Chapter 18

Question 1

List 3 arterial blood variables that influence ventilation.

Answer 1

• oxygen
• pH
• carbon dioxide

Question 2

Diagram the normal partial pressures of O2 and CO2 in the atmosphere, alveoli, arterial blood, resting cells, and venous blood.

Answer 2

Atmosphere:
- P O2 = 160 mmHg
- P CO2 = 0.25 mmHg

Alveoli:
- P O2 = 100 mmHg
- P CO2 = 40 mmHg

Arterial Blood:
- P O2 = 100 mmHg
- P CO2 = 40 mmHg

Resting Cells:
- P O2 <= 40 mmHg
- P CO2 => 46 mmHg

Venous Blood:
- P O2 <= 40 mmHg
- P CO2 => 46 mmHg

Question 3

Describe all the factors that influence gas exchange between the atmosphere and arterial blood.

Answer 3

• composition of inspired air –> low alveolar P O2 if inspired air has abnormally low oxygen content
  - higher altitude decreases P O2
• alveolar ventilation –> low alveolar P O2 if alveolar ventilation is inadequate (hypoventilation)
  - decreased lung compliance
  - increased airway resistance
  - CNS depression

Question 4

Individual gases diffuse along _______ ________ ________ until equilibrium.

Answer 4

partial pressure gradients

Question 5

What is the gas exchange like between alveoli and blood (the relationships between alveoli air and blood)?

Answer 5

• P O2 alveolar air > P O2 blood
• P CO2 blood > P CO2 alveolar air

Question 6

What is the gas exchange like between tissues and blood (the relationships between tissues air and blood)?

Answer 6

• P O2 blood > P O2 tissue
• P CO2 tissue > P CO2 blood

Question 7

Describe all the factors that influence gas exchange between the alveoli and tissues.

Answer 7

• concentration gradient
• diffusion rate = SA x conc. gradient x barrier
  permeability

Question 8

What is the equation that describes the relationship between diffusion rate and distance?

Answer 8

diffusion rate (proportional to)=1 / (distance)^2

Question 9

What are the constants in gas exchange with respect to diffusion rate?

Answer 9

• surface area
• barrier permeability
• diffusion distance

Question 10

Explain the difference between the concentration of a gas in solution and the partial pressure of that gas in solution, using O2 and CO2 as examples.

Answer 10

Oxygen:
- [O2] –> concentrations not equal + measured in mmol/L
- P O2 –> reach equilibrium + measured mmHg

Carbon Dioxide –> 20x more soluble than oxygen –> don’t need as much as a conc. drive for diffusion
- [CO2] –> concentrations not equal + measured in mmol/L
- P CO2 –> reach equilibrium + measured mmHg

Question 11

The movement of gases is directly proportional to what?

Answer 11

• pressure gradient of the gas
• solubility of the gas in liquid
• temperature

Question 12

Explain the role of hemoglobin in oxygen transport from the molecular level to the systemic level.

Answer 12

• O2 enters capillaries
• O2 dissolves in plasma + stays there (2% of the time)
• O2 enters RBCs –> binds to hemoglobin (98%) –> forms oxyhemoglobin (HbO2)
• transports to cells
• HbO2 breaks down into hemoglobin and oxygen
• O2 is dissolved in plasma
• O2 crosses capillary barrier to cells
• O2 used in cellular respiration

Question 13

Describe the relationship between plasma P O2 and oxygen transport.

Answer 13

• P O2 determines oxygen-Hb binding
  
  • depends on Plasma O2 and amount of
    hemoglobin

Question 14

Draw the oxyhemoglobin saturation curve and draw shifts in the curve that result from changes in pH, temp, and 2,3-BPG.

Answer 14

look at notebook

Question 15

Describe the law of mass action.

Answer 15

• oxygen binding obeys the law of mass action:
  - increase in P O2 shifts reaction to right
  (Hb + O2 –> HbO2)
  - decreased in P O2 shifts reaction to left
  (Hb + O2 <– HbO2)

Question 16

What does the partial pressure of oxygen in the plasma determine?

