Key Stage 4 Blood Vessels Boardworks Ltd 2003

Key Stage 4 Blood Vessels © Boardworks Ltd 2003

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Now, let’s consider the blood vessels. . . We can get an idea of what they could look like from considering the job they have to do. Let us look at a small section of the circulatory system. There seems to be 3 types of blood vessel present One joins the other two together One takes blood away from the heart Lungs One takes blood to the heart © Boardworks Ltd 2003

So we have 3 types of blood vessels doing 3 different jobs. 1. Blood vessels that take blood away from the heart are known as ARTERIES Remember, arteries (away) 2. Blood vessels that take blood back to the heart are known as VEINS Remember, veins in (into in the heart) © Boardworks Ltd 2003

3. Finally, if arteries take blood away from the heart and veins take blood back to the heart, when does an artery turn into a vein? Well, our third type of blood vessel links the two. In other words, we find it present where an artery finishes and a vein is about to begin. This third type of blood vessel is known as a CAPILLARY. © Boardworks Ltd 2003

Let us consider each vessel in turn to see how its shape is related to the job it has to do. In each case we will look at a cross-section of the vessel ARTERY small lumen thick muscle and elastic fibres © Boardworks Ltd 2003

The small lumen means that blood will be under high pressure. (Imagine using a water hose and putting your thumb half over the open end. The water is released under higher pressure and it flows faster. ) The thick fibrous wall strengthens the artery. The elastic allows the artery to stretch under pressure whilst the muscle can contract to push the blood along. © Boardworks Ltd 2003

This stretching of the artery is what allows us to feel a pulse. As the heart beats, it releases regular surges (increased volumes) of blood. As these pass along the arteries, the vessel must stretch to allow it to pass. This stretching pushes on the skin, which we sense as a pulse. skin surface Blood flow © Boardworks Ltd 2003

The blood flowing through an artery will be under high pressure and moving extremely fast. There is no chance that the blood will turn around and start travelling in the opposite direction. Therefore there are no valves present in arteries. © Boardworks Ltd 2003

VEINS large lumen thin muscle and elastic fibres © Boardworks Ltd 2003

The lumen of a vein is much thicker than the wall that surrounds it. There is less of a need to maintain a high pressure. The walls still contain elastic and muscle but there is far less present compared to the artery. You will appreciate that the blood is flowing far less quickly through veins compared to arteries. © Boardworks Ltd 2003

The veins are carrying blood back towards the heart. Materials have been exchanged and now it is running out of energy. It needs to return to the heart to receive another pump. Unfortunately, this could lead to a real human leg vein Problem. . What happens if blood loses so much energy that it stops and turns around? © Boardworks Ltd 2003

This situation could arise where blood is flowing against gravity. However, there is a solution to this problem. It comes in two parts. 1. Firstly, veins have valves which act to stop the blood from going in the wrong direction. (These valves are similar to those found in the heart) valves open valves close blood © Boardworks Ltd 2003

2. The second part of the solution has to get the blood flowing again whilst overcoming the problem of a lack of muscle in the lining of the vessel. The solution comes in the form of general body muscles that surround the veins. When these muscles contract to move the body, they also squeeze the veins and push the blood along the vessel. © Boardworks Ltd 2003

CAPILLARIES These vessels link arteries with veins. They are found all over the body and are essential for the exchange of materials between the blood and other body cells. artery vein capillaries © Boardworks Ltd 2003

Capillaries are so small that they can only be seen using a microscope. A collection of capillaries is known as a capillary bed very narrow lumen The wall of a capillary is only one cell thick! © Boardworks Ltd 2003

Substances can diffuse across the lining of the capillary. This allows useful substances which are dissolved within the blood to move into surrounding cells whilst cellular waste moves in the opposite direction. 3 1 2 The exchange of materials between the blood and the body can only occur through capillaries. © Boardworks Ltd 2003

One such exchange that occurs in the capillaries is that of oxygen and carbon dioxide. © Boardworks Ltd 2003

Multiple choice questions © Boardworks Ltd 2003

What is the name of blood vessels take blood away from the heart? that A veins B tubes C capillaries D arteries © Boardworks Ltd 2003

Which of the following vessels has a wall that is only one cell thick? A capillaries B arteries and capillaries C veins D arteries © Boardworks Ltd 2003

Blood returning to the heart from the body has a higher percentage of carbon dioxide within it. Which of the following statements explains this phenomenon? A The blood has produced more carbon dioxide as it flows around the body. B The blood has picked up the carbon dioxide from cells that have been performing respiration. C The body has turned the blood cells into carbon dioxide. D The oxygen in the blood has turned into carbon dioxide. © Boardworks Ltd 2003

When blood returns from the lungs to the heart, it contains more oxygen than it did when it left. Which of the following statements explains why this is so? A The blood returning from the lungs has a low concentration of carbon dioxide. B The haemoglobin in the red blood cells binds to the oxygen. C The carbon dioxide is dissolved in the plasma. D The blood contains a higher concentration of oxygen than the air when it arrives back at the lungs. © Boardworks Ltd 2003

As red blood cells flow through the capillaries between muscle cells they… A pass out of the capillaries. B pick up oxygen. C will release carbon dioxide. D release oxygen by splitting up their oxy-haemoglobin molecules. © Boardworks Ltd 2003

The blood flows through the arteries… A slowly at high pressure. B quickly at low pressure. C slowly at low pressure. D quickly at high pressure. © Boardworks Ltd 2003

Blood flows through the veins… A slowly at high pressure. B quickly at low pressure. C slowly at low pressure. D quickly at high pressure. © Boardworks Ltd 2003

In the organs, blood flows through… A large, thick-walled blood vessels. B narrow, thick-walled blood vessels. C large, thin-walled blood vessels. D narrow, thin-walled blood vessels. © Boardworks Ltd 2003

What is the job of the valves that are found within both the heart and veins? A To stop blood going in the wrong direction. B To speed up the flow of blood. C To check the contents of blood. D To stop the blood flowing. © Boardworks Ltd 2003

Which of the following statements describes the flow of blood through a vein? A The veins contract and relax in a wave like fashion, forcing the blood in the right direction. B The veins have valves, which prevent blood from flowing backwards. Skeletal muscles squeeze against the veins and push the blood along. C The veins have valves which push the blood in the right direction and elastic walls which force the blood along. D As blood is pumped out of the heart the blood is sucked along the veins. © Boardworks Ltd 2003