Term
| what are the effectors of ventilation? |
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Definition
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Term
| what are the central controllers of ventilation? |
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Definition
| groups of neurones located in the pons, medull and other brain areas |
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Term
| what are the sensors of ventilation? |
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Definition
chemoreceptors (central and peripheral)
lungs
other receptors |
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Term
| what si the primary role of the respiratory system? |
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Definition
| to match alveolar ventilation to perfusion so that the oxygen requirement of the respiring tissues is met |
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Term
| What is ventilation determined by? |
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Definition
rate and depth of breathing
both are under neural control via the motor nerve supply to the respiratory muscles |
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Term
| Regulation and modification: voluntary or involuntary? |
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Definition
regulation = involuntary
modification = voluntary |
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Term
| What do chemoreceptors detect? where are they chemoreceptors? |
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Definition
they detect changes in chemical composition of the blood
this is changed if the rates of o2 delivery and co2 removal do not match the rates of o2 consumption and co2 production |
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Term
| Where are the most important minute by minute chemoreceptors in ventilation located? |
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Definition
| central chemoreceptors are located near the ventral surface of the medulla |
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Term
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Definition
| they are exposed to CSF and respond to changes in CSF acidity (an increase in [H+] stimulates ventilation, whereas a decrease inhibits it |
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Term
| What separates CSF and the blood? |
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Definition
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Term
| What is the BBB im/permeable to? |
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Definition
permeable to lipid soluble substances (O2 and CO2)
impermeable to ions like H+ and HCO3- |
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Term
| What do central chemoreceptors indirectly respond to? |
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Definition
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Term
| How do central chemoreceptors indirectly respond to PaCO2? |
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Definition
1. co2 diffuses across the BBB into CSF where carbonic anhydrase catalyses the formation of H+ and HCO3-
2. they detect changes in CSF [H+] |
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Term
| What do changes in [H+] stimulate? |
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Definition
increase = stimulates ventilation
decrease = inhibits it |
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Term
| Where does input from the central chemoreceptors go to? |
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Definition
| respiratory control centres in the pons and medulla |
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Term
| Where are the peripheral chemoreceptors located? |
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Definition
| in the carotid bodies (alongside the carotid sinus) and in the aortic bodies (in the aortic arch) |
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Term
| What are the peripheral chemoreceptors? |
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Definition
| specialised cells that are chemically sensitive and measure changes in arterial blood composition |
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Term
| What do peripheral chemoreceptors respond to? |
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Definition
decreases in PaO2 and pH
increases in PaCO2 |
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Term
| How do the peripheral chemoreceptors communicate? |
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Definition
| project via afferent neurones to respiratory control centres via the carotid sinus nerve |
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Term
| What effect does low PaO2 have on carotid bodies? |
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Definition
1. inactivates membrane K+ channels, reducing K+ efflux
2. depolarises cell
3. influx of Ca2+, triggers NO release (DA?)
4. NT binds to receptors on afferent nerve ending, leading to depolarisation and increase in AP frequency |
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Term
| What effect does PaO2 decrease have on respiration via chemoreceptors? |
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Definition
- decrease PaO2 increase minute ventilation
- response is only significant when PaO2 drops below 60mmHg |
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Term
| What effect does PaCO2 decrease have on respiration via chemoreceptors? |
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Definition
- very small increase leads to a large rise in ventilation
- decrease in PaCO2 reduces ventilation |
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Term
| What level of PaCO2 is associated with a coma? |
|
Definition
90mmHg
further rises are fatal |
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|
Term
| What is the major chemical controller of ventilation? |
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Definition
PaCO2
mainly via its indirect effect on central chemoreceptors |
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Term
| What changes happen in hypoventilation? |
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Definition
| alveolar ventilation is less than it needs to be in order to maintain normal PaO2 and PaCO2 |
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Term
| What causes an increase in ventilation during hypoventilation? |
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Definition
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Term
| What causes an decrease in ventilation during hyperventilation? |
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Definition
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Term
| What is the optimum pH range? |
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Definition
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Term
| What effects happen outside the pH range 7.35-7.45? |
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Definition
alterations in nerve excitability
decreases in enzyme activity
alterations in whole body K+ levels |
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Term
| What pH readings produce acidosis and which produce alkalosis? |
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Definition
<7.35 acidosis
>7.35 alkalosis |
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Term
| What systems regulate pH? |
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Definition
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Term
| What are the acid and base sources? |
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Definition
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Term
| Describe dietry sources of acids and bases |
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Definition
proteins and fats (more acid than base)
NET increase in [H+] |
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Term
| Describe metabolic sources of acids and bases |
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Definition
CO2 (which increases [H+])
lactic acid
ketoacids |
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Term
| How are acids and bases removed? |
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Definition
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Term
| What is the Henderson-Hasselblach Equation |
|
Definition
related pH to bicarbonate ion conc and PCO2
pH = pK + log([HCO3-]/alpha[PCO2]) |
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Term
| Therefore, how can blood conc be altered? |
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Definition
1. regulating blood PCO2 (respiratory system)
2. regulating blood HCO3- (renal system) |
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Term
| Explain how increasing PCO2 decreases pH |
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Definition
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Term
| Therefore, what is the appropriate response to respiratory acidosis? |
|
Definition
increase in ventilation
decrease PaCO2 |
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Term
| Therefore, what is the appropriate response to respiratory alkalosis? |
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Definition
decrease in ventilation
increase PaCO2 |
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Term
| What disturbances does the respiratory system compensate for? |
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Definition
those that are not respiratory in origin
e.g. metabolic |
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Term
| How are respiratory disturbances compensated for? |
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Definition
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Term
| How does metabolic acidosis arise? |
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Definition
addition of acids to plasma
addition of H+ or loss of HCO3- |
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Term
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Definition
| decrease in pH and decrease in HCO3- |
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Term
| What does decrease in pH stimulate? |
|
Definition
peripheral chemoreceptors
increase ventilation (depth and rate) |
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Term
| What does the decrease in HCO3- stimulate? |
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Definition
| drives the equation to the left, decreases [H+] therefore increasing pH |
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Term
| is it a full compensation? |
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Definition
no, only partial
decreased PaCO2 depresses respiration via its effects on central chemoreceptors |
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|
Term
| What are the causes of metabolic acidosis? |
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Definition
1. diabetic ketacidosis (abnormal fat metabolism)
2. diarrhoea (loss of HCO3-)
3. heavy exercise (production of lactic acid)
4. renal failure (reduced H+ excretion) |
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Term
| How does metabolic alkasis arise? |
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Definition
removal of acids from the plasma
loss of H+ or addition of HCO3- |
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Term
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Definition
| increase in pH and increase in HCO3- |
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Term
| What is the effects of a decrease in [H+]? |
|
Definition
decrease ventilation via effect on peripheral chemoreceptors
increases PaCO2, drives equation to right = increase pH |
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|
Term
| Is it a full compensation? |
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Definition
no
increased PaCO2 increases ventilatory drive via central chemoreceptors |
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Term
| What are the causes of metabolic alkalosis? |
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Definition
1. excessive ingestion of antacids
2. vomitting (loss of HCl) |
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