Answer 16

the % saturation of Hb

Question 17

what does the amount of hemoglobin determine?

Answer 17

total # of Hb binding sites

Question 18

How is the total number of Hb binding sites calculated?

Answer 18

(Hb content per RBC) x (# of RBCs)

Question 19

Explain the physiological significance of the shape of the oxyhemoglobin saturation curve.

Answer 19

• partial pressure of oxygen is high –> saturation of hemoglobin is high
  - direct relationship
• due to the physiological affinity that hemoglobin has for oxygen at the different partial pressures –> when oxygen binds to hemoglobin –> causes hemoglobin to want more oxygen

Question 20

What is the % saturation of Hb affected by?

Answer 20

• partial pressure of CO2
• pH
• temperature
• 2,3-BPG

Question 21

Write the chemical reaction for the conversion of CO2 to HCO3-, including carbonic anhydrase.

Answer 21

H2O + CO2 –(CA)–> 1) HCO3-
–> 2) H+ + Hb –> HbH

Question 22

Map the transport of carbon dioxide in arterial and venous blood, including the exchanges of CO2 between the blood and the alveoli or cells.

Answer 22

1) CO2 diffuses out of cells into systemic capillaries
2) only 7% of the CO2 remains dissolved in plasma
3) nearly 1/4 of the CO2 binds to hemoglobin, forming carbaminohemoglobin
4) 70% of the CO2 load is converted to bicarbonate and H+ ; hemoglobin buffers H+
5) HCO3- enters the plasma in exchange for Cl- (chloride shift)
6) at the lungs, dissolved CO2 diffuses out of the plasma
7) by the law of mass action, CO2 unbinds from hemoglobin and diffuses out of the RBC
8) the carbonic acid reaction reverses, pulling HCO3- back into the RBC and converting it back to CO2

Question 23

What percentage of carbon dioxide is dissolved in the blood?

Answer 23

7%

Question 24

When carbon dioxide diffuses into RBCs, what percentage is bound to hemoglobin.

Answer 24

23%

Question 25

When carbon dioxide diffuses into RBCs, what percentage is converted to HCO3-.

Answer 25

70%

Question 26

Map the reflex control ventilation including appropriate neurotransmitters and their receptors.

Answer 26

look in notebook

Question 27

Diagram the current model for the brain stem neural networks that control breathing.

Answer 27

• respiratory neurons in the medulla control inspiratory and expiratory muscles
• neurons in the pons integrate sensory info + interact with medullary neurons to influence ventilation
• rhythmic pattern of breathing arises from a neural network of spontaneously discharging neurons
• ventilation is subject to continuous modulation by chemoreceptor- and mechanoreceptor-linked reflexes + higher brain centers

Question 28

Explain the mechanisms by which peripheral chemoreceptors monitor CO2 and O2 levels.

Answer 28

1) stimulus –> low partial pressure of oxygen in glomus cell in carotid body
2) K+ channels close
3) cell depolarizes
4) voltage gated Ca2+ channel opens
5) Ca2+ enters
6) exocytosis of neurotransmitters
7) action potential on sensory neurons signals to medullary centers to increase ventilation

Question 29

Explain the mechanisms by which central chemoreceptors monitor CO2 and O2 levels.

Answer 29

look in notebook

Question 30

Where are peripheral chemoreceptors located?

Answer 30

in glomus cells of carotid bodies

Question 31

Where are central chemoreceptors located?

Answer 31

CNS

Question 32

What do peripheral chemoreceptors sense change in?

Answer 32

sense changes in P O2, pH, and P CO2

Question 33

What do central chemoreceptors sense change in?

Answer 33

respond to changes in P CO2 (indirectly) –> detects protons that are created because of CO2

Question 34

In order for peripheral chemoreceptors to be activated, what must the partial pressure of oxygen fall below?

Answer 34

below 60 mmHg

Question 35

In the central chemoreceptors, what is CO2 converted to?

Answer 35

bicarbonate and H+