CO2 Transport

48, 52, RBCs

Total CO2 content of blood

• Arterial blood = __ ml CO2/dL blood

• Venous blood = __ ml CO2/dL blood

• 75% of CO2 in blood is in __, 25% in plasma

Higher, lower

• How does CO2 content compare to O2 content of arterial blood?

  • __ CO2 content compared to O2

• How does PCO2 compare to PO2 in arterial blood?

  • __ PaCO2 compared to PaO2

Plasma, RBCs

Dissolved CO2

• Dissolved in __, and dissolved in cytoplasm of __

Carbonic Anhydrase

Enzyme in RBCs catalyzes reaction of CO2 with H2O to form carbonic acid

H+, HCO3-

Carbonic acid rapidly dissociates to __ and __ (cation, anion)

PCO2

CO2 dissolved in blood determines…

0.067 ml CO2

Solubility of CO2 = __ __ __/dl blood

not, fraction, Higher

Carbon dioxide binding to Hb and other proteins

• __ (does/not) directly contribute to PCO2

• Relatively small __ of total CO2 in blood

• Alters Hb-O2 affinity

  • __ CO2 bound to Hb → lower affinity of Hb for O2

not, majority, pH

Carbon dioxide as bicarbonate ions

• __ (does/not) directly contribute to PCO2

• __ of total CO2 in blood (~90%)

• Important for __ regulation

Chloride Shift

HCO3- is transported out of RBCs in exchange for Cl-

RBCs, buffering, acidification

Chloride Shift

• Allows conversion of CO2 to H+ and HCO3- to continue in the __

• H+ ions bind to Hb in RBCs, H+ can’t cross RBC membrane

  • The __ by Hb prevents the __ of RBCs

Tissues, Alveoli

Hemoglobin toggles between oxygenated and reduced states

• RBCs at __ - Increase CO2 stimulates O2 unloading with H+ binding to Hb

• RBCs at __ - Increase O2 stimulates CO2 release, displacing H+ from Hb

(Tissues vs alveoli)

Medulla, dorsal respiratory group, phrenic

• Pacemaker cells in __ initiate quiet breathing

  • Inspiratory center located in the __ __ __

  • The inspiratory center then acts on the diaphragm via the __ nerve

Carotid, aortic, pH, respiratory rate

Central chemoreceptors

• Located in medulla __ and __ bodies

• Highly sensitive to PaO2, PaCO2, __

  • Once across, CO2 is converted to H+ and HCO3-

  • H+ activates central chemoreceptors to increase __ __

Decrease, peripheral chemo, IX, X, medulla, 60, phrenic, diaphragm, respiratory rate

PaO2 Loop

• Regulated Variable = __ in PaO2

• Sensor = __ __receptors (bodies)

• Input Signal = CN __ and CN __ (afferent neurons)

• Control Center = Inspiratory control center of __

  • Set point: PaO2 greater than __

• Output Signal = __ nerve

• Effectors = __

• Controlled Variables = Increase __ __

Increase, peripheral chemo, IX, X, medulla, 40, phrenic, diaphragm, respiratory rate

PaCO2 Loop

• Regulated Variable = ___ in PaCO2

• Sensor = __ __receptors (bodies)

• Input Signal = CN __ and CN __ (afferent neurons)

• Control Center = Inspiratory control center of __

  • Set point: PaO2 equal to __

• Output Signal = __ nerve

• Effectors = __

• Controlled Variables = Increase __ __

Increase, decrease, chemo, afferent, inter, medulla, 7.4, phrenic, diaphragm, respiratory rate

Peripheral/central chemoreflex loop for H+

• Regulated Variable = An __ in H+, or __ in pH

• Sensor = __receptors (carotid bodies + medulla)

• Input Signal = __ neurons and __neurons

• Control Center = Inspiratory control center of __

  • Set point: pH of __

• Output Signal = __ nerve

• Effectors = __

• Controlled Variables = Increase __ __

5-HT, increase, GABA, decrease

Peripheral/central chemoreflex loop for H+

• Low pH is excitatory with neurot __ → Net result is __ RR

• High pH is inhibitory with neurot __ → Net result is __ RR