Blood Cells and Blood Film

Study Notes

Blood consists of four major elements: red blood cells (erythrocytes), white blood cells (leukocytes), platelets (thrombocytes), and plasma.
Red blood cells transport oxygen from the lungs to peripheral tissues.
White blood cells have a defensive role, destroying infecting organisms and assisting in the removal of dead or damaged tissues.
Platelets are the first line of defense against damage to blood vessels, adhering to defects and participating in the blood clotting system.
Plasma is a proteinaceous solution that carries nutrients, metabolites, antibodies, hormones, proteins of the blood clotting system, and other molecules throughout the body.

Haemopoiesis is the formation of blood cellular components.
All cellular blood components are derived from haematopoietic stem cells (HSCs).
The site of blood cell formation changes during fetal development, starting with the yolk sac and then the liver and spleen.
In adult life, blood cells are made in the bone marrow.

The bone marrow contains two kinds of stem cells: haematopoietic stem cells and bone marrow stromal stem cells.
Haematopoietic stem cells can form all types of blood cells and are useful clinically for bone marrow transplants.
Bone marrow stromal stem cells or mesenchymal stem cells can generate bone, cartilage, fat, cells that support the formation of blood, and fibrous connective tissue.

Pluripotential stem cells are capable of forming any type of blood cell.
They divide and give rise to cells with a more restricted line of growth.
These cells are found in small numbers in sites of blood cell formation and can be identified by immunohistochemical techniques.

Bone marrow failure can affect red blood cells, white blood cells, and platelets.
Causes include haemopoietic cell damage, maturation defects, differentiation defects, and bone marrow infiltration.

Red blood cells are highly deformable and specialized for carrying oxygen.
They are responsible for oxygen transport and appear as rounded, bright pink-stained cells in peripheral blood smears.
The biconcave shape of red blood cells maximizes their surface area/volume ratio and thereby maximizes oxygen exchange.

Hereditary spherocytosis is caused by an abnormal arrangement of the internal cytoskeleton of red cells.
The defect in spectrin or the ankyrin binding of spectrin leads to the formation of round, convex red cells that are abnormally brittle and less deformable than normal red cells.
These abnormal red cells are trapped in the splenic microcirculation and rapidly destroyed, leading to hemolysis.