Respiratory - Alveolar ventilation Flashcards
What is the alveolar volume?
The difference between the tidal volume and the dead-space (i.e. the volume of fresh air that goes into the lungs per breath)
What is the purpose of alveolar ventilation?
Maintains the partial pressures of O2 and CO2 in the blood as it controls the amount of O2 and CO2 available for gas exchange
What is the equation for the rate of alveolar ventilation?
V_T = tidal volume
V_D = dead space
f_R = frequency of breathing
What is pulmonary ventilation? How does it differ from alveolar ventilation?
Pulmonary = the amount of air that goes into the lungs per min (tidal volume)
Alveolar = the amount of fresh air that gets to the alveoli per min
What is hypo and hyper ventilation?
Hypo = low rate of breath
Hyper = high rate of breath
What remains constant during hypo or hyper ventilation? Why?
The amount of CO2 and O2 going into/out of the blood remains constant because the energy consumption doesn’t change much (increased breathing rate has negligible energy increase)
What changes during hypo and hyper ventilation? How does it change?
The partial pressures of CO2 and O2 change
Hypo-ventilation causes increased PCO2 and decreased PO2
Hyper-ventilation causes increased PO2 and decreased PCO2
How does hyperventilation change the oxyhemoglobin equilibrium?
Hyperventilation causes decreased CO2 which causes a shift to the left in the equilibrium therefore less O2 gets dropped off per pressure drop
What causes and what happens due to a decrease in the CO2 in the alveoli?
Hyperventilation causes an increase of arterial pH (more basic) as there is a decrease PCO2 in the alveoli and arteries (CO2 is removed from the lungs more which means that more CO2 is removed from the blood)
What causes and what happens due to an increase in the CO2 in the alveoli?
Hypoventilation causes a decrease of arterial pH (more acidic) as there is an increase of PCO2 in the alveoli and arteries (CO2 can accumulate for longer in alveoli therefore more diffuses into the blood)
What does large changes in blood pH due to hyper and hypo ventilation lead to?
Hyper = alkalotic coma
Hypo = acidotic coma or lack of oxygen
What is the bodies responsiveness to PO2 for the respiration rate? Explain
It is relatively unresponsive as the rate of breathing only measurably increases once the oxygen levels are near critical and this response varies greatly among people
What senses the oxygen levels in the body?
Chemoreceptors
What is the bodies responsiveness to pH for the respiration rate? Explain
The body is very sensitive to changes as the acidity increases but this then decreases rapidly as well. This is because it is damaging the nervous system so it is not a direct response to O2 levels
What is the bodies responsive to CO2 for the respiration rate? Explain
There is a very strong relationship between CO2 and respiratory rate. The respiratory rate begins to fall way after ~10% CO2 because the patient goes into a acidotic coma
Where does the respiratory rhythm originate from?
From the medullary centres (in the medulla oblongata FYI)
What are apart of the medullary centres that control respiration? What do they control?
Dorsal respiratory group (DRG) are active during inspiration
Ventral respiratory group (VRG) are active throughout the breath (inspiration, expiration and in the transition)
How does the respiratory system control the volume of breath? Where are the sensors located?
Slowly adapting stretch receptors that are located in the walls of the bronchi and bronchioles send signals via myelinated vagus nerve to the medullary centres. Activating these receptors stops inspiration.
How does the respiratory system respond to particles? What are some of these particles?
Irritant sensors in the airways activate myelinated and unmyelinated C-fibres in the vagus nerve causing reflex constriction of the bronchioles, coughing, rapid shallow breathing and increased mucous secretion
The irritant sensors respond to noxious mechanic and chemical stimuli (smoke, smog, pollen….), histamine from allergic reactions and lung hyperinflation
How is PCO2 measured? Where are these sensors?
Using chemoreceptors in:
- the carotid bodies (chemoreceptors off the carotid vessels [vessels going to and from the brain])
- the aortic bodies (chemoreceptors off the aorta)
- central chemoreceptors on the ventral (front) of the medulla
What makes the carotid and aortic bodies ideal for measuring PCO2?
They are located just before/after important organs (carotid before/after the brain, aortic after the heart) and are highly vascularised (have a high blood flow relative to their metabolic needs)
How do the carotid and aortic bodies transmit their information about the CO2 concentration?
Carotid bodies via the carotid sinus nerves which connects with the glossopharyngeal nerve IX (sympathetic nerve FYI)
Aortic bodies via the vagus nerve (parasympathetic nerve FYI)
What does the central chemoreceptors measure?
the pH of the cerebrospinal fluid
Label the diagram
What is the function of the carotid sinus?
It measures the blood pressure
What do the carotid vessels go into/out of?
The brain
What is the ventral medulla surrounded by?
Cerebrospinal fluid
What is a challenge the ventral medulla faces in measuring the pH of the blood?
protons cannot cross the blood brain barrier to get to the ventral surface of the medulla
How can the ventral medulla measure pH without protons being able to cross the blood brain barrier?
CO2 can easily diffuse across all membranes and gets into the cerebrospinal fluid. In here it can form the weak acid carbonic acid which disassociates to produce a proton therefore can measure the acidity
What are the two measure which ventilation is most sensitive to (i.e. what changes in the air we breathe are we most sensitive to)?
- Peripheral PCO2 (in the carotid and aortic bodies)
- Ventral medullary pH (the pH of the cerebrospinal fluid surrounding the medulla)
What is this result of this graph showing?
The top graph is when PCO2 is kept a constant 42.6mmHg and the PO2 is dropped.
The bottom graph is when PO2 is decreased and PCO2 is not controlled.
It shows that the respiratory system is hypersensitive to oxygen concentration but only when PCO2 is not influencing the respiratory rate. This is because, as seen in the bottom graph when PCO2 decreases due to hyperventilation, PCO2 is the MAIN driving factor for the respiratory rate but when it is not influencing the respiratory rate, the body is very sensitive to decreasing PO2
