Red Blood Cell Production and Its Control

Red blood cell formation (erythropoiesis) initially occurs in the yolk sac, liver, and spleen. After an infant is born, these cells are produced almost exclusively by tissue lining the spaces in bones, filled with red bone marrow.

C>0 Reconnect with chapter 7, Blood Cell Formation, page 208.

Within the red bone marrow, hemocytoblasts give rise to erythroblasts that can synthesize hemoglobin molecules at the rate of 2 million to 3 million per second. The erythroblasts also divide and give rise to many new cells. The nuclei of these newly formed cells soon shrink and are extruded by being pinched off in thin coverings of cytoplasm and cell membrane. The resulting cells are erythrocytes. Some of these young red cells may contain a netlike structure (reticulum) for a day or two. This network is the remainder of the endoplasmic reticulum, and such cells are called reticulocytes. This is the stage that exits the bone marrow to enter the blood. When the reticulum degenerates, the cells are fully mature.

The average life span of a red blood cell is 120 days. During that time, a red blood cell travels through the body about 75,000 times. Many of these cells are removed from the circulation each day, yet the number of cells in the circulating blood remains relatively stable. This observation suggests a homeostatic control of the rate of red blood cell production.

A negative feedback mechanism utilizing the hormone erythropoietin (e-rith