Flashcards in Physiology Deck (81):
According to Boyle's Law, alveolar pressure must be lower than atmospheric pressure for inspiration. How does this happen?
1) Chest wall expands
2) Intrapleural pressure falls
3) Increased pressure gradient between the intrapleural space and alveoli
4) Alveoli expand and pressure decreases
What 2 things cause chest wall movement to expand the lungs?
Intrapleural fluid cohesiveness and negative intrapleural pressure
What is intrapleural fluid cohesiveness?
Water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart
What does negative intrapleural pressure do?
Forces the lungs to expand outwards when the chest wall squeezes inwards
What type of process is inspiration and how is it brought about?
Active process brought about by the contraction of inspiratory muscles
What type of process is expiration and how is brought about?
Passive process brought about by relaxation of inspiratory muscles
In expiration the lungs recoil. How is this brought about?
Elastic connective tissue in the lungs and alveolar surface tension
What reduces alveolar surface tension?
How would you describe resistance in the lungs and what does this mean?
The lungs have very low resistance which means air moves with a small pressure gradient
What is airway resistance determined by?
The radius of the conducting airway
What do obstructive diseases cause?
Resistance to airflow, making expiration more difficult than inspiration
What is needed to produce a given change in volume when lungs are compliant?
Greater change in pressure
What causes increased work of breathing?
Decreased compliance and elastic recoil, increased airway resistance and when increased ventilation is required
What is anatomical dead space?
Inspired air remaining in the airways
When is gas exchange best?
When rates of ventilation and perfusion are the same
What is alveolar dead space?
Ventilated alveoli which are not adequately perfused
How would you increase airflow if perfusion was greater?
1) Increase CO2
2) Relaxation of airway smooth muscle
3) Dilation of local airways
4) Decreased airway resistance
How would you increase blood flow if airflow was greater?
1) Increase O2
2) Relaxation of pulmonary arteriolar smooth muscle
3) Dilation of blood vessels
4) Decreased vascular resistance
Which chemoreceptors detect arterial PaCO2 and pH?
Central and peripheral chemoreceptors
Which chemoreceptors detect arterial PO2?
Peripheral chemoreceptors only
What is the most important factor detected by chemoreceptors?
What does an increased PaCO2 do to ventilation?
Causes an almost linear rise in litres ventilated per min
If PaCO2 goes above 10kPa, what happens and why?
Ventilation starts to decrease due to suppression of central respiratory neurones
What does metabolic acidosis do to the CO2-ventilation curve?
What does metabolic alkalosis do to the CO2-ventilation curve?
What does a rise in [H+] ions from increased PCO2 cause?
What has a bigger effect on the CO2-ventilation curve, increasing or decreasing PaO2?
Decreasing (by a lot)
When does a decreasing PaO2 begin to have an effect on ventilation?
When it gets below 8kPa
What are central chemoreceptors and where are they located?
Diffuse collection of neurones which are located near the ventrolateral surface of the medulla
What are central chemoreceptors sensitive to?
pH of cerebrospinal fluid
What is the blood brain barrier impermeable to? Give examples of what can't/can pass through.
Polar substances- H+ and HCO3- cannot pass through but CO2 can
What is the pH of cerebrospinal fluid determined by?
What is significant about the CSF not being a good buffer?
Small changes in PaCO2 can have a big effect on the pH
What does the stimulation of the central chemoreceptor by decreased CSF pH/increased PaCO2 cause?
What is the relative speed of increased ventilation through central chemoreceptors?
Where are the peripheral chemoreceptors located?
Aortic and carotid bodies
Where specifically are peripheral chemoreceptors at the carotid body and what are they innervated by?
Bifurcation of the common carotid, above the coronary sinus. Innervated by the carotid sinus nerve into the glossopharyngeal nerve
Where specifically are peripheral chemoreceptors at the aortic body and what are they innervated by?
Around the aortic arch, innervated by the vagus nerve
What do carotid bodies respond to?
Increased PaCO2/[H+] or decreased PaO2
How do carotid bodies respond to increased PaCO2/[H+] or decreased PaO2?
Increased firing rate in the carotid sinus nerve to increase ventilation
What is the relative speed of ventilation through peripheral chemoreceptors?
What is hypoxic drive?
Loss in sensitivity to increased PaCO2 and ventilation is therefore controlled by PaO2
How much oxygen should you give people with hypoxic drive?
What can increased altitude cause?
Hypocapnia and alkalosis
What is the part in the brainstem which sets the basic rhythm and pattern of breathing and controls respiratory muscles?
Central pattern generator
What modulates the central pattern generator?
Feedback from chemoreceptors and lung mechanoreceptors
Where is the central pattern receptor?
Pons and medulla
What type of neurones does the central pattern receptor have?
Inspiratory and expiratory
What is reciprocal inhibition?
Activity of inspiratory neurones inhibits activity of expiratory neurones and vice versa
What are the 2 groups of respiratory neurones in the medulla?
Dorsal and ventral respiratory groups
What does the dorsal respiratory group contain?
How does the dorsal respiratory group receive impulses from the central and peripheral chemoreceptors?
What does the ventral respiratory group contain?
Inspiratory and expiratory neurones- and pre and botzinger complezxes
What does the pre-Botzinger complex contain?
Pacemaker neurones which may only be associated with gasping
Where is the pneumotaxic centre located?
What happens if there is an absence of vagal input and sectioning of the midpons?
Where are stretch receptors located?
Smooth muscle of bronchial walls
What does stimulation of stretch receptors cause?
Inspiration to be shorter and shallower and delays the next cycle
What is the pre-Botzinger complex?
A network of neurones which controls the basic rhythm of breathing- they display pacemaker activity and are located near the upper end of the medullary respiratory centre
What is the pneumotaxic centre?
Stimulation of this terminates inspiration when dorsal neurones fire. Without this mechanism, breathing is prolonged inspiratory gasps known as apneusis
What is the apneustic centre?
Impulses from neurones here excite the inspiratory area of the medulla and prolong inspiration
What would the FVC/FEV1/ratio be for an obstructive disease?
FVC- low (COPD)/high (asthma), FEV1- low, ratio- low
What would the FVC/FEV1/ratio be for a restrictive disease?
FVC- low, FEV1- low, ratio- normal
What would the FVC/FEV1/ratio be for a combination disease?
FVC- low, FEV1- low, ratio- low
What is physiological dead space?
Alveolar dead space plus anatomical dead space
What are the 4 factors which influence the rate of gas exchange across the alveolar membrane?
Partial pressure gradient of O2 and CO2, diffusion coefficient for O2 and CO2, surface area of and thickness of alveolar membrane
Why does CO2 have a smaller partial pressure gradient than O2?
CO2 is more soluble in membranes
What would a big different in gradient between PaCO2 and PaO2 suggest?
Gas exchange problems or right to left shunt in the heart
What is the common and uncommon way to transport oxygen?
Common- bound to haemoglobin
What can oxygen delivery to the tissues be impaired by?
How many haem groups are in myoglobin?
What does myoglobin in the blood indicate?
What 3 ways can CO2 be transported?
Bicarbonate (most common), carbamino substances or in solution
What respiratory group is associated with inspiration?
Dorsal- fire in bursts to contract inspiratory muscles
What is increased firing of dorsal neurones associated with?
What does increased firing of dorsal neurones cause?
Excites ventral neurones
Pneumotaxic centre is stimulated when what neurones fire?
Where is rhythm of breathing generated and where is it modified?
Generated by medulla but modified by inputs from the pons
What do joint receptors do?
Impulses from moving limbs increases breathing- contributes to increased ventilation during exercise
Where is the centre for the cough reflex?