Blood transports materials and distributes heat around the body. It also helps to protect against disease. Blood contains plasma, which is a liquid that cells and cell fragments are suspended in.
Plasma is a straw-coloured liquid that makes up just over half the volume of blood.
Types of blood cell and cell fragments:
This table explains the functions of various blood components.
|Plasma||Transporting carbon dioxide, digested food molecules, urea and hormones; distributing heat|
|Red blood cells||Transporting oxygen|
|White blood cells||Ingesting pathogens and producing antibodies|
|Platelets||Involved in blood clotting|
Haemoglobin can combine reversibly with oxygen. This is important - it means that it can combine with oxygen as blood passes through the lungs, and release the oxygen when it reaches the cells.
There are several main types of white blood cell.
Lymphocytes make up about 25% of white blood cells. They are also part of the body's immune system. Lymphocytes produce soluble proteins called antibodies when a foreign body such as a microorganism enters the body.
Platelets are cell fragments produced by giant cells in the bone marrow.
Platelets stop bleeding in two main ways:
Blood products are components of blood that are given to a patient by transfusion. They include:
Blood products are produced from blood from blood donors.
Blood products can then be given to patients depending on their needs. Patients rarely receive transfusions of whole blood in modern medicine.
Blood products are screened for:
Blood for transfusion must be compatible with that of the patient's blood, for instance, their blood group. Before a transfusion, white blood cells are often removed to reduce the risk of infections or immune reactions.
You may be given some prepared slides of blood to examine with a microscope.
Many types of blood cell are 10 μm in size or less. You will need high power to examine them.
The slides will have been stained to show the cells and cell features. The micrograph shows many red blood cells and three white blood cells.
An example of a commonly-used stain is Giemsa stain. It aids identification by staining: