Respiratory Physiology (Part 3) Flashcards by Alli Volkens

Describe the shape of the O2-hemoglobin dissociation curve

Percent saturation increases steeply as PO2 increases from zero to approximately 40 mmHg, and then it levels off between 50 mmHg and 100 mmHg

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The shape of the steepest portion of the curve is the result of what?

a change in affinity of the heme groups for O2 as each successive O2 molecule binds, such that binding of the first molecule of O2 to a heme group increases the affinity for the second O2 moles, so on and so forth

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When PO2 is 25 mmHg, percent saturation is __% and referred to as P(50)

50%

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An increase in P50 reflects a(n) ____ in affinity and a decrease in P50 reflects a(n) ____ in affinity

decrease

increase

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At the highest values of PO2 (in systemic arterial blood), the affinity of hemoglobin is ______.

highest

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At lower values of PO2 (in mixed venous blood), the affinity of hemoglobin is ______.

lower

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Alveolar air, pulmonary capillary blood, and systemic arterial blood all have a PO2 of ___ mmHg

100 mmHg

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Mixed arterial blood has a PO2 of ___ mmHg

40 mmHg

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A PO2 of 40 mmHg corresponds to approximately __% saturation and a ____ affinity of hemoglobin for O2. What is the significance of this?

lower

These changes n affinity facilitate loading of O2 in the lungs (where PO2 and affinity are highest) and unloading of O2 in the tissues (where PO2 and affinity are lower).

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In the lungs, hemoglobin is __% saturated because affinity is _____.

100%

highest

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In the tissues, hemoglobin is __% saturated because affinity is _____.

75%

decreased

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Shifts of the O2-hemoglobin dissociation curve reflect what?

changes in the affinity of hemoglobin for O2

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Shifts of the O2-hemoglobin dissociation curve produce changes in what?

P50

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When does the O2-hemoglobin dissociation curve shift to the right?

When there is a decreased affinity of hemoglobin for O2

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A decreased affinity of hemoglobin for O2 is reflected in a(n) ____ P50. What does this mean?

increase

This means that 50% saturation is achieved at higher-than-normal value of PO2

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When the affinity decreases, unloading of O2 in the tissues is _______.

facilitated

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What 4 things cause a decrease in affinity and a right shift in the O2-hemoglobin dissociation curve?

increases in PCO2
decreases in pH
increases in temperature
increases in 2,3-DPG concentration

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The effect of PCO2 and pH on the 02-hemoglobin dissociation curve is called the ____ effect

Bohr

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An increase in temperature shifts the curve to the right which does what?

provides more O2 to the tissue

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Under what conditions does 2,3-DPG concentration increase?

under hypoxic conditions, such as living at high altitude

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When does the O2-hemoglobin dissociation curve shift to the left?

When there is an increased affinity of hemoglobin for O2

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An increased affinity of hemoglobin for O2 is reflected in a(n) ____ P50. What does this mean?

decrease

This means that 50% saturation occurs at a lower-than normal value of PO2

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When the affinity increases, unloading of O2 in the tissues is _______. Why?

more difficult

binding is tighter

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What 4 things cause an increase in affinity and a left shift in the O2-hemoglobin dissociation curve?

decreases in PCO2
increases in pH
decreases in temperature
decreases in 2,3-DPG concentration

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Describe why the presence of hemoglobin F causes a shift to the left

The binding of 2,3-DPG does not bind as avidly to the gamma chains of the hemoglobin F as it does to the beta chains of hemoglobin A. This results in increased O2 affinity

Why is this increase in affinity beneficial to the fetus?

Their Pa(O2) levels are low (approximately 40 mmHg)

Carbon monoxide _______ the amount of O2 bound to hemoglobin

decreases

CO binds to hemoglobin with an affinity that is ___ times that of O2 to form what?

250 carboxyhemoglobin

What is the siginificance of CO having a much higher affinity to hemoglobin that O2?

The heme groups that are bound to CO decrease the number of O2-binding sites available on the hemoglobin. This means that the O2 content of blood and the delivery to tissues decreases dramatically

The effect of carbon monoxide causes a ____ shift of the O2-hemoglobin dissociation curve

left

The heme groups not bound to CO have an ______ affinity for O2. How does this affect P50 and what does it result in?

increased P50 decreases, making it more difficult for O2 to be unloaded in the tissues

The overall effect of CO is that there is _____ O2-binding capacity of hemoglobin and the remaining heme sites bind O2 _____.

reduced more tightly

What are the 3 forms CO2 is carried in the blood?

