A & P (1) - Respiratory System, Gas Exchange And Hemoglobin

Front 1

What are the contents of alveolar fluid?

Back 1

Water, surfactant

Front 2

What is surfactant?

Back 2

Complex mixture of phospholipids and lipoproteins that lowers the surface tension of alveolar fluid, reducing the tendency of alveoli to collapse

Front 3

Besids type I and II alveolar cells, what other cells are present in alveoli?

Back 3

Alveolar macrophages (dust cells)

Fibroblasts

Front 4

How many alveoli are there estimated to be between the two lungs?

Back 4

300 million

Front 5

When put together, how large a surface area do the alveoli provide for gas exchange?

Back 5

70 square meters, about the size of a racquetball court

Front 6

What is different about the way pulmonary vessels respond to localized hypoxia compared to the way systemic vessels respond to localized hypoxia?

Back 6

Pulmonary vessels constrict rather than dilate in response to local hypoxia so as to divert blood from poorly ventilated (hypoxic) areas to well ventilated regions

Front 7

What is ventilation-perfusion coupling?

Back 7

The constriction of pulmonary vessels in response to hypoxia so as to divert blood to better ventilate areas

Front 8

What structures of the lung make up the respiratory zone (zone of gas exchange)?

Back 8

Respiratory bronchioles, alveolar ducts, alveoli

Front 9

What percentage of tidal volume actually makes it to the respiratory zone?

Back 9

75% (350mL)

Front 10

What is the anatomic dead space?

Back 10

Those portions of the respiratory tract where gas exchange does not occur (conducting airways of nose, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles)

Front 11

What is Dalton's Law?

Back 11

Each gas in a mixture of gases exerts its own pressure as if no other gas was present.

The total pressure exerted by a gaseous mixture is the sum of the individual partial pressures exerted by each gas in the mixture.

Front 12

What is Henry's Law?

Back 12

Henry's Law states that the quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas above the liquid as well as the solubility of the gas in the liquid.

The higher the partial pressure of a gas over a liquid and the higher the solubility, the more gas will stay in solution.

Everyday example: gas bubbles emerging from a soft drink when the pressure above it is released.

Front 13

Which has greater solubility: CO2 or O2?

Back 13

Carbon dioxide has much greater solubility at the same pressure

Front 14

Why does nitrogen not enter the bloodstream under normal conditions if 79% of the atmosphere is nitrogen?

Back 14

Very low solubility in water

Front 15

What is nitrogen narcosis and how is it explained by Henry's Law?

Back 15

When divers breathe air under high pressure the high partial pressure of nitrogen is enough for some to dissolve into the bloodstream despite its low solubility in blood plasma

Excessive amounts of nitrogen may produce giddiness and other symptoms similar to alcohol intoxication

Nitrogen narcosis also called "rapture of the deep"

Front 16

What is decompression sickness/the bends?

Back 16

Symptoms of joint pain, dizziness, shortness of breath, extreme fatigue, paralysis and unconsciousness

Result of diver coming to surface too quickly

Nitrogen comes out of solution too quickly and forms gas bubbles in tissues, particularly nervous tissue

Front 17

What is the respiratory membrane?

Back 17

Tissue across which gas exchange occurs in the lungs

Alveolar wall (type I and type II cells)

Epithelial basement membrane

Capillary basement membrane

Capillary endothelium

Front 18

What percentage of atmospheric air is nitrogen? Oxygen? Carbon dioxide?

Back 18

Nitrogen: 78.6%

Oxygen: 21%

Carbon dioxide and other gases: less than 1%

Front 19

Why does air reaching the alveoli have a lower percentage of oxygen than atmospheric air?

Back 19

Air becomes humidified as it passes through the moist mucosal linings

Front 20

What is the partial pressure of oxygen in deoxygenated blood?

Back 20

40 mmHg

Front 21

What is the partial pressure of oxygen in alveolar air?

Back 21

105 mmHg

Front 22

What is the partial pressure of oxygen in oxygenated blood as it leaves the alveolar capillaries?

Back 22

105 mmHg

Front 23

What is the partial pressure of oxygen in pulmonary veins and systemic arteries?

Back 23

100 mmHg (blood that passed through alveolar capillaries had 105 mmHg but later mixed with blood that did not pass through areas of gas exchange, dropping it to 100)

Front 24

What is the partial pressure of carbon dioxide in deoxygenated blood?

