The Circulatory System in Animals (AQA A Level Biology): Flashcards
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Define the term closed circulatory system.
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Define the term closed circulatory system.
A circulatory system in which blood is contained within blood vessels and does not flow freely through body cavities.
What is meant by a double circulatory system?
A system in which blood passes through the heart twice for each complete circuit of the body.
Name the two circuits of the double circulatory system and state the role of each.
The pulmonary circulatory system carries deoxygenated blood from the right side of the heart to the lungs for gas exchange.
The systemic circulatory system carries oxygenated blood from the left side of the heart to the body.
True or False?
In an open circulatory system, blood is pumped directly into body cavities rather than being contained within vessels.
True.
In an open circulatory system, e.g. in insects, blood is not contained within blood vessels but is pumped directly into body cavities.
Why is the mammalian circulatory system described as a mass transport system?
It ensures that body cells receive a constant supply of reactants for metabolism, e.g. oxygen and glucose, over large distances.
State the function of the aorta.
The aorta carries oxygenated blood out of the heart towards the body.
State the function of the vena cava.
The vena cava carries deoxygenated blood into the heart from the body.
What is the function of the coronary arteries?
The coronary arteries supply the heart muscle with oxygenated blood.
True or False?
The pulmonary vein is the only vein in the circulatory system that carries oxygenated blood.
True.
The pulmonary vein carries oxygenated blood from the lungs to the heart, making it the only vein to contain oxygenated blood.
The pulmonary artery carries blood away from the heart towards the .
The pulmonary artery carries deoxygenated blood away from the heart towards the lungs.
Name the four chambers of the human heart.
The two upper chambers are the left and right atria.
The two lower chambers are the left and right ventricles.
State the function of the septum.
The septum is a wall of muscular tissue that separates the left and right sides of the heart, ensuring that oxygenated and deoxygenated blood do not mix.
Which side of the heart contains oxygenated blood, and which contains deoxygenated blood?
The left side of the heart contains oxygenated blood.
The right side of the heart contains deoxygenated blood.
What is the role of the valves in the heart?
Valves ensure that blood flows forwards in the correct direction and does not flow backwards.
Name the two atrioventricular valves and state their locations.
The right atrioventricular valve, or tricuspid valve, separates the right atrium and right ventricle.
The left atrioventricular valve, or bicuspid valve, separates the left atrium and left ventricle.
Name the two semilunar valves and state their locations.
The right semilunar valve, or pulmonary valve, separates the right ventricle and pulmonary artery.
The left semilunar valve, or aortic valve, separates the left ventricle and aorta.
Why is the muscle wall of the left ventricle thicker than that of the right ventricle?
The left ventricle must pump blood a greater distance, all around the body, so it generates a higher pressure.
The right ventricle only pumps blood a short distance to the lungs, so its wall is thinner.
Why are the walls of the atria thinner than those of the ventricles?
The atria only pump blood a short distance to the ventricles.
This requires less pressure, so thinner muscular walls are sufficient.
True or False?
The pulmonary artery carries blood away from the heart towards the lungs.
True.
The pulmonary artery transports deoxygenated blood away from the heart towards the lungs.
The valve separates the left atrium and left ventricle, while the valve separates the right atrium and right ventricle.
The bicuspid valve separates the left atrium and left ventricle, while the tricuspid valve separates the right atrium and right ventricle.
Define the term cardiac cycle.
The series of events that take place in one heart beat, including muscle contraction (systole) and relaxation (diastole).
Distinguish between systole and diastole.
Systole is the contraction of the heart muscle.
Diastole is the relaxation of the heart muscle.
Explain how the contraction of a heart chamber affects its volume and pressure.
Contraction decreases the volume of the chamber.
This decrease in volume causes the pressure within the chamber to increase.
Describe what happens during atrial systole.
The atria and ventricles are both relaxed.
Pressure in the ventricles drops below that in the aorta and pulmonary artery, forcing the semilunar valves closed.
The atria fill with blood, raising atrial pressure above ventricular pressure and forcing the AV valves open, so blood flows passively into the ventricles.
Describe what happens during ventricular systole.
The walls of the ventricles contract, decreasing ventricular volume and increasing ventricular pressure.
Ventricular pressure rises above atrial pressure, forcing the AV valves closed and preventing backflow.
Ventricular pressure rises above that in the aorta and pulmonary artery, forcing the semilunar (SL) valves open so blood is forced out of the heart.
Describe what happens during diastole.
The atria and ventricles are both relaxed.\n\nPressure in the ventricles drops below that in the aorta and pulmonary artery, forcing the semilunar valves closed.\n\nThe atria fill with blood, raising atrial pressure above ventricular pressure and forcing the AV valves open, so blood flows passively into the ventricles.
Under what pressure conditions do the heart valves open and close?
