perfusion and gas transport Flashcards
define ventilation, perfusion and shunt
ventilation - movement of air into and out of the lungs
perfusion - flow of blood through the pulmonary capillaries surrounding the alveoli
shunt - blood that bypasses the alveoli and does not participate in gas exchange.
Describe the mismatch condition in the lungs where ventilation is less than perfusion, and how autoregulation occurs:
at lung base
ventilation < perfusion = <1.0
Condition - Shunt
→ alveoli that are perfused but under-ventilated
→ passage of blood through areas of the lung that are poorly ventilated.
Autoregulation (matching ventilation to perfusion):
Alveolar PO2 falls → Pulmonary Vasoconstriction
Alveolar PCO2 rises → Bronchial Dilation
Describe the mismatch condition in the lungs where ventilation is more than perfusion, and how autoregulation occurs:
lung apex
Ventilation > Perfusion ratio = > 1.0
Condition - Alveolar Dead Space
→ alveoli that are ventilated but under-perfused
→ poor passage of blood through areas of the lung that are well-ventilated.
Autoregulation (matching ventilation to perfusion):
Alveolar PO2 rises → Pulmonary Vasodilation
Alveolar PCO2 falls → Bronchial Constriction
describe respiratory sinus arrhythmia:
variation in heart rate that synchronises with respiration due to vagus nerve activity.
minimises ventilation:perfusion mismatch during the breath cycle.
Describe how O2 transport through the blood, including volume:
O2 travels in two forms in the blood:
- in solution in plasma
- bound to haemoglobin protein in red blood cells
200ml of O2 per litre of whole blood
197ml of which is bound to haemoglobin in red blood cells
3ml of O2 dissolve per litre of plasma
Identify the forms in which CO2 is carried in the blood:
7% dissolves directly in plasma.
23% binds to the amino groups (-NH₂) on the globin part of haemoglobin, forming carbaminohemoglobin
70% reacts with water (H₂O) to form carbonic acid (H₂CO₃), catalyzed by carbonic anhydrase
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-
Carbonic acid quickly dissociates into bicarbonate ions (HCO₃⁻) and protons (H⁺).
The bicarbonate ions diffuse out of red blood cells into the plasma, while chloride ions (Cl⁻) move into the red blood cells to maintain ionic balance (chloride shift).
Describe the role of haemoglobin in the movement of O2 from the alveoli to the capillaries:
it removes O2 from the plasma
maintains a partial pressure gradient that continues to suck O2 out of the alveoli, until the haemoglobin becomes saturated with O2.
Oxygenation reaction
Explain the Oxygen-haemoglobin dissociation curve:
normal systemic arterial PO2 (100mmHg)
- haemoglobin is almost 100% saturated
Even at PO2 of 60 mmHg, haemoglobin is still 90% saturated with O2.
- permits a relatively normal uptake of oxygen by the blood even when alveolar PO2 is moderately reduced
Describe the factors that increase the O2 saturation of haemoglobin (increase affinity & decrease O2 unloading) & what would happen to the oxyhemoglobin dissociation curve:
↑ pH (↓ H+) → alkalosis
↓ PCO2
↓ Temperature
↓ 2,3-DPG
It would shift to the left (Haldane effect)
Describe the factors that decrease the O2 saturation of haemoglobin (decrease affinity & increase O2 unloading) & what would happen to the oxyhemoglobin dissociation curve:
↓ pH (↑ H+) → acidosis, exercising muscle (prod. lactic acid)
↑ PCO2
↑ Temperature
↑ 2,3-DPG
It would shift to the right (Bohr effect)
define 2,3 -DPG (diphosphoglyceric acid):
binds with greater affinity to deoxygenated haemoglobin than oxygenated haemoglobin due to conformational differences.
once bound to deoxygenated haemoglobin beta subunits, it decreases the affinity for oxygen and releases the remaining oxygen molecules bound to the haemoglobin to tissues that need it
Explain why the shape of the oxyhemoglobin dissociation curve aids O2 loading in the lungs and unloading in the tissues:
Plateau region shifting doesn’t have much effect on O2 loading in the lungs:
→ aids the loading of O2 due to the partial pressure gradient between alveoli and blood
Steep region shifting has a big effect on O2 unloading to the tissues:
→ aids the unloading of O2 due to the partial pressure gradient between arterial blood and tissues
Explain what happens to PaO2 in anaemia and why:
Nothing.
PaO2 is normal despite total blood O2 content being low.
Identify the factors which favour CO2 unloading to the alveoli at the lungs:
- rate of H2CO3 dissociation to CO2 & H2O
- concentration gradient of dissolved CO2 between blood & alveoli
- amount of chloride available (exchange between Cl- in haemoglobin & HCO3- in plasma)
- partial pressure gradient of CO2 between blood & alveoli
Compare myoglobin, foetal haemoglobin, and adult haemoglobin, in terms of their affinity and how it relates to their role:
myoglobin in tissues → allows extraction of O2 from normal (adult) haemoglobin for muscle usage
foetal haemoglobin (HbF) in fetuses → allows extraction of O2 from maternal (adult) haemoglobin
Both have higher affinity than adult haemoglobin (i.e. the % of O2 saturation to haemoglobin is higher)
→ necessary for extracting O2 from maternal/arterial blood
what are the 5 types of hypoxia?
- Hypoxaemic Hypoxia (most common)
- reduction in O2 diffusion in lungs either due to decreased PatmosO2 or tissue pathology - Anaemic Hypoxia
→ Reduction in O2 carrying capacity of blood due to anaemia. - Stagnant Hypoxia
→ Heart disease results in inefficient pumping of blood to the lungs/around the body - Histotoxic Hypoxia
→ Blood poisoning prevents cells from utilising oxygen delivered to them e.g. carbon monoxide/cyanide - Metabolic Hypoxia
→ Oxygen delivery to the tissues does not meet increased oxygen demand by cells..4.4.
explain what happens to pulmonary and systemic arteries in response to hypoxia:
Pulmonary arteries - constrict
(deoxygenated blood is redirected to better-ventilated alveoli)
Systemic arteries - dilate
(to deliver oxygenated blood to tissues)