Back 24

45 mmHg

Front 25

What is the partial pressure of carbon dioxide in alveolar air?

Back 25

40 mmHg

Front 26

What is the partial pressure of carbon dioxide in oxygenated blood leaving the pulmonary capillaries?

Back 26

40 mmHg

Front 27

What is the partial pressure of oxygen in deoxygenated (venous) blood?

Back 27

40 mmHg

Front 28

What would be the partial pressures of oxygen and carbon dioxide in a normal arterial blood gas?

Back 28

Oxygen: Around 100 mmHg

Carbon dioxide: Around 40 mmHg

Front 29

What would be the partial pressures of oxygen and carbon dioxide in a normal venous blood gas?

Back 29

Oxygen: Around 40 mmHg

Carbon dioxide: Around 45 mmHg

Front 30

What are the partial pressures of oxygen and carbon dioxide at the tissue cells?

Back 30

Oxygen: 40 mmHg

Carbon dioxide: 45 mmHg

Front 31

Describe the structure of the hemoglobin molecule.

Back 31

The hemoglobin molecule consists of 4 globin chains, each with a single heme group that can bind a single molecule of oxygen gas.

1) 4 globin polypeptide chains: 2 alpha chains and 2 non-alpha chains. The non-alpha chains determine which kind of hemoglobin it is (e.g. HbF has gamma non-alpha chains, HbA has beta non-alpha chains)

2) Each of the four polypeptide chains contains one heme group

3) Each heme group consists of an atom of iron surrounding by a porphyrin ring

Front 32

What is a heme group?

Back 32

A heme group is an atom of iron contained within a porphyrin ring.

Each of the 4 globin chains of hemoglobin contains a heme group.

Each heme group can bind 1 molecule of oxygen gas. Thus a single molecule of hemoglobin can bind 4 molecules of oxygen gas.

Front 33

How many molecules of oxygen gas can bind to each hemoglobin molecule?

Back 33

4

Front 34

What is porphyrin?

Back 34

Porphyrin is an organic molecule composed of 4 modified pyrrole subunits arranged into a larger ring.

In the body, porphyrin forms the backbone of heme, with an atom of iron in the middle of the ring.

In the catabolism of heme, iron is reused but the ring-like porphyrin is broken into a long chain becoming bilirubin.

Front 35

What material reality accounts for the variable affinity of hemoglobin for oxygen?

Back 35

The shape of hemoglobin changes between two opposite conformations.

In the taut (T) conformation, hemoglobin has low affinity for oxygen. This means that it binds oxygen LESS readily and releases oxygen MORE readily.

In the relaxed (R) conformation, hemoglobin has higher affinity for oxygen. This means that it binds oxygen MORE readily and releases oxygen LESS readily.

Factors such as the partial pressure of oxygen, partial pressure of carbon dioxide, pH, temperature, and presence of BPG can drive hemoglobin towards one conformation or the other, thus increasing or decreasing its affinity for oxygen.

Front 36

What is the most important determinant of oxygen's affinity for hemoglobin and thus the % saturation of hemoglobin?

Back 36

Numero uno, the most important, is the partial pressure of oxygen in the blood (oxygen tension), which essentially forces the binding of oxygen. The binding of oxygen promotes a conformational change towards the R conformation, increasing oxygen affinity.

This phenomenon of oxygen binding promoting further oxygen binding is known as cooperativity.

Front 37

What is the Haldane effect?

Back 37

The Haldane effect describes the reciprocal binding of carbon dioxide and oxygen to hemoglobin.

At the tissues, CO2 tension is high and CO2 binds to hemoglobin, driving the molecule towards its taut (T) configuration and thus facilitating oxygen release.

At the lungs, oxygen tension is high and oxygen binds to hemoglobin, driving the molecule towards its relaxed conformation and facilitating CO2 release.

Front 38

What is the Bohr effect and how does it work on a molecular level?

Back 38

The Bohr effect describes the reciprocal binding of oxygen and protons to hemoglobin, and thus the relationship between acidity and the oxygen affinity of hemoglobin.

At the tissues, an increase in acidity (drop in pH) enhances the unloading of oxygen from hemoglobin. Why? The binding of protons drives hemoglobin toward its taut (T) conformation, facilitating the release of oxygen. The release of oxygen, in turn, facilitates the binding of more protons, since deoxyhemoglobin is a stronger base than oxyhemoglobin.

