obj 5 pt 2 Flashcards
what are the 2 phases of pulmonary ventilation?
inspiration
expiration
gases flow into lungs
inspiration
gases exit lungs
expiration
pressure exerted by air surrounding the body
atmospheric pressure
pressure in alveoli
fluctuates with breathing
always eventually equalizes with atmospheric pressure
intrapulmonary pressure
pressure in pleural cavity
fluctuates with breathing
always a negative pressure in order to keep lungs inflated
intrapleural pressure
difference between intrapulmonary and intrapleural pressures
determines the size of the lungs
if equal, causes lung collapse
transpulmonary pressure
consists of inspiration and expiration
mechanical process that depends on volume changes in thoracic cavity
volume changes lead to pressure changes
pressure changes lead to the flow of gases to equalize pressure
gases always move from an area of high pressure to an area of low pressure
pulmonary ventilation
active process involving inspiratory muscles (contraction of diaphragm and external intercostals)
As thoracic cavity volume increases, lungs are stretched as
they are pulled out with thoracic cage
Intrapulmonary pressure drops
Because of difference between atmospheric and
intrapulmonary pressure, air rushes into lungs until
intrapulmonary and atmospheric pressures are equalized
inspiration
what are the actions of the diaphragm?
when dome-shaped diaphragm contracts, moves inferiorly and flattens out; there is an increase in thoracic volume
what are the actions of the intercostal muscles?
when external intercostals contract, rib cage is lifted up and out
results in increase in thoracic volume
passive process
depends on lung elasticity more than muscle contraction
inspiratory muscles relax, thoracic cavity volume decreases, lungs recoil
volume decrease causes intrapulmonary pressure to increase so air flows out of lungs down its pressure gradient until intrapulmonary pressure is equal to atmospheric pressure
expiration
may modify normal respiration rhythm
most result from reflex action, although some are voluntary
non-respiratory air movements
what are the 3 factors that influence the ease of air passage and the amount of energy required for ventilation?
airway resistance
alveolar surface tension
lung compliance
major non-elastic source of resistance to gas flow
decreases air passage
causes breathing movements to become more strenuous
greatest resistance to airflow occurs in midsize bronchi
F(gas flow) = P/R
airway resistance
the attraction of liquid molecules to one another at gas-liquid interface
surface tension
tends to draw liquid molecules closer together and reduce contact with dissimilar gas molecules
resists any force that tends to increase surface area of liquid
tends to cause alveoli to shrink to smallest size- that is, collapse
surfactant, a fat-protein complex, prevents alveolar collapse
alveolar surface tension
measure of how much “stretch” the lung has
lung compliance
why is lung compliance normally high?
distensibility of lung tissue
surfactant, which decreases alveolar surface tension
how do we assess ventilation?
- Several respiratory volumes can be used to assess
respiratory status - Respiratory volumes can be combined to calculate
respiratory capacities, which can give information on a
person’s respiratory status - Respiratory volumes and capacities are usually abnormal in
people with pulmonary disorders
amount of air moved into and out of lung with each breath
averages ~500ml
tidal volume
amount of air that can be inspired forcibly beyond the tidal volume (2100-3200ml)
inspiratory reserve volume
amount of air that can be forcibly expelled from lungs after a normal tidal expiration (1000-12000ml)
expiratory reserve volume
amount of air that always remains in lungs
residual volume
sum of tidal volume + inspiratory reserve volume
inspiratory capacity
sum of residual volume + expiratory reserve volume
functional residual capacity
sum of tidal volume + inspiratory reserve volume + expiratory reserve volume
vital capacity
sum of all lung volumes (TV + IRV + ERV +RV)
total lung capacity
what are the pulmonary functions tests can measure rate of gas movement?
forced vital capacity
forced expiratory volume
amount of gas forcibly expelled after taking deep breath
forced vital capacity
amount of gas expelled during specific time interval of FVC
forced expiratory volume
total amount of gas that flows into or out of respiratory tract in 1 min
minute ventilation
flow of gases into and out of alveoli during particular time
alveolar ventilation rate
occurs between lungs and blood as well as blood and tissues
gas exchange
diffusion of gases between blood and lungs
external respiration
diffusion of gases between blood and tissues
internal respiration
what are both external and internal respiration subject to?
