What process do gasses move down their concentration gradients from high to low pressure?
Diffusion
Are concentration gradients the same as pressure gradients?
Yes
What changes as you go down the respiratory tree from the bronchioles to the alveoli?
- Airways branch into smaller and more numerous until terminating at a group of alveoli
- Each division result in an increase in number, a decrease in diameter and an increase in surface area
What must the sum of the partial pressures or tensions of a gas be equal to?
The total pressure
At sea level what does atmospheric pressure equal?
760 mmHg (barometric pressure)
How can you work out the partial pressure of a gas if you are given the % of it in the air?
Pgas = fraction of gas (Fgas) (percentage) in the mixture x barometric pressure (760mmHg)
What are the conducting airways?
- Bronchi containing cartilage and non-respiratory bronchioles
- They do not participate in gas exchange
- They form anatomic dead space
What is anatomic dead space?
Conducting airways that are not involved in gas exchange so gas exchange of air does not occur until it reaches the lower bronchioles/alveoli
What are respiratory airways?
- Bronchioles with alveoli where gas exchange occurs (from terminal bronchiole to alveoli)
- The region is around 5mm long and around 2500ml in volume
What is the respiratory unit/gas exchange unit?
The basic physiological unit of the lung consisting of respiratory bronchioles, alveolar ducts and alveoli
In adults how many alveolar sacs are there?
Around 300-400 million
What shape are alveoli?
Polygonal in shape
What types of epithelial cells are alveoli composed of?
Type 1 and type 2
Why are alveoli ideal for gas exchange?
- They have a huge surface area and thin walls
- They also have good diffusion characteristics
What are type 1 epithelial cells and how abundant are they?
- Primary site of gas exchange
- Occupy 97% of surface area of the alveoli
What are type 2 epithelial cells and how abundant are they?
- Produce pulmonary surfactant (reduces surface tension)
- Occupies 3% of surface area
What is the function of alveolar macrophages?
- Removal of debris
What are the 2 different blood supplies of the lungs?
- Pulmonary circulation: brings deoxygenated blood from the hear to the lungs and oxygenated blood from the lungs to the heart and then rest of body
- Bronchial circulation: brings oxygenated blood to ling parenchyma (functioning part of the lung)
What is the total blood volume in the pulmonary circulation?
500mls (10% of total)
What is the distance between alveoli and red blood cells?
1-3 micrometres
How quickly do RBC pass through capillaries?
In less than 1 second - sufficient time for CO2 and O2 gas exchange
Where does O2/CO2 go in the pulmonary circuit?
- O2 enters blood
- CO2 leaves the blood
Where does O2/CO2 go in the systemic circuit?
- O2 leaves the blood
- CO2 enters the blood
Why is the pressure gradient for O2 much bigger than for CO2?
Because CO2 is more diffusible
