Blood Gas Transport + Breathing Control Flashcards
(10 cards)
Outline the forms by which O2 and CO2 are carried in blood
(specify their contents in arterial and venous blood)
Two types of oxygen transport:
1. physically dissolved in blood (2%)
2. chemically bound to hemoglobin (98%)
Oxygen content:
in arterial blood:
CaO2 = 20 ml O2 / 100 ml blood
in venous blood:
CvO2 = 15 ml O2 / 100 ml blood
Three types of carbon dioxide transport:
1. physically dissolved in blood (7%)
2. physically dissolved as bicarbonate ion, HCO3- (70%)
3. chemically bound to Hb molecule (23%)
Carbon dioxide content:
in arterial blood:
CaCO2 = 48 ml CO2 / 100 ml blood
in venous blood:
CvCO2 = 52 ml CO2 / 100 ml blood
Describe the physioloigcal significance of the oxy-gemoglobin dissociation curve.
(How does the right/left shift of curve relate to the affinity of hemoglobin for oxygen and its ability to load oxygen in lungs and unload it to the tissues)
y-axis: % Hb saturation
x-axis: PO2 (mm Hg)
mixed Venous blood
(blood leaving circulatory system)
- 75% Hb saturation and PO2 = 40
blood interfacing with alveoli (arterial blood leaving pulmonary system)
- 98% Hb saturation and PO2 = 100
Plateau region (PO2: 60 - 100)
(“loading oxygen at lungs”)
- safety margin for transport in cases where lung PO2 is low
- increase PO2 above 100 does not improve oxygen saturation
Plateau to steep
(arterial blood reaches tissues –> O2 unbinds from Hb )
- PaO2 falls from 98 to 40 mmHg (PvO2)
Steep region
- small decreases in tissue PO2 result in substantial unbinding from O2 from Hb
- tissue PO2 depends on tissue’s metabolic average (avg = 40 mmHg which is used to indidcated mixed venous blood)
P50
- PO2 required for 50% of Hb to become O2 bound
= 26.6 mmHg in normal human aterial blood (assumes pH = 7.4, PCO2 = 40 mmHg, body temp = 37C)
Shifts in curve
1. left shift
- high affinity of Hb for O2
2. right shift
- low affinity of Hb for O2
Describe the impact of PCO2, pH, temp, 2,3-BPG, anemia, and carbon monoxide on the oxy-hemoglobin dissociation curve
(interpret their physiologic outcome)
PCO2
- increased CO2 –> right shift
(ex. exercise produces CO2 resulting in easy unloading of O2 into muscle tissue)
2,3 BPG
- increase [2,3 BPG] –> right shift
Temperature
- increase –> right shfit
pH
- increase in pH –> left shift
(decrease in h+ causes less oxygen to be offloaded –> more oxygen used to make carbaminohemoglobin)
Anemia
- flattens curve (decreases Hb –> decreases O2 carrying capacity and O2 content)
- does NOT change O2 saturation (x-axis)
Carbon monoxide
- increase –> left shift (interferes w/ O2 unloading –> tissue hypoxia)
(CO has higher affinity to Hb than O2 –> competition for binding heme site)
Describe the significance of the enzyme, carbonic anhydrase, in transport of carbon dioxide in blood
location:
- resides in blood cells
Function:
- accelerates formation of carbonic acid (H2CO3) from CO2 and water by 1000X
Carbonic acid is part of a series of downstream pathways that creates carbaminohemoglobin (CO2HHb)
Explain how O2 and CO2 influence the transport of each other by hemoglobin (reference the Bohr and Haldane Effects)
Haldane Effect:
- CO2 dissociation curve influenced by oxygenation state of Hb
(CO2 transport depends on O2 release from Hb –> so CO2 can bind to Hb)
Molecular basis of Haldane effect
- Hb is better at binding H+ and CO2 than O2
–> forms CO2HHb (carbaminogemoglobin)
- CO2HHb assists blood in loading more CO2 from the tissue (acts as a sink which maintains partial pressure gradient for CO2 diffusion out of tissues into plasma and red blood cells)
Identify key structures responsible for automatic control of breathing rhythm and the sources of input to them
Breathing is established in CNS
- initiated by medulla
Medullary Respiratory Groups
1. Dorsal Respiratory Group (DRG)
- inspiratory neurons driving inspiratory muscles
- receive input from peripheral chemo/mechano-receptors
- Ventral Respiratory Group (VRG)
- expiratory neurons driving expiratory muscles
- active during active expiration
Bulbospinal and spinal nerves
- sends info from medulla to muscles of respiration
1. Phrenic nerves
- (C3,4,5 keep the diaphragm alive
- motor output to diaphragms
- Intercostal nerves
- exit thoracic + lumbar spine
- motor output to intercostal and abdominal muscles - cranial nerves
- motor output to upper airway dilator muscles
Specify location of central and periphereal chemoreceptors and describe their impact on ventilation in response to changes in arterial PCO2, PO2 and pH
- Central chemoreceptors
Location:
- few mm below ventral surface of medulla
Impact:
- stimulated by small changes in PaCO2 via changes in brain ECFluid
[H+] levels
- regulates breathing (low PaCO2 –> decreases ventilation) - Periphereal chemoreceptors
Location:
- carotid + Aortic bodies
Impact:
- key oxygen sensors
- ventilatatory response to low PaO2 (below 60 mmHg) = hyperventilation
- Carotid –> sensory info caried by glossopharyngial (CN IX) afferent nerve fibers
- Aortic –> sensory info carried by vagal (CN X) afferent nerve fibers
Describe how metabolic acidosis accompanying intense exercise or diabetes impacts ventilation and arterial PO2 and PCO2
Metabolic acids stimulate peripheral chemoreceptors
ex. lactic acids produced in skeletal muscle during intense exercise
ex. diabetic ketoacidosis
Increased acid content (acidosis)
–> increased ventilation
Increased basic content (alkalosis)
–> decreased ventilation
Specify the effects of hyperventiliation and hypoventilation on arterial blood gases (PaCO2 and PaO2)
Hyperventilation
–> hypocapnia (PaCO2 below resting levels)
–> hyperoxia (PaO2 above resting levels)
Hypoventilation
(opp of hyperventilation)
Describe how congenital hypoventilation syndrome, its treatment and how it informs us about automatic versus the conscious/voluntary control of breathing
rare disorder in children
- breathing adequate when awake
–> conscious/voluntary ventilation intact - breathing inadequate during sleep
–> inadequate automatic control results in alveolar hypoventilation during sleep
