Respiratory Physiology: Gases

Respiration

exchange of O2 and CO2 between an organism and environment

Three structures required for respiration

1.) lungs

2.) transport tubes connecting lungs to outside (trachea, bronchi, bronchioles)

3.) diaphragm

Three respiratory functions of the lungs:

1.) supply O2 to tissues from circulation

2.) eliminate CO2 produced by tissue metabolism

3.) regulate pH and acid-base balance

Oxygen is supplied from the ________ to the _________

environment; blood

CO2 is eliminated from the _________ to the _____________

blood; environment

How is the CNS required for effective respiration?

it generates the active signal to breathe, which travels to the phrenic and intercostal motor nerves

phrenic and intercostal motor nerves

Transmit signals to respiratory muscles

Respiratory muscles

diaphragm and intercostal muscles that generate a force to expand the chest

Intact pleural space

transmits force generated by movement of chest to the lungs

Three goals of respiration

1.) get O2 from environment to blood

2.) get CO2 from blood to the environment

3.) match these processes to metabolic demand

Metabolic demand is altered by...

-exercise

-disease

-thermal stress

Acheiving the three goals of respiration requires three processes:

1.) aveolar ventilation

2.) bidirectional diffusion of O2 and CO2

3.) perfusion of metabolizing tissues

aveolar ventilation

getting air into and out of the aveoli

bidirectional diffusion of O2 and CO2

O2 coming from the aveolar lumen into the blood and vice versa for CO2

perfusion of metabolizing tissues

the transport of O2 to tissues from blood and CO2 from tissues to blood

The respiratory cycle has three main phases:

1.) inspiration

2.) expiration

3.) period betwen breaths

inspiration

process of ribs expanding and diaphragm contracting to draw air through the conducting airways into the aveoli

expiration

process of ribs contracting and diaphragm relaxing to force air back out of aveoli

period betwen breaths

time period post expiration until the next inspiration

During the respiratory cycle, the ________ ventricle pumps blood round __________ circulation to the __________

right; pulmonary; aveoli

Three things needed for the lungs to expand:

1.) lung compliance

2.) pleural space empty with negative pressure

3.) chest wall intact

Partial pressure

individual pressure contributed by a single gas in a mixture to the total pressure

Gas pressure is proportional to (2):

1.) temperature

2.) concentration

Dalton's Law of partial pressures

in a mixture of gases, the pressure exerted by each gas is independent of the pressures exerted by other gases present

Composition of atmospheric air:

1.) nitrogen (78%)

2.) oxygen (21%)

3.) carbon dioxide (<1%)

4.) miscellaneous (He, Ar, etx)

Partial pressures of O2 and CO2 must remain within __________ limits

narrow

subscript a denotes partial pressure in an _______

subscript A denotes partial pressure in an _______

subscript v denotes partial pressure in a _______

artery

aveoli

vein

Mean Pa of O2

95

Normal range of Pa of O2

80-110

Mean Pa of CO2

40

Normal range of Pa of CO2

35-45

uppercase I and A abbreviations mean...

inspired and alveolar

lowercase a, c, and v abbreviations mean...

vascular (artery, capillary, vein)

Vx denotes ________ of compartment X

volume

V•x denotes ________ of gas X

flow rate

PB abbreviation means...

atomspheric pressure (760 mm Hg)

Fx abbreviation means...

fraction of gas X in a mixture of gasses (%)

VA abbreviation means...

aveolar volume (mL)

V•A abbreviation means...

aveolar ventilation rate (mL/min)

Partial pressure of gasses equation

Px = PB x Fx

Partial pressure of O2 in the atmosphere

160 mmHg

PIO2 = 760 x .21 = 160 mmHg

Two mechanisms of gas movement:

1.) bulk flow

2.) diffusion

bulk flow

non-random movement from high total pressure to low total pressure (movement down a pressure gradient)

bulk flow is ___________ of the composition of gas

independent

example of bulk flow

movement of air into and out of lungs during ventilation

diffusion

random movement from high partial pressure to low partial pressure

diffusion is ___________ of the composition of gas

dependent

example of diffusion

diffusion of O2 across aveolar-capillary barrier

Ventilation

movement of air in and out of the lungs; exchange of air between the atmosphere and aveoli

Does ventilation use bulk flow or diffusion?

bulk flow

Air moves in and out of the lungs because aveolar pressure continuously cycles _________ and _______ atmospheric pressure

below and above

Changes in aveolar pressure are due to...

changes in lung volume due to respiratory muscles contracting and relaxing

Without a pressure difference between the alveoli and atmopshere, air _______ ______ flow!

will not

In the lungs, bulk flow is equal to...

the difference between atmospheric and aveolar pressure divided by resistance to bulk flow

Gas exchange

exchange of O2 and CO2 between aveolar air and aveolar capillary blood, or of O2 and CO2 between tissue capillary blood and cells

Does gas exchange use bulk flow or diffusion?

diffusion

Transport

transfer of O2 and CO2 through pulmonary and systemic circulation

Does transport use bulk flow or diffusion?

