BIO 360 - Exam 4 - Chapter 18 Summary Questions Flashcards
Normal alveolar and arterial PO2 is about ___ mm Hg.
Normal alveolar and arterial PCO2 is about ___ mm Hg.
Normal venous PO2 is ___ mm Hg.
Normal venous PCO2 is ___ mm Hg.
Diffusion goes to equilibrium, and the PO2 of arterial blood leaving the lungs is the same as in the alveoli: 100 mm Hg.
100 / 40 / 40 / 46
Fig. 18.2 Gases diffuse down concentration gradients:
Because PO2 is ______ in the cells, oxygen diffuses down its partial pressure gradient from ______ into cells.
Conversely, PCO2 is higher in ______ than in systemic capillary blood because of CO2 production during metabolism.
lower / plasma / tissues
What three variables influence the efficiency of alveolar gas exchange and determine whether arterial blood gases are normal (Fig. 18.3a)?
(1) Adequate oxygen must reach the alveoli. A decrease in alveolar means that less oxygen is available to enter the blood.
(2) There can also be problems with the transfer of gases between the alveoli and pulmonary capillaries.
(3) Blood flow, or perfusion, of the alveoli must be adequate. If something impairs blood flow to the lung, then the body is unable to acquire the oxygen it needs.
There are two possible causes of low alveolar PO2:
(1) the inspired air has low oxygen content.
(2) alveolar ventilation is inadequate.
Body sensors monitor blood oxygen, CO2 and pH in an effort to avoid hypoxia and hypercapnia.
What is hypoxia and hypercapnia?
Hypoxia is a state in which oxygen is not available in sufficient amounts at the tissue level to maintain adequate homeostasis.
Hypercapnia (hypercarbia) is when you have high levels of carbon dioxide in your blood.
Low alveolar ventilation is also known as hypoventilation and is characterized by lower-than-normal volumes of fresh air entering the alveoli.
Pathological changes that can result in alveolar hypoventilation (Fig. 18.3c) include:
(1) decreased lung compliance [p. 548]
(2) increased airway resistance [p. 550]
(3) central nervous system (CNS) depression that slows ventilation rate and decreases depth.
Compliance: the property of a material of undergoing elastic deformation or (of a gas) change in volume when subjected to an applied force.
The diffusion rate is directly proportional to?
From the general rules for diffusion, we can add a fourth factor: diffusion distance. Diffusion is inversely proportional to?
Diffusion rate directly proportional to surface area x concentration gradient x barrier permeability.
Diffusion is inversely proportional to the square of the distance.
Pathological changes that adversely affect gas exchange include:
(1) a decrease in the amount of alveolar surface area available for gas exchange.
(2) an increase in the thickness of the alveolar-capillary exchange barrier.
(3) an increase in the diffusion distance between the alveolar air space and the blood.
(4) fluid distance between the alveoli and pulmonary capillaries.
The movement of gas molecules from air into a liquid is directly proportional to three factors:
Carbon dioxide is 20 times more soluble in aqueous solutions than oxygen is.
(1) the pressure gradient of the gas.
(2) the solubility of the gas in the liquid.
(3) temperature.
What is solubility?
If a gas is very soluble, ______ numbers of gas molecules go into solution at a ______ gas partial pressure.
The ease with which a gas dissolves in a liquid.
large / low
Why is solubility important in physiology (3 things) ?
(1) Oxygen’s low solubility in aqueous solutions means that very little oxygen can be carried dissolved in plasma.
(2) Its low solubility also means oxygen is slower to cross the increased diffusion distance present in pulmonary edema.
(3) Diffusion of oxygen into alveolar capillaries does not have time to come to equilibrium before the blood has left the capillaries. The result is decreased arterial PO2 even though alveolar PO2 may be normal.
What is Mass Flow?
We can calculate the mass flow of oxygen traveling from lungs to the cells by using the oxygen content of the _______________.
If arterial blood contains, on average, 200 mL O2/L blood and the cardiac output is 5 L/min, then oxygen transport to cells is?
The amount of x moving per minute.
Mass Flow = concentration x volume flow.
Arterial blood x cardiac output.
200mL O2/L x 5L/min = 1000mL O2/min to cells
Oxygen is transported dissolved in plasma (<2%)
and bound to hemoglobin (>98%)
Why is hemoglobin an effective oxygen carrier?
Hemoglobin (Hb) is a tetramer with four globular protein chains (globins), each centered around an iron-containing heme group.
The central iron atom of each heme group can bind reversibly with one oxygen molecule. The iron-oxygen interaction is a weak bond that can be easily broken without altering either the hemoglobin or the oxygen.
With four heme groups per hemoglobin molecule, one hemoglobin molecule has the potential to bind four oxygen molecules. Hemoglobin bound to oxygen is known as oxyhemoglobin,
The amount of oxygen that binds to hemoglobin depends on two factors:
(1) the PO2 in the plasma surrounding the red blood cells.
(2) the number of potential Hb binding sites available in the red blood cells.
