120 quiz 4 ch 9

Most of CO2 produced at tissue cells is carried to lungs in the form of ____

HCO3 (bicarbonate)

Arterial blood enters the systemic capillary with a PCO2 of about ____ mmHg

40 mmHg

At rest, the body’s tissues produce about ___ mL of CO2 each minute

200 mL

CO2 is a byproduct of what?

oxidative (aerobic) metabolism

Inspired atmospheric gas containes a _____ amount of CO2

negligible

The presence of CO2 in the blood is evidence of blood’s exposure to what? 

metabolically active tissues 

A steady state exists in which blood flow removes CO2 at the same rate that the body’s tissues produce it, maintaining an average tissue PCO2 of about ___ mmHg

46

The steady state in which blood flow removes CO2 at the same rate that the body’s tissues produce it

creates an average CO2 diffusion gradient of about 6 mmHg between what two things?

between tissues and the arterial blood entering the capillaries

The CO2 diffusion gradient between tissues and the arterial blood entering the capillaries causes CO2 to diffuse into the _____ _____. 

systemic capillaries 

The PCO2 of blood perfusing the systemic capillaries ______ with tissue PCO2.

equilibrates 

Venous PCO2 is about 46 mmHg. Venous blood returns to the  lungs, where it it exposed to an average alveolar PCO2 of about ___ mmHg 

40 

Normal alveolar ventilation eliminates CO2 at the same rate that it is brought to the lungs, maintaining the PACO2 at about ___ mmHg 

40 

an average CO2 diffusion gradient of about 6 mmHg between capillary blood and alveoli causes CO2 to diffuse into the ____

alveoli

CO2 =

Body produces = ~

Average tissue PCO2 = ~

Capillary PCO2 =

PvCO2 =

Alveolar PCO2 =

CO2 = by-product of oxidative (alveolar) metabolism

Body produces = ~ 200 mL/min at rest

Average tissue PCO2 = ~46 mmHg

Capillary PCO2 = 40 mmHg

PvCO2 = 46 mmHg

Alveolar PCO2 = 40 mmHg

What reaction represents hydrolysis of CO2? 

H2O + CO2 → H2CO3 → HCO3^- + H⁺

CO2 hydrolysis reaction is left shifted. What does this mean?

At equilibrium, the concentration of H2CO3 is much greater than the concentrations of HCO3^- and H⁺

Concentration of dissolved CO2 is about ____ times greater than that of H2CO3

500

H2CO3 is a ___ acid: it is equilibrium with a gas (CO2) that can be eliminated from the body

volatile

Dissolved venous CO2 enters pulmonary capillaries and equilibrates with what? 

alveolar gas CO2 

At 37C, 0.03 mmol of CO2 dissolves in 1 L plasma for each mmHg PCO2.

• so, if PaCO2 = 40 mmHg, what is the dissolved CO2?

40 mmHg x 0.03 mmol of CO2/L

= 1.2 mmol/L dissolved CO2

There are =~ ___ molecules of dissolved CO2 for every molecule of H2CO3

340

eucapnia

steady state conditions in which ventilation eliminates CO2 at exactly the same rate that the body tissues generate CO2^-

producing an alveolar and arterial CO2 of = ~40 mmHg

carbonic anhydrase (CA) 

enzyme that facilitates the rapid hydration of CO2 to form carbonic acid H2CO3 and its dissociative ions HCO3⁺ and H⁺

According to Henry’s Law, the amount of CO2 dissolving in plasma is proportional to what?

the PCO2 to which the plasma is exposed

In the lung, gaseous CO2 in the alveoli establishes equilibrium with dissolved CO2 in the capillary blood ____

plasma

Dissolved CO2 is directly proportional to the ____ concentration, making it possible to treat CO2 as if it were acid instead of H2CO3

carbonic acid

How are CO2, PCO2, and CO2 hydrolysis, and required ventilatory work to eliminate CO2 affected during hypoventilation?

CO2 production momentarily exceeds CO2 elimination. 

↑ CO2 = ↑PCO2 = hydrolysis reaction right shift 

less ventilatory work to eliminate CO2, blood acid levels are higher

How are CO2, PCO2, and CO2 hydrolysis, and required ventilatory work to eliminate CO2 affected during hyperventilation?

CO2 elimination momentarily exceeds CO2 production

↓ CO2 = ↓PCO2 = hydrolysis reaction left shift

more ventilatory work to eliminate CO2, but lower blood acid levels

Small amount of CO2 is dissolved in plasma (3 mL/dL in venous blood.

CO2 hydrolysis is about 13,000x faster in RBC than in plasma. Why? 

carbonic anhydrase is present in RBC but not in plasma

What are the Hb binding sites of O2 and CO2?

O2 combines with heme

CO2 combines with amino groups of protein.

Hb affinity for CO2 is greater when not combined with O2. this is the ____ effect

Haldane

CO2 trasnport mechanisms and approx. % of total CO2 transported to the lungs 

IN PLASMA 

Carbamino compound: __% 

Bicarbonate: __% 

Dissolved CO2: __% 

IN RED BLOOD CELLS 

Dissolved CO2: __% 

Carbamino-Hb: __% 

Bicarbonate: __% 

CO2 trasnport mechanisms and approx. % of total CO2 transported to the lungs 

IN PLASMA 

Carbamino compound: 1 % 

Bicarbonate: 5 % 

Dissolved CO2: 5 % 

IN RED BLOOD CELLS 

Dissolved CO2: 5 % 

Carbamino-Hb: 21 % 

Bicarbonate: 63 %