocalization Enhances venous return
Air passages
Mouth/nose Pharynx Larynx Trachea Bronchi Bronchioles Alveoli
Bronchioles
Bronchoconstrict or dilate
Control air flow
Smooth muscle
Alveoli
Site of gas exchange Thin walled Large surface area (75m2) Contain fine elastic fibres Pores of kohn connect adjacent alveoli (helps equalize air pressure)
Types of alveolar cells
Type 1 = make up the wall
Type 2 = secrete surfactant (decreases surface tension)
Macrophages = immune function
Respiration
Ventilation
External respiration (gas exchange between alveoli and blood)
Gas transport
Internal respiration (gas exchange between blood and tissues)
Mechanics of breathing
2 phases = inspiration (gases flow into the lungs), expiration (gases exit the lungs)
Dependant on pressure differences
Pressure relationships in the thoracic cavity
Atmospheric (air) pressure (Patm) = 70 mm Hg at sea level
Respiratory pressures are relative to Patm = alveolar and pleural pressures
Respiratory mechanics
Pressures = Atmospheric (air) Intra-alveolar (in alveoli) Intra-pleural (pleural space) Transpulmonary (difference)
Pulmonary ventilation
Mechanical processes depends on volume changes in the thoracic cavity
Volume changes = pressure changes
Pressure changes = gases flow to equalize pressure
Boyle’s law
Pressure exerted by a gas varies inversely with volume of gas
Volume increases, pressure decreases (vice versa)
Quiet inspiration
Inspiratory muscles contract (diaphragm and external intercostals) Thoracic volume increases (lungs stretch) Intrapulmonary decreases (air flows into the lungs down its pressure gradient until Ppul = Patm)
Forced inspiration
Recruit scalenus and sternocleidomastoid Greater increase in thoracic volume Larger decrease in thoracic pressure Larger pressure gradient More air flow in
Quiet expiration
Passive process Inspiratory muscles relax Thoracic cavity volume decreases Elastic lungs recoil Increase in alveolar pressure Air flows out of lungs
Forced expiration
Recruit abdominals and internal intercostals Larger decrease in thoracic volume Larger increase in thoracic pressure Larger gradient More air flow out
Physical factors influencing pulmonary ventilation
4 factors = Airway resistance Alveolar surface tension Lung compliance Elastic recoil
Airway resistance
Relationship between flow (F), pressure (P), and resistance (R)
F = 🔺P/R
Radius of bronchioles is the biggest determinant
Pressure gradient between atmosphere and alveoli
Asthma
Severe constriction or obstruction of bronchioles (prevents ventilation)
Epinephrine dilates bronchioles and reduces air resistance
Alveolar surface tension
Surface tension
Surfactant
Surface tension
Attracts liquid molecules to one another at a gas-liquid interface
Resists any force that tends to increase surface area of liquid
Surfactant
Detergent-like lipid and protein complex produced by type 2 alveolar cells
Decreases surface tension of alveolar fluid (discourages alveolar collapse)
Premature infants = decreased amount of surfactant, respiratory distress
Lung compliance
Expanding of the lungs = change in lung volume with a given change in pressure
Relates to effort required to distend the lungs
Lung compliance normally high due to
Distensibility of the lung tissue (connective tissue)
Alveolar surface surfactant
Lung compliance diminished by
Non elastic scar tissue (fibrosis)
Reduced production of surfactant
Decreased flexibility of thoracic cage (eg-paralysis of respiratory muscles)
Elastic recoil
How the lungs rebound after being stretched (help lungs return to their pre-inspiratory volume)
Depends on = connective tissue in lungs (elastic/collagen), alveolar surface tension (reduces tendency of alveoli to recoil)
Respiratory volumes
Used to asses a persons respiratory status
Lung volume and capacities (tidal volume)
Volume of air entering or leaving lungs during a single breath
Average value = 500ml
Lung volumes and capacities (inspiratory reserve volume)
Extra volume of air that can be maximally inspired over and above the typical resting tidal volume
Average volume = 3000ml
Lung volumes and capacities (inspiratory capacity)
Maximum volume of air that can be inspired at the end of a normal quiet expiration (IC = IRV + IV)
Average volume = 3500ml
Lung volumes and capacities (expiratory reserve volume)
Extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume
Average volume = 1000ml
Lung volumes and capacities (residual volume)
