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Respiratory System NPB 101 Cheat Sheet (DRAFT) by

Physiology of the respiratory system.

This is a draft cheat sheet. It is a work in progress and is not finished yet.

general anatomy

pharynx
common passage for lungs and stomach
larynx
voice box at entry of trachea
trachea
tube for air to go into the lungs
bronchi
division of trachea into two main branches
bronch­ioles
small branches of respir­atory airway
alveoli
small, thin-w­alled sacs where gas exchange takes place
conducting zone
top of trachea to respir­atory bronch­ioles
respir­atory zone
where gas exchange occurs
pleural sacs
pair of thin, fluid filled membranes that enclose the lungs
pleural cavity
space between pair of membranes
pleurae
two flattened, closed sacs with pleural fluid- form serosa

Respir­atory Mechanics

Pressure Gradient
air moves from high to low pressure; respir­atory pressure relative to atmosp­heric
Inspir­ation
diaphragm and external interc­ostal muscles contract- increase dimensions of thoracic cavity
Passive Expiration
inspir­atory muscles relax- ribs, sternum, diaphragm return to resting position
Active Expiration
abdominal and internal interc­ostal muscles contract- reduce size of thoracic cavity
Determ­inants of Lung Compliance
stretc­hab­ility of lung tissue (elastin) and alveolar surface tension
Surfactant
reduces cohesive forces on alveolar surface- lowers surface tension- secreted by type II alveolar cells

Opposing Forces Acting on Lung

Forces Keeping Alveoli Open
transmural pressure gradient
pulmonary surfac­tant- opposes alveolar surface tension
Forces Promoting Alveolar Collapse
elasticity of stretched elastin fibers in connective tissue
alveolar surface tension

4 Important Factors for Ventil­ation

1. Atmosp­heric
2. Intra-­Alv­eolar
lower during respir­ation bc thoracic wall expands
boyle's law- at constant temp the pressure of a gas varies inversely with its volume
3. Intrap­leural Pressure
chest wall pulls out, lungs pull in, small vacuum forms causing negative pressure inside pleural cavity
always less than intra-­alv­eolar
4. Transmural Pressure Gradient
pushes out on lungs, stretching them to fill larger thoracic cavity

Anatomy

  

Gas Exchange

exchange of O2 and CO2 between external enviro­nment and tissues
gas movement by passive diffusion (high to low pressure)
exchange across pulmonary and systemic capill­aries
partial pressure of water vapor in lungs -> alveolar PO2 < atmosp­heric PO2

Factors That Influence Rate of Gas Exchange

partial pressure gradients of O2 & CO2
direct relati­onship
 
major determ­inant of rate
surface area of alveol­ar-­cap­illary membrane
direct relati­onship
 
constant under resting conditions
 
increase during exercise; decrease with pathol­ogical conditions
thickness of alveol­ar-­cap­illary membrane
inverse relati­onship
 
usually constant; increase with pathol­ogical conditions
diffusion constant
direct relati­onship
 
CO2 20x greater than O2

Gas Transport

process of O2 & CO2 transp­ort­ation between systemic tissues and lungs
Two Forms of O2 Transport
dissolved in blood (1.5%) & chemically bound to hemoglobin (98.5%)
Hemoglobin
soluble cytopl­asmic protein in erythr­ocytes- reversibly binds 4 molecules of O2
Oxygen Storage
hemoglobin stores O2 without affecting partial pressure gradient
Hemoglobin Saturation
propor­tional to PO2 of blood; follows S-shaped "­oxygen hemoglobin dissoc­iation curve"

Partial Pressures and Functions

Partial Pressure Gradients
from difference in partial pressures between two areas; gas moves from area of high partial pressure to low
Partial Pressures of CO2 and O2 are Different
higher solubility of CO2 compen­sates for smaller gradient; allows for approx equal exchange rates of O2 and CO2
Alveolar PO2 < Atmosp­heric PO2
due to partial pressure of water vapor in the lungs, and mixing of inspired air with residual alveolar air
Systemic PCO2 Higher in the Tissues
due to production of CO2 during oxidative metabolism

Respir­atory Conditions

Pneumo­thorax
condition occurring when air is allowed to enter plural cavity
transmural pressure gradient is lost
lungs collapse, thoracic wall expands
Newborn Respir­atory Distress Syndrome (RDS)
condition occurring when lungs are not fully developed and lack surfactant
affects premature infants, typically born before 32 weeks
Pleurisy
infection or inflam­mation of pleura- often from pneumonia
 

Ventil­ation

pulmonary
volume of air breathed in/out per min
alveolar
volume of air exchanged between atmosphere and alveoli per min

Lung Volume

Spirometer
device for measuring the volume of air breathed in and out
Tidal Volume
volume of air inhaled and exhaled during a single normal breath
Residual Volume
The volume of air that remains in the lungs and airways even after a maximal exhalation
Total Lung Capacity
maximum volume of air that the lungs can hold
Anatomical Dead Space
volume of air not involved in gas exchange- approx 150 ml in healthy adults

Factors Affecting Hemoglobin

Promote Unloading of O2 from Hemoglobin at Tissues
a. low: partial pressure of O2
b. high: partial pressure of CO2
c. low: pH
d. high: temper­ature
Promote Uploading of O2 From Hemoglobin at Lungs
a. high: partial pressure of O2
b. low: partial pressure of CO2
c. high: pH
d. low: temper­ature

Carbon Dioxide Transport

Dissolved in Blood (10%)
Chemically Bound to Hemoglobin (30%)
haldane effect- increased carrying capacity of CO2 on hemoglobin when hemoglobin gives up oxygen
-tissue- reduced Hb has greater affinity for CO2, facili­tates transport of CO2 out of tissue
-lungs- promotes CO2 unloading, facili­tates release of CO2 from blood into alveoli
Bicarb­onate HCO3 (60%)
CO2 converted into HCO3 within red blood cells by carbonic anhydrase

Control of Respir­ation

Neural Control
Effects of hypove­nti­lation and hyperv­ent­ilation
Respir­atory Centers
located in pons & medulla
 
establish rhythmic firing pattern to drive motor neurons in spinal cord to stimulate skeletal inspir­atory muscles
Central Chemor­ece­ptors
located near respir­atory centers in medulla
 
respond to change in arterial PCO2 by increasing activity and ventil­ation rate