Physiology Flashcards
What are the 4 steps of external respiration?
- Ventilation
- Gas exchange between alveoli and blood
- Gas transport in the blood
- Gas exchange at the tissue level
What is ventilation?
The mechanical process of moving air between the atmosphere and the alveolar sacs.
Explain what is meant by internal and external respiration.
Internal refers to the intraceullar processes which consume O2 and produce CO2.
External refers to the sequence of events leading to the exchange of O2 and CO2 between the external environment and the cells of the body
What forces hold the thoracic wall and the lungs in close opposition?
The intrapleural fluid cohesiveness (water molecules)
The negative intrapleural pressure creates a transmural pressure gradient.
What three pressures are important in respiration?
Atmospheric
Intra-alveolar/intrapulmonary
Intrapleural/interthoracic
Describe which muscles are involved in respiration and what their functions are.
The diaphragm contracts (flattening its dome shape), increasing the thorax vertically.
The external intercostal muscle contracts, this lifts the ribs and moves out the sternum.
Which nerve supplies the diaphragm and where does the nerve come from?
The phrenic nerve from cervical spinal nerve 3, 4 and 5
what is Boyle’s law?
as volume of gas increases, the pressure exerted by the gas decreases
how do the lungs recoil during expiration?
alveolar surface tension alongside elastic connective tissue
what is the law of Laplace?
smaller alveoli have a higher tendency to collapse P =2T/r
what is respiratory distress syndrome caused by?
premature babies not producing enough surfactant
what are the muscles of active expiration?
internal intercostal muscles and abdominal muscles
what muscles are used for normal inspiration?
diaphragm and external intercostal muscle
what are the accessory muscles of inspiration?
sternocleidomastoid, scalenus
what is inspiratory capacity?
max vol of air that can be inspired at the end of normal quiet expiration
what is vital capacity?
max vol of air that can be moved out during single breath following max inspiration
what is the total lung capacity?
vital capacity + residual volume
what is the total lung capacity?
the maximum volume of air the lungs can hold
why would residual volume increase?
if elastic recoil of the lungs is lost (eg: in emphysema)
what changes would be seen in FVC and the FEVI/FVC ratio in obstructive and restrictive lung diseases?
Obstructive = decrease in FEV1/FVC ratio as FVC is the same and FEV1 is reduced.
Restrictive has a normal ratio and a decreased FVC and FEV1
what does emphysema result in?
hyper-inflated lungs meaning the lungs have increased compliance and patients have to work harder to get air out of the lungs
what is pulmonary ventilation?
the volume of air breathed in and out per minute
what is alveolar ventilation?
the volume of air exchanged between the atmosphere and the alveoli per minute
what is alveolar dead space?
areas where ventilated alveoli are not adequately perfused with blood
what are the four factors which influence gas transfer across alveolar membranes?
partial pressure gradient of O2 and CO2
diffusion coefficient for O2 and CO2
surface area of alveolar membrane
thickness of alveolar membrane
what is Dalton’s law of partial pressures?
total pressure = sum of each individual component in the gas mixture
what is Fick’s law of diffusion?
the amount of gas that moves across a tissue is proportional to the area but inversely proportional to the thickness (thicker = less exchange)
what is Henry’s law?
the amount of a gas dissolved in a given type and volume of liquid at constant temperature is proportional to the partial pressure of the gas in equilibrium with the liquid.
how many haem groups can one Hb molecule carry?
4
what shape is the haemoglobin dissociation curve?
sigmoidal
what is the Bohr effect?
release of O2 by conditions of the tissue leads to shift of the curve to the right, meaning more oxygen is released.
what shape is the myoglobin dissociation curve?
hyperbolic
what is the purpose of myoglobin?
to provide short term storage of O2 in anaerobic conditions
what ways can CO2 be carried in the blood?
solution
bicarbonate
carbamino compounds
what is the Haldane effect?
increased affinity for O2, meaning less dissociation of O2 from Hb occurs (curve shifts left)
where is the Pre-Botzinger complex located and what does it do?
medulla
causes breathing rhythm
increased firing from the dorsal group in the medulla causes what?
excitation of the ventral group causing forceful expiration.
what is passive expiration controlled by?
firing from the pre-botzinger complex stopping
where is the dorsal respiratory group located and what is its function?
inspiratory center located in dorsal medulla.
Function = set basic rhythm of breathing
how does the dorsal respiratory group influence breathing?
receives sensory input from CN IX, X from peripheral chemoreceptors. This stimulates sending a motor output to the mechanoreceptors in the lung to contract the diaphragm via phrenic nerve (motor)
where is the ventral respiratory group located and what is its function?
expiratory center located in the ventral medulla. is inactive during normal breathing, provides high respiratory drive when ventilation needs to increase
where is the pneumotaxic center located and what is its function?
located in upper pons function is to inhibit the dorsal respiratory group to limit tidal volume and increase respiratory rate
where is the apneustic center and what is its function?
located in lower pons
prolongs the dorsal respiratory group inspiratory signal, causing prolonged diaphragm contraction resulting in inspiratory gasps (associated with damage to pons)
what role does the cerebral cortex play in breathing?
it can voluntarily override the autonomic control
what does hyperventilation cause?
decrease in pCO2
what does hypoventilation cause?
increase in pCO2 and decrease in pO2
