Respiratory System Flashcards
4 Primary Functions of Respiratory System
- exchange of gases btwn the atmosphere and blood
- homeostatic regulation of body pH
- protection from inhaled pathogens and irritating substances
- vocalization
Air Exchange Principles
- occurs by bulk flow
1. flow occurs from region of high pressure to low pressure
2. muscular pump creates the pressure gradients
3. resistance is primarily influenced by diameter of tubes that air flows through
Cellular Respiration
- convert organic molecules to ATP
ex) Aerobic metabolism of glucose
External Respiration
- the movement of gases between the environment and the cells within the body
4 Steps of External Respiration
- exchange I: atmosphere to lungs (ventilation)
- exchange II: lung to blood
- transport of gases in the blood
- exchange III: blood to cells
Structure Involved in Ventilation/Gas Exchange
- conducting system or airways
- alveoli
- bones and muscles of the thorax (chest cavity)
Lungs
- composed of light spongy tissue
- volume occupied mostly by air-filled spaces
- right lung slightly larger
- surrounded by pleural sac
Pleural Sac
- double-walled, two layers
- visceral pleura and parietal pleura
Visceral Pleura
- connected to the outside surface of the lungs
Parietal Pleura
- connected to the inside surface of the thoracic cavity
Jobs of Pleural Sac
- creates moist slippery surface
2. holds lungs tight to thoracic wall
Airway Pathway
- air enters pharynx
- air flows through larynx
- air flows to trachea
Conducting Surface
- Trachea
- Primary Bronchi
- Smaller Bronchi
Exchange Surface
- Bronchioles
2. Alveoli
Velocity of Airflow
- inversely proportional to total cross sectional area
V=Q/A
Important Role of Upper Airways and Bronchi
- Warming air to body temp
- Adding water vapour
- Filtering out foreign material
- these are more efficient with nose breathing
Nasal Cavity
- large surface area, rich blood supply and nasal hair
- shop of nasal airway causes particles to embed in mucus in back of pharynx and slide down esophagus
Air Filtration
- filtered in trachea and bronchi
- contains cilia, goblet cells
Ciliated Cells
- cilia move mucus layer toward the pharynx, removing trapped pathogens and particulate matter
- move saline layer which pulls mucus layer
- without saline, cilia would become embedded in thick mucus and unable to move
Goblet Cells
- secretes mucus
Saline
- produced by the epithelial cells
- overtop of saline is a layer of mucus
Mucus
- contains immunoglobulins
- produced by goblet cells
Mucocilliary Escalator
- epithelial cells contain cilia which push the mucus towards the pharynx
Cystic Fibrosis
- autosomal recessive mutation in gene producing CFTR
- reduced production of saline
- mucus can’t be cleared properly, so bacteria can colonize in airways = reoccurring lung infections
- also affects GI and pancreas
Alveoli
- site of gas exchange
- make up bulk of lung tissue
- clustered at the ends of bronchioles
- heavily vascularized (80-90% alveoli covered) and huge surface area
Exchange Surface of Alveoli
- endothelium layer
- fused basement membrane
- surfactant
Type I Alveolar Cell
- for gas exchange
- 95% surface area
Type II Alveolar Cell
- surfactant cell
- synthesizes surfactant
Pulmonary Circulation
- high-flow, low pressure
- rate of blood flow through lungs is very high
- *CO is equal in pulmonary and systemic circuit**
- 25/8 vs 120/80 mmHg
Low Pressure of Pulmonary Circulation
- due to low resistance (shorter length circuit, more distensible and larger total cross sectional area of arterioles)
- low pressure means minimal filtration of fluid out of capillaries
- lymphatics remove any fluid that does get filtered and keep diffusion distance to a minimum
Daltons Law
- the total pressure exerted by a mixture of gases is the sum of the pressure exerted by each gas
- also dependent on humidity of air
- partial pressure
Air Flow
- gases move down pressure gradients
- air moves by bulk flow: from a region of high pressure to low pressure
Inspiration Pressure Gradient
- alveolar pressure lower than atmospheric pressure
Expiration Pressure Gradient
- alveolar pressure higher than atmospheric pressure
Boyle’s Law
- describes pressure-volume relationships
P1V1=P2V2 - helps explain how a change in lung volume results in a change in lung pressure driving the bulk flow of air