- Basic properties of gases
- Composition of alveolar gas
the total pressure of a mixture pf gases is the sum of the partial pressures of the individual components
Dalton’s law of partial pressures
the pressure exerted by an individual gas in a mixture. is proportional to the percentage of that gas in the gas mixture
partial pressure
PO2 is high
PCO2 is low
bcuz inspiration occurred
alveoli
PO2 is low
PCO2 is high
blood just came from tissues
pulmonary capillaries
PO2 is low
PCO2 is high
bcuz tissues using oxygen
tissues
PO2 is high
PCO2 is low
because blood just came from lungs
tissue capillaries
- the relative concentration of gases (their partial
pressures) does not change as the pressure and
volume of the gas mixture changes - so air inhaled into the lungs will have the same
relative concentration of gases as atmospheric air. - In the lungs, the relative concentration of gases
determines the rate at which each gas will diffuse
across the alveolar membranes
Dalton’s law
- predicts how gasses will dissolve in the alveoli and
bloodstream during gas exchange. - The amount of oxygen that dissolves into the
bloodstream is directly relational to the partial pressure
of oxygen in alveolar air
Henry’s law
what happens for gas mixtures in contact with liquid?
- Each gas will dissolve in the liquid in proportion to its
partial pressure - At equilibrium, partial pressures in two phases will be
equal
what does the amount of each gas that dissolves depend on?
- Solubility: CO2 more soluble in water than O2
- Temperature: at temp of liquid rises, solubility
decreases
what is the composition of alveolar gas?
- Alveoli contain more CO2 and water vaporand less O2 than
atmospheric air because: - Gas exchanges in lungs (O2 diffuse out of lungs and CO2
diffuse into lung) - Humidification of air by conducting passages
- Mixing of alveolar gas with each breath
- Newly inspired air mixes with air that was left in
passageways between breaths
what is exchange of external respiration influenced by?
- pressure gradients (Dalton’s Law) and gas solubilities
(Henry’s Law) - Thickness and surface area of respiratory membrane
- The thicker the membrane, the less diffusion; thinner
the membrane, more diffusion. This affects the rate of
gas exchange
a steep partial pressure gradient for O2 exists between blood and lungs
partial pressure gradients and gas solubilities
40 mm Hg
venous blood P02
104mm Hg
alveolar P02
what is the partial pressure gradient for CO2?
venous blood PCO2 = 45 mm Hg
alveolar PCO2 = 40mm Hg
- Gas movement occurs by diffusion
- Rate of diffusion depends on the concentration of
the gas and the barrier; especially the thickness
of the respiratory membranes - Respiratory membranes are very thin
- 0.5 to 1 m thick
- Large total surface area of the alveoli is 40 the
surface area of the skin
thickness and surface area of the respiratory membrane
what are the 2 ways molecular O2 is carried in the blood?
- dissolved in plasma
- bound to hemoglobin (Hb) in RBCs
hemoglobin-O2 combination
oxyhemoglobin
hemoglobin that has released O2
deoxyhemoglobin
all four heme groups carry O2
fully saturated
when only one to three hemes carry O2
partially saturated
what are the factors that influence hemoglobin saturation?
- PO2
- Other factors such as:
- Temperature
- Blood pH
- PCO2
- Concentration of BPG
what is the influence of PO2 on hemoglobin saturation?
PO2 heavily influences binding and release of O2 with
hemoglobin
what is the influence of PO2 on hemoglobin saturation in arterial blood?
- Hgb is 98% saturated
- Further increases in PO2 (as in deep breathing)
produce minimal increases in O2 binding
what is the influence of PO2 on hemoglobin saturation in venous blood?
- Hgb is still 75% saturated
- Venous reserve: oxygen remaining in venous blood
that can still be used
what are the 3 forms that CO2 is transported in blood?
