Plasma
Plasma ( or serum ) can be visualised when whole blood is spun down in a centrifuge . It consists of approximately 90 % water . Within the plasma are gases such as carbon dioxide , along with nutrients and waste products .
Other products can also be found in plasma , including plasma proteins . These help to maintain blood pressure through osmosis ( the passage of water from areas of low concentration to areas of higher concentration ).
Important plasma proteins include :
• Fibrinogen and prothrombin , which help the blood to clot when bleeding occurs .
• Albumin , which helps to maintain the osmotic pressure within the blood .
• Immunoglobulins , which are produced by the immune system and constitute the body ' s antibodies [ 1 ] .
Blood cells
The solid component of blood consists of blood cells . There are three types of blood cells ( Figure 1 ):
• Leucocytes ( white blood cells ), which defend the body against infection .
• Erythrocytes ( red blood cells ), which are the most prominent cell within the body . Their function is to carry products , usually oxygen , throughout the body .
• Thrombocytes ( platelets ), which are involved in the blood clotting process [ 1 ] .
Red blood cells Erythrocytes
Blood cells
Platelets
Thrombocytes
Blood cells can be visualised and identified by creating a blood smear . A small drop of whole blood is placed on a microscope slide , then another slide is used to disperse and spread the blood cells across the slide in a thin , even layer . Blood smears can be stained in the in-house laboratory , with certain cells taking up a specific colour of dye . Cells can then be viewed using microscopy .
Capillaries , veins and arteries
Blood is carried throughout the body via a network of blood vessels called capillaries , veins and arteries . Blood vessels are small , tube-shaped structures that allow blood to flow through them towards different tissues and organs [ 2 ] . Each vessel has a different role and allows different processes to occur as a result of its anatomy .
Capillaries
Capillaries are the smallest vessels in the body . They have permeable walls , due to their single layer of epithelial cells [ 1 ] . The thin walls of capillaries allow gaseous exchange to take place in the lungs , as well as the passage of oxygen , nutrients and waste products [ 2 ] .
Veins
Veins are blood vessels that carry deoxygenated blood from tissues and organs and send it back towards the heart . Veins are characterised by the function of carrying deoxygenated blood away from organs , in contrast to arteries , which carry oxygenated blood towards organs . The only vein in the body that carries oxygenated blood is the pulmonary vein , which returns oxygenated blood back to the heart from the lungs . Veins start as smaller structures called venules , which get larger the closer they get to the heart [ 2 ] .
As veins do not have a muscle layer to maintain pressure , they rely on valves to keep the blood moving [ 2 ] ( Figure 2 ). The valves periodically open and close to help move blood back towards the heart .
Vein
|
White blood cells
Leucocytes
|
Smooth muscle |
Inner layer |
Valve |
Outer layer |
Basophil |
Neutrophil |
Monocyte |
Valve |
Lymphocyte |
Smooth muscle |
Elastic layer |
Inner layer |
Artery |
Eosinophil
Outer layer
Figure 1 . Red blood cells , platelets and white blood cells .
Figure 2 . Anatomy of a vein and an artery .
52 Veterinary Nursing Journal