Compression
decrease volume
increase pressure
Decompression
increase volume
decrease pressure
Spirometer
- measures lung volume changes during ventilation
Lung Volumes
- Tidal Volume
- Inspiratory Reserve Volume
- Expiratory Reserve Volume
- Residual Volume
- don’t overlap
Tidal Volume (TV)
~500 ml
- total ventilation during rest represents the product of tidal volume and frequency of breaths
Total Pulmonary Ventilation
= TV x frequency of breaths
Inspiratory Reserve Volume (IRV)
~3000 ml
- the additional air that could still be inspired after quiet inspiration
Expiratory Reserve Volume (ERV)
~1100 ml
- at the end of quiet expiration, the volume of air that still remains within the lungs that can be expired
Residual Volume
~1200 ml
- even with maximal expiratory effort air always remains in the lungs
- can’t be measured with spirometer
2 Important Functions of the Residual Volume
- prevents airway collapse, after a collapse it takes an unusually large pressure to re-inflate it
- it allows continuous exchange of gases
Lung Capacities
- made up of diff. combinations of the 4 primary volumes
1. Total Lung Capacity
2. Functional Residual Capacity
3. Inspiratory Capacity
4. Vital Capacity
Total Lung Capacity
- the sum of all 4 volumes
Functional Residual Capacity
- the capacity of air remaining in the lungs after quiet expiration, the sum of ERV and RV
Inspiratory Capacity
- the sum of IRV and TV representing the maximal amount of air that one can inspire
Vital Capacity
- the sum of IRV, TV, and ERV representing the maximal achievable tidal volume
Pulmonary Function Test
- involves testing an individuals forced vital capacity (FVC) and comparing it to their Forced expired volume in one second (FEV1)
FEV1
- is normally ~80% of vital capacity
- below 80% indicative of obtrusive pulmonary disease (increased resistance)
- low initial FVC indicative of restrictive pulmonary disease (decrease in lung compliance)
Inspiration
- occurs when alveolar pressure decreases
- Boyle’s Law: increase in volume will cause a decrease in pressure
- use inspiratory muscles (skeletal) to increase volume of alveoli –> decrease in pressure
Main Inspiratory Muscle
- diaphragm
- 60-75% of inspiratory volume change
Movement of Rib Cage for Inspiration
- accounts for 25-40% of inspiratory volume change
Pump Handle Motion
- motion caused by the external intercostals of upper ribs and scalene attached to sternum
Bucket Handle Motion
- motion caused by external intercostals in lower ribs
Expiration
- occurs when alveolar pressure increases
- diaphragm relaxes
- thoracic volume decreases
Quiet Expiration
- passive
- relaxation of inspiratory muscles (external intercostals and scalene muscles)
Muscles of Forced Inspiration
- additional accessory/secondary muscles become activated
1. sternocleidomastoids
2. neck and back muscle
3. upper respiratory tract muscles
Sternocleidomastoids
- lift the sternum outward
- contributes to water pump handle effect
Neck and Back Muscles
- elevate pectoral girdle increasing thoracic volume and extend back
Upper Respiratory Tract Muscles
- decrease airway resistance
- internal muscle to help open airway
Muscles of Forced Expiration
- accessory muscles of forced expiration:
1. abdominal muscles
2. internal intercostals and triangular sterni
3. neck and back muscles
External Intercostal Muscles
- inspiration
- slope obliquely btwn ribs, forward and downward
- attachment to lower rib is farther forward from axis of rotation so contraction raises lower rip more than it depresses upper rib
Internal Intercostal Muscles
- expiration
- slope obliquely btwn ribs, backward and downward
- depressing upper rib more than raising lower rib
Pleural Sac
- between lung and thoracic wall
- keeps lungs from going into natural recoiled state
- keeps thoracic cavity from natural outward recoil
Intrapleural Pressure
~ -3
- negative pressure at all times because of tension Pleural Sac is under at all times
Intrapleural Cavity
- inspiratory muscles pull parietal layer away from visceral layer
- increases volume of intrapleural cavity
- negative pressure
Decrease in Intrapleural Pressure
- pulls alveoli open
- decreases alveolar pressure and air flows in
When does Air Flow Stop?
