Physiology - Introduction to the respiratory system Flashcards
What makes up the composition of dry atmospheric air?
O2 - 20.95%
CO2 - 0.03%
N - 78.09%
Ar - 0.93%
Why is respiration important?
Needed to replace energy (i.e. for metabolism)
- a process similar to charcoal combustion
note: most metabolism occurs outside lung in tissue
What types of alveolar cells are there?
Type 1 pneumocytes = squamous epithelial cell
- gas exchange
Type 2 pneumocytes = thicker cell
- produce surfactant that lines alveoli
What is connective tissue of the lung made out of?
Collagen fibres
Elastin fibres
This if interspersed between the capillaries in the alveoli walls
What forms the lung parenchyma and what’s it’s appearance?
By the linkage of connective tissue and alveoli
Appears sponge-like
What interconnects neighbouring alveoli?
Pores of Kohl
- small air passages
What is the formula for time of molecule diffusion in one direction?
(x^2) is proportional to t
x = distance t = time
Where does diffusion in the lungs occur?
Across the alveolar-capillary membrane in both directions
What is convection?
The bulk flow of substances driven by pressure constant difference
- pressure gradient drives air along airways
The transportation method over long distance
- occurs through capillaries, vessels, heart
What is ventilation?
The rate at which gas enters or leaves the lungs
What are the eight volume and capacities which make up the ventilation (spirometry) graph?
Residual volume
Expiratory reserve volume
Tidal volume
Inspiratory reserve volume
Functional residual capacity
Inspiratory capacity
Vital capacity
Total lung capacity
How are lungs expanded to fill the pleural cavity?
When intrapulmonary (alveolar) pressure is relatively -ve - i.e. intrapulmonary pressure < atmospheric pressure
What is the definition of a pneumothorax in terms of pressures?
Intrapleural pressure >= atmospheric pressure
note: intrapleural=intrathoracic
What pressure changes occur during inspiration?
Intrapleaural pressure become relatively more negative
When does expiration occur?
When intrapulmonary pressure > atmospheric pressure
What is lamina flow and where does it occur?
Constant resistance to flow for a tube of given dimensions
Flow is lamina by the time it gets to small airways
What is turbulent flow and where does it occur?
Flow rate is high and occurs in large diameter, irregularly branches tubes
E.g. upper airways (nose, pharynx, larynx)
What is the dead space?
Two types:
Anatomical dead space
- inhaled air that doesn’t mix with air in the alveoli
Physiological dead space
- volume of inhaled air that doesn’t take part in gas exchange
How does oxygen diffuse from alveoli to venous blood?
When the pO2 in alveoli > pO2 in venous blood
What if the formula for dead space?
Dead space = tidal volume - air volume entering alveoli
How is dead space affected in a disease such as emphysema?
Physiological dead space can be increased
How does ventilation vary throughout the lung?
Lower lobes more ventilated on standing and slow inspiration and normal expiration, even more after forced
The difference of ventilation between lobes is reduced if subject is lying down
What are the three causes of uneven pulmonary ventilation?
Volume of lower chest can increases more
Diaphragm descent expands lower lobes more
Lung compliance in not uniform
What is the pulmonary systolic pressure?
25 mmHg
What is the pulmonary diastolic pressure?
8 mmHg
What proportion of systemic vascular resistance is the pulmonary vascular resistance?
one tenth
What is the formula that links vascular resistance to cardiac output?
Pressure gradient = Cardiac output x vascular resistance
Describe a Va/Q ratio of 0?
Poorly ventilated
Describe a Va/Q ratio tending to infinity?
Poorly perfused
How does COPD affect Va/Q ratio?
Becomes high
- due to loss of alveolar walls resulting in destruction of alveoli
Describe the process of respiratory ventilation
=> Higher centres
=> Pons
=> Medulla
=> Lower respiratory neurons
=> Lung stretch receptors
What are the higher centres of respiratory ventilation?
Cerebral cortex
Hypothalamus
What does the medulla do in control of the resp. ventilation?
The central respiratory rhythm generator
Receives inputs from
- peripheral chemoreceptors (carotid and aortic bodies)
- the vagus nerve
Upper respiratory motor neurones for the:
- contralateral phrenic nerve
- the intercostal nerve
What are the lower respiratory neurones and what do they do?
Contralateral phrenic nerve
- activates the diaphragm
Intercostal nerves
- activate intercostal muscles
What are the upper respiratory neurones and what do they do?
Dorsal respiratory neurones
- inspiratory neurones
Ventral respiratory neurones
- receive signal from dorsal respiratory neurones
- both insp. and exp. neurones
How does the cycle of pulmonary ventilation continue?
Activating chemoreceptors (in medulla)
Activating lung stretch receptors sending signals to higher centres