Maximum volume of air remaining in the lungs even after a maximal expiration
Average volume = 1200ml
Lung volumes and capacities (functional residual capacity)
Volume of air in lungs at end of normal passive expiration
(FRC = ERV + RV)
Average volume = 2200ml
Lung volumes and capacities (vital capacity)
Maximum volume of air that can be moved out during a single breath following a maximal inspiration (VC = IRV + TV + ERV)
Average volume = 4500ml
Lung volumes and capacities (total lung capacities)
Maximum volume of air that the lungs can hold (TLC = VC + RV)
Average volume = 5700ml
Dead space
Inspired air that doesn’t contribute to exchange
Anatomical dead space = volume of air passageways (~150ml)
Alveolar dead space = alveoli with no gas exchange due to collapse or obstruction
Pulmonary function tests
Minute ventilation = total amount of gas flow into or out of the respiratory tract in one minute
Forced vital capacity (FVC) = gas forcibly expelled after taking a breath
Forced expiratory volume (FEV) = the amount of gas expelled during specific time intervals of FVC
Obstructive disease
High compliance Low recoil Easy to breathe in Hard to breathe out Less “fresh air” each breath Eg = emphysema, asthma
Restrictive disease
Low compliance High recoil Hard to breathe in Easy to breathe out Hard to hold air in long enough for gas exchange Eg = fibrosis
Non respiratory air movements
Most result from reflex action Cough Sneeze Crying Laughing Hiccups Yawn
Gas exchange
Exchange oxygen and carbon dioxide between the alveolar air and blood and tissues External respiration (alveoli to blood) Internal respiration (blood to tissue) Need a concentration (partial pressure) gradient, gas will move from higher partial pressure to lower partial pressure
Dalton’s law
Partial pressure of each gas is directly proportional to its % in the mixture
Dalton’s law (Partial pressures)
Fraction of a gas in an atmosphere x the atmospheric pressure (or barometric pressure)
O2 = 21%
N2 = 79%
Co2 and others = <1%
Dalton’s law (gas exchange)
If atmospheric pressure at sea level is 760mmHg then:
Partial pressure of O2 = 0.21 x 760 = 160mmHg in dry air
Partial pressure of N2 = 0.79 x 760 = 600mmHg in dry air
Since 0.03% of air is Co2 partial pressure = 0.23mmHg in dry air
Fraction of O2, Co2, and N2 is the same in air…
At any altitude
Partial pressure of O2 is different at different locations because atmospheric pressure is different
Composition of alveolar gas
Alveoli contain more Co2 and water vapour than atmospheric air due to = gas exchanges in lungs, humidification of air, mixing of alveolar gas that occurs with each breath
External respiration
Exchange of O2 and Co2 across respiratory membrane
Influenced by = partial pressure gradients, gas solubility, ventilation-perfusion coupling, structural characteristics of respiratory membrane
Diffusion depends on
Concentration gradient
Diffusion distance
Solubility
Surface area (alveoli)
Ficks law
Rate of diffusion = k x A x (P2-P1/D)
K = diffusion constant (depends on solubility of gas and temperature)
A = surface area available for exchange
D = distance (thickness of barrier to diffusion)
P2-P1 = difference in partial pressure of gas on either side of barrier to diffusion (partial pressure gradient for gas)
Thickness and surface area of respiratory membrane
Respiratory membranes = 0.5-1 micrometers thick
Large total surface area (40x more than skin)
Thickness if lungs become waterlogged (edema) and has exchange decreases
Surface area decreases with emphysema (walls of adjacent alveoli break down)
Partial pressure gradients
Partial pressure gradient for O2 in lungs is steep
Venous blood pO2 = 40mmHg
Alveolar pO2 = 104mmHg
O2 partial pressures reach equilibrium
At 104mmHg in ~0.25 seconds
About 1/3 the time a red blood cell is in a pulmonary capillary
Partial pressure gradients and gas solubilities
Partial pressure gradient for Co2 in the lungs is less steep
Venous blood pO2 = 45mmHg
Alveolar pCo2 = 40mmHg
But Co2 is 20x more soluble in plasma than oxygen
Co2 diffuses in equal amounts with oxygen
Internal respiration
Capillary gas exchange in body tissues
Partial pressures and diffusion gradients are reversed compared to external respiration
pO2 in tissue is always lower than in systemic arterial blood
pO2 of venous blood is 40mmHg and pCo2 is 45mmHg
Ventilation-perfusion coupling
Ventilation = amount of gas reaching alveoli
Perfusion = blood flow reaching alveoli
