Histology Guide

virtual microscopy laboratory

Chapter 7 - Peripheral Blood

Blood is a specialized connective tissue composed of cells (red blood cells, white blood cells, and platelets) circulating in a fluid called plasma. It provides a mechanism by which gases, nutrients, wastes, and cells can be transported throughout the body.

Red Blood Cells

Red blood cells (erythrocytes) are the most abundant type of blood cell (98% of all cells). They function entirely within the circulatory system.


Platelets (thrombocytes) are small cell fragments that plug damage blood vessel walls and are involved in the formation of blood clots.


White blood cells (leukocytes) perform their functions in tissues and use the circulatory system to reach their destination.


Granulocytes have a multilobed nucleus and contain specific granules in their cytoplasm. They are divided into three groups (neutrophils, eosinophils, and basophils) according to the staining properties of their specific granules.


Neutrophils (or polymorphonuclear leukocytes) are the most abundant white blood cell (60 to 70%). Phagocytic cells that engulf and kill microbes (bacteria, fungi, and protozoa).


Eosinophils are a small proportion of white blood cells (2 to 4%). They are involved in many inflammatory processes, including parasitic infections, allergic diseases, and asthma.


Basophils are the least common white blood cell (<1%). They are secretory cells that increase inflammation.


Agranulocytes are white blood cells (lymphocytes and monocytes) without specific granules in their cytoplasm.


Lymphocytes are a large component of white blood cells (20 to 25%). They recirculate through tissues and back to the circulation via blood and lymphatic vessels.


Monocytes a small proportion of white blood cells (3 to 8%). They migrate into tissues and differentiate into the various macrophages of the mononuclear phagocytotic system.

Plasma Cell

Plasma cells usually differentiate from B-lymphocytes in tissues and produce large amounts of antibodies. This is a rare example of one found in blood.