Overview
This lecture covers leukocytes (white blood cells) and platelets, their types, functions, origins, and clinical significance within the blood.
Leukocytes (White Blood Cells)
- Leukocytes are white blood cells involved in immunity and defense against disease.
- They are the only complete cells among blood's formed elements.
- Leukocytes make up less than 1% of total blood volume.
- Leukocytes can exit blood vessels to reach infection sites through diapedesis.
- Five types of leukocytes exist: neutrophils, lymphocytes, monocytes, eosinophils, basophils.
- The mnemonic "Never Let Monkeys Eat Bananas" orders them by abundance: neutrophils, lymphocytes, monocytes, eosinophils, basophils.
- Leukocytes are classified as granulocytes (with granules: neutrophils, eosinophils, basophils) and agranulocytes (without granules: lymphocytes, monocytes).
Types and Functions of Leukocytes
- Neutrophils: Most abundant, have multi-lobed nuclei, neutral staining, function in phagocytosis ("eat" pathogens).
- Lymphocytes: About 25% of leukocytes, large dark nucleus with a rim of cytoplasm, provide specific immunity and some produce antibodies.
- Monocytes: Large cells with kidney bean-shaped nucleus, become macrophages in tissues for phagocytosis and work with lymphocytes.
- Eosinophils: Bi-lobed (lung-shaped) nucleus, red granules, counterattack against parasitic worms.
- Basophils: Least abundant, S-shaped nucleus (usually obscured), dark purple granules, release histamine (vasodilation) and heparin (prevents clotting).
Formation of Leukocytes and Platelets
- Both leukocytes and platelets originate from pluripotent stem cells in red bone marrow.
- Hematopoiesis is blood cell formation; leukopoiesis refers to leukocyte formation.
- Specific formation pathways, such as lymphopoiesis (lymphocytes), are complex processes.
Platelets (Thrombocytes)
- Platelets are cell fragments derived from megakaryocytes, not complete cells.
- Platelets function in blood clotting (coagulation), working with fibrin strands to form clots.
- "Thrombus" means a clot; "thrombocytes" is another name for platelets.
- Embolus is a clot that travels; Deep Vein Thrombosis (DVT) and pulmonary embolism are serious clot-related pathologies.
Key Terms & Definitions
- Leukocyte — white blood cell involved in immunity.
- Diapedesis — process by which leukocytes exit blood vessels to reach tissues.
- Granulocyte — leukocyte with cytoplasmic granules (neutrophils, eosinophils, basophils).
- Agranulocyte — leukocyte without granules (lymphocytes, monocytes).
- Hematopoiesis — formation of blood cells in bone marrow.
- Platelet (Thrombocyte) — cell fragment involved in blood clotting.
- Thrombus — a stationary blood clot.
- Embolus — a traveling blood clot.
- Deep Vein Thrombosis (DVT) — a clot in a deep vein, often in the legs.
Action Items / Next Steps
- Review blood types, antigens, and antibodies as the next lecture topic.
- Prepare for discussions on the lymphatic system and detailed immunity mechanisms.