Mass Transport Flashcards
Topic 3 revision
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 haem groups &
Three factors affecting oxygen-haemoglobin binding
- Partial pressure/ conc. of oxygen
- Partial pressure/ conc. of carbon dioxide
- Saturation of haemoglobin with oxygen
How does partial pressure of oxygen affect oxygen-haemoglobin binding?
As partial pressure of oxygen increases, 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, conditions become acidic causing haemoglobin to change shape. Affinity of haemoglobin for oxygen therefore decreases, so oxygen is released from haemoglobin. Known as Bohr Effect
How does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding?
Hard for first oxygen molecule to bind but once it does, it changes shape to make it easier for second and third molecule to bind (known as positive cooperativity). Then slightly harder for 4th oxygen molecule to bind because low chance of finding a binding site.
Explain why oxygen binds to haemoglobin in lungs
- Partial pressure of oxygen is high
- Low conc. of carbon dioxide in 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 conc. 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 haemoglobin has a higher affinity for oxygen
How does carbon dioxide affect position of an oxyhaemoglobin dissociation curve?
Curve shifts to the right because haemoglobin’s affinity for oxygen has decreased
Three common features of a mammalian circulatory system
- Suitable medium for transport, water-based to allow substances to dissolve
- Means of moving medium and maintaining pressure throughout body, such as the heart.
- Means of controlling flow so it remains unidirectional, such as valves
Relate structure of chambers to their functions
- Atria: thin-walled & elastic, so they can stretch when filled with blood
- Ventricles: thick muscular walls pump blood under high pressure. Left ventricle is thicker than right because it has to pump blood all the way around body
Relate structure of vessels to their function
- Arteries have thick walls to handle high pressure without learning, and are muscular & elastic to control blood flow
- Veins have thin walls due to lower pressure, so requiring valves to ensure blood doesn’t flow backwards. Have less muscular & elastic tissue as they don’t have to control blood flow.
Why are two pumps (left & right) needed instead of one?
To maintain blood pressure around whole body. When blood passes through narrow capillaries of lungs, pressure drops sharply & so would not be flowing strongly enough to continue around whole body. So it is returned to heart to increase pressure
Describe what happens during cardiac diastole
Heart is relaxed. Blood enters atria, increasing pressure & pushing open atrioventricular valves. Allows blood to flow into ventricles. Pressure in heart is lower than in arteries, semilunar valves remain closed
Describe what happens during atrial systole
Atria contract, pushing any remaining blood into ventricles
Describe what happens during ventricular systole
Ventricles contract. Pressure increases, closing atrioventricular valves to prevent backflow, & opening semilunar valves. Blood flows into arteries
Name nodes involved in heart contraction & where they are situated
- Sinoatrial node (SAN) = wall of right atrium
- Atrioventricular node (AVN) = in between two atria
Explain how the heart contracts
- SAN initiates & spreads impulse across atria, so they contract
- AVN receives, delays, & then conveys the impulses down bundle of His.
- Impulse travels into Purkinje fibres which branch across ventricles, so they contract from bottom up.
Why does impulse need to be delayed?
If impulse spread straight from atria into ventricles, there would not be enough time for all blood to pass through & for valves to close
How is structure of capillaries suited to their function?
- Walls are only one cell thick; short diffusion pathway.
- Very narrow, so can permeate tissues & red blood cells can lie flat against wall, effectively delivering oxygen to tissues
- Numerous & highly branched, providing large surface area
What is tissue fluid?
Watery substance containing glucose, amino acids, oxygen, & other nutrients. It supplies these to the cells, while also removing any waste materials.