- dissolved CO2 - carbaminohemoblogin - bicarbonate (HCO3-)

Which form of CO2 in the blood is the most important quantitatively?

bicarbonate

What law gives the concentration of CO2 in solution?

Henry's law

What does Henry's law state?

The concentration of dissolved CO2 in blood is the partial pressure multiplied by the solubility of CO2

Dissolved CO2 accounts for _% of the total CO2 content of blood

When CO2 is bound to hemoglobin, what is it called?

carbaminohemoblogin

Carbaminohemoblogin accounts for _% of the total CO2 content of blood

O2 bound to hemoglobin changes its affinity for CO2, such that when less O2 is bound, the affinity of hemoglobin for CO2 ______. What is this effect called?

increases Haldane effect

In the tissues, as CO2 is produced and binds to hemoglobin, hemoglobin's affinity for O2 is ______, which causes what?

decreased, which results in the release of O2 to the tissues more readily

Release of O2 from hemoglobin ______ its affinity for the CO2 that is being produced in the tissues.

increases

Bicarbonate accounts for __% of the total CO2 content of blood

Describe the reactions that occur to produce bicarbonate from CO2

Co2 combines with H2O to form a weak acid H2CO3. H2CO3 then dissociates into H+ and HCO3-. *Both reactions are reversible

What enzyme catalyzes the hydration of CO2 and the dehydration of H2CO3?

carbonic anhydrase, which is present in most cells

Describe bicarbonate generation in the tissues.

CO2 is generated from aerobic metabolism and is added to system capillary blood where it is converted to HCO3- and transported to the lungs

What happens to the H+ that is produced via the disassociation of H2CO3?

It is buffered as that the pH of the blood cells stays within physiological range

The H+ is buffered in the red blood cells by what?

Deoxyhemoglobin

What happens to the HCO3- that is produced via the disassociation of H2CO3?

It is exchanged for Cl- across the RBC membrane and then is carried to the lungs where it is reconverted to CO2 and expired

What is pulmonary blood flow?

Cardiac output of the right heart, which is equal to the cardiac output of the left heart

Pulmonary blood flow is _____ proportional to the pressure gradient between the pulmonary artery and the left atrium and is ______ proportional to the resistance of the pulmonary vasculature.

directly inversely

In comparison to systemic circulation, pulmonary circulation is characterized by _____ pressures and resistances

lower

Pulmonary blood flow ____ systemic blood flow

equals

Altering the resistance of the arterioles in the pulmonary circulation is mediated by what?

local vasoactive substances, especially O2

What is by far the most major factor regulating pulmonary blood flow?

The partial pressure of O2 in alveolar gas (PAO2)

Decreases in PAO2 produces pulmonary vaso______. What is this known as?

vasoconstriction hypoxic vasoconstriction

In the lungs, hypoxic vasoconstriction occurs as an adaptive mechanism, in which pulmonary blood flow _____ to poorly ventilated areas. Why?

decreases Because blood flow to these areas would be "wasted"

Hypoxic vasoconstriction is the mechanism by which pulmonary blood flow is directed ____ poorly ventilated regions of the lung and _____ well ventilated regions of the lung

away from toward

The mechanism of hypoxic vasoconstriction involves a direct action of what?

alveolar PO2 on the vascular smooth muscle of pulmonary arterioles

What happens if PAO2 is reduced below 70 mmHg?

the vascular smooth muscle cells sense this hypoxia, vasoconstrict, and reduce pulmonary blood flow in that region

Inhibition of nitric oxide synthase _____ hypoxic vasoconstriction

enhances

Inhaled nitric oxide ____ hypoxic vasoconstriction

reduces

Describe how hypoxic vasoconstriction functions to increase pulmonary vascular resistance at high altitude

PAO2 is reduced due to the low O2 mixture of the air. This produces global vasoconstriction of pulmonary arterioles and an increase in pulmonary vascular resistance.

Other than high altitude, what is another example of global hypoxic vasoconstriction?

fetal circulation

Because the fetus does not breathe, PAO2 is ____ in the fetus than in the mother, producing vaso_____ in the fetal lungs.

much lower vasoconstriction

Vasoconstriction of fetal lungs ______ pulmonary vascular resistance and ______ pulmonary blood flow

increases decreases

Describe what happens when a baby takes its firs breath

PAO2 increases to 100 mmHg, hypoxic vasoconstriction is reduced, and pulmonary blood flow increases

What are 3 other substances that alter pulmonary vascular resistance?