At the lungs, the binding of oxygen to hemoglobin facilitates the release of protons. Oxygen affinity increases because of increased oxygen tension in the alveolar capillaries. Oxygenated hemoglobin is less basic than deoxyhemoglobin, so protons are released.

Front 39

What effect does raising the body temperature have on oxygen affinity? Lowering the temperature?

Why does this occur?

Back 39

Raising temperature reduces hemoglobin's affinity for oxygen and thus promotes the release of oxygen from hemoglobin.

Lowering temperature has the opposite effect, increasing oxygen affinity

These effects of temperature on hemoglobin's affinity for oxygen are phsyiologically useful. Metabolically active cells give off more heat. They also require more oxygen. Conversely, slow metabolic activity will have less heat, and less O2 will be released.

Front 40

What metabolic pathway is BPG a product of?

Back 40

Glycolysis

Front 41

What is BPG?

Back 41

2,3-bisphosphoglycerate, a side product of glycolysis

Front 42

What effect does the binding of BPG have on hemoglobin's oxygen affinity?

Back 42

Decreases oxygen affinity

Front 43

On a graph representing an equation for the relationship between two variables, which axis is the independent variable and which axis is the dependent variable?

Back 43

The x axis (horizontal) is the independent variable.

The y axis (vertical) is the dependant variable, "dependant" because it depends on the value of x.

Front 44

Which two variables are displayed on the oxygen-hemoglobin dissociation curve?

Which variable is the independent variable?

Which variable is the dependent variable?

Back 44

The oxygen-hemoglobin dissociation curve shows the relationship between the partial pressure of oxygen and the percent saturation of hemoglobin.

The partial pressure of oxygen is the independent variable and the percent saturation of hemoglobin is the dependent variable. This is because PO2 is the single most important factor determining how much O2 binds to hemoglobin.

Front 45

On the oxygen-hemoglobin dissociation curve, which axis represents the P02 and which axis represents the % saturation of hemoglobin?

Back 45

PO2 is the x axis (independent variable)

% saturation of hemoglobin is the y axis (dependent variable)

Front 46

What is the normal PO2 in venous blood?


What is the % saturation of hemoglobin at this PO2?

Back 46

40 mmHg

75%

This means that hemoglobin in venous blood is still about 75% saturated with oxygen.

Front 47

Under stable conditions, what percentage of oxygen bound at the lungs is actually released at the tissues for use by cells?

Back 47

About 25%

Think of it this way:

In arterial blood the PO2 is 100 mmHg and the % saturation of hemoglobin is 100%.

In venous blood the PO2 is 40mmHg and the % saturation of hemoglobin is 75%.

This means only 25% has been unloaded!

Front 48

At what partial pressure of oxygen does the % saturation of hemoglobin approach 90%.

Back 48

60 mmHg

Front 49

At what partial pressure of oxygen does the % saturation of hemoglobin begin to nosedive?

Back 49

40 mmHg

At this point curve becomes steep, and small drops in PO2 produce large drops in % saturation.

Front 50

Sum up the shape of the oxygen-hemoglobin dissociation curve and the material reality that this shape represents.

Back 50

The curve essentially has two portions, a steep portion between a PO2 of 0 mmHg and 40 mmHg, as well as a flat portion from a PO2 of 40 mmHg and up.

What this means is that changes in PO2 above 40 mmHg have relatively little effect on the % saturation of oxygen.

Changes in PO2 below 40 mmHg, on the other hand, result in large changes in % saturation of hemoglobin.

Front 51

Under conditions in which hemoglobin has decreased affinity for oxygen, which direction would the oxygen-hemoglobin dissociation curve shift?

Back 51

To the right (you need greater PO2 to achieve the same % saturation of hemoglobin)

Front 52

Under conditions in which hemoglobin has increased affinity for oxygen, which direction would the oxygen-hemoglobin dissociation curve shift?

Back 52

To the left (you need lower PO2 to achieve the same % saturation of hemoglobin)

Front 53

What does a shift to the right in the oxygen-hemoglobin dissociation curve indicate?

Back 53

This means that a greater PO2 is required to achieve the same % saturation of hemoglobin as under normal conditions.

It reflects a state of decreased hemoglobin affinity for oxygen (a shift towards the taut confirmation)

Front 54

What does a shift to left in the oxygen-hemoglobin dissociation curve indicate?

