Structure and function of leucocytes and platelets

Leucocytes Leucocytes are cells of the immune system which are carried around in the blood and are responsible for defending the body against pathogens Leucocytes are categorised as granular or agranular depending on whether or not they have granules in their cytoplasm.

Leucocytes Leucocytes develop from cells in the bone marrow which are able to differentiate into different types of cells within the same family. These are known as multipotent cells. For example, haematopoetic stem cells are capable of developing into different types of white blood cells but not into brain cells.

Leucocyte There are two types of leucocytes. The granulocytes (also known as polymorphonuclear leucocytes) have granules in their cytoplasm, e.g. neutrophils, basophils and eosinophils depending on their staining reaction. These make up 70% of leucocytes in the blood.

Leucocytes The second type of leucocyte are said to be agranulocytes (mononuclear leucocytes), which are characterized by the lack of granules in their cytoplasm, e.g. lymphocytes, monocytes and macrophages. These make up 30% of leucocytes

Function of leucocytes The following animation shows, step by step, the physiological process of haemostasis as it occurs in flowing blood:

Formation of blood cells & platelets Platelets are produced in blood cell formation (thrombopoiesis) in bone marrow, by budding off from megakaryocytes. What is budding and where did we come across this before – yeast cells budding during asexual reproduction Draw a simplified chart showing platelet formation – make it as simple as possible

Formation of blood cells & platelets

Platelets This is a resting platelet

Platelets This is a platelet on the move which is sending out pseudopodia

Platelets This is a spreading platelet

Functions of platelets Platelets have adhesive and cohesive functions which enable them to coagulate and form a haemostatic plug. They play an important role in blood clotting. Platelets also have a secretory function. They secrete adhesive proteins and coagulation and growth factors. Consequently, they play a major role in wound healing.

Platelets in action-Platelet s & f The following animation shows, step by step, the physiological process of haemostasis as it occurs in flowing blood: http://www.platelet-research.org/3/hemostasis.htm

Too few or too many platelets If there are too few platelets, it may take a long time for bleeding to stop if the individual is injured. However, if there are too many platelets, blood clots can form (thrombosis), which may obstruct blood vessels and result in a stroke, heart attack (myocardial infarction), pulmonary embolism or the blockage of blood vessels to other parts of the body, such as the extremities of the arms or legs What genetic disease does having too few platelets remind you of? Haemophilia How is this disease inherited, could you draw a genetic diagram showing how it is inherited assuming that it follows the rules of monohybrid inheritance?