- dissolved in plasma as PCO2
- bound to hemoglobin
- Accumulating CO2 lowers blood pH
- Depletion of CO2 in blood raises blood pH
what is carbon dioxide transport?
- Most carbon dioxide molecules entering the plasma quickly
enter RBCs. The reactions that convert carbon dioxide to
bicarbonate for transport mostly occur inside RBCs because
they contain carbonic anhydrase, an enzyme that reversibly
catalyzed the conversion of carbon dioxide and water to
carbonic acid. - Hydrogen ions are released during the reaction bind to
hemoglobin triggering the bohr effect. The carbon dioxide
loading enhances oxygen release. - In systemic capillaries, after bicarbonate is created, it quickly
diffuses from RBCs to plasma - This outpouring of bicarbonate from RBCs is balanced as
chloride moves into RBCs from plasma (chloride shift) - In pulmonary capillaries, the process occurs in
reverse - Bicarbonate moves into RBCs while Chloride
moves out of RBCs back into plasma - Bicarbonate binds with H+ to form H2CO3
(carbonic acid) - Carbonic acid is split by carbonic anhydrase into
CO2 and H20 - CO2 diffuses into alveoli
helps blood resist changes in pH
carbonic acid-bicarbonate buffer system
what are respiratory rhythms regulated by?
higher brain centers
chemoreceptors
other reflexes
involve neurons in reticular formation of medulla and pons
neural controls
clustered neurons in two areas of medulla
medullary respiratory centers
sets normal respiratory rate and rhythm
ventral respiratory group
assists VRG
dorsal respiratory group
- Neurons in this center influence and modify
activity of Ventral Respiratory Group (VRG) - Act to smooth out transition between inspiration
and expiration and vice versa - Transmit impulses to VRG that modify and fine-
tune breathing rhythms during vocalization,
sleep, exercise
pontine respiratory centers
determined by how actively the respiratory center stimulates respiratory muscles
depth
determined by how long center is active
rate
what are respiratory centers affected by?
- Chemical factors
- Influence of higher brain centers
- Pulmonary irritant reflexes
- Inflation reflex
- Most important of all factors affecting depth and
rate of inspiration - Changing levels of CO2, O2, and pH are most
important
chemical factors
located throughout brain stem
central chemoreceptors
found in aortic arch and carotid arteries
peripheral chemoreceptors
- Most potent and most closely controlled
- blood PCO2 levels rise (hypercapnia), its most
powerful respiratory stimulant - Respiratory centers increase depth and rate
of breathing, which act to lower blood PCO2,
and pH rises to normal levels - If blood PCO2 levels decrease (hypocapnia),
respiration becomes slow and shallow
influence of PCO2
- Peripheral chemoreceptors in aortic and carotid bodies
sense arterial O2 levels - Declining PO2 normally has only slight effect on
ventilation because of huge O2 reservoir bound to Hgb - Requires substantial drop in arterial PO2 (below
60 mmHg) to stimulate increased ventilation - When excited, chemoreceptors cause respiratory
centers to increase ventilation
influence of PO2
- pH can modify respiratory rate and rhythm
even if CO2 and O2 levels are normal - Mediated by peripheral chemoreceptors
- Decreased pH may reflect CO2 retention,
accumulation of lactic acid, or excess ketone
bodies - Respiratory system controls attempt to raise
pH by increasing respiratory rate and depth
influence of arterial pH
modify rate and depth of respiration
hypothalamic controls
bypass medullary controls
cortical controls
- Receptors in bronchioles respond to irritants such
as dust, accumulated mucus, or noxious fumes - Receptors communicate with respiratory
centers via vagal nerve - Promote reflexive constriction of air passages
- Same irritant triggers a cough in trachea or
bronchi or a sneeze in nasal cavity
pulmonary irritant reflexes
- Stretch receptors in pleurae and airways are
stimulated by lung inflation - Send inhibitory signals to medullary
respiratory centers to end inhalation and
allow expiration - May act as protective response more than as
a normal regulatory mechanism - a reflex triggered to prevent over-inflation of
the lung
hering-breuer reflex
