3B: Mass transport Flashcards
Describe 3 adaptations of red blood cells
- Biconcave shape = maximises SA for gas exchange
- Small + flexible = to pass through narrow capillaries (pressed to the sides to maximise gas exchange)
- No nucleus = more room to carry respiratory gases
What is the function of red blood cells?
To transport O₂ around the body
How does haemoglobin allow RBCs to carry respiratory gases (especially oxygen)
- It has an affinity for oxygen (can carry up to 4 O2 molecules)
- Oxygen binds to the ‘haem’ Fe2 + group of haemoglobin
What is haemoglobin called when it becomes oxygenated?
Oxyhaemoglobin
What are the haemoglobins?
- The haemoglobins are a group of chemically similar molecules found in many different organisms.
- They are protein molecules with quaternary structures
Describe the primary structure of a haemoglobin molecule.
Sequence of amino acids in the 4 polypeptide chains
Describe the secondary structure of a haemoglobin molecule.
Each of the 4 polypeptide chains is coiled into a helix
Describe the tertiary structure of a haemoglobin molecule.
Each polypeptide chain is folded into a precise shape
Why is the tertiary structure of a haemoglobin molecule so important?
- The tertiary structure of a protein determines the 3D shape of the protein
- For haemoglobin this is an important factor in its ability to carry oxygen
Describe the quaternary structure of a haemoglobin molecule.
- All 4 polypeptides are linked together to form an almost spherical molecule
- Each polypeptide is associated with a haem group
What does each haem group, in haemoglobin, contain?
Each haem group contains a ferrous group (Fe2+) ion
- Each iron ion can combine with a single oxygen molecule
= a total of 4 O2 molecules can be carried
In humans, where does the loading/ associating of haemoglobin & oxygen take place?
In the lungs
In humans, where does the unloading/ dissociating of haemoglobin & oxygen take place?
In the tissues
What is the process by which haemoglobin binds with oxygen called?
Loading/ associating
What is the process by which haemoglobin releases its oxygen called?
Unloading/ dissociating
What is the role of haemoglobin?
To transport oxygen from gas exchange surafces to respiring tissues
To be efficient at transporting oxygen, haemoglobin must:
- Readily associate with oxygen at the surface where gas exchange takes place
- Readily dissociate from oxygen at those tissues requiring it
What adaptation allows haemoglobin to readily associate + dissociate from oxygen in different environments?
The fact that haemoglobin can change its affinity for oxygen under different conditions.
How does haemoglobin change its affinity for oxygen in different environments?
Because its shape changes in the presence of certain substances, e.g carbon dioxide
Describe what happens to haemoglobin in respiring tissue.
- In respiring tissue there’s a high CO₂ conc. and a low O₂ conc.
- In the presence of carbon dioxide, the new shape of the haemoglobin molecule binds more loosely to oxygen
- It has a low affinity for O₂
= resulting in the haemoglobin unloading its oxygen
Describe what happens to haemoglobin at the gas exchange surface.
- At the exchange surface there’s a high O2 conc. and a low CO2 conc.
- This means that the haemoglobin will have a high affinity for O2
= resulting in the haemoglobin loading its oxygen
Why do different hemoglobins have different affinities for oxygen?
Due to the shape of the molecule
Why do different organisms have haemoglobins with different shapes - and therefore oxygen affinities?
- Because each species produces a haemoglobin with a slightly different amino acid sequence
- Therefore the haemoglobin of each species will have a different tertiary + quaternary structure
= and hence different oxygen binding properties
What is the partial pressure of oxygen (PO2) referring to?
The amount of oxygen in the tissue
What is PO2 measured in?
kPa
What is the graph that shows the relationship between the saturation of haemoglobin + O2 and the PO2 known as?
The oxygen dissociation curve
What shape is the graph that shows the relationship between the saturation of Hb + O2 and the PO2 known as?
An S-shape
Why is the oxygen dissociation curve shallow initially?
- The shape of the Hb molecule makes it difficult for the first O2 molecule to bind to 1 of the sites on its 4 polypeptide subunits because they are closely united
- Therefore in low O₂ conc.s little O₂ binds to Hb
What does Hb refer to?
