Blood

Circulatory system

The circulatory system involves The Heart, the Blood vessels and the blood. Without blood, the system doesn't work! Have a look below at the role, function and components of blood.

Composition of blood

Blood is composed of 4 main parts, and we will discuss each component in detail below!

• Plasma is the liquid suspension that holds the rest of the components of blood.

  Plasma has a yellow colour, do not make the mistake of thinking that it is red!

• Platelets are small cell fragments which are involved in the formation of clots and scabs. This prevents blood loss. As you can imagine, this is an extremely important aspect of the healing process of wounds!

• The final two important components of blood are white blood cells and red blood cells. Red blood cells are involved in carrying oxygen, whereas white blood cells are involved in defending the body against disease. These cells, as well as the platelets, will be found in the blood plasma.

How does blood donation work and what are the different types of blood?

You may have heard of blood groups before. We will have a look at what these are and which groups can donate blood to each other or not.

The 4 main types of blood are – A, B, AB and O. Your blood group is determined by the Genes you inherit from your parents. This system is called the ABO blood system. The letters in these blood groups signify what antigens are found in your blood. For example, blood group A contains A-antigens. Whether we can donate blood to other blood groups depends on these antigens and the Antibodies that counteract them.

The donation of blood from one person to another is completely dependent on the antigens present in the donated blood, and the Antibodies present in the recipient's blood. Let's list the antigens and antibodies present in each blood group.

Table 1 Antigens and antibodies present in different blood groups.

You can see that blood group A has anti-B antibodies. This means that if we were donate blood group B blood to a person with blood group A, the anti-b antibodies from the recipient's blood and the B antigens from the donated blood would react with each other. This reaction is called agglutination. The antigens would clump together with the antibodies, forming clots and restricting blood flow, potentially leading to serious and fatal consequences. However, if we donate from blood group A to blood group A, the A antigens from the donor will not react with the anti-B antibodies, so no agglutination occurs and we have a successful blood transfusion.

Blood group O is the universal donor. This means that people with blood group O can donate blood to anyone. This is because there are no A or B antigens in their blood, so they will not react with any other blood types negatively. Blood type AB is the universal recipient. This means that people with blood group AB can receive blood from anyone. This is because this blood type contains no antibodies for A and B antigens!

What is blood pressure?

Blood pressure refers to the pressure at which blood travels through the lumen of different blood vessels. This is linked to our heart health, as The Heart partially controls the pressure at which blood travels through these vessels. Large increases or decreases in normal blood pressure can negatively impact our health.

High blood pressure is linked to obesity and Diabetes as well as other non-communicable diseases such as Cardiovascular Disease. Low blood pressure can also be detrimental to our health. Low blood pressure means that your organs may not be getting adequately supplied with oxygen. This lack of oxygen can lead to dizziness or fainting in the short term if there is a sudden decrease in blood pressure, or even death and organ failure if the blood pressure is decreased by a large amount over a prolonged period of time.

What is the function of blood?

Blood has many different functions. To start with, blood plays an important role in transporting glucose, oxygen and other important solutes around our body. Without blood, respiring cells and tissues would not have a constant supply of oxygen and glucose to carry out these important processes. Blood also plays an important role in removing waste products from different tissues around the body.

Finally, blood plays an important role in fighting against disease. It does so through its white blood cells. These cells, such as lymphocytes and phagocytes, help to defend the body against pathogens.

Blood cells

There are many different types of blood cells that have different roles in the body. A lot of students get blood cells and blood vessels confused. Blood vessels are the tubes that carry blood around the body, including arteries, veins and capillaries. Blood cells are the components of the blood that is transported in these different vessels, including red blood cells and white blood cells. We do not include platelets as blood cells, as they are too small. Instead, they are considered cell fragments.

How are blood cells produced?

Blood cells are formed in the bone marrow. The bone marrow contains the Stem Cells that can go on to produce red blood cells, white blood cells and platelets!

• White blood cells help to defend the body against disease. White blood cells do this in a variety of different ways, as there are many different types of white blood cells. The two white blood cells that we need to know about are lymphocytes and phagocytes!
• Red blood cells carry oxygen around the body. They do this by using Haemoglobin. Haemoglobin is a protein found in the blood which contains iron. These red blood cells have many different adaptations to maximise their ability to transport oxygen as efficiently as possible.

• Platelets are also found in blood, however, we rarely describe them as blood cells. Instead, we describe them as small cell fragments. Platelets play an important role in blood clotting. Platelets prevent extensive bleeding and are involved in scab-formation.

What are red blood cells?

As we mentioned above, red blood cells transport oxygen around the body. They do this by using haemoglobin. Red blood cells contain a lot of haemoglobin to which oxygen can bind and so be transported around the body. Haemoglobin contains a haem group and this haem group contains iron.

Red blood cells have many different particular adaptations. One of these adaptations is that these cells have a biconcave shape. This increases the surface area for the transport of oxygen. These cells also do not contain a nucleus. Again, this helps to increase the space available for the transport of oxygen. As you can see, all of the above adaptations help the red blood cells to transport oxygen as efficiently as possible.

• Here is a list of the most relevant adaptations of red blood cells:

  • Biconcave Shape - Increases surface area for transporting oxygen

  • No Nucleus - Increases space available for transport of oxygen

  • Lots of haemoglobin - Transport as much oxygen as possible

  • Small size - Allows them to travel through all blood vessels efficiently

What are white blood cells?

There are many types of white blood cells, but for the most part, their role is to defend the body against disease. Phagocytes are the first type of white blood cell that we will discuss. The role of phagocytes is to ingest and engulf pathogens once they get past the body’s first line of defence.

The next white blood cell that we will talk about are lymphocytes. Lymphocytes have two important functions:

• They produce antibodies. They produce these antibodies in response to antigens that are found on the surface of pathogens. These antibodies clump the pathogens together so that they can be destroyed by phagocytes and other white blood cells!

• They produce antitoxins. These antitoxins counteract the toxins that pathogens can produce.

Blood has an extremely important role in the functioning of our body overall. Understanding that blood is pumped around the body by the heart, and transported through blood vessels is very important! It's also vital for us to understand the role that blood plays in helping fight against disease through white blood cells.