Definition of a Red Blood Cell (Erythrocyte)
A red blood cell, also known as an erythrocyte, is a specialized type of blood cell in vertebrates primarily responsible for transporting oxygen from the lungs to the body's tissues and carbon dioxide from the tissues back to the lungs. They are the most abundant cell type in blood, giving it its characteristic red color.
Key Characteristics and Components
Mature red blood cells in humans are unique because they lack a nucleus and most other organelles, which allows more space for hemoglobin. They have a distinctive biconcave disc shape, which increases their surface area-to-volume ratio, facilitating efficient gas exchange, and also provides flexibility to squeeze through narrow capillaries. The primary component of red blood cells is hemoglobin, an iron-containing protein that binds to oxygen.
Function in Oxygen and Carbon Dioxide Transport
The main function of red blood cells is oxygen transport. In the lungs, oxygen binds to the iron atoms in hemoglobin, forming oxyhemoglobin, which gives arterial blood its bright red color. As red blood cells circulate through the body, they release oxygen to tissues. They also play a role in transporting carbon dioxide, carrying about 20-25% of it back to the lungs, mainly as carbaminohemoglobin or as bicarbonate ions in the plasma.
Life Cycle and Production
Red blood cells have a relatively short lifespan of about 100-120 days. They are produced in the bone marrow through a process called erythropoiesis, which is regulated by the hormone erythropoietin. Old or damaged red blood cells are removed from circulation by macrophages, primarily in the spleen and liver, and their components are recycled.