Red Blood Cells (RBCs):
Structure:
RBCs, also known as erythrocytes, are biconcave cells without a nucleus.
Their unique shape provides a large surface area for efficient gas exchange.
The absence of a nucleus allows more space for hemoglobin (Hb), the protein responsible for oxygen transport.
Function:
RBCs play a crucial role in oxygen transport from the lungs to body tissues and organs.
Hemoglobin binds to oxygen in the lungs and releases it where needed.
RBCs also help transport a small amount of carbon dioxide back to the lungs for exhalation.
Life Cycle:
Formation (Erythropoiesis):
Occurs in the bone marrow (mainly in the vertebrae, sternum, and pelvis).
Stimulated by the hormone erythropoietin (EPO) produced by the kidneys.
Maturation and Release:
RBCs mature and lose their nuclei.
Released into the bloodstream.
Circulation:
RBCs circulate for about 120 days.
During this time, they transport oxygen and remove carbon dioxide.
Removal (Erythrophagocytosis):
Old or damaged RBCs are removed by macrophages in the spleen and liver.
Hemoglobin is broken down, and iron is recycled.
Hemoglobin:
Each RBC contains approximately 270 million hemoglobin molecules.
Hemoglobin consists of four protein chains (globins) and four heme groups.
Heme binds to oxygen, allowing RBCs to carry it efficiently.