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Respiratory System Cheat Sheet by

BIO1203 Respiratory System

Lung Anatomy

Occupy all of the thoracic cavity except medias­tinum
site of vascular, bronchial attach­ments
Costal surface
anterior, lateral, posterior surfaces

Structures of the Lungs

Upper Respir­atory Tract

conduc­tion, filtra­tion, humidi­fic­ation and warming of inhaled air
Nasal Cavity
Nasal conchae, nasal vestibule, nostril
Paranasal Sinuses
Maxillary, frontal, sphenoidal and ethmoidal sinuses
Nasoph­arynx, oropha­rynx, laryng­oph­arynx
Larynx (superior)
Vocal cords, epiglo­ttis, vestibular fold, thyroid cartilage, vocal fold, cricoid cartilage, thyroid gland

Lower Respir­atory Tract

conduc­tion, gas exchange
cervical, thoracic
left primary bronchus, right primary bronchus
respir­atory bronch­iole, terminally bronch­iole, alveoli
left lung, right lung (larger)

Functional Anatomy

Respir­atory zone: site of gas exchange
Micros­copic struct­ures: respir­atory bronch­ioles, alveolar, ducts, alveoli
~300 million alveoli account for most of the lungs' volume, main site for gas exchange
Surrounded by fine elastic fibres
Contain open pores that connect adjacent alveoli, allow air pressure throughout lung to be equalised
House alveolar macrop­hages that keep alveolar surfaces sterile
Conducting zone
Conduits to gas exchange sites
Includes all other respir­atory structures
Windpipe: from larynx into medias­tinum
Wall composed of 3 layers: mucosa, submucosa, adventitia
Carina: Last tracheal cartilage, point where trachea branches into two bronchi
Conducting zone structures
Trachearight and left primary bronchi
Primary bronchussecondary bronchi3rd, 4th etc.
Bronch­ioles: < 1mm diameter
Terminal bronch­ioles: < 0.5mm diameter
Respir­atory muscles
Diaphragm and other muscles that promote ventil­ation

Respir­atory Volumes

Adult Male average
Adult Female average
Tidal volume (TV)
amount of air inhale­d/e­xhaled each breath at rest
Inspir­atory reserve volume (IRV)
amount of air during forceful inhalation after normal TV
Expiratory reserve volume (ERV)
amount of air during forceful exhalation after normal TV exhalation
Residual volume (RV)
amount of air remaining in lungs after forced exhalation

Respir­atory Capacities

Adult Male average
Adult Female average
Total lung capacity (TLC)
max amount of air contained in lungs after max inspir­atory effort: TLC = TV+IRV­+ERV+RV
Vital capacity (VC)
max amount of air that can be expired after max inspir­atory effort: VC = TV+IRV+ERV
Inspir­atory capacity (IC)
max amount of air that can be inspired after normal expira­tion: IC = TV+IRV
Functional residual capacity (FRC)
volume of air remaining in lungs after normal TV expira­tion: FRC = ERV+RV

Pulmonary Function Tests

instrument used to measure respir­atory volume­s/c­apa­cities
Can distin­guish between
Obstru­ctive pulmonary disease: increased airway resistance e.g. bronch­itis, asthma
Restri­ctive disorders: reduction in TLC due to struct­ura­l/f­unc­tional lung changes e.g. fibrosis, tuberc­ulosis (TB)
Minute ventil­ation
Total amount of gas flow into/out of respir­atory tract in 1 minute
Forced vital capacity (FVC)
Gas forcibly expelled after taking a deep breath
Forced expiratory volume (FEV)
Amount of gas expelled during specific time intervals of FVC

Partial Pressure Gradient

Dalton's Law of Partial Pressures
Total pressure exerted by mixture of gases is the sum of pressures exerted by each
Partial pressure of each gas is directly propor­tional to its percentage in the mixture
Atmosp­heric pressure is 760mmHg at sea level
Oxygen consti­tutes ~21% of the atmosphere
21% x 760 = 159mmHg

Mechanisms of Breathing: Pulmonary Ventil­ation

Inspir­ation and expiration
Inspir­ation: gases flow into lungs
Expira­tion: gases exit the lungs
Mechanical processes dependant on volume changes in thoracic cavity
Volume changespressure changes
Pressure changesgases flow to equalise pressure
Boyle's Law
Relati­onship between pressure and volume of a gas

