Lecture Notes: Platelets and Blood Cells

Overview of Formed Elements

• Formed Elements: Refers to blood cells, which include erythrocytes, leukocytes, and platelets.
• Platelets: Also known as thrombocytes, are technically not cells but are important for blood clotting.

Platelets (Thrombocytes)

• Origin: Fragments of a larger cell called megakaryocyte.
• Size: Very small.
• Function: Essential for blood clotting; form temporary plugs to seal breaks in blood vessels.

Activation and Regulation

• Inactive State: Platelets remain inactive as long as healthy cells release nitric oxide and prostacyclin.

Formation Process

• Thrombopoiesis: The process of forming platelets, also known as thrombocytes.
• Derived From: Megakaryoblasts, which are stage one megakaryocytes.
• Cell Division: Megakaryoblasts undergo mitosis without cytokinesis, leading to large megakaryocytes.
• Stage 4 Megakaryocyte: Very large cell that extends cytoplasmic projections into capillary lumen.
• Platelet Formation: Projections break off into the bloodstream to form platelets.

Lifespan

• Lifespan: Short, about 10 days due to lack of nutrient supply, division, or regeneration capability.

Summary of Formed Elements

• Erythrocytes: Longer lifespan compared to leukocytes.
• Leukocytes: Shorter lifespan as they die fighting infections.
• Platelets: Short lifespan, derived from stage four megakaryocytes.

Important Concepts

• Understand the role of each type of leukocyte and identify if they are granulocytes or agranulocytes.
• Comprehend the role and origin of platelets and how they function in the clotting process.