bulk flow

Four important gasses in the aveolar lumen

1.) H2O

2.) O2

3.) CO2

4.) N2 (physiologically irrelevant)

The fraction (and therefore partial pressure) of O2 and CO2 in the aveolar lumen depends on...

rate of aveolar ventilation relative to rates of perfusion and tissue metabolic activity

The partial pressure of inspired oxygen is ________ mmHg

The partial pressure of aveolar oxygen is _______ mmHg

160 mmHg

105 mmHg

Why is the partial pressure of aveolar oxygen lower than partial pressure of inspired oxygen?

some O2 leaves the aveoli and enters the pulmonary capillaries

The partial pressure of inspired carbon dioxide is ________ mmHg

The partial pressure of aveolar carbon dioxide is _______ mmHg

0 mmHg

40 mmHG

Why is the partial pressure of aveolar carbon dioxide higher than partial pressure of inspired carbon dioxide?

CO2 enters aveoli from pulmonary capillaries

Four factors that determine the partial pressure of alveolar oxygen

1.) partial pressure of inspired oxygen

2.) rate of aveolar ventilation

3.) rate of bodily oxygen consumption (metabolism)

4.) cardiac output

Decreased partial pressure of inspired oxygen will ________ partial pressure of aveolar oxygen

reduce

Generally, the partial pressure of inspired oxygen remains ________ unless...

constant; altitude alters (such as going into higher altitudes where the fraction of oxygen is less)

Decreased rate of aveolar ventilation will ________ partial pressure of aveolar oxygen

reduce

Why will partial pressure of aveolar oxygen decrease with decreased rate of aveolar ventilation?

less fresh air is entering the aveolus, and more oxygen is being taken by the blood

Increased consumption rate of oxygen (metabolism) will __________ parital pressure of aveolar air. Why?

reduce; more oxygen is being taken away from the blood for use

Decreased cardiac output will __________ partial pressure of aveolar air. Why?

decreased; decreased perfusion of the lungs

The ratio of _______ to ________ determines the partial pressure of alveolar oxygen

O2 consumption to aveolar ventilation

Two factors that determine the partial pressure of aveolar carbon dioxide:

1.) rate of aveolar ventilation

2.) rate of bodily CO2 production (metabolism)

Decreased rate of alveolar ventilation will ____________ partial pressure of alveolar CO2. Why?

increase; less fresh air is coming in to dilute CO2 entering the alveoli from the blood

Increased rate of CO2 production will ___________ partial pressure of alveolar CO2. Why?

increase; more CO2 will enter the alveoli from the bloodstream per unit time

The partial pressure of inspired CO2 has ______ _____________ on the partial pressure of aveolar CO2

no effect

The ratio of _______ to ________ determines the partial pressure of aveolar carbon dioxide

CO2 generation to aveolar ventilation

If CO2 generation is constant and alveolar ventilation decreases, then partial pressure of aveolar carbon dioxide will _________

increase

There is a direct relationship between the partial pressure of ___________ carbon dioxide and partial pressure of ___________ carbon dioxide

aveolar; arterial

Measuring the partial pressure of ___________ carbon dioxde can tell you if an animal is hypo/hyperventilating

arterial

The lungs are not ____________ contractile. Therefore...

spontaneously; there must be a respiratory pump to move air in and out

F is the abbreviation for...

bulk flow

R is the abbreviation for...

resistance to bulk flow

VL is the abbreviation for...

lung volume (mL)

PTP is the abbreviation for...

transpulmonary pressure (mmHg)

PIP is the abbreviation for...

pleural fluid pressure (mmHg)

FRC is the abbreviation for...

functional residual capacity

Boyle's Law

at a constant temperature, the pressure of a gas in a container is inversely proportional to container volume

On inspiration, lung volume __________

This causes partial pressure of alveolus to ________ _________ partial pressure of atmosphere

increases; decrease below

When the partial pressure of aveolus decreases below partial pressure of atmosphere, this creates...

a pressure gradient for air to flow from the atmosphere into the aveoli

On expiration, lung volume __________

This causes partial pressure of aveolus to ________ _________ partial pressure of atmosphere

decreases; increase above

When the partial pressure of aveolus increases above partial pressure of atmosphere, this creates...

a pressure gradient for air to flow from the alveoli into the atmosphere

Two factors determining lung volume:

1.) transpulmonary pressure

2.) lung compliance

transpulmonary pressure

pressure difference between the inside (aveolus) and outside of lungs (intrapleural space)

transpulmonary pressure = ________ pressure - _________ pressure

aveolar; intrapleural fluid

At rest, intrapleural fluid is slightly __________ relative to atmospheric pressure

negative

Why is the intrapleural fluid pressure slightly negative at rest?

the lungs naturally want to collapse inward while the chest wall wants to spring outward. This opposite pulling creates a small vacuum in the pleural space, which keeps the lungs expanded by generating a positive transpulmonary pressure

the lungs naturally want to collapse _________ while the chest wall wants to spring _____________

inward; outward

Force balance

point at which the forces between the lungs and chest wall are equal

Functional residual capacity

balance position at which the lungs and chest wall opposing forces are equal