Haemoglobin
How does the binding of the 1st O2 change the hemoglobins structure?
- The binding of the first O₂ changes the quaternary structure of the Hb molecules
- Which causes it to change shape
- This change makes it easier for the other subunits to bind to an O₂ molecule
Why does the gradient of the oxygen dissociation curve then steepen?
Hint: positive cooperativity
- After the 1st O2 binds, it takes a smaller increase in the PO2 to bind the 2nd oxygen molecule than it did to bind the 1st one.
- This is known as positive cooperativity because the binding of the first molecule makes it easier for the next one and so on.
Why does the gradient of the oxygen dissociation curve reduce and flatten off?
- After the binding of the 3rd oxygen, the probability of the last binding site being filled is lower
- This is because with the majority of the binding sites occupied, it is less likely that a single oxygen molecule will find an empty site to bind to
The further to the left the curve, the _______ is the affinity of Hb for oxygen.
The further to the left the curve, the greater is the affinity of Hb for oxygen.
What does it mean for the haemoglobin molecule if it has a high affinity for oxygen?
It means it will load oxygen readily but will unload it less easily
What does it mean for the haemoglobin molecule if it has a low affinity for oxygen?
It means it will load oxygen less readily but will unload it more easily
The further to the right the curve, the _____ is the affinity of Hb for oxygen.
The further to the right the curve, the lower is the affinity of Hb for oxygen.
What is carbon dioxides effect on haemoglobin’s affinity for oxygen?
In the presence of CO2, Hb has a reduced affinity for O2
- The greater the conc. of CO2 the more readily the Hb releases its oxygen (The Bohr effect)
Describe the behaviour of haemoglobin at the gas exchange surface (e.g lungs)
- Low conc. of CO2
- High conc. of O2
- The affinity of Hb for O2 is increased
= O2 is readily loaded by haemoglobin - The reduced CO2 conc. has shifted the oxygen dissociation curve to the left
Why is the conc. of carbon dioxide low at the gas- exchange surface (e.g lungs)
The conc. of CO2 is low because it diffuses across the exchange surface and is excreted from the organism
Describe the behaviour of haemoglobin in rapidly respiring tissues
- High conc. of CO2
- Low conc. of O2
- The affinity of Hb for O2 is reduced
= O2 is readily unloaded from the Hb into the muscle cells - The increased CO2 conc. has shifted the oxygen dissociation curve to the right
Why does the greater the CO2 conc. mean the more readily Hb will unload O2?
This is because dissolved carbon dioxide is acidic and the low pH causes Hb to change shape
What is the pH like at the gas exchange surface? What does this mean for Hb and oxygen loading?
- The pH is slightly raised due to the low conc. of carbon dioxide
- The higher pH changes the shape of Hb into one that enables it to load oxygen readily
- This shape also increases the affinity of Hb for oxygen, so it’s not released while being transported in the blood to the tissues
What is the pH of carbon dioxide in solution like?
It is acidic (low pH)
What is the pH of the blood within the respiring tissues like?
- CO₂ is acidic in solutions
- So the pH of the blood within the tissues is lowered
How does a lower pH (in respiring tissues) effect haemoglobin?
Lower pH changes the shape of Hb = lowers affinity for O₂
- Therefore Hb unloads O₂ into the respiring tissues
Explain how: the more active a tissue, the more oxygen is unloaded.
The higher the rate of respiration –> the more CO2 the tissues produce –> the lower the pH –> the greater the Hb shape change –> the more readily the O2 is unloaded –> the more O2 is available for respiration
In humans, where does haemoglobin become saturated with oxygen?
When it passes through the lungs
What is the overall saturation of haemoglobin at atmospheric pressure? Why?
97%
- Not all Hb molecules are loaded with their maximum 4 oxygen molecules
When haemoglobin reaches a tissue with a low respiratory rate, how many oxygen molecules will be released?
Only 1 oxygen will normally be released
After reaching a tissue with a low respiratory rate, what will the oxygen % of the blood (containing haemoglobin) returning to the lungs be like?
