Chapter 18 Flashcards
List 3 arterial blood variables that influence ventilation.
- oxygen
- pH
- carbon dioxide
Diagram the normal partial pressures of O2 and CO2 in the atmosphere, alveoli, arterial blood, resting cells, and venous blood.
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
Describe all the factors that influence gas exchange between the atmosphere and arterial blood.
- 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
Individual gases diffuse along _______ ________ ________ until equilibrium.
partial pressure gradients
What is the gas exchange like between alveoli and blood (the relationships between alveoli air and blood)?
- P O2 alveolar air > P O2 blood
- P CO2 blood > P CO2 alveolar air
What is the gas exchange like between tissues and blood (the relationships between tissues air and blood)?
- P O2 blood > P O2 tissue
- P CO2 tissue > P CO2 blood
Describe all the factors that influence gas exchange between the alveoli and tissues.
- concentration gradient
- diffusion rate = SA x conc. gradient x barrier
permeability
What is the equation that describes the relationship between diffusion rate and distance?
diffusion rate (proportional to)=1 / (distance)^2
What are the constants in gas exchange with respect to diffusion rate?
- surface area
- barrier permeability
- diffusion distance
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.
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
The movement of gases is directly proportional to what?
- pressure gradient of the gas
- solubility of the gas in liquid
- temperature
Explain the role of hemoglobin in oxygen transport from the molecular level to the systemic level.
- 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
Describe the relationship between plasma P O2 and oxygen transport.
- P O2 determines oxygen-Hb binding
- depends on Plasma O2 and amount of
hemoglobin
- depends on Plasma O2 and amount of
Draw the oxyhemoglobin saturation curve and draw shifts in the curve that result from changes in pH, temp, and 2,3-BPG.
look at notebook
Describe the law of mass action.
- 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)
What does the partial pressure of oxygen in the plasma determine?
the % saturation of Hb
what does the amount of hemoglobin determine?
total # of Hb binding sites
How is the total number of Hb binding sites calculated?
(Hb content per RBC) x (# of RBCs)
Explain the physiological significance of the shape of the oxyhemoglobin saturation curve.
- 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
What is the % saturation of Hb affected by?
- partial pressure of CO2
- pH
- temperature
- 2,3-BPG
Write the chemical reaction for the conversion of CO2 to HCO3-, including carbonic anhydrase.
H2O + CO2 –(CA)–> 1) HCO3-
–> 2) H+ + Hb –> HbH
Map the transport of carbon dioxide in arterial and venous blood, including the exchanges of CO2 between the blood and the alveoli or cells.
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
What percentage of carbon dioxide is dissolved in the blood?
7%
When carbon dioxide diffuses into RBCs, what percentage is bound to hemoglobin.
23%
When carbon dioxide diffuses into RBCs, what percentage is converted to HCO3-.
70%
Map the reflex control ventilation including appropriate neurotransmitters and their receptors.
look in notebook
Diagram the current model for the brain stem neural networks that control breathing.
- 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
Explain the mechanisms by which peripheral chemoreceptors monitor CO2 and O2 levels.
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
Explain the mechanisms by which central chemoreceptors monitor CO2 and O2 levels.
look in notebook
Where are peripheral chemoreceptors located?
in glomus cells of carotid bodies
Where are central chemoreceptors located?
CNS
What do peripheral chemoreceptors sense change in?
sense changes in P O2, pH, and P CO2
What do central chemoreceptors sense change in?
respond to changes in P CO2 (indirectly) –> detects protons that are created because of CO2
In order for peripheral chemoreceptors to be activated, what must the partial pressure of oxygen fall below?
below 60 mmHg
In the central chemoreceptors, what is CO2 converted to?
bicarbonate and H+
