Flashcards in 597 - 598 - Respiratory Physio Deck (38)
Do the lungs intrinsically tend to collapse inward or expand? How about the chest wall?
Lungs - collapse inward
Chest wall - spring outward
What forces are balanced at FRC?
1. Inward pull of lung
2. Outward pull of chest wall
Total pressure of system = atmospheric pressure
At FRC, what is the pressure of:
- intrapleural space?
- airways = 0
- alveoli = 0
- intrapleural space = negative to prevent pneumothorax
At FRC, describe the PVR (pulmonary vascular resistance).
PVR is at minimum
What is lung compliance?
change in lung volume for a given change in pressure
Explain how each of the following affect lung compliance:
- pulmonary fibrosis
- pulmonary edema
- normal aging
- pulmonary fibrosis ↓
- emphysema ↑
- pulmonary edema ↓
- normal aging ↑
- pneumonia ↓
What is the basic structure of hemoglobin?
4 polypeptide subunits (2 α and 2 β)
What are the two forms of hemoglobin?
T (taut) form with low affinity for O2
R (relaxed) form with high affinity for O2 (300x)
Hb exhibits ______ (positive/negative) cooperativity and ______ (positive/negative) allostery.
Which factors favor the taut form of Hb?
When Hb transitions to the taut form, what happens to O2?
"Taut in Tissues, Relaxed in Respiratory tract"
What subunits make up fetal Hb?
2 α and 2 γ subunits
Does fetal Hb have lower or higher affinity for O2 than adult Hb?
Higher affinity (b/c has lower affinity for 2,3-BPG)
Why do hemoglobin modifications lead to tissue hypoxia?
↓ O2 sat and ↓ O2 content
What is methemoglobin?
Oxidized form of Hb (ferric, Fe3+) that does not bind O2 as readily, but has ↑ affinity for cyanide
Is iron in Hb normally in an oxidized or reduced state? What is this form called?
reduced; ferrous (vs. oxidized ferric)
How does methemoglobinemia present?
cyanosis and chocolate-colored blood
How is methemoglobin involved in the treatment of cyanide poisoning?
Nitrates are used to oxidize Hb to methemoglobin, which binds cyanide (then thiosulfate can be used to bind the cyanide → thiocyanate → renal excretion)
How is methemoglobinemia treated?
How do nitrates cause poisoning?
oxidizing Fe2+ → Fe 3+ (i.e. Hb → Met Hb → decreased affinity for O2)
What is carboxyhemoglobin?
Form of Hb bound to CO in place of O2
Why is carboxyhemoglobin no bueno?
Causes ↓ oxygen-binding capacity with a left shift in the oxygen-hemoglobin dissociation curve → ↓ O2 unloading in tissues
Compare the affinity of Hb for CO vs. O2:
CO = 200x greater
What shape does the oxygen-hemoglobin dissociation curve? Why?
sigmoid due to positive cooperativity (i.e. tetrameric Hb molecule that can bind 4 O2 molecules and has a higher affinity for ea. subsequent O2 molecule bound)
What is the shape of the oxygen-myoglobin dissociation curve? Why?
It is a steep curve that quickly flattens without sigmoid curve. Myoglobin is monomeric → does not show positive cooperativity → no sigmoid curve
What happens when the O2-Hb dissociation curve shifts to the right?
↓ affinity of Hb for O2 (facilitates unloading in tissues)
An increase in which factors cause a right shift in the O2-Hb dissociation curve?
Is the fetal Hb-O2 dissociation curve shifted to the right or left relative to the adult curve?
Left (has a higher affinity for O2)
What is the equation for O2 content of the blood?
O2 content = (O2 binding capacity x % saturation) + dissolved O2