Gas Exchange & Acid-Base Regulation

Question 1

things that may widen the A-a gradient

Answer 1

1. alveolar problems (ex. emphysema)
2. interstitial problems (ex. pulmonary fibrosis, interstitial edema)
3. capillary problems (pulmonary HTN, shunting)

Question 2

factors contributing to rapid oxygen diffusion to blood from lungs

Answer 2

*large surface area
*small diffusion distance
*O2 has a relatively large blood/air pressure gradient

Question 3

one gram of hemoglobin can bind ?mL of O2?

Answer 3

one gram of Hb can bind 1.34 mL of O2 (when all sites are bound to oxygen)

Question 4

% Hb saturation = ?

Answer 4

% Hb saturation = O2 bound to Hb / O2 capacity of Hb x 100%

Question 5

oxygen content of blood - formula

Answer 5

oxygen bound to hemoglobin + dissolved oxygen

([Hb] x 1.34 x %saturation) + 0.003(PaO2)

Question 6

oxygen delivery to tissues - formula

Answer 6

oxygen delivery = cardiac output x oxygen content

CO x (([Hb] x 1.34 x %saturation) + 0.003(PaO2))

Question 7

haldane effect

Answer 7

when less oxygen is bound, the affinity of hemoglobin for CO2 increases

Question 8

Bohr effect

Answer 8

when more H+ is present (lower pH), the affinity of hemoglobin for O2 decreases (more likely to release oxygen) and H+ is able to bind to Hb

Question 9

chloride shift

Answer 9

occurs whereby Cl- enters the red blood cell from plasma in exchange for HCO3-

Question 10

cooperative binding

Answer 10

each molecule of O2 bound to hemoglobin increases the affinity for the next (this is why the oxyhemoglobin association curve is so steep)

Question 11

factors that cause the oxyhemoglobin curve to the right (increase P50)

Answer 11

*decreased pH (increased H+)
*increased 2,3 DPG
*increased CO2
*increased temperature

anything that shifts the curve to the right makes hemoglobin more likely to release its oxygen molecule

Question 12

partial pressures & pH in the lungs

Answer 12

*O2: 100 mmHg (100% saturation)
*CO2: 40 mmHg
*pH: 7.40

Question 13

partial pressures & pH in the tissues

Answer 13

*O2: 40 mmHg (75% saturation)
*CO2: 46 mmHg
*pH: 7.35

note - Bohr effect unloads O2 in tissues; Haldane effect loads CO2 in tissues

Question 14

normal physiologic pH

Answer 14

7.40

pH < 7.35 is acidemia
pH > 7.45 is alkalemia
carbonic acid (H2CO3) is the buffer

Question 15

bicarbonate buffer system equation

Answer 15

Question 16

normal bicarbonate concentration

Answer 16

24 mEq

Question 17

arterial blood gas analysis (ABGs)

Answer 17

*used to determine a person’s acid-base status
*reports the following:
-pH
-PaCO2
-PaO2
-HCO3-
-base excess
-O2 saturation (SpO2)

Question 18

RESPIRATORY alkalosis/acidosis

Answer 18

*disorders of PCO2
*this is because PCO2 is under control of the lung
*if PCO2 increases, it results in an acidosis
*if PCO2 decreases, it results in alkalosis

Question 19

METABOLIC acidosis/alkalosis

Answer 19

*disorders of [HCO3-]
*this is because HCO3- is under control of the kidney
*if [HCO3-] increases, it results in alkalosis
*if [HCO3-] decreases, it results in acidosis

Question 20

respiratory acidosis - simple

Answer 20

increased PCO2

Question 21

respiratory alkalosis - simple

Answer 21

decreased PCO2 → high pH

Question 22

metabolic acidosis - simple

Answer 22

decreased [HCO3-]

Question 23

metabolic alkalosis - simple

Answer 23

increased [HCO3-]

Question 24

expected acid-base changes

Answer 24

*if PCO2 changes, we expect a corresponding change in [HCO3-] (and vice versa)
*these corresponding changes are due to buffering
*the body will take additional action to try and return pH closer to normal (compensation)

Question 25

respiratory acidosis - compensatory mechanisms

Answer 25

*recall: respiratory acidosis = PCO2 rises, resulting in a decreased pH
*compensatory mechanism = KIDNEYS CONSERVE HCO3- (takes 2-3 days)

Question 26

metabolic acidosis - compensatory mechanisms

Answer 26

*recall: metabolic acidosis = [HCO3-] decreases, resulting in a decreased pH
*compensatory mechanism = LUNGS ELIMINATE MORE CO2

Question 26

respiratory alkalosis - compensatory mechanisms

Answer 26

*recall: respiratory alkalosis = PCO2 decreases, resulting in an increased pH
*compensatory mechanism = KIDNEYS EXCRETE ADDITIONAL HCO3- (takes 2-3 days)

Question 27

metabolic alkalosis - compensatory mechanisms

Answer 27

*recall: metabolic alkalosis = [HCO3-] increases, resulting in an increased pH
*compensatory mechanism = LUNGS ALLOW CO2 to rise

Question 28

innervation of the diaphragm

Answer 28

C3, C4, and C5 [note- loss of these nerves can lead to respiratory failure]

Question 29

brainstem sites of respiratory control

Answer 29

*pons:
-Pontine Respiratory Group (PRG)
-apneustic center

*medulla:
-Dorsal Respiratory Group (DRG)
-Ventral Respiratory Group (VRG)

Question 30

peripheral chemoreceptors

Answer 30

*outside of the CNS
*locations: CAROTID BODIES and AORTIC BODIES
*respond to blood pH and PaCO2
*carotid bodies also respond to PaO2
*sends the information to upper brain levels

Question 31

central chemoreceptors

Answer 31

*found in the brainstem
*respond to changes in pH and PCO2 of CSF
*the blood-brain barrier introduces a delay (~60s) before CSF pH equilibrates with blood pH