Question

Describe the structure of a red blood cell, including the molecule hemoglobin. What is the role of red blood cells in the blood? How is the production of red blood cells regulated? (pages \(118-20\) )

Short answer

Red blood cells (erythrocytes) have a flexible, biconcave shape lacking nuclei and organelles. They contain the protein hemoglobin, composed of four subunits, each with a heme group capable of binding to oxygen. Red blood cells transport oxygen from the lungs to body tissues and carry carbon dioxide away to be exhaled. The production of red blood cells is regulated by the hormone erythropoietin (EPO), primarily produced by the kidneys, which responds to blood oxygen levels, ensuring a stable oxygen supply.

Step-by-step solution

Structure of a Red Blood Cell

A red blood cell, or erythrocyte, is a flexible, biconcave shape that is designed to carry oxygen throughout the body. They are enclosed by a plasma membrane, lack nuclei, and do not contain any organelles such as mitochondria. The main content of a red blood cell is the protein hemoglobin.

Molecule Hemoglobin

Hemoglobin is a protein composed of four subunits, two alpha and two beta chains, each surrounding a heme group. The heme groups contain an iron ion which is able to bind to an oxygen molecule. The binding of oxygen to hemoglobin occurs in the lungs, where the oxygen concentration is high, enabling the transportation of oxygen to body tissues.

Role of Red Blood Cells in the Blood

The primary role of red blood cells is to transport oxygen from the lungs to the body tissues and to carry carbon dioxide, a waste product of metabolism, away from those tissues to be exhaled through the lungs. This process is facilitated by the presence of hemoglobin within the red blood cells that allow them to bind and release oxygen depending on the conditions in the surrounding environment.

Regulation of Red Blood Cell Production

The production of red blood cells, known as erythropoiesis, is regulated by the hormone erythropoietin (EPO), which is primarily produced by the kidneys. When the oxygen levels in the blood are low (hypoxia), the kidneys release more EPO, stimulating the bone marrow to produce more red blood cells to increase the oxygen-carrying capacity of the blood. Conversely, when the oxygen levels are adequate, the production of EPO decreases, and the rate of erythropoiesis is reduced. This feedback mechanism helps maintain a stable level of red blood cells and oxygen availability in the body.