Respiratory system overview Flashcards
What is respiration?
External - breathing, the process which brings O2 from the atmosphere and transfers CO2 in opposite direction.
Internal - cellular, energy producing processes in cells - anaerobic and aerobic respiration.
What is metabolic rate?
The rate of O2 consumption in ml/min.
What are normal values of gases?
VO2 = 250ml/min
VCO2 = 200ml/min
What is respiratory quotient?
Respiratory quotient (RQ) = VCO2 / VO2
= 0.8
For carbohydrates, RQ = 1
For fats, RQ = 0.7
For proteins, RQ = 0.8.
When metabolising fats or proteins, it uses more oxygen than the CO2 produced, so RQ is less than 1.
What happens when there are changes in metabolism during exercise and there was no change in respiration?
VO2 and VCO2 increases to 3000ml/min.
Blood O2 would fall and tissues would become hypoxic.
Blood CO2 would rise, and cause pH disturbances.
What is the relationship between ventilation and metabolism in healthy individuals?
Ventilation changes in direct proportion to metabolic demand.
e.g. if VO2 doubles, respiration doubles.
So blood gases and pH are relatively constant.
What is the relationship between ventilation and metabolism in diseased individuals?
Respiration cannot meet metabolism demands at rest (severe) or changes in demand in exercise (less severe).
Blood gases and pH are abnormal.
What are the non-respiratory functions of the respiratory system?
Traps and dissolves blood clots, although if too big causes pulmonary embolism.
Defends against microbes.
Ventilation through airways contributes to heat and water loss.
Important reservoir for blood.
Phonation - production of sound.
Metabolic functions.
What are the zones of the human airways?
Each generation is a split in the airway.
Conducting zone is generations 0 to 16, it conducts air from the environment to the alveolae by bulk flow.
Transitional and respiratory zones - generation 17 to 23, for gas exchange.
What is the pathway of airways?
Trachea
Bronchi
Bronchioles.
Terminal bronchioles.
Respiratory bronchioles
Alveolar ducts
Alveolar sacs
There are 23 generations so thousands of airways.
What is the relationship between area and flow?
Total flow = speed x area
As the cross-sectional area of the respiratory zone increases, speed of gas decreases, so total flow is constant.
This slowing down is good for gas diffusion.
What is the basic structure of the respiratory tract?
The trachea is infront of oesophagus.
There are mucous glands to secrete mucous.
The trachea and bronchi have rings of cartilage so they don’t collapse on expiration - because the pressure outside becomes a lot greater than inside.
The bronchioles have no cartilage so are susceptible to collapse?
What are respiratory conditions?
The bronchioles are susceptible to collapse and particularly in conditions like emphysema can struggle to breathe air out.
The lungs are not elastic enough to generate big pressures, so the pressure falls too quickly as it goes to the mouth and the airways collapse.
Other conditions such as COPD and asthma.
What is the mucociliary escalator?
Moves mucous that has trapped dirt and microbes up into the mouth, to be swallowed, so it does not going into airways.
How is the mucociliary escalator affected?
Nicotine from smoking paralyses the cilia, and allows the bacteria to invade, so smokers have more infections.
Inflammation and asthma increases the viscosity of the mucous so it is harder to move.
What does gas exchange require?
Gas exchange requires airflow and blood flow.
The blood flow should be matched to airflow in the alveolus, but this is not perfect so there is dead space.
What is dead space?
The volume of gas within the respiratory system where no gas exchange takes place.
Either because there is no airflow - no alveoli or unventilated alveoli.
Or there is no blood flow - no perfusion.
What is anatomic dead space?
No gas exchange takes place in the conducting zone as there are no alveoli.
This is anatomic dead space, of 150ml.
How is anatomic dead space affected?
Body size - 2ml/kg.
Age - increases with age.
Drugs - bronchodilators and constrictors.
Posture - decreased when lying down.
What is alveolar dead space?
The volume of alveoli in the respiratory zone with no or inadequate blood flow (perfusion) for gas exchange.
The alveolus is ineffective in oxygenating venous blood.
<5ml.
Can increase during disease - pulmonary embolus.
What is physiological dead space?
Anatomic dead space + alveolar dead space = physiological dead space.
What is tidal volume?
The volume of air breathed in and out in one breath.
Avg 500ml.
What is respiratory frequency?
The number of breaths/min
Avg 12 breaths/min.
What is minute ventilation?
Minute ventilation = tidal volume x respiratory frequency.
Avg 6000ml/min.
The total air moving in and out of the respiratory system in 1 minute.
What is the importance of physiological dead space?
Some of the 6L of air per minute remains in the anatomical dead space, and is not involved in gas exchange.
Not all the air entering makes it into the respiratory zone.
How does dead space ventilation affect minute ventilation?
Dead space ventilation = volume of dead space x respiratory frequency.
150ml x 12 = 1800ml/min.
So alveolar ventilation is more useful.
What is alveolar ventilation?
The ventilation involved in gas exchange.
Alveolar ventilation = minute ventilation - dead space ventilation.
= 4200ml/min.
