Physiology Flashcards
Ventilation
The mechanical process of moving gas in and out of the lungs
The Four Steps of External Respiration
Ventilation
Gas exchange between alveoli and blood
Gas transport in the blood
Gas exchange at the tissue level
Boyle’s Law
At any constant temperature the pressure exerted by a gas varies inversely with the volume of the gas
as the volume of a gas increases the pressure exerted by the gas decreases
Two forces hold the thoracic wall and the lungs in close opposition
The intrapleural fluid cohesiveness
The negative intrapleural pressure:
The intrapleural fluid cohesiveness
The water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart. Hence the pleural membranes tend to stick together.
The negative intrapleural pressure
The sub-atmospheric intrapleural pressure create a transmural pressure gradient across the lung wall and across the chest wall. So, the lungs are forced to expand outwards while the chest is forced to squeeze inwards.
Inspiration
During which the diaphragm descends on contraction, increasing the vertical dimension of the thoracic cavity.
Contraction of the external intercostal muscles elevates the ribs and subsequently the sternum to enlarge the thoracic cavity from front to back and from side to side.
Respiratory Distress Syndrome of the New Born
Developing foetal lungs are unable to synthesize surfactant until late in pregnancy
Premature babies may not have enough pulmonary surfactant
This causes respiratory distress syndrome of the new born
Major inspiratory muscles
Diaphragm and external intercostal muscles
Accessory muscles of inspiration (contracts only during forceful inspiration)
Sternocleidomastoid, scalenus, pectoral
Muscles of active expiration (contracts only during active expiration)
Abdominal muscles and internal intercostal muscles
Total lung capacity
Maximum volume of air that the lungs can hold
FVC
Forced Vital Capacity (maximum volume that can be forcibly expelled from the lungs following a maximum inspiration)
FEV1
FEV1 = Forced Expiratory volume in one second. Volume of air that can be expired during the first second of expiration in an FVC (Forced Vital Capacity) determination.
Primary determinant of airway resistance
The radius of the conducting airway
Compliance
A measure of effort that has to go into stretching or distending the lungs
Volume change per unit of pressure change across the lungs
Alveolar Ventilation
Is the volume of air exchanged between the atmosphere and alveoli per minute
To increase pulmonary ventilation
Both the depth (tidal volume) and rate of breathing (RR) increase. 🡪 because of dead space
The partial pressure
The pressure that one gas in a mixture of gases would exert if it were the only gas present in the whole volume occupied by the mixture at a given temperature.
Fick’s Law of diffusion
The amount of gas that moves across a sheet of tissue in unit time is proportional to the area of the sheet but inversely proportional to its thickness
Alveolar Gas Equation
PAO2 = PiO2 – [PaCO2/0.8]
The Haldane effect
Removing O2 from Hb increases the ability of Hb to pick-up CO2 and CO2 generated H+.
Where is breathing rhythm generated?
Pre-botzinger complex in the medulla
Pre-botzinger complex
Excites dorsal respiratory group neurones (inspiratory) - fire in bursts - leads to contraction of inspiratory muscle and inspiration
The apneustic centre
Prolong inspiration
Peripheral chemoceptors
Located at the carotids
Sense tension of CO2, O2 AND H+ in blood
Central chemoceptors
Near medulla
Responds to H+ changes in CSF
