Blood Composition: Red Blood Cells

Blood Composition

• 1 microliter of blood contains approximately 5,000,000 red blood cells (RBCs)
• RBCs make up about 40% of blood volume
• 1 microliter of blood also contains around 200,000 platelets

Red Blood Cell Production

• Red blood cells are produced in the bone marrow
• RBCs have a lifespan of approximately 120 days
• The process of creating RBCs is called erythropoiesis
• Erythropoiesis involves the division of precursor cells, which lose their nuclei to become mature RBCs
• RBCs are produced in the bone marrow and then enter the bloodstream through blood vessels

Platelet Production

• Platelets are fragments of cells called megakaryocytes
• Megakaryocytes have lots of cytoplasm and release many small platelets through a process called budding
• Platelets have a short lifespan of only a few days
• Platelets are produced in the bone marrow and enter the bloodstream through blood vessels

Blood Cell Removal

• Old or damaged RBCs and platelets are removed from the bloodstream by the spleen
• The spleen recognizes and removes old RBCs and platelets, breaking them down into their component parts
• The cells responsible for removing old RBCs and platelets are called monocytes
• The spleen recycles iron and amino acids from broken-down RBCs for further use

Regulation of Blood Cell Production

• The primary purpose of RBCs is to deliver oxygen to the body's tissues
• Low oxygen levels trigger the production of erythropoietin, a hormone that stimulates the bone marrow to produce more RBCs
• Erythropoietin is produced in the kidney in response to low oxygen levels
• The production of platelets is also controlled by a hormone called thrombopoietin
• Erythropoietin and thrombopoietin are both hormones that communicate between different parts of the body to regulate blood cell production

This quiz is about the composition of human blood, focusing on red blood cells. It explores the number of red blood cells in a microliter of blood and their percentage of blood volume.