The blood returning to the lungs will therefore contain Hb that is still 75% saturated with oxygen
If tissue is very active, how many oxygen molecules are normally unloaded?
3 oxygen molecules will usually be unloaded from each Hb molecules
How have some organism’s haemoglobin molecules evolved to live in an environment with a low PO2?
- Animals that live in an environment with a lower PO2 have evolved haemoglobin that has a higher affinity for oxygen
- Compared to the haemoglobin of animals that live where the PO2 is higher
What is the oxygen dissociation curve of a lugworms haemoglobin like? What does this mean?
- The dissociation curve is shifted far to the left of that of a human
- This means that the haemoglobin of the lugworm is fully loaded with oxygen even when there if little available in its environment
How are llamas adapted to their environment?
Answer in relation to its haemoglobin
- Llamas live at high altitudes = the atmospheric pressure is lower and so is the PO2
- It is therefore difficult to load haemoglobin with oxygen
- Llamas have a type of haemoglobin that has a higher affinity for oxygen than human haemoglobin
- The oxygen dissociation curve will shift to the left of human Hb
What happens to the SA:V when the size of the organism increases?
The SA:V decreases
Why are specialised exchange surfaces required for larger organisms?
- Because as the size of an organism increases it’s SA:V decreases
- SA:V decreases to a point where the needs of the organism cannot be met by the body surface/ diffusion alone
The lower the SA:V the _____ active the organism, the _____ is the need for a more __________ transport system with a ____.
The lower the SA:V the More active the organism, the Greater is the need for a more Specialised transport system with a Pump.
Give an example of a suitable medium used in many organisms transport systems to carry materials.
Blood
Why is the suitable transport medium in may organisms transport systems water based?
- Suitable mediums are normally a liquid based on water
- This is because water readily dissolves substances
- Also water can be moved around easily, as it can also be a gas (e.g air breathed out of the lungs)
What is a common feature of transport systems, relating to it being a closed and tubular?
Commonly transport systems are:
- Closed
- Consisting of tubular vessels that contain the transport medium and forms a branching network to distribute it to all parts of the organism
What type of circulatory system do mammals have?
A closed, double circulatory system
Why does blood pass through the heart twice for each complete circuit of the body?
- Because when blood is passed through the lungs, its pressure is reduced
- If the blood passed straight to the rest of the body, circulation would be very slow (due to the low pressure)
- Blood is returned to the heart to boost its pressure before it is sent to the rest of the body
If mammals have a high body temp, what does this mean for their metabolism?
High body temp = high metabolism
Which side of the heart deals with oxygenated blood? Where does this come from?
- The left
- It comes from the lungs (via the pulmonary vein)
Which side of the heart deals with deoxygenated blood? Where does this come from?
- The right
- It comes from the body
Describe the atrium
- Thin- walled
- Elastic
- Stretches as it collects blood
- Above the ventricle
Describe the ventricle
- Much thicker muscular wall than the atrium
- Below the atrium
Why does the ventricle have a thicker, more muscular wall than the atrium?
Because it has to contract strongly to pump blood some distance, either to the lungs or the rest of the body
Why does the left ventricle have a thicker muscular wall than the right ventricle?
- The right ventricle pumps blood only to the lungs so it can be at a lower pressure
- The left ventricle pumps blood to the rest of the body, the thick muscular wall enables it to contract to create a high pressure
What are the valves between the atrium and ventricle called?
The atrioventricular valves
What are the two types of atrioventricular valve?
The right & the left atrioventricular valves
What type of valve is the right atrioventricular valve?
The right atrioventricular valve is tricuspid
What type of valve is the left atrioventricular valve?
The left atrioventricular valve is bicuspid
In what direction do the ventricles pump blood?
The ventricles pump blood away from the heart and into the arteries
What do the atria receive blood from?
The atria receive blood from the veins
What are the vessels that connect the heart to the lungs called?