Valves open when the pressure of blood behind them is greater than the pressure in front of them.
Valves close when the pressure of blood in front of them is greater than the pressure behind them.
What causes the atrioventricular valves to close during ventricular systole?
As the ventricles contract, ventricular pressure rises above atrial pressure.
This higher pressure forces the AV valves shut, preventing backflow of blood into the atria.
True or False?
The semilunar valves are open during atrial systole.
False.
During atrial systole the semilunar valves are closed; they only open during ventricular systole, when ventricular pressure rises above that in the aorta and pulmonary artery.
The semilunar valves close during diastole when the pressure in the ventricles drops that in the aorta and pulmonary artery.
The semilunar valves close during diastole when the pressure in the ventricles drops below that in the aorta and pulmonary artery.
Define cardiac output.
The total volume of blood pumped by the heart per unit of time.
State the equation for cardiac output.
cardiac output = heart rate × stroke volume
Define stroke volume.
The volume of blood pumped out of the left ventricle during one cardiac cycle.
Define heart rate.
The number of times the heart beats per minute, i.e. the number of cardiac cycles per minute.
How would you calculate stroke volume from cardiac output and heart rate?
stroke volume = cardiac output ÷ heart rate
Why are Daphnia suitable for investigating the effect of a variable on heart rate?
Daphnia have transparent bodies, so their internal organs, e.g. the beating heart, can be observed directly using a light microscope.
When investigating Daphnia heart rate, how do you convert a count of heartbeats over 20 seconds into beats per minute?
Multiply the number of beats counted in 20 seconds by three, as there are three 20-second intervals in one minute.
State two limitations of investigating the effect of exercise on human heart rate.
Exercise intensity must be quantified, otherwise individuals may not all be exercising at the same level.
Heart rate begins to slow immediately after exercise, so it must always be measured at the same point for each repeat.
State two ways to minimise potential harm to Daphnia during an investigation.
Handle the animals gently and keep examination periods as short as possible, returning them promptly to the holding tank afterwards.
Avoid extreme experimental conditions, e.g. extremes of temperature or strong caffeine solutions.
Cardiac output is calculated by multiplying the heart rate by the .
Cardiac output is calculated by multiplying the heart rate by the stroke volume.
Describe the function of arteries.
Arteries transport blood away from the heart at high pressure.
Explain how the thick walls of arteries relate to their function.
Arteries have thick walls containing smooth muscle and elastic fibres.
These withstand the high pressure generated by the heart.
The elastic fibres stretch as the heart beats and recoil to maintain blood pressure when the heart relaxes.
How does the narrow lumen of an artery relate to its function?
The narrow lumen helps to maintain the high blood pressure needed to carry blood away from the heart.
How is the structure of arterioles adapted to their function?
Arteriole walls contain a large number of muscle cells.
These muscles can contract to adjust blood flow to specific organs, e.g. reducing flow to the intestine during exercise while increasing flow to the muscles.
Describe the function of veins.
Veins transport blood back to the heart at low pressure.
Why do veins have a large lumen?
The large lumen allows a high volume of blood to flow through the veins at low pressure.
Why do veins contain valves?
Valves prevent the backflow of blood, ensuring it continues to flow towards the heart at low pressure.
True or False?
Veins have thicker walls than arteries because they carry blood at high pressure.
False.
Veins have thinner walls than arteries, with fewer muscle and elastic fibres, because the blood they carry is at low pressure.
Why do arterioles contain a lower proportion of elastic fibres than arteries?
Blood pressure in arterioles is lower than in arteries, so elasticity is less essential for maintaining pressure.
Arteries have walls containing elastic fibres, which recoil to maintain blood when the heart relaxes.
Arteries have thick walls containing elastic fibres, which recoil to maintain blood pressure when the heart relaxes.
How does the one-cell-thick wall of a capillary aid its function?
The wall being one cell thick provides a short diffusion distance, allowing rapid exchange of substances between the blood and the tissues.
Why do the walls of capillaries have pores between their cells?
The pores allow small molecules in the blood to leak out into the surrounding tissues, forming tissue fluid.
How does the narrow lumen of a capillary aid the exchange of substances?
The lumen is roughly the diameter of a single red blood cell, forcing blood to travel slowly.
This provides more time for the diffusion of substances between the blood and the tissues.
Define tissue fluid.
The fluid that surrounds body cells, formed when plasma leaks out through gaps in the walls of capillaries.
How does the composition of tissue fluid differ from that of blood plasma?
Tissue fluid contains fewer large proteins than plasma, as plasma proteins are too large to pass out through the capillary walls.
Explain how tissue fluid is formed at the arterial end of a capillary.
At the arterial end, the hydrostatic pressure in the capillary is greater than the osmotic pull.