- Thromboxane A2 - Prostacyclin - Leukotrienes

How does Thromboxane A2 alter pulmonary vascular resistance?

It is a powerful local vasoconstrictor of both arterioles and veins

How does Prostacyclin alter pulmonary vascular resistance?

It is a potent local vasodilator

Leukotrienes causes constriction of what?

airway constriction

What does the distribution of blood flow within the lung depend on?

gravity

Describe the pattern of blood flow in a person who is standing

Zone 1: blood flow is the lowest Zone 2: blood flow is medium Zone 3: blood flow is highest

The arterial pressure in zone one (apex) is _____ than alveolar pressure and _______ than venous pressure

lower greater

Describe what happens in zone one if arterial pressure is decreased (due to hemorrhage)

Alveolar pressure becomes greater than arterial pressure, which causes the blood vessels to compress and close. This results in zone 1 not being perfused and no gas exchange occurs

The arterial pressure in zone 2 is _____ than alveolar pressure and _______ than venous pressure

greater greater

What drives blood flow in zone 2?

The difference between arterial and alveolar pressure

The arterial pressure in zone 3 is _____ than alveolar pressure and _______ than venous pressure

greater greater

Zone 3 is the only zone in which alveolar pressure is _____ than both arterial venous pressures?

less

What drives blood flow in zone 3?

The difference between arterial and venous pressure

What are 3 types of pulmonary shunts?

- Physiologic shunt - Right-to-left shunts - Left-to-right shunts

What shunt type is the most common?

Left-to-right shunts

Describe the 2 parts of the physiologic shunt

- Part is the bronchial blood flow, which serves the metabolic functions of the bronchi - The other is the small amount of coronary blood flow that drains directly into the left ventricle through the thesbian veins and never perfuses the lungs

When does shunting from the right heart to the left hear occur?

If there is a defect in the wall between the right and left ventricles

What always occurs in a right-to-left shunt? Why?

Hypoxemia, because a significant fraction of the CO is not delivered to the lungs for oxygenation

What is a defining characteristic of the hypoxemia caused by a right-to-left shunt?

It can NOT be corrected by having the person breathe a high O2 gas bevause the shunted blood never goes to the lungs to be oxygenated

Left-to-right shunts are more ______.

common

Do left-to-right shunts cause hypoxemia?

What are 2 causes for a left-to-right shunt?

- patent ductus arteriosus | - traumatic injury

Pulmonary blood flow (right-heart CO) becomes _____ than system blood flow (left heart CO) in the presence of a left-to-right shunt

greater

In the presence of a left-to-right shunt PO2 in the blood on the right side of the heart ____. Why?

increase, because oxygenated blood that has just returned from the lungs is added directly to the right heart without being delivered to the tissues

The ventilation/perfusion ratio is a ratio between what 2 things?

alveolar ventilation to pulmonary blood flow

Alveoli must be perfused in order for what to occur?

gas exchange

What is the normal vatilation/perfusion (V/Q) ratio? What does this mean?

0.8 This means that alveolar ventilation is 80% of the value for pulmonary blood flow

In what zone is the V/Q the highest? Lowest?

highest in zone 1 lowest in zone 3

In zone 1 blood flow is _____, alveolar ventilation is _____, V/Q is _____, PAO2 is _____, and PACO2 is _____.

``` Zone 1: blood flow = lowest alveolar ventilation = lower V/Q = highest PAO2 = highest PACO2 = lower ```

In zone 3 blood flow is _____, alveolar ventilation is _____, V/Q is _____, PAO2 is _____, and PACO2 is _____.

``` Zone 3: blood flow = highest alveolar ventilation = higher V/Q = lowest PAO2 = lowest PACO2 = higher ```

A mismatch of ventilation and perfusion is called what?

V/Q mismatch or V/Q defect

What does V/Q mismatch result in?

abnormal gas exchange

What may cause a V/Q defect?

- ventilation of lung regions that are not perfused (dead space) - perfusion of lung regions that are not ventilated (shunt)

Dead space is illustrated by what?

A pulmonary embolism, in which blood flow to a portion of the lung is occluded

In regions of dead space, what does PAO2 and PACO2 equal?

PAO2 is 150 mmHg PACO2 is 0 mmHg

A shunt is illustrated by what?

Airway obstruction and right-to-left cardiac shunts

In regions of a shunt, what does PAO2 and PACO2 equal?

PAO2 is 40 mmHg PACO2 is 46 mmHg

Respiratory Physiology (Part 3) Flashcards

(104 cards)