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pneumocyte 1
The reduction in diffusion distances is met by squamous type 1 pneumocytes, which are very thin (0.1 - 0.2 μm) and flattened out |
These cells have few organelles and a diameter of 50um |
Make up 95% of space, squamous |
pneumocyte 2
Contain many organelles and have distinct secretory vesicles (lamellar bodies) that are responsible for secreting surfactant into the alveolar space |
Surfactant is made of phospholipids and proteins and is essential to prevent the alveoli from collapsing |
Only 5% of space, cuboidal shape |
haemoglobin
Oxygen is transported throughout the body in red blood cells, which contain an oxygen-binding protein called haemoglobin
Haemoglobin is composed of 4 polypeptide chains, each with an iron-containing haem group that binds reversibly
As such, each haemoglobin can reversibly bind up to 4 oxygen molecules
As each O2 molecule binds, it alters the conformation of haemoglobin, making subsequent binding easier (increased oxygen affinity of the other heme group = cooperative binding)
Conversely, haemoglobin will have a lower affinity for O2 when an oxygen dissociates
adult vs foetal haemoglobin
Haemoglobin is different before and after birth, foetal haemoglobin is gradually replaced by adult haemoglobin several months after birth
Foetal hemoglobin has a higher affonity for oxygen than adult haemoglobin
dissociation curves
Oxygen dissociation curves show the relationship beyween oxygen levels and haemoglobin saturation
For an adult haemoglobin, the curve is sigmoidal (s S-shaped) due to cooperative binding
The rate of oxygen uptake by haemoglobin increases rapidly as the partial pressure of oxygen increases but it eventually levels off because haemoglobin becomes fully saturated with oxygen in areas of higher partial pressures of oxygen such as the lungs
As foetal haemoglobin has a higher affinity for O2 than adult haemoglobin, the dissociation curve will shift to the left
bohr shift
Carbon dioxide lowerrs the pH of the blood by forming carbonic acid which causes haemoglobin to release it's oxygen
This is known as the bohr shift - a decrease in pH and an increase in CO2 shifts the oxygen dissociation curve to the right (lower affinity)