Ventilation and perfusion must be matched (coupled) for efficient gas exchange
Ventilation-perfusion coupling (carbon dioxide and oxygen)
Carbon dioxide = bronchioles - increase causes bronchodilation, decrease causes bronchoconstriction
Oxygen = alveoli - increase causes vasodilation, decrease causes vascocontriction
Oxygen transport in blood
Molecular oxygen is carried in the blood
1.5% dissolved in plasma
98.5% loosely bound to each Fe of hemoglobin (Hb) in RBCs
4 oxygen per hemoglobin
Gas transport
Most oxygen in the blood is transported and bound to hemoglobin
Hb + O2 -> HbO2
Rate of loading and unloading of oxygen is regulated by
PO2 Temperature Blood pH PCo2 Concentration of DPG
Hypoxia
Inadequate of oxygen delivery to tissues Due to = Too few RBCs Abnormal or too little hemoglobin Blocked circulation Metabolic poisons Pulmonary disease Carbon monoxide
Carbon monoxide poisoning
Carbon monoxide has 200x the affinity for hemoglobin
Binds to hemoglobin and doesn’t let go
Blocks sites for oxygen
Carbon dioxide transport
Transported in blood in 3 ways =
7-10% dissolved in plasma
20% bound to goo in of hemoglobin (carbaminohemoglobin)
70% transported as bicarbonate ions (HCO3-) in plasma
Carbon dioxide combines with water to form
Carbonic acid (H2CO3) which quickly dissociates CO2 + H2O H2CO3 H+ + HCO3-
Transport and exchange of CO2 (systemic capillaries)
HCO3- quickly diffuses from RBCs into the plasma
The chloride shift occurs = outrush of HCO3- from RBCs is balanced as Cl- moves in from plasma
Transport and exchange of CO2 (pulmonary capillaries)
HCO3- moves into the RBCs and binds with H+ to form H2CO3
H2CO3 is split by carbonic anhydrase into CO2 and water
CO2 diffuses into alveoli
Control of respiration
Involves neurons in the reticular formation of the medulla and pons
Respiratory centres in brain stem establish a rhythmic breathing pattern
Includes = medullary respiratory centre, Pre-Bötzinger complex, Pneumotaxic centre, apneustic centre, and hering-Breuer reflex
Medullary respiratory centre
Dorsal respiratory group (DRG) = mostly inspiratory neurons
Ventral respiratory group (VRG) = inspiratory and expiratory neurons
Receive input from chemoreceptors
Pre-Bötzinger complex
Widely believed to generate respiratory rhythm
Pneumotaxic centre
Sends impulses to DRG that help “switch off” inspiratory neurons
Dominates over apneustic centre
Apneustic centre
Prevents inspiratory neurons from being switched off
Provides extra boost to inspiratory drive
Hering-Breuer reflex
Triggered to prevent over inflation of the lungs
Stretch receptors
Central chemoreceptors
Medulla = sensitive to changes in increased H+ via increase CO2
Peripheral chemoreceptors
Carotid bodies are located in the carotid sinus
Aortic bodies are located in the aortic arch
Responds to increased H, increased CO2, and decreased oxygen
Depth and rate of breathing
Hyperventilation =
increased depth/rate of breathing
High removal of CO2
Causes CO2 levels to decline (hypocapnia) (loose “trigger” for inspiration, longer breath holds possible, may cause cerebral vasoconstriction and cerebral ischemia)
Summary of chemical factors
Increased CO2 is the most powerful respiratory stimulant
If arterial PO2 < 60mmHg it becomes the major stimulus (eg-high altitudes)
Increase in arterial H+ (eg-lactic acid) also acts as a respiratory stimulant
Influence of higher brain centres
Hypothalamus/limbic system = modify rate and depth of respiration (eg-breath holding that occurs in anger or gasping with pain)
Increased body temperature acts to increase respiratory rate
Cortical controls bypass medullary controls (eg-voluntary breath holding)
Pulmonary irritant reflexes
Receptors in the bronchioles respond to irritants (promote reflexive constriction of air passages (allergies/asthma))
Receptors in the larger airways mediate the cough and sneeze reflexes
Inflation reflex
Hering-Breuer reflex = stretch receptors in the pleurae and airways are stimulated by lung inflation (inhibitory signals to the medullary respiratory centres end inhalation and allow expiration to occur)
Acts more as a protective response than a normal regulatory mechanism
Respiratory adjustments (exercise)
Increased CO2 production and O2 consumption (larger gradients for gas exchange)
Three neural factors increase ventilation as exercise begins =
Psychological = anticipation of exercise
Cortical activation of skeletal muscles and respiratory centres
Sensory feedback from muscles