Mechanics of Breathing: Inspir­ation

Sequence of events
1. Inspir­atory muscles contract diaphragm descends, rib cage rises
1. Inspir­atory muscles relaxdiaphragm rises, rib cage descends due to costal cartilage recoil
2. Thoracic cavity volume increases
2. Thoracic cavity volume decreases
3. Lungs are stretchedintrap­ulm­onary volume increases
3. Elastic lungs recoil passivelyintrap­ulm­onary volume decreases
4. Intrap­ulm­onary pressure drops -1mmHg
4. Intrap­ulm­onary pressure rises+1mmHg
5. Air flows into lungs down its pressure gradient until intrap­ulm­onary volume = 0 (equal to atmosp­heric pressure)
5. Air flows out of lungs down its pressure gradient until intrap­ulm­onary pressure is 0

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 in 40mmHg
pCO2 is 45mmHg

External Respir­ation

Exchange of O2 and CO2 across the respir­atory membrane
Influenced by:
Partial pressure gradients
Gas solubi­lities
Ventil­ati­on-­per­fusion (V/Q) coupling
Structural charac­ter­istics of the respir­atory membrane

Control of Respir­ation

Medullary Respir­atory Centres
Pontine Respir­atory Centres
Chemical Factors
Involves neurons in the reticular formation of the medulla and pons
Influence and modify activity of the VRG
Influence of pO2
1. Dorsal respir­atory group (DRG)
Smooth out tradition between inspir­ati­on/­exp­iration and vice versa
Peripheral chemor­ece­ptors in the aortic and carotid bodies are O2 sensors
Near the root of cranial nerve IX
(when excited, they cause respir­atory centres to increase ventil­ation)
Integrates input from peripheral stretch and chemor­ece­ptors
Substa­ntial drops in arterial pO2 (to 60mmHg) must occur in order to stimulate increased ventil­ation
2. Ventral respir­atory group (VRG)
Influence of arterial pH
Rhythm­-ge­ner­ating and integr­ative centre
Can modify respir­atory rate/r­hythm even if CO2 and O2 levels are normal
Sets eupnea (12-15 breath­s/min)
Decreased pH may reflect CO2 retention, accumu­lation of lactic acids, excess ketone bodies in diabetic Pts
Inspir­atory neurone excite the inspir­atory muscles via the phrenic and interc­ostal nerves
Respir­atory system controls will attempt to raise the pH by increasing respir­atory rate and depth
Expiratory neurone inhibit the inspir­atory neurone

Oxygen Transport

Molecular O2 is carried in the blood
1.5% dissolved in plasma
98.5% loosely bound to each Fe of haemog­lobin (Hb) in RBCs
4x bound O2 per Hb
O2 and Hemoglobin
Oxyhem­oglobin (HBO2): hemogl­obin-O2 combin­ation
Reduced hemoglobin (HSB): haemog­lobin that has released O2
Influence of pO2 on Hemoglobin Saturation
Oxygen­-he­mog­lobin dissoc­iation curve
Shows how binding and release of O2 is influenced by the pO2
Hemoglobin Saturation Influe­ncing Factors
Increases in temper­ature, H+, pCO2, and 2,3-bi­pho­sph­ogl­ycerate (BPG)
Modify Hb structure decreasing affinity for O2
Occur in systemic capill­aries
Increases O2 unloading
Shifts HbO2 dissoc­iation curve to the right
Decreases in these factors shift the curve to the left by decreasing O2 unloading

Carbon Dioxide Transport

CO2 is transp­orted in the blood in three forms
7-10% dissolved in plasma
20% bound to globin of Hb (carba­min­ohe­mog­lobin)
70% transp­orted as bicarb­onate ions (HCO3-) in plasma
CO2 combines with water to form carbonic acid (H2CO3), which quickly dissoc­iates
CO2 + H2O H2CO3 H+ + HCO3-
In systemic capill­aries
HCO3- quickly diffuses from RBCs into plasma
Chloride shift occurs when outrush of HCO3- from the RBCs is balanced as Cl- moves in from plasma
In pulmonary capill­aries
HCO3- moves into RBCs, binds with H+ to form H2CO3
H2CO3 is split by carbonic anhydrase into CO2 and H2O
CO2 diffuses into the alveoli


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