Mass transport Flashcards
Describe the structure of haemoglobin.
Globular, water soluble. Consists of four polypeptide chains, each carrying a haem group (quaternary structure).
Describe the role of haemoglobin.
Present in red blood cells. Oxygen molecules bind to the haem groups and are carried around the body to where they are needed in respiring tissues.
Name three factors affecting oxygen-haemoglobin binding.
- Partial pressure / concentration of oxygen.
- Partial pressure / concentration of carbon dioxide.
- Saturation of haemoglobin with oxygen.
How does partial pressure of oxygen affect oxygen-haemoglobin binding?
As partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases, so oxygen binds tightly to haemoglobin. When partial pressure is low, oxygen is released from haemoglobin.
How does partial pressure of carbon dioxide affect oxygen-haemoglobin binding?
As partial pressure of carbon dioxide increases, the conditions become acidic causing haemoglobin to change shape. The affinity of haemoglobin for oxygen therefore decreases, so oxygen is released from haemoglobin. This is known as the Bohr effect.
How does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding?
It is hard for the first oxygen molecule to bind. Once it does, it changes shape to make it easier for the second and third molecules to bind, known as positive cooperativity. It is then slightly harder for the fourth oxygen molecule to bind because there is a low chance of finding a binding site.
Explain why oxygen binds to haemoglobin in the lungs.
- Partial pressure of oxygen is high.
- Low concentration of CO2 in the lungs, so affinity is high.
- Positive cooperativity (after first oxygen molecule binds, binding of subsequent molecules is easier).
Explain why oxygen is released from haemoglobin in respiring tissues.
- Partial pressure of oxygen is low.
- High concentration of carbon dioxide in respiring tissues, so affinity decreases.
What do oxyhaemoglobin dissociation curves show?
Saturation of haemoglobin with oxygen (in %), plotted against partial pressure of oxygen (kPa). Curves further to the left show the haemoglobin has a higher affinity for oxygen.
How does CO2 affect the position of the oxyhaemoglobin dissociation curve?
Curve shifts to the right because haemoglobin’s affinity for oxygen has decreased.
Name the three common features of a mammalian circulatory system.
- Suitable medium for transport, water-based to allow substances to dissolve.
- Means of moving the medium and maintaining pressure throughout the body, such as the heart.
- Means of controlling flow so it remains unidirectional, such as valves.
Relate the structure of the chambers to their function.
- Atria: thin-walled and elastic, so they can stretch when filled with blood.
- Ventricles: thick muscular walls pump blood under high pressure. The left ventricle is thicker than the right because it has to pump blood all the way around the body.
Relate the structure of the vessels to their function.
- Arteries have thick walls to handle high pressure without tearing and are muscular and elastic to control blood flow.
- Veins have thin walls due to low pressure, therefore requiring valves to ensure blood doesn’t flow backwards. Have less muscular and elastic tissue as they don’t have to control blood flow.
Why are two pumps (left and right) needed instead of one?
To maintain blood pressure around the whole body. When blood passes through the narrow capillaries of the lungs, the pressure drops sharply and therefore would not be flowing strongly enough to continue around the whole body. Therefore, it is returned to the heart to increase the pressure.
Describe what happens during cardiac diastole.
The heart is relaxed. Blood enters the atria, increasing the pressure and pushing open the atrioventricular valves. This allows blood to flow into the ventricles. Pressure in the heart is lower than in the arteries, so semilunar valves remain closed.