Ch. 22.3 Gas Exchange and transport

Composition of air

78.6 nitrogen

20.9 oxygen

0.04 CO2

other

Total atmospheric pressure

sum of all gases

daltons law

Partial pressure

separate contribution of each gas in a mixture

P

Why does alveolar air and atm air differ?

3 reasons

1.) its humidified by contact with the mucous membranes, ph2o is higher

2.) Freshly inspired air mixes with residual air so its o2 is diluted and enriched with co2

3.) Alveolar air exchanges o2 and co2 with the blood, so the po2 of alveolar is is 65% of inhaled air and its pco2 is 130 times higher than atm

Alveolar Gas Exchange

For O2 to get into blood it must dissolve in water film of alveoli

For CO2 to leave blood it must pas the other way and diffuse out

Why does O2 and CO2 diffuse in their directions?

each gas diffuses down its own partial pressure gradient

water and air - gases diffuse down their gradients until the partial pressure of each gas is equal

Henry's law

at the air water interface the amount of gas that dissolves in the water is determined by its solubility in water

-so the greater the pO2 in alveolar air the more O2 the blood picks up

what does o2 and co2 exchange involve

Erythrocytes

efficiency of that process depends on?

how long and rbc spends in an alveolar capillary compared with how long it takes for each gas to be fully loaded or unloaded

Variables affecting the efficiency of alveolar gas exchange

-pressure gradients of the gases

-solubility of gases

-membrane thickness

-membrane area

ventilation perfusion coupling

Why does the po2 drop to 95 mm hg before leaving lungs

because the dilution occurs because the pulmonary veins anastomose with bronchial veins in the lung and o2 poor and o2 rich blood mix

Ventilation perfusion coupling

the physiological responses that match airflow to blood flow

-poor ventilation = poor blood flow = low PO2 = stimulates vasoconstriction

vice versa

What is the change in Po2 as blood travels from the lungs to the systemic circulation?

Po2 drops from 104 to 95 mmHg due to mixing with systemic blood.

What is the Po2 level when blood gives up O2 to respiring tissue?

Po2 drops to 40 mmHg.

What happens to Po2 after blood gives up O2 to respiring tissue?

It remains at 40 mmHg until the blood is reoxygenated.

What is the Pco2 level when blood leaves the lungs?

Pco2 is 40 mmHg.

What happens to Pco2 as blood picks up CO2 from respiring tissue?

Pco2 rises to 46 mmHg.

What happens to Pco2 after it rises to 46 mmHg?

It remains at that level until the blood returns to the lungs and unloads CO2.

conversion of bicarbonate back into carbon dioxide

1.) bicarbonate (hco3-) diffuses into rbc in exchange for chloride ions

2.) hemoglobin releases hydrogen ions

3.) hco3+h= carbonic acid

4.) carbonic acid catalyzes breakdown of carbonic acid

5.) = water and co2

Gas transport

the process of carrying gases from the alveoli to the systemic tissues and vice versa

Hemoglobin

specialized for oxygen transport

oxyhemoglobin

when one or more molecules of o2 are bound to hemoglobin

deoxyhemoglobin

no oxygen bound

cause of CO poisoning

competes with oxygen for the same binding site

binds 210x tigher than oxygen

why doesnt carbon dioxide compete with o2?

because co2 and o2 bind to different sites on the hemoglobin molecule

-simultaneous transportation

90% of co2 forms what?

carbonic acid

co2 + h2o -->h2co3-->hco3+h+

Reduction of partial pressure of oxygen results in ?

decrease in hb saturation

vice versea

what percentage of co2 is transported as carbaminohemogobin

23%

what % of co2 remains dissolved in plasma

5-7%

how is majority co2 transported

converted to bicarbonate for transport

How does Hgb increase buffering capacity of the bicarbonate system?

H+ ions bind to hgb buffering and pH changes

Systemic gas exhange

the unloading of o2 and loading of co2 at the systemic capillaries

Aerobic respiration

produces 1 co2 for each o2 consumed

what causes hemoglobin to release o2?

when h+ binds yo oxyhemoglobin (hbo2), it reduces the affinity of hgb for o2 and releases it

utilization coefficient

amount of oxygen Hb has released 22%

Venous reserve of oxygen

o2 remaining in blood after it passes through capillary bed

-sustains life for 4-5 mins in the event of respiratory arrest

Bohr effect

a decrease in the amount of oxygen associated with hemoglobin and other respiratory compounds in response to a lowered blood pH resulting from an increased concentration of carbon dioxide in the blood.

Haldane effect

Deoxygenation of the blood increases its ability to carry carbon dioxide

Factors adjusting rate of oxygen unloading to the metabolic rates of different tissues

-Ambient Po2

-Temperature

-Ambient pH

-BPG

Ambient Po2

(factor 1 adj. o2 rate)

-active tissue consumes oxygen

-po2 remains low

Temperature

-elevate temp promotes oxygen unloading

Ambient pH

Active tissue generates CO2

-raised H+

-lowers pH

-weakened bond between hbg and o2

-o2 unloaded

BPG

binds to hgb and promotes o2 unloading

-elevated body temp stimulates bpg

-thyroxine

-growth hormone

test

epi

Acidosis

blood pH lower than 7.35

Alkalosis

pH above 7.45

Pco2 of arterial blood

37-43 mm hg

Hypocapnia

insufficient carbon dioxide

less than 37 mmhg

Hypercapnia

excessive carbon dioxide in the blood

ketoacidosis

excessive production of ketones, making the blood acid

hypoxic drive

A "backup system" to control respiration; senses drops in the oxygen level in the blood.

feed forward mechanism

reflex that starts the response loop in anticipation of the stimulus or change