Water and small molecules are forced out of the capillary down a hydrostatic pressure gradient, forming tissue fluid.
Large plasma proteins remain in the blood, as they are too large to leave the capillary.
Explain how tissue fluid returns to the blood at the venous end of a capillary.
At the venous end, the hydrostatic pressure has fallen, so the osmotic pull is now greater.
Plasma proteins lower the water potential of the blood, creating a water potential gradient.
Water is drawn back into the capillary down this water potential gradient.
Why is the hydrostatic pressure lower at the venous end of a capillary than at the arterial end?
Hydrostatic pressure decreases due to the loss of fluid volume as plasma leaves the capillary.
There is also resistance to flow in the narrow capillary.
How can high blood pressure affect tissue fluid formation?
High blood pressure forces extra fluid out of the capillaries.
This means an increased volume of fluid is left behind in the tissues after reabsorption by osmosis.
At the arterial end of a capillary, the pressure is greater than the osmotic pull, forcing fluid out to form fluid.
At the arterial end of a capillary, the hydrostatic pressure is greater than the osmotic pull, forcing fluid out to form tissue fluid.
Define cardiovascular disease (CVD).
Any disease of the heart and blood vessels, e.g. coronary heart disease, stroke and congenital heart disease.
What is meant by a risk factor for CVD?
Any factor that increases the risk of developing cardiovascular disease, e.g. high blood pressure, smoking, diet or genetic factors.
How can high blood pressure act as a risk factor for CVD?
High blood pressure can damage the walls of blood vessels.
This leads to the formation of fatty deposits and blood clots that can reduce blood flow.
Why can data linking a risk factor to CVD usually only show a correlation, not a causal relationship?
A correlation shows only that two variables are associated.
Other uncontrolled risk factors, e.g. age, diet or biological sex, may be influencing the results, so it cannot be concluded that the risk factor causes the disease.
When describing data on a risk factor and CVD, what should you always include to gain full marks?
You should quote specific figures from the data.
For example, stating that non-smokers exposed to 20 or more cigarettes per day have the highest risk, with a relative risk of 1.31.
Why might a small sample size reduce the validity of a CVD study?
A small sample, e.g. 523 people, may not represent an entire population.
More studies would be needed to confirm whether the results are reliable.
What is meant by conflicting evidence in CVD research, and how should it be resolved?
Conflicting evidence is data that shows a different pattern to evidence gained elsewhere.
When it arises, more research is needed to determine which pattern is correct.
Why should a CVD study include an experimental control, such as a placebo group?
A control group allows the effect of the treatment to be compared against no treatment.
This helps to show whether any observed difference is genuinely due to the factor being tested.
True or False?
A study is more reliable if the lead scientists benefit financially from its results.
False.
If the scientists benefit financially from the results, the study may be biased, reducing the reliability of its conclusions.
Because other risk factors may be affecting the results, data can only show a between a risk factor and CVD, rather than proving that it is a relationship.
Because other risk factors may be affecting the results, data can only show a correlation between a risk factor and CVD, rather than proving that it is a causal relationship.
Why is dissecting a mammalian heart useful?
It allows the main chambers, valves and associated blood vessels to be observed directly, helping to link structure to function.
State two safety precautions when carrying out a heart dissection.
Wear a lab coat, gloves and eye protection to prevent contamination with biological material.
Use dissection tools safely, e.g. cutting away from the body and keeping fingers away from blades.
How can the front of a heart be identified during dissection?
The front can be identified by the coronary arteries, which cross the front of the heart between the left and right ventricles.
Which tools would you use to make the vertical cuts through the ventricles during a heart dissection?
Use dissecting scissors to make the two vertical cuts, as this is easier than using a scalpel.
Forceps, fingers or a mounted needle can then be used to open out the muscle tissue.
Name three internal structures that can be identified once the heart is opened.
The left and right ventricle walls, whose muscle thickness can be compared.
The septum and the atrioventricular valves.
How can the thickness of the ventricle walls observed in a dissection be linked to function?
The left ventricle wall is thicker than the right.
This generates a higher pressure to pump blood all the way around the body.
State two limitations of using a dissected specimen to study the heart.
Dead tissue may not reflect the appearance or flexibility of a living organ, e.g. it may be dry or stiffened.
Small structures, such as valve flaps, may be difficult to locate, and using only one specimen limits reliability.
State two ethical considerations relating to a heart dissection.
Specimens should come from reputable sources, and biological waste must be disposed of responsibly.
Some students may have ethical concerns about animal use, or religious beliefs that prevent them taking part.
True or False?
There is only one correct way to dissect the heart.
False.
There is more than one way to dissect each organ.
The front of the heart can be identified by the arteries, which cross between the left and right ventricles.
The front of the heart can be identified by the coronary arteries, which cross between the left and right ventricles.
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