Flashcards in BIOL 0800 Reading- Chapter 13 Deck (113)
What is the major disease-induced cause of inadequate oxygen movement between alveoli and pulmonary capillary beds?
What is the major effect of ventilation-perfusion inequality?
To lower the PO2 of systemic arterial blood
Why is the PO2 of blood in circulation normally about 5 mmHg less than that of average alveolar air?
Because gravity causes a different blood flow distribution in the lung, which contributes to ventilation-perfusion inequality, which reduces PO2
What is shunt?
Blood flow to an area without ventilation
What is the main homeostatic mechanism to avoid ventilation-perfusion inequality for low ventilation and low perfusion?
When there is low alveolar PO2 (due to decrease in ventilation), the vessel vasoconstricts and directs blood elsewhere to properly ventilated areas; of when there is low alveolar PCO2, the bronchioles constrict and direct airflow elsewhere
What is hemoglobin?
Four subunits made of one polypeptide and one heme each (a globin and four heme groups); heme groups contain iron for cooperative binding to oxygen
What is percent hemoglobin saturation?
(O2 bound to Hb) / (maximal capacity of Hb to bind to O2) x 100
What factors determine the % Hb saturation?
What is the oxyhemoglobin dissociation curve?
The experimentally determined quantitative relationship between blood PO2 and the combination of oxygen with hemoglobin; sigmoid because of cooperative binding
What is the approximate shape/range of the oxyhemo dissoc curve?
Steep slope from 10-60 mmHg, plateaus at 70-100 mmHg PO2; **at a PO2 of 60 mmHg, 90% hemoglobin saturation
What is the biological significance of the plateau in the oxyhemo dissoc curve?
Safety net! Even if atmospheric PO2 decreased from 100 to 60 mmHg, total hemoglobin saturation would only decrease by 10% or so
What is the biological significance of the steep slope of the oxyhemo dissoc curve?
Allows for easy unloading of oxygen: small PO2 changes can lead to a big decrease in hemoglobin saturation
How does temperature affect the OHD curve?
Increased temperature shifts the curve right: makes it more difficult to unload oxygen
How does acidity affect the OHD curve?
Increased acidity (lower pH) shifts the curve right: makes it more difficult to unload oxygen
How does DPG concentration affect the OHD curve?
Increased DPG concentration shifts curve right: makes it more difficult to unload oxygen
How does PCO2 affect the OHD curve?
Increased PCO2 increases H+ concentration, which increases acidity: shifts curve right: lowers affinity of Hb for O2
How do CO2 and H+ affect hemoglobin's affinity for oxygen?
Allosterically modulate the globin
How does DPG affect Hb's affinity for oxygen?
DPG = released during glycolysis (only respiration for RBCs, so lots of DPG in RBCs); allosterically modulates Hb
Which is more soluble in water, CO2 or O2? Why is this important?
CO2: blood carries more dissolved CO2 than dissolved O2
How is CO2 transported in the blood?
Some by dissolving, some by binding with Hb to form carbaminohemoglobin, and most converted to bicarbonate and hydrogen ions by carbonic anhydrase
What is carbaminohemoglobin?
When CO2 binds to Hb (deoxyhemoglobin, which has a higher affinity for CO2 than for O2, than does HbO2)
Why is it important that the chloride-bicarbonate exchange removes HCO3- from the RBC?
So that the reaction still favors dissociation of bicarbonate
Why is venous blood slightly more acidic than arterial blood?
Because dissociation of bicarbonate produces H+, which binds to deoxyhemoglobin, but there's still some left: decreases the pH (more acidic)
What is associated with hypo/hyperventilation, respiratory acidosis or alkalosis?
Acidosis associated with hypoventilation, alkalosis associated with hyperventilation
What initiates nerves impulses to the respiratory skeletal muscles?
Medulla oblongata activity: in medullary respiratory center
What are the two components of the medullary respiratory center?
The dorsal and ventral respiratory groups (DRG and VRG)
What is the DRG?
Primarily fire during inspiration; input to spinal motor neurons that activate inspiratory muscles: diaphragm and inspiratory intercostal muscles
What is the nerve that innervates the diaphragm?
What is the VRG?
Rhythm generator: pacemaker cells and complex neural network that sets basal respiratory rate; respiratory rhythm generator located in the pre-Botzinger complex in the upper VRG; nerves in lower half that fire for inspiration AND expiration