Lecture 17: CO2 transport and the chemical control of breathing Flashcards
How is CO2 transported in the blood?
- Dissolves in solution 2. Chemical in form of HCO3 (Carbonic anhydrase) 3. Combines to amine groups (NH2) 4. As H2CO3 and CO3 ions CO2 solubility in blood is 20 times higher than O2
Describe CO2 composition in the blood:
RBC have carbonic anhydrase (only found here) - Rapidly converts CO2 to bicarbonate (20% of total CO2) - Some CO2 remains bound to Hb (5%) - Some CO2 remains in solution in RBC (5%) - Bicarb rapidly moves down concentration gradient into the blood and diffuses into the plasma (60%). - Some HCO3 is in solution, some bound to protein (10%) 30% CO2 found in RBC, 70% found in plasma
Whats important about CO2 and O2 uptake and release at the tissues?
When CO2 is taken up into the RBC and H2O is also taken in to form the HCO3 and H+ H+ causes O2 release HCO3 moves down the Conc. gradient out of the cell, CL- ions flux in to maintain electroneutrality.
Whats important about CO2 and O2 uptake and release at the lungs?
Whole process is reversed! O2 is taken up into the cell and H ions are released H ions bind with HCO3 which is also taken up, to form H2O and CO2. CO2 is released. CL ions are also released when HCO3 is taken in
Describe the CO2 dissociation curve:
- Linear over range of PCO2 - No saturation as CO2 is very soluble - Difference in venous and arterial blood - At lungs, reduced affinity so CO2 is released - At low PO2 i.e tissues the greater affinity for CO2 uptake - Enhances unloading of CO2 from tissues into blood
What is the haldane effect? get more notes?
Right shift of the CO2 dissociation curve
What are the types of resp. chemoreceptors?
Peripheral chemoreceptors located near major art. These stimulate Central chemoreceptors, located within the medulla oblongata
Define: - Hypoxia - Anoxia - Asphyxia - Hypercapnia - Hypocapnia - Hyperventilate - Hypoventilate - Ischemia - Apnoea - Dyspnoea
- Hypoxia -> Low levels of oxygen - Anoxia -> No oxygen - Asphyxia -> Deprived of oxygen - Hypercapnia -> High Co2 - Hypocapnia -> Low CO2 - Hyperventilate -> Excessive breathing - Hypoventilate -> Shallow breathing - Ischemia -> Inadequate blood supply to an organ - Apnoea -> No breathing - Dyspnoea -> Sensation of breathlessness
How does the chemoreceptor feedback loop work?
Chemoreceptors CNS Respiratory pump muscles = Homeostasis of blood gases (PO2 and PCO2)
Where are the carotid chemoreceptors located?
Sinus nerves joins glossopharyngeal nerve then to the nucleus tractus solitari in medulla oblongata (part of dorsal respiratory group (DRG))
Where are the aortic chemoreceptors located?
Aortic nerve joins vagus nerve then to the nucleus tractus solitarii in medulla oblongata (DRG)
How do peripheral chemoreceptors work?
Peripheral chemoreceptors sense: hypoxia and many more things. The higher the PO2 the lower the rate of firing. And communicates with CNS to change resp. drive
Where are the peripheral chemoreceptors located?
Carotid body and aortic arch
What else do peripheral chemoreceptors sense and whats the time frame for their action?
- Hypxoia 2. Hypercapnia 3. Combination of 1&2 4. Haemorrhage 5. Acidosis (decrease blood pH) 6. Increased sympathetic activity Response time fast - within a breath
Describe how a peripheral chemoreceptor works on a molecular level:
Glomus (Type 1 cell) is stimulated by hypoxia which can release: ATP, Dopamine, NA, ACh, Substance P Binds to receptor on chemreceptor afferent fibre and rthe AP continues to the CNS
Describe this curve: / The ventilatory response to hypoxia
- No central chemoreceptor detection, comes from peripheral receptors - At extremely low PaO2 apnoea occurs become central command is depressed by low O2. Gasping occurs as an auto-ventilatory response - As PaO2 drops before apnoea / the depression we have a peak ventilatory response (hyperventilation)
Describe the response to hypercapnia:
- Detected by peripheral (20%) and central (80%) chemoreceptors - As PaCO2 increases, there is a steep response curve (i.e very sensitive to increase CO2)
