Vet Phys - Respiratory 3

What 2 circulations does the lung have?

1. high-pressure, low-flow

2. low pressure, high-flow

What does high-pressure, low-flow circulation involve?

Bronchial arteries: systemic arterial blood to the trachea and bronchial tree

• Contains oxygenated blood

• Empties into pulmonary veins

  • 1-2% greater blood volume enters left ventricle

what does low pressure, high flow circulation involve?

Pulmonary artery: deoxygenated blood from body to alveolar capillaries for gas exchange, returned by pulmonary veins to heart

What are the special characteristics of the pulmonary arteries?

1. Typically slightly smaller than aorta and shorter than most arteries. Arterioles are also typically larger than what are seen systemically.

2. Thin-walled and distensible

3. Large compliance → accommodates stroke volume of right ventricle

What are the special characteristics of the pulmonary lymphatics?

1. Found in supportive tissue of the lungs

2. Empty into right thoracic lymph duct

3. Removes particulate matter and plasma protein leaking from lung capillaries

how does oxygen move?

via diffusion (no active transport)

What is O2 exchange necessary?

• O₂ is the final electron acceptor in cellular respiration

• Food + oxygen → ATP

what are rates of diffusion dictated by?

the size of the concentration gradient

what is concentration?

the term typically used to describe diffusion within a single aqueous solution (one phase)

what is an issue with O2 and CO2 diffusion?

O₂ and CO₂ diffuse between a gas mixture and aqueous solution

how do you calculate the partial pressure of gas in a gaseous mixture?

• pV = nRT

• Easy enough to calculate if you know proportions of gases in the mixture

How do you calculate concentration?

• Concentration (amount per unit volume) → n/V = p

• The partial pressure and the concentration of a gas in an aqueous solution are proportional to each other 

what is the nature of partial pressure of gas in an aqueous mixture?

• The partial pressure and the concentration of a gas in an aqueous solution are proportional to each other, but the nature of this proportionality is more complicated than that in gas phases.

• C_z = AP_z

• A = absorption coefficient, a measure of gas solubility, and varies depending on the gas, temperature, and salinity

what are 3 important characteristics of partial pressure?

1. Solubilities of different gases are different, specifically, CO₂ is higher than O₂ and N₂

2. The solubilities of gases in aqueous solutions decrease strongly with increasing water temperature.

3. The solubilities of gases in aqueous solutions decrease with increasing salinity.

what is the law of gas diffusion?

it states that gases diffuse from areas of relatively high partial pressure to areas of relatively low partial pressure

• This is true within gas mixtures, within aqueous solutions, and across gas–water interfaces

• Does NOT necessarily mean that diffusion occurs in the direction of the concentration gradient

When is equilibrium reached for a gas in a system?

when the partial pressure of the gas is uniform everywhere in a system

What does the Krogh diffusion coefficient describe?

The Krogh diffusion coefficient describes the gas permeability of a tissue, indicating how easily a gas can diffuse through that tissue.

• August Krogh (1874-1949)

What is the diffusion limit of oxygen through water for living tissues?

Diffusion through water can meet the oxygen requirements of living tissues only if the diffusion distance is less than 1 mm.

is it easier for gas to diffuse through air or water?

air

• loggerhead sea turtles and anoxia

What animal is often studied for tolerance to anoxia (lack of oxygen)?

Loggerhead sea turtles are notable for their ability to tolerate periods of anoxia.

Which gas molecules contribute to the partial pressure of a gas?

Only gas molecules that exist as free gas molecules contribute to a gas's partial pressure. Molecules bound to other substances do not contribute directly to partial pressure.

What are the normal pressures across the pulmonary circulation?

• Pulmonary arterial pressure: < 30 mmHg

• Pulmonary capillary pressure: ~ 7 mmHg

• Left atrial/pulmonary venous pressure: ~ 2 mmHg

What determines the zones of pulmonary blood flow?

