Blood is the red viscous liquid which is circulated in arteries and veins, by a pump: the heart.
Its composition is complex and its circulation rapid. It irrigates every tissue and performs many functions.
The flow of blood through a series of very small vessels (the capillary net between the arterial and the venous circulation) allows the transport of gases (oxygen and carbon dioxide), nutritional substances (carbohydrates, fats and proteins) and all the elements that are necessary for our defense against micro-organisms i.e. bacteria, parasites and viruses. This defense mechanism uses a multitude of different components found in blood - antibodies and different types of white cells (e.g. neutrophils, monocytes, lymphocytes and eosinophils).
The contractions of the cardiac muscle ensure the blood circulation. Every beat of the heart sends about half its volume of blood towards the lungs where the carbon dioxide is removed and expelled in the expired air, while at the same time oxygen is absorbed and bound in the red cells. The other half volume of blood is sent via the aorta (arterial circulation) to the various tissues and returns to the heart via the vena cava (venous circulation).
About half the volume of blood is composed of cells (red cells, white cells and platelets) while the other half is liquid, the plasma. Red cells or red corpuscles are scientifically known as erythrocytes. White cells or white corpuscles are scientifically known as leukocytes (many different types exist: neutrophils, monocytes, lymphocytes, eosinophils ans basophils).
Red Cells (Erythrocytes) contain the haemoglobin. Their fundamental role is to carry the oxygen from the lungs to the tissues.
White Cells (Leukocytes) consist of a number of different cell types:
Platelets (aka thrombocytes) are small circulating cells which, together with coagulation factors (proteins in the plasma) play an essential role in fibrin clot formation in the haemostatic process (stopping the haemorrhage)
Plasma is a yellow liquid, composed mainly of slightly salted water (0.9%) that contains variable quantities of other components including nutritional materials, proteins and waste products.
Its physiochemical properties are remarkably constant, especially the pH (the degree of acidity), which is maintained at pH7.42 and the concentration of various inorganic ionized elements (mainly sodium, potassium, chlorine, phosphates...).
The larger proteins cannot leave the blood vessels and migrate to the tissues and therefore help to retain the water in the plasma. This process is called oncotic pressure, which helps to keep the blood volume constant.
Many diseases cause changes in blood composition that can be measured in a blood sample.
Blood analysis gives information about the content of cells, proteins, antigens, antibodies and gasses.
There are 3 common types of blood analyses:
The first part of any analysis involves collecting a blood sample. After placing a pressure cuff on the arm above the planned puncture point, blood is collected from a vein in the bend of the arm via a needle. In some cases, when only a few drops of blood are needed, it can be collected by pricking a fingertip.
The results of the tests are compared to standard norms that may vary according to the age and sex of the patient, but also to the method used by the laboratory performing the analysis.
Now let's get to the heart of the topic : what is Haemostasis?