Pulmonary vessels
Describe the role of the aorta
- Connected to the left ventricle
- Carries oxygenated blood to all parts of the body except the lungs
Describe the role of the vena cava
- Connected to the right atrium
- Brings deoxygenated blood back from the tissues of the body (except the lungs)
Describe the role of the pulmonary artery
- Connected to the right ventricle
- Carries deoxygenated blood to the lungs
- Where the it is replenished and its CO2 is removed
- Unusually for an artery it carries deoxygenated blood
Describe the role of the pulmonary vein
- Connected to the left atrium
- Brings oxygenated blood back from the lungs
- Unusually for a vein it carrys oxygenated blood
How is oxygen supplied to the heart?
- Although oxygenated blood passes through the left side of the heart, the heart does not use this oxygen to meet its own requirements
- The coronary arteries supply the heart with oxygenated blood
Describe the coronary arteries
- Supply the heart muscle with oxygen
- They branch off the aorta shortly after it leaves the heart
What can the blockage of the coronary arteries lead to?
Blockages of these arteries, e.g by a blood clot, lead to myocardial infarction
What is myocardial infarction also known as?
A heart attack
Describe what happens during myocardial infarction.
- Because an area of the heart muscle is deprived of blood and therefore oxygen
- The muscle cells in this region are unable to respire (aerobically) and so die
What are 4 risk factors that increase the risk of the individual suffering from cardiovascular disease?
- Smoking
- High blood pressure
- Blood Cholesterol
- Diet
Why does the carbon monoxide in tobacco cause heart diseases?
Carbon monoxide:
- It combines easily + irreversibly with haemoglobin (=carboxyhemoglobin) which reduces its oxygen-carrying capacity.
- To supply the same quantity of oxygenated blood the heart must work harder
- This can lead to raised blood pressure which increases the risk of coronary heart disease + strokes
How does the carbon monoxide in tobacco cause chest pain/ heart attack?
- The reduction in the oxygen-carrying capacity of blood means it may be insufficient to supply the heart muscle during exercise
- Leads to angina (chest pain) or, in severe cases a myocardial infarction (heart attack)
What are the two main components of tobacco that cause heart diseases?
Nicotine and carbon monoxide
How does the nicotine in tobacco cause heart diseases?
Nicotine:
- Stimulates the production of the hormone adrenaline, which increases the heart rate and raises blood pressure
= There is a greater risk of smokers suffering coronary heart disease/ stroke
- ALSO: makes the platelets in the blood ‘sticky’
= Leads to a higher risk of thrombosis and hence strokes/ myocardial infarction
What lifestyle factors increase blood pressure?
- Excessive prolonged stress
- Certain diets
- Lack of exercise
Why does high blood pressure increase the risk of heart disease?
(How hard the heart works…)
- Higher pressure in the arteries means the heart must work harder to pump blood into them –> more prone to failure
What is an aneurysm?
The weakening of the wall of an artery
Why does high blood pressure make it more likely to develop a haemorrhage?
The high pressure in the arteries means that they are more likely to develop an aneurysm and burst causing haemorrhage
What do the walls of arteries do to try and combat high blood pressure, and why can this be an issue?
The walls of the arteries tend to become thickened and may harden
- Which restricts the flow of blood
What is cholesterol and how is it transported?
- Cholesterol is a lipid that is an essential component of membranes
- It is transported in the blood plasma as tiny spheres of lipoproteins
What are the two types of lipoproteins?
- High density lipoproteins (HDLs)
- Low density lipoproteins (LDLs)
Describe high-density lipoproteins
HDLs:
- Remove cholesterol from tissues + transport it to the liver for excretion
- they protect arteries against heart disease
Describe low- density lipoproteins
LDLs:
- Transport cholesterol from the liver to the tissues including the artery walls which they infiltrate
= leading to the development of atheroma which may lead to heart disease
How does diet increase the risk of heart diseases?
- High levels of salt increases blood pressure
- High levels of saturated fat increase low density lipoprotein levels and hence blood cholesterol conc.
What types of foods reduce the risk of heart disease?
- Foods that act as antioxidants e.g vitamin C
- Non-starch polysaccharide (dietary fibre)
What are the two phases of the cardiac cycle?
- Contraction (systole)
- Relaxation (Diastole)
What is diastole?
The relaxation of the heart
During diastole, how does the blood return to the atria of the heart?
Blood returns to the atria of the heart through the pulmonary vein (from lungs) and the vena cava (from body)
During diastole, what happens to the pressure of the atria and what does this cause to happen?
- They fill up with blood so the pressure in them rises
- This pressure exceeds that in the ventricles so the atrioventricular valves open allowing blood to pass into the ventricles
During diastole, what force is the passage of blood aided by?
The passage of blood is aided by gravity
During diastole, what are the ventricle + atria walls like?
The muscular wall of both the atria and ventricle are relaxed
During diastole, what does the relaxation of the ventricle walls cause them to do?
- What is a result of this?
- It causes them to recoil and this reduces the pressure within the ventricle
- This causes the pressure to be lower than in the aorta and the pulmonary artery
= the semi-lunar valves in the aorta + pulmonary artery CLOSE
What makes the ‘dub’ sound of the heart beat?
The semi-lunar valves in the aorta + pulmonary artery closing makes a ‘dub’ sound
- During diastole
Describe what happens in atrial systole.
- The contraction of the atrial walls + the recoil of the relaxed ventricle walls
= forces the remaining blood into the ventricles from the atria
What is atrial systole?
The contraction of the atria
During atrial systole, what is the muscle of the ventricle walls like?
The muscle of the ventricle walls remains relaxed
What is ventricular systole?
The contraction of the ventricles
Describe what first happens in ventricular systole.
- After a short delay to allow the ventricles to fill with blood, their walls contract simultaneously
During ventricular systole, what does the contraction of the ventricle walls result in?
- Increases the blood pressure in the ventricles
- Which forces the atrioventricular valves shut (preventing the backflow of blood into the atria)
What makes the ‘lub’ sound of the heart beat?
The ‘lub’ sound is made by the closing of the atrioventricular valves during ventricular systole
During ventricular systole, what happens to the pressure in the ventricles after the atrioventricular valves close?
With the atrioventricular valves closed, the pressure in the ventricles rises further
- Once the pressure exceeds that in the aorta + pulmonary artery blood is forced into them
During ventricular systole, the ventricular walls contract forcefully.
What feature of the ventricles makes this possible, and what does this create?
Thick muscular walls
- This creates the high pressure necessary to pump blood around the body
Blood will always move from an area of ______ pressure to one of _____ pressure.
Blood will always move from an area of higher pressure to one of lower pressure.
What is the role of valves?
To prevent the backflow of blood
Describe the atrioventricular valves & their role
- Between the left atrium and left ventricle & the right atrium and right ventricle
- Prevent backflow when contraction of the ventricles means that ventricular pressure exceeds atrial pressure
- When the ventricles contract = these are closed, so:
Blood moves to the aorta + pulmonary artery rather than back to the atria
Describe the semi-lunar valves & their role
- In the aorta and the pulmonary artery
- Prevent backflow into ventricles when the pressure of these vessels exceed that in the ventricles
What has happened to make the pressure of the aorta and pulmonary artery exceed that in the ventricles?
- This happens when the elastic walls of the aorta + pulmonary artery recoil increasing the pressure in them & when the ventricle walls relax reducing the pressure in them
What has happened to make the ventricular pressure exceed the atrial pressure?
The contraction of the ventricles (ventricular systole)
What is cardiac output?
The volume of blood pumped by one ventricle of the heart in 1 min `
What 2 factors do the cardiac output depend on?
- The heart rate
- The stroke volume
What is the stroke volume?
The volume of blood pumped out at each beat
What are the 4 different types of blood vessel?
- Arteries
- Arterioles
- Capillaries
- Veins
What is the outer layer that arteries, arterioles and capillaries all have?
Tough fibrous outer layer
- resists pressure changes from both within and outside
What is the function of arteries?
To carry blood away from the heart and into arterioles at high pressure
What is the function of arterioles?
Smaller arteries that control blood flow from arteries to capillaries, blood is at a lower pressure than arteries
What is the function of capillaries?
Tiny vessels that link arteries to veins, they exchange metabolic materials e.g O2, CO2 between the blood and body cells
What is the function of veins?
