respiration - gas exchange Flashcards
What is the inspiratory reserve volume (IRV)?
the maximum volume of additional air that can be inhaled after a normal breath
What is the inspiratory capacity?
The volume of air breathed in from quiet expiration to maximum inspiration.
What is the vital capacity?
The maximum volume of air that can be expired from the lungs after a maximum inspiration.
What is residual volume?
The volume of air left in the lungs after max expiration
What is functional residual capacity?
The volume of air left in the lungs after quiet expiration
What homeostasis does breathing maintain?
Blood gas homeostasis
What is the partial pressure of oxygen at rest?
PO2 = 100 +- 2 mmHg
What is the partial pressure of carbon dioxide at rest?
PO2 = 40+-2 mmHg
What is the ventilation rate at rest?
6-7 L/min (12-15 breaths/min, 500ml/breath)
What volume of O2 is consumed per minute?
250ml/min
What volume of CO2 is expired per minute?
200ml/min
How to calculate the partial pressure of a gas
fraction of gas x barometric pressure
Which part of the lung makes up the conducting airways?
Bronchi and nonrespiratory bronchioles
Why are conducting airways considered to be anatomic dead space?
They don’t participate in gas exchange and take up 150ml volume (30% of breath doesn’t reach alveoli)
What structures form the respiratory airways?
bronchioles with alveoli where gas exchange occurs (terminal bronchioles, respiratory bronchioles, alveoli)
What volume is the conducting airways?
150 ml
What volume is the respiratory airways?
2500ml
How long is the respiratory airways?
5mm
What is a respiratory unit?
the basic physiological unit of the lung involved in gas exchange consisting of respiratory bronchioles, alveolar ducts and alveoli.
How many alveoli are there in adults?
300-400 million alveolar sacs
Shape of alveoli
polygonal, 250 um diameter
What cells make up the alveoli?
type 1 and type 2 (septal) epithelial cells / pneumocytes
Function of type 1 pneumocytes
primary site of gas exchange
What percentage of the alveoli surface are is type 1 epithelial cells?
97%
What are type 2 pneumocytes also known as?
Septal / surfactant cells
How much of the alveolar surface area is occupied by type 2 pneumocytes / surfactant / septal cells?
3%
Function of type 2 pneumocytes
Produce pulmonary surfactant which reduces surface tension, allowing the lungs to expand duringeach breath.
What cells remove debris from alveolar sacs?
Alveolar macrophages
What feature of the lung may mean that babies born prematurely (before 28 weeks) might not survive?
Their septal/surfactant cells have not yet differentiated
Why are alveoli efficient for gas exchange?
large surface area (100m2), very thin walls (0.5um), large capillary network
What are the 2 blood circulations in the lungs?
pulmonary circulation and bronchial circulation
Function of the pulmonary circulation
brings deoxygenated blood from the RV to the lungs where it is oxygenated and returned to the LA and then pumped around the rest of the body.
Function of the bronchial circulation
brings oxygenated blood to the lung parenchyma (part of systemic circulation)
What is the total blood volume in the pulmonary circulation?
500ml (10% of total)
What is the volume of blood in the alveolar-capillary network at rest?
75ml
What is the volume of blood in the alveolar-capillary network during exercise?
150-200ml
How does the volume of blood in the alveolar-capillary network increase (more than x2) during exercise?
New capillaries are recruited and there is an increase in blood pressure.
How do arteries in the pulmonary circulation differ compared to the systemic circulation?
thinner walls, larger diameter, lower resistance and lower pressure.
What is the distance between the alveoli and an erythrocyte?
1-2um
What structures must O2 diffuse through to reach Hb?
type 1 pneumocyte, basement membrane (fused basal lamina), endothelial cell, erythrocyte plasma membrane.
How long does it take erythrocytes to pass through capillaries?
less than 1 second - very efficient as it is enough time for O2 and CO2 gas exchange
Does O2 or CO2 have a greater pressure gradient between the alveolar air and venous blood?
O2 has a steeper conc gradient
Ventilation definition
process by which air moves in and out of lung
perfusion definition
process by which deoxygenated blood passes through the lung and becomes oxygenated
What is the V/Q ratio?
The relationship between ventilation and perfusion which is a major determinant of normal gas exchange and levels of PO2 and PCO2.
V/Q in healthy lungs
0.8