Back 54

This means that a lower PO2 is required to achieve the same % saturation of hemoglobin as under normal conditions.

It reflects a state of greater hemoglobin affinity for oxygen (a shift towards the relaxed confirmation)

Front 55

What effect would a decrease in pH (increase in acidity) have on the oxygen-hemoglobin dissociation curve?

Why does this occur?

Back 55

The curve would shift to the right, reflecting a decrease in hemoglobin's affinity for oxygen.

This occurs due to the reciprocal binding of H+ and oxygen to hemoglobin, a phenomenon known as the Bohr effect. As Hb picks up more H+, it releases O2 more readily.

Front 56

What effect would an increase in PCO2 have on the oxygen-hemoglobin dissociation curve?

Why does this occur?

Back 56

The curve would shift to the right reflecting hemoglobin's decreased affinity for oxygen.

This occurs due to the reciprocal binding of CO2 and O2 to hemoglobin, a phenomenon known as the Haldane effect.

The binding of CO2 facilitates the release of O2.

Front 57

What effect does an increase in temperature have on the oxygen-hemoglobin dissociation curve?

Back 57

Increased temperature shifts the curve to the right.

This is a dumb way of saying that increased temperature decreases hemoglobin's affinity for oxygen.

Thus more oxygen is released in warmer regions. This is physiologically useful because areas of higher metabolism are both warmer and have higher oxygen demand.

Front 58

What effect does a decrease in temperature have on the oxygen-hemoglobin dissociation curve?

Back 58

A decrease in temperature shifts the curve to the left, which is a fancy way of saying that decreasing temperatures cause oxygen's affinity for oxygen to increase.

Less oxygen is released in cooler areas. This is physiologically useful because cooler areas are less metabolically active and require less oxygen.

Front 59

What is the proximate reason fetal hemoglobin has greater oxygen affinity than adult hemoglobin?

What is the ultimate reason fetal hemoglobin NEEDS greater oxygen affinity?

Back 59

Fetal hemoglobin binds BPG less readily (BPG decreases oxygen affinity)

Maternal blood in the placenta has low oxygen saturation, so it's important for the fetal hemoglobin to rip off as much as possible

Front 60

Describe what happens to carbon dioxide as it enters the bloodstream (i.e. what are the three pathways it follows in the blood):

Back 60

In short: 1) 7% dissolved CO2, 2) 23% carbaminohemoglobin, 3) bicarbonate

1) Simply dissolves and travels through blood in dissolved form to the lungs where it diffuses into alveolar air. Only 7% of CO2 follows this pathway

2) Binds to proteins forming carbamino compounds. Mostly binds to hemoglobin forming carbaminohemoglobin. Through the Haldane effect, CO2 unloading is facilitated at the lungs and CO2 diffuses into the alveolar air. 23% of CO2 travels this way

3) Enters erythrocytes, forms carbonic acid (reaction catalyzed by carbonic anhydrase) which dissociates to form protons and bicarbonate. Bicarbonate diffuses down gradient out of erythrocyte into bloodstream where it travels to the lungs. At lungs converted back into CO2. About 70% of CO2 travels through the blood this way

Front 61

Why does the reaction of water and carbon dioxide to yield carbonic acid proceed so readily within erythrocytes?

Back 61

Due to the presence of relatively high amounts of the enzyme carbonic anhydrase.

Front 62

What is the chloride shift and why does it occur?

Back 62

At the tissues, some CO2 is converted to bicarbonate in the RBCs. Bicarbonate diffuses down its concentration gradient out of the RBC into the blood. To maintain electrical balance, negatively charged chloride ions enter the RBC to replace the negatively charged bicarb ions that diffuse out.

Front 63

Describe the chemical conversion of CO2 to bicarbonate at the tissues:

Back 63

CO2 + H2O (in presence of carbonic anhydrase) --> H2CO3 --> H+ + HCO3-

Front 64

Describe the chemical conversion of bicarbonate back into CO2 at the lungs

Why does this reaction proceed?

Back 64

HCO3- + H+ --> H2C03 --> H2O + CO2

Proceeds because hemoglobin releases its bound H+ at the tissues, giving the necessary fuel for the fire.

Front 65

A patient has an arterial pO2 of 60 mmHg.

Assuming the oxyhemoglobin curve is not shifted, approximately what percentage of his hemoglobin will be saturated?

Back 65

90%