The zones of pulmonary blood flow are determined by the relationship between alveolar air pressure and local pulmonary capillary pressure.

What is Zone 1 pulmonary blood flow?

Zone 1 = No blood flow

• Alveolar air pressure is greater than local capillary pressure throughout the cardiac cycle.

• Capillaries are compressed, preventing blood flow.

What is Zone 2 pulmonary blood flow?

Zone 2 = Intermittent blood flow

• Alveolar air pressure is sometimes greater than local capillary pressure.

• Blood flow occurs during parts of the cardiac cycle but may cease when capillary pressure falls below alveolar pressure.

• Most likely during diastole.

What is Zone 3 pulmonary blood flow?

Zone 3 = Continuous blood flow

• Alveolar air pressure is less than local capillary pressure.

• Capillaries remain open throughout the cardiac cycle, allowing continuous blood flow.

What forces tend to move fluid out of pulmonary capillaries and into the pulmonary interstitium?

Three forces favor outward movement of fluid:

1. Pulmonary capillary pressure: +7 mmHg

2. Interstitial fluid colloid osmotic pressure: +14 mmHg

3. Negative interstitial fluid pressure: +8 mmHg

• Total outward force = 29 mmHg

What force causes absorption of fluid into the capillaries?

Colloid osmotic pressure (-28)

Why does excess fluid normally not accumulate in the pulmonary alveoli?

• The alveolar walls are extremely thin.

• Fluid that enters the alveoli is mechanically drawn into the lung interstitium.

• The fluid is then carried away by the lymphatic system.

What happens to pulmonary blood flow during exercise?

Exercise increases blood flow throughout all parts of the lung.

How does exercise change the pulmonary blood flow zones?

Pulmonary vascular pressure rises, converting the lung apices from Zone 2 → Zone 3

Does a large increase in cardiac output cause a large increase in pulmonary artery pressure during exercise?

No. Increased cardiac output does not cause a proportionally large increase in pulmonary artery pressure.

How can the lungs accommodate increased blood flow during exercise without a large rise in pulmonary artery pressure?

Through:

• Capillary recruitment → previously unperfused capillaries open

• Capillary distension → existing capillaries widen

• These increase pulmonary vascular capacity and limit the rise in pulmonary pressure.

Why are the lungs considered a blood reservoir?

The lungs store roughly 9% of the body's total blood volume in normal circumstances (healthy and at rest)

what is blood flow matched for?

blood flow is matched for optimal blood exchange

What happens to pulmonary blood vessels during hypoxia?

Hypoxia → increase in vascular resistance → diverts blood flow (opposite of systemic vessels)

Why is pulmonary blood flow distributed preferentially to certain areas of the lungs?

Blood flow is directed toward better-aerated areas of the lungs to optimize oxygen uptake and gas exchange.

Which pulmonary circuit is low-pressure, high flow circulation?

a.Bronchial arteries

b. Pulmonary Artery 

c. All of the above

b. Pulmonary Artery 

What characteristic of gases and partial pressure is NOT true?

a. Solubilities of different gases are different

b. The solubilities of gases in aqueous solutions decrease strongly with increasing water temperature.

c. The solubilities of gases in aqueous solutions decrease with increasing salinity.

d. All of the above are true

d. All of the above are true

If atmospheric oxygen has a higher concentration and a higher atm than inside the lung, which direction with it diffuse?

a. It will diffuse into the lungs

b. It will diffuse out of the lungs

c. It will not diffuse at all, because it is already at equilibrium

d. Not enough info given

a. It will diffuse into the lungs

What are the force(s) that cause fluid absorption into the capillaries?

a. Low pulmonary capillary pressure

b. Negative interstitial fluid

c. Capillary osmotic pressure

d. A and B

c. Capillary osmotic pressure

True or false: The blood vessels of pulmonary and systemic vessels behave in a similar fashion with hypoxia.

False