Physiology of Respiratory Flashcards
What are the main functions of nasal breathing?
Heating and moistening the air
Removing particulate matter
How long does it take for inhaled particles to be removed?
15 minutes if they deposit in the nasal cavity and 60-120 days if they reach the alveolus
How does nasal breathing protect against bacterial infection?
Nasal secretions contain IgA antibodies, lyzosomes and interferons
Cilia also sweep the mucus gel rapidly to the back of the oropharynx where it’s swallowed
How do viruses attack the nasal airway?
They bind to receptors on the epithelial cells, most rhinoviruses bind to intercellular adhesion molecule 1 (ICAM-1) which is shared by neutrophils and eosinophils
What is Boyle’s Law?
At any constant temperature the pressure exerted by a gas varies inversely with volume of gas (as the volume of gas increases the pressure the gas exerts decreases)
The thorax and lungs are linked by what 2 forces?
The intrapleural fluid cohesiveness – water molecules in the intrapleural fluid are attracted to each other and resist being separated so the membranes tend to stick together
The negative intrapleural pressure – the sub-atmospheric intrapleural pressure creates a pressure gradient across the entire lung wall and chest wall hence the lungs are forced to expand out and the chest is forced to squeeze inwards
The main inspiratory muscles are
The diaphragm and external intercostal muscles (responsible for moving the ribcage and sternum)
What are the accessory muscles of inspiration? (when forceful inspiration is needed)
sternocleidomastoid, scalenus and pectoral
What happens in expiration?
The lungs recoil to their original shape and alveolar surface tension causing the intra-alveolar pressure to increase and air to leave the lungs
What are the accessory muscles for active expiration?
abdominal muscles and internal intercostal muscles
Where do the motor nervous discharges originate from?
The respiratory centre in the brainstem, they travel down the phrenic and intercostal nerves
What is the main driver of respiration in healthy individuals?
Arterial pH – closely linked to arterial CO2
How does airflow velocity change through the lung?
It decreases as you move to the periphery, it is greatest in the trachea and in the terminal bronchioles air only moves by diffusion
Tidal Volume (TV)
volume of air entering or leaving the lungs in a single breath
Inspiratory reserve volume (IRV)
extra volume of air that can be maximally inspired over and above typical resting TV
Expiratory reserve volume (ERV)
extra volume of air which can be actively expired by maximal contraction beyond the normal volume of air after a resting TV
Residual volume (RV)
minimum volume of air which remains in the lungs even after maximal expiration
Inspiratory Capacity (IC)
Maximum volume of air that can be inspired at the end of a normal quiet expiration IC=IRV + RV
Functional Residual Capacity (FRC)
Volume of air in lungs at the end of normal passive expiration FRC=ERV + RC
Vital Capacity (VC)
maximum volume of air that can be moved out during a single breath following maximal inspiration VC=IRV + TV + ERV (very important measure)
Total Lung Capacity (TLC)
Total volume of air the lungs can hold TLC=VC + RV. As residual volume can’t be measured by spirometry TLC can’t be measured by spirometry, residual volume will increase as elastic recoil of the lungs is lost e.g. in emphysema
What stimulates the carotid and aortic bodies to cause respiration?
The arterial pressure of oxygen to be below 8kPa, this is known as hypoxic drive and doesn’t stimulate respiration in healthy people but does in some people with COPD
What rhythm does airway tone show?
Carcadian
What stimuli can result in bronchoconstriction via the vagus?
Cigarette smoke Solvents Inert dust Cold air This is worse in asthmatic patients
