3.4- Mass Transport Flashcards
Describe structure of haemoglobin
Globular, water soluble. Consists of four polypeptide chains, each carrying a haem group (quaternary structure)
Describe role of haemoglobin
Present in red blood cells. Oxygen molecules bind to the haem groups and are carried around the body where they are needed in respiring tissues.
Name 3 factors affecting oxygen-haemoglobin binding
- Partial pressure of oxygen
- Partial pressure 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. Affinity of haemoglobin for oxygen therefore decreases, so oxygen is released from haemoglobin. This is known as the Bohr Shift.
How does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding?
It is hard for first oxygen molecule to bind. Once it does, it changes shape to make it easier for 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 carbon dioxide increases 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 (in kPa). Curves further to the left show the haemoglobin has a higher affinity for oxygen.
How does carbon dioxide affect the position of the oxyhaemoglobin dissociation curve?
Curve shifts to right because haemoglobin’s affinity for oxygen has decreased
Name 3 common features of mammalian circulatory system
1: Suitable medium for transport, water-based to allow substances to dissolve
2: Means of moving the medium and maintaining pressure throughout the body, such as the heart.
3. Means of controlling flow so it remains unidirectional, such as valves
Relate structure of chambers of the heart to their function
Atria: thin-walled and elastic so they can stretch when filled with blood
Ventricles: thick muscular walls pump blood under higher pressure. The left ventricle is thicker than the right because it has to pump blood all way around the body
Relate structure of vessels to their function
- Arterioles have thick walls to handle high pressure without tearing, and are muscular and elastic to control blood flow
- Veins have thin walls due to lower pressure, therefore requiring vessels 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
Heart is relaxed. Blood enters the atria, increasing 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.
Describe what happens during atrial systole
The atria contract, pushing any remaining blood into the ventricles
Describe what happens during ventricular systole
Ventricles contract. Pressure increases, closing the atrioventricular valves to prevent backflow and opening the semilunar valves. Blood flows into the arteries
Name nodes in heart contraction and where they are situated
- Sinoatrial node (SAN)= wall of right atrium
- Atrioventricular node (AVN)= in between the two atria
What does myogenic mean?
The heart’s contraction is initiated from within the muscle itself, rather than by nerve impulses.
Explain how the heart
- SAN initiates and spreads impulse across the atria, so they contract
- AVN receives, delays, and then conveys the impulse down the bundle of His
- Impulse travels into the Purkinje fibres which branch across the ventricles, so they contract from the bottom up.
Why does the impulse need to delayed?
If the impulse spread straight from the atria into the ventricles, there would not be enough time for all the blood to pass through and for the valves to close.
How is the structure of capillaries suited to their function?
- Walls only one cell thick; short diffusion pathway
- Very narrow, so can permeate tissues and red blood cells can lie flat against wall, effectively delivering oxygen to tissues
- Numerous and highly branched, providing a large surface area
What is tissue fluid?
A watery substance containing glucose, amino acids, oxygen and other nutrients. It supplies these to the cells, while also removing any waste materials
How is tissue fluid formed?
As blood is pumped through increasingly small vessels, this creates hydrostatic pressure which forces fluid out of the capillaries. It bathes the cell, and then returns to the capillaries when the hydrostatic pressure is low enough
