Back to B2 Home
B2 K) Circulatory System – The Components of Blood
B2 K) Circulatory System – The Components of Blood
Blood is the transport medium in the circulatory system. It is a complex tissue that is made out of 4 different components;
- Red blood cells
- White blood cells
- Platelets
- Plasma
Red Blood Cells
Red blood cells take oxygen around the body. The oxygen travels from the lungs to wherever it is needed in the body (such as a muscle or an organ). Some red blood cells are shown below.
Red blood cells take oxygen around the body. The oxygen travels from the lungs to wherever it is needed in the body (such as a muscle or an organ). Some red blood cells are shown below.
Red blood cells contain haemoglobin, which is what makes the red blood cells red. In the lungs where there is a high concentration of oxygen, the haemoglobin binds with oxygen to form oxyhaemoglobin. Around the body where there is a low concentration of oxygen, the oxyhaemoglobin splits to form haemoglobin and oxygen; the oxygen that is released enters cells where it is used for respiration reactions.
The reaction above is reversible (it can go in both directions). The reaction goes from left to right when there is a high concentration of oxygen (the lungs), and the reaction goes from right to left when there is a low concentration of oxygen (the rest of the body).
Here are some of the key characteristics of red blood cells:
Here are some of the key characteristics of red blood cells:
- Red blood cells are biconcave in shape (disc like or a filled in Cheerio). This shape gives them a very high surface area, which enables the efficient exchange of oxygen (both the loading and unloading of oxygen). It also means that they can carry as much oxygen as possible.
- They do not have a nucleus. By not having a nucleus, red blood cells can contain more haemoglobin and can therefore carry more oxygen.
- Red blood cells are thin meaning that the distances for diffusion are short.
- Red blood cells are flexible, which enables them to squeeze through capillaries. The diameter of the capillaries is only slightly bigger than the diameter of red blood cells.
White Blood Cells
White blood cells fight off pathogens. Pathogens are foreign microorganisms, such as viruses and bacteria.
There are two different types of white blood cells; phagocytes and lymphocytes. Both phagocytes and lymphocytes have nucleuses.
Phagocytes are white blood cells that engulf and digest pathogens – the process is known as phagocytosis.
Lymphocytes produce antibodies and antitoxins. Antibodies fight pathogens and the antitoxins neutralise the toxins that the pathogens produce.
We will be looking at white blood cells and how the body protects itself against pathogens in more detail in the “infection and response” section.
White blood cells fight off pathogens. Pathogens are foreign microorganisms, such as viruses and bacteria.
There are two different types of white blood cells; phagocytes and lymphocytes. Both phagocytes and lymphocytes have nucleuses.
Phagocytes are white blood cells that engulf and digest pathogens – the process is known as phagocytosis.
Lymphocytes produce antibodies and antitoxins. Antibodies fight pathogens and the antitoxins neutralise the toxins that the pathogens produce.
We will be looking at white blood cells and how the body protects itself against pathogens in more detail in the “infection and response” section.
Platelets
Platelets are made from small fragments of larger cells made in bone marrow. Their role is to clot blood when the skin is cut/ broken, which seals a wound. Blood clotting has two benefits.
Platelets are made from small fragments of larger cells made in bone marrow. Their role is to clot blood when the skin is cut/ broken, which seals a wound. Blood clotting has two benefits.
- The first benefit of blood clotting is that it reduces blood loss/ stop you bleeding.
- The second benefit of blood clotting is that it prevents the entry of pathogens, which reduces the chances of infection.
Plasma
Plasma is the liquid part of blood, which is mainly water. It is pale yellow in colour and carries many different substances around the body. Here are some of the substances taken in plasma:
Plasma is the liquid part of blood, which is mainly water. It is pale yellow in colour and carries many different substances around the body. Here are some of the substances taken in plasma:
- Red blood cells, white blood cells and platelets
- Carbon dioxide that has been produced by cells during respiration
- Nutrients from digested food in the gut (e.g. glucose and amino acids)
- Urea, which is a waste product from cells
- Hormones that are secreted from glands in the body (e.g. insulin, oestrogen, adrenaline etc.)
- Proteins
- Antibodies and antitoxins that have been produced by white blood cells
- Plasma also distributes heat around the body