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B2 J) Circulatory System – Blood Vessels
B2 J) Circulatory System – Blood Vessels
There are three different types of blood vessels; arteries, capillaries and veins. Blood is pumped out of the heart through arteries. The arteries then branch off into many capillaries. The capillaries then join together to form veins, and the veins take blood back to the heart.
Arteries
Blood is pumped out of the heart through arteries. The artery that goes from the heart to the lungs is the pulmonary artery, and the artery that goes from the heart to the rest of the body is the aorta. Blood is pumped out of the heart at high pressure and in spurts because of the ventricles in the heart. A cross section of an artery is shown below.
Blood is pumped out of the heart through arteries. The artery that goes from the heart to the lungs is the pulmonary artery, and the artery that goes from the heart to the rest of the body is the aorta. Blood is pumped out of the heart at high pressure and in spurts because of the ventricles in the heart. A cross section of an artery is shown below.
The central cavity of an artery is known as a lumen. The lumen for arteries is quite small relative to the lumen for veins. Arteries have thick walls of elastic fibres and muscle tissue, which stretch and recoil as blood passes through them. The walls of arteries are not permeable; none of the contents of blood can leave the arteries and enter into cells (or vice versa).
Capillaries
Arteries branch off into loads of capillaries, which carries blood really close to every cell in the body. They have permeable walls, which means that certain substances can diffuse between the bloodstream and cells. The walls of the capillaries are usually one cell thick, which means that the distances for diffusion are short, which increases the rate of diffusion. Examples of substances that are exchanged to or from the capillaries and cells are oxygen, carbon dioxide, glucose, amino acids etc. Capillaries are tiny and can only be seen through a microscope.
Arteries branch off into loads of capillaries, which carries blood really close to every cell in the body. They have permeable walls, which means that certain substances can diffuse between the bloodstream and cells. The walls of the capillaries are usually one cell thick, which means that the distances for diffusion are short, which increases the rate of diffusion. Examples of substances that are exchanged to or from the capillaries and cells are oxygen, carbon dioxide, glucose, amino acids etc. Capillaries are tiny and can only be seen through a microscope.
Veins
Capillaries join together to form veins, which take blood back to the heart. The blood pressure in veins is very low because the blood has already passed through the arteries and capillaries before reaching the veins. The pulse of blood also becomes weaker as blood leaves the heart and travels through arteries, then the capillaries and finally onto the veins.
Veins have a similar structure to arteries but there are some differences. A cross section of a vein is shown below.
Capillaries join together to form veins, which take blood back to the heart. The blood pressure in veins is very low because the blood has already passed through the arteries and capillaries before reaching the veins. The pulse of blood also becomes weaker as blood leaves the heart and travels through arteries, then the capillaries and finally onto the veins.
Veins have a similar structure to arteries but there are some differences. A cross section of a vein is shown below.
Veins have a larger lumen compared to arteries (the lumen is the central cavity). The larger lumen helps blood to flow back to the heart despite the lower blood pressure. Veins have a thinner wall of elastic fibres and muscle tissue compared to arteries. The wall is thinner because blood flows through veins at a lower pressure compared to arteries. The walls of arteries are not permeable.
Veins also have valves, which ensures that blood flows in the correct direction back to the heart; the valves prevent any backflow of blood. The diagram below shows these values.
Veins also have valves, which ensures that blood flows in the correct direction back to the heart; the valves prevent any backflow of blood. The diagram below shows these values.
For the above diagram, blood should be flowing back to the heart from left to right. When blood is flowing from left to right (the correct way), the valves will let blood pass through. However, when blood tries to go from right to left (the wrong way), the valves will shut preventing blood travelling the wrong way.
Calculating Blood Flow
We can calculate the rate of blood flow by using the following equation:
We can calculate the rate of blood flow by using the following equation:
The volume of blood is measured in millilitres (ml), the number of minutes is measure in minutes (mins) and the rate of blood flow is measured in millilitres per minute (ml/min). Let’s have an example.
Example 1
2,262 ml of blood passes through an artery in 6.5 minutes. Find the rate of blood flow through this artery giving your answer in ml/min.
We answer this question by subbing the values into the formula. The question tells us that the volume of blood is 2,262 ml and the number of minutes is 6.5 minutes. Both of these values are in the correct units, so we can sub them into the formula.
Example 1
2,262 ml of blood passes through an artery in 6.5 minutes. Find the rate of blood flow through this artery giving your answer in ml/min.
We answer this question by subbing the values into the formula. The question tells us that the volume of blood is 2,262 ml and the number of minutes is 6.5 minutes. Both of these values are in the correct units, so we can sub them into the formula.
This tells us that the rate of blood flow is 348 ml/min.