A Beginner's Guide to Blood Cells

Barbara J. Bain

• Publisher: Wiley-Blackwell
• Year: 2017
• ISBN:
  9781119367833
• Edition: 3
• Topic: Medicina
• Subtopic: Hematología

The third edition of this popular pocket book, A Beginner's Guide to Blood Cells written by Professor Barbara Bain, provides a concise introduction to normal and abnormal blood cells and blood counts for trainees in haematology.

• Includes a brand new chapter on emergency morphology, designed to make the clinical significance and urgency of certain laboratory findings clear for biomedical scientists and to assist trainee haematologists in the recognition of major clinically important abnormalities
• Contains exceptional full colour images throughout
• Introduces important basic concepts of hematology, setting haematological findings in a clinical context
• Provides a fully updated self-assessment section
• An essential resource for trainee haematologists, biomedical scientists, and biomedical science and medical students

CHAPTER 1
The Blood Film and Count

Blood

Blood is a life‐sustaining fluid that circulates through the heart and blood vessels. It carries oxygen and nutrients to the tissues and waste products to the lungs, liver and kidneys, where they can be removed from the body. Usually when blood is removed from the body it forms a solid blood clot. However, if clotting is prevented by mixing with an anticoagulant, the blood separates, under the influence of gravity, into three layers (Fig. 1.1). The bottom layer is deep red in colour and is composed of red cells. The top layer is clear and pale yellow. It is called plasma and is composed of various salts and proteins dissolved in water. In between is a narrow layer called the buffy coat because of its buff or yellowish white colour. The buffy coat is composed mainly of cells of a variety of types, collectively known as white cells. In addition there are small cellular fragments, called platelets, which have a role in blood clotting.

Fig. 1.1 Diagram of a tube of anticoagulated blood that has been allowed to sediment, showing the separation of blood into red cells, a buffy coat (white cells and platelets) and plasma.

The blood film

Although we can judge the proportions of red cells and white cells in a tube of sedimented blood, we get far more information if the blood is carefully mixed and a thin layer is spread on a glass slide to form a blood film. The blood cells are then preserved by exposure to the alcohol methanol, a process known as fixation. The fixed film of blood is stained with a mixture of several dyes so that the individual cells can be recognized when they are examined with a microscope. After staining, the colour of red cells is enhanced and the white cells and platelets, which would otherwise be transparent and colourless, have acquired a variety of colours that allow their detailed structure to be recognized. One of the commonest mixtures of dyes used to stain blood cells is the May–Grünwald–Giemsa (MGG) stain, named after its inventors. All the photographs in this book are of MGG‐stained blood films.

Red cells

The most numerous cells in a blood film are the red cells, also known as erythrocytes. Normal red cells are disc‐shaped but are thinner in the centre (Fig. 1.2). As a consequence, on a stained blood film, they have a circular outline and a paler central area (Fig. 1.3). Red cells owe their pinkish‐brown colour to the presence of a complex protein, haemoglobin, which is their major constituent. Enhancement of their colour in a stained film is because haemoglobin takes up eosin, one of the dyes of the MGG stain. In the body it is haemoglobin of the red cells that, in the lungs, combines with oxygen from inspired air and transports it to tissues where it is needed for the metabolic processes supplying the energy needs of the body. Mature red cells in humans (although not in some other species) differ from most body cells in that they do not have a nucleus. Red cells are produced in the bone marrow and usually lose their nuclei when they are released into the blood stream.

Fig. 1.2 A diagram of a red cell viewed from above and in cross‐section.

Fig. 1.3 Normal red cells (erythrocytes) showing little variation in size and shape, an approximately round outline and a small area of central pallor in some of the cells. The small structures containing lilac‐staining granules between the red cells are platelets.

White cells

In healthy people there are at least five types of white cell, or leucocyte, in the circulating blood. Unlike red cells, white cells have retained their nuclei. The cell is therefore made up of a nucleus and cytoplasm. The cytoplasm is the site of protein synthesis and other cellular functions. The nucleus is composed of chromatin, which is mainly deoxyribonucleic acid (DNA), carrying genetic messages. Genetic messages are transmit...