Gas Transport Flashcards by Camelita Thrift

Fick’s Law equation

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How can the diffusion constant of a particulary gas be calculated?

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What is the normal diffusion distance?

0.2-0.5 microns

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Which conditions can cause a thickened barrier?

Fibrosis

Intersitial edema

NOTE: Patients with diffusion deficits often have decreases in blood O2 occur more early than CO2 increases in the blood.

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What are the methods of O2 transport?

Dissolved in plasma- 2%
Chemically bound to hemoglobin in erythrocytes - 98%

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What is the oxygen concentration in air?

21%

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Partial pressure of O2 in air

160 mmHg

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Pressure of oxygen in trachea

150 mmHg

*The decrease is due to dilution with water

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The concentration of DISSOLVED oxygen in the blood is _________ (directly/indirectly) proportional to the partial pressure of oxygen (the PO2) in the gas.

Directly

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What’s the normal amount of dissolved oxygen in plasma?

0.3 mL O2 per 100 mL of blood

*This is 10% of the body’s metabolic demand. So, dissolved O2 alone does not come close to meeting the body’s O2 demands

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Transport of O2 from the lungs to the peripheral tissues is dependent on _____ and ________.

Diffusion; perfusion

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What is the effect of venous mixture on changes in PO2?

Mixing of blood occurs in the pulmonary capillaries which cause a decrease in the O2 entering the left heart to about 95-100 mmHg. This occurs for 2% of the blood entering the left atrium

NOTE: The other 98% of blood enters the left atrium with a PO2 of 104 mmHg.

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Mixing of blood that reduces oxygen pressure in pulmonary capillaries is do to what?

Thebesian veins of the myocardium allow the bypassing of lung bronchial circulation

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The iron found in hemoglobin is in its ________ state.

Ferrous (Fe2+)

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What is the total carrying capacity of hemoglobin?

197 mL O2/ L og blood

*This satisfies 90% of O2 consumption at the tissue level

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Oxygen- Hemoglobin Dissociate Curve

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What are the three anchor points of the oxygen hemoglobin dissociation curve?

PO2 at approximately 100 mmHg for the arterial blood
PO2 at approximately 40 mmHg for the mixed venous blood
At 50% saturation, PO2 is approximately 27 mmHg in arterial blood and approximately 29 mmHg for mixed venous blood

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On the flat portion of the oxygen-hemoglobin dissociation curve, a drop in PO2 from 100 mmHg down to 60 mmHg still results in 90% saturation of Hb. At what PO2 is oxygen delivery compromised?

Below 60 mmHg

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Which factors shift the dissociation curve to the right?

Increase in CO2
Increase in H+
Increase in 2,3-BDG
Increase in Temp

*This is Bohr’s law

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Which factors shift the dissociation curve to the left?

Decrease H+
Decrease CO2
Decreased temp
Decrease 2,3 DPG

*This is the Haldane effect

Will exercise shift the dissociation curve to the right or the left?

Right

*Shift to the right reduces hemoglobin’s affinity for O2, which is perfect because the tissues need more oxygen to be released during exercise

In what conditions are 2,3 DPG elevated?

Obstructive pulmonary disease
Cystic fibrosis
Congestive heart failure and some congenital heart defects
Most types of anemia
High altitudes
In pregnancy
Hyperthyroidism
After vigorous exercise

NOTE: 2,3-DPG in RBCs increases in response to anemia/hypoxia and causes a rightward shift of the oxygen dissociation curve, allowing a more effective oxygen delivery.

H+ rises in response to entry of _______.

CO2

Diffusion-limited Gas Exchange

Describes the scenario in which the rate at which gas is transported away from functioning alveoli and into tissues is principally limited by the diffusion rate of the gas across the alveolar membrane.

*Results in incomplete equilibration

Perfusion-limited gas exchange

the rate of gas transport from the lung can only be increased by **increasing pulmonary blood flow** \*The result is **complete equilibration**

Transfer of CO is limited by the \_\_\_\_\_\_\_\_\_.

**RATE OF DIFFUSION** \*Not the amount of blood available (perfusion)

What are some common sources of CO?

Cigarette Car exhaust

Treatment for CO poisoning

* Administration of high concentration of supplemental O2 to displace CO from the Hb * Hyper-barometric chamber

At what pressures is O2 highly soluble?

20-60 mmHg \*Relatively insoluble at 100 torr because more Hb binding sites are already bound

CO solubility is very large at a partial rpessure of \_\_\_\_\_.

1-2 torr

Why is CO so toxic to the oxygen transport system?

CO binding affinity for Hb results in a decrease in O2 content of arterial blood by 50%

How do you calculate O2 consumption?

VO2= O2 consumption Qt= Cardiac output CaO2= Delivery to tissues CvO2= Amount remaining after release to tissues

What is the normal amount of O2 delivered per minute?

1000 mL O2/ min

How oxygen delivery calculated?

Clinical Calculation of Total O2 content

Dissolved O2 + Hb O2

Normal SaO2

98%

Types of Hypoxia

* **Circulatory (Stagnant) Hypoxia** * Result of diminished blood flow to an organ * **Hypoxic hypoxia** * Reduced PaO2 and or CaO2 with a subsequent decrease in O2 delivery * **Histotoxic Hypoxia** * Block of electron transport chain system, which prevents utilization of oxygen * **Anemic Hypoxia** * ****Reduction in the ability to transport O2

Causes of Hypoxic hypoxia

**High altitude** * Reduced FIO2, Reduced PAO2, Reduced PaO2 **Emphysema** * Deterioration of alveolar Type I cell membrane and loss of gas exhange surface area **Fibrosis** * Thickening of alveolar membrane **NOTE:** COPD and Neuromuscular disease could lead to hypoxic hypoxia as well

Causes of stagnant hypoxia

Vascular disease Arterial-venous shunt Sickle cell anemia crisis Blood clots

Causes of anemic hypoxia

Reduced hemoglobin CO poisoning

Causes of histologic hypoxia

CN- poisoning Sodium Azide poisoining Pesticide Rotenone

What are the three ways that CO2 is transported?

* Physically dissolved in plasma- **7%** * Bound to hemoglobin - **23%** * Bicarbonate ions in RBCs- **70%** **NOTE:** CO2 is more soluble in blood than O2

Uptake of carbon dioxide by the blood in the tissue capillaries is dependent on ___ and \_\_\_\_\_\_\_\_\_\_\_\_.

Passive diffusion; partial pressure gradients

PCO2 of blood entering is ________ torr. PCO2 of blood exiting is ________ torr.

45; 40

What do the blood CO2 equilibrium curves are different hemoglobin saturation levels reveal?

1. Deoxygenated mixed venous blood can transport _more_ CO2 2. CO2 curves are essentially straight lines between a PCO2 of 20-80 mmHg linear relationship

Haldane approximately __________ the amount of CO2 release from blood in the lungs and doubles the amount picked up in the tissues.

Doubles

The rate of CO2 output to O2 uptake is referred to as the \_\_\_\_\_\_\_\_\_.

**Respiratory exchange ratio** Normal ratio= 0.825, based on average diet amounts of protein, fats, and carbohydrates

CO2 diffuses _____ times faster than O2.