- when air pressure in alveoli begins to match atmospheric pressure
Pneumothorax
- collapsed lungs
- an interruption in intrapleural pressure
Traumatic Pneumothorax
- interruption in parietal pleura
- lung goes into natural recoil
Spontaneous Pneumothorax
- lung and visceral pleura ruptures
- ~70% due to COPD (emphysema)
Lung Compliance
- degree of lung expansion at any time is proportional to the change in pressure
Compliance
- “stretchability” of the lungs
- determines how much any given change in P expands the lungs
Lung Elastance
- elastic recoil
- reciprocal of compliance
- the ability to resist being deformed
Compliance Equation
Compliance = ∆V/∆P
Pulmonary Fibrosis
- formation or development of excess fibrous connective tissue in lungs
- ex. of decreased compliance
- inhalation of pollutants (metals, asbestos, certain gases)
- infections
- idiopathic (age, genetic predisposition)
Emphysema
- proteolytic enzymes secreted by leukocytes (neutrophils) attack alveolar tissue
- weakens alveoli walls creating airway resistance
- alveoli merge: loss of capillaries and reduction surface area
- loss of lung recoil
- cause: smoking
Surface Tension
- a determinant of compliance
- a major determinant of the lungs elastic recoil (air water interface of airways)
- measure of the force acting to pull a liquid’s molecules together at air-water interface
Laplace’s Equation
- surface tension
P = 2T/r
Relationship between Alveoli Radius and Pressure Needed
- decrease radius = higher pressure needed
Surfactant
- surface active agent
- helps overcome surface tension: interferes with intermolecular bond of water
- detergent-like molecule secreted by Type II alveolar cells
- ~90% phospholipids, 10% protein
- amphipathic
Jobs of Surfactant
- increased compliance
2. ensures alveoli of all size inflate
Rapidly Expanding Alveolus
- expands radius of 100µm to one of 150µm during inflation
- greatly reduces surface density of surfactant
- surface tension and elastic recoil rise, putting “brake” on expansion
Slowly Expanding Alveolus
- radius has only expanded from 100µm to 120µm
- surfactant is less diluted, putting less of a “brake” on expansion
Infant Respiratory Distress Syndrome
- in premature infants
- developmental insufficiency of surfactant production and immaturity of lungs
- prevalence decreases with gestational age
- prevention: glucocorticoid injection
- treatment: artificial surfactant, CPAP, intubate
Poiseuille’s Equation
- airway resistance
R = 8nl / (pi)r^4
F = ∆P * (pi)r^4 / 8nl
Factors that Affect Airway Resistance
- length of the system
- viscosity of air
- diameter of airways
- upper airways
- bronchioles
Airway Resistance: Length of the System
- constant: not a factor
Airway Resistance: Viscosity of Air
- usually constant
- humidity and altitude may alter slightly
Airway Resistance: Upper Airways
- affected by physical obstruction
- mediated by mucus and other factors
Airway Resistance: Bronchioles
- affected by bronchoconstriction
- -> mediated by parasympathetic neurons, histamine, leukotrienes
- affected by bronchodilation
- -> mediated by CO2, epinephrine, beta2-receptors
90% of Airway Resistance Occurs in…
- trachea and bronchi
- constant (smallest total cross-sectional area)
Controls of Bronchoconstriction/Dilation
- paracrine control
- CO2 is the major determiner of diameter
- histamine
- parasympathetic nerves
CO2 Control of Bronchoconstriction/Dilation
- high levels = dilation
- low levels = constriction
Histamine Control of Bronchoconstriction/Dilation
- released from mast cells bronchoconstricts
Parasympathetic Nerves Control of Bronchoconstriction/Dilation
- innervate bronchiole smooth muscle
- activate PLC-IP3 pathway via M3 muscarinic receptor (constriction)
Asthma
- constricted bronchioles
- infrequent attacks: beta2-adrenergic agonist
- oppose bronchoconstriction
- more frequent attacks:
- weekly inhaled corticosteroid
Efficiency of Breathing
- determined by total pulmonary ventilation: the volume of air moved into and out of the lungs each minute
- normal ventilation rate = 12-20 breaths/min
- tidal volume = 500 ml
Minute Ventilation
- volume of air moved into and out of the lungs each minute
Total Pulmonary Ventilation Equation
= ventilation rate x tidal volume (VT)
Alveolar Ventilation Equation
= ventilation rate x (tidal volume - dead space)
How much Air Leaves the Lungs?
- 350 mL leaves the alveoli
- stale air
- 150 mL is still considered as “fresh air” and left in the lungs
Normal Tidal Volume
- 500 mL
- alveolar ventilation = 4200 mL/min
Shallow Tidal Volume
- 300 mL
- alveolar ventilation = 3000 mL/min
Deep Tidal Volume
- 750 mL
- alveolar ventilation = 4800 mL/min
Maximal Voluntary Ventilation
= 125 - 175 L/min
Gas Composition in the Alveoli
- gas composition in the alveoli determines rate of O2 and CO2 diffusion between alveoli and capillaries
Why does PO2 and PCO2 Remain Constant during Quiet Respiration
- O2 entering = O2 uptake
- fresh air diluted upon entering the lungs
Alteration in Ventilation Rate
- independent of changes in the CV system will alter partial pressures of O2 and CO2
- alters diffusion
Perfusion
- the passage of fluid through CV system or lymphatic system to an organ or tissue
- refers to the delivery of blood to a capillary bed in tissue
Ventilation and Alveolar Blood Flow Relationship
- matched
- blood flow must be high enough to pick up the available O2
- wasted ventilation/perfusion
Local Regional Control: Gravity
- lungs have zone 1, 2, 3
- more negative intrapleural pressure due to gravity at apex
Zone 1 in Lungs
- perfusion is absent
Zone 2 in Lungs
- perfusion is sporadic
Zone 3 in Lungs
- perfusion is constant
Gravity at Apex Means…
- alveoli are partially open even and filled at rest
- don’t take much air during respiration
Local Control of Ventilation and Perfusion
- very little autonomic innervation of the pulmonary arterioles
- pulmonary arterioles primarily influenced by decreasing O2 levels around them
- bronchioles sensitive to CO2 levels
Decreases in O2
- causes constriction
- opposite of CV system
- presence of O2 sensitive K+ channels
Increase in PCO2
- bronchioles = dilate
- pulmonary arteries = (constrict)*
- systemic arteries = dilate
Decrease in PCO2
- bronchioles = constrict
- pulmonary arteries = (dilate)
- systemic arteries = constrict
Increase in PO2
- bronchioles = (constrict)
- pulmonary arteries = (dilate)
- systemic arteries = constrict
Decrease in PO2
- bronchioles = (dilate)
- pulmonary arteries = constrict
- systemic arteries = dilate
What Happens when a Blood Clot is Present in Arteriole
- blood clots prevent gas exchange
- alveolar PO2: increase
- alveolar PCO2: decrease
- tissue PO2: increase
- tissue PCO2: decrease
- bronchiole smooth muscle constricts
Local Control of Ventilation/Perfusion
- gravity
- gas levels in tissues near bronchiole and arteriole smooth muscle
Local Control: Gravity
- causes similar regions of lungs to receive matching ventilation and perfusion
Local Control: Gas Levels
- bronchiole smooth muscle sensitive to CO2
- arteriole smooth muscle sensitive to decreases in O2