Carry blood from capillaries in tissues back to the heart, under low pressure
What is the function of the muscle layer in arteries, arterioles and veins?
The muscle layer can contract and so control the flow of blood
Describe the function of the elastic layer that arteries, arterioles and veins all have.
Helps to maintain blood pressure by stretching and springing back (recoiling)
Describe the thin inner lining (endothelium) that arteries, arterioles and veins all have.
Smooth to reduce friction and thin to allow diffusion
Describe the lumen that arteries, arterioles and veins all have.
Not actually a layer but the central cavity of the blood vessel through which blood flows
What differs between each type of blood vessel?
The relative proportions of each layer
Describe the structure of the artery related to function (4 features)
- Thick muscle layer compared to veins
- Thick elastic layer compared to veins (stretching & recall happens = important that high blood pressure is kept high to reach everywhere in the body)
- Overall very thick walls (resists the vessel bursting under pressure)
- No valves (except in arteries leaving heart) because blood is under constant high pressure so it tends not to flow backwards
Describe the structure of the arteriole related to function (2 features)
- Muscle layer relatively thicker than arteries (contraction allows for constriction of the lumen = restricts blood flow & controls its movement into the capillaries)
- Elastic layer relatively thinner than in arteries because blood pressure is lower
Describe the structure of the vein related to function (4 features)
- Muscle layer relatively thin compared to arteries (bc veins carry blood away from tissues so their constriction/ dilatation can’t control the flow)
- Elastic layer relatively thin compared to arteries (low blood pressure = no bursting and too low to create recoil reaction)
- Overall thin walls (low pressure, allows them to be flattened easily)
- Valves throughout (no back flow - low pressure) When muscles contract, the veins are compressed (inc. pressure) so the valves ensure the blood flows in 1 direction only (towards the heart)
Describe the structure of capillaries related to function (5 features)
- Walls consist of mostly the lining layer (very thin so diffusion pathway is short = faster diffusion between cells blood)
- Numerous + highly branched (large SA)
- Narrow diameter (can permeate tissues = no cell is far from a capillary so short diffusion pathway)
- Very narrow lumen (RBCs flattened against the side of the capillary = bringing them closer to the cells they are supplying O2 to = again reducing diffusion pathway)
- Spaces between lining cells (allow white blood cells to escape to deal with infections)
What is tissue fluid & what is it’s function?
- It is a watery liquid that contains glucose, amino acids, fatty acids, ions in solution and oxygen
- It supplies all of these substances to the tissues and in return it receives carbon dioxide & other waste materials from tissues
What is tissue fluid formed from?
Blood plasma
The formation of tissue fluid: What type of pressure does the heart pumping create?
When the heart pumps blood it creates hydrostatic pressure at the arterial end of the capillaries
The formation of tissue fluid: What does the hydrostatic pressure cause to happen?
The hydrostatic pressure causes tissue fluid to be forced out of the blood plasma
The formation of tissue fluid: What 2 forces oppose the outward pressure?
The outward pressure is however, opposed by 2 other forces:
- The hydrostatic pressure of the tissue fluid outside the capillaries, which resists outward movement of liquid
- The lower water potential of the blood, due to the plasma proteins, that causes water to move back into the blood within the capillaries
The formation of tissue fluid: The combined effect of all the forces causes what to happen?
The combined effect of all these forces creates an overall pressure that pushes tissue fluid out of the capillaries at the arterial end
The formation of tissue fluid: The pressure is only enough for what to happen? what is this called?
This pressure is only enough to force small molecules out of the capillaries, leaving all cells & proteins in the blood because these are too large to cross the membranes
- this filtration under pressure is called ultrafiltration
When does tissue fluid return to the circulatory system?
Once it has exchanged metabolic materials with the cells it bathes its returns to the circulatory system
Describe tissue fluids return to the circulatory system
- The loss of tissue fluid from the capillaries reduces the hydrostatic pressure inside them = by the time blood reaches the end of the capillary network its hydrostatic pressure is usually lower than that of the tissue outside it
- Therefore the tissue fluid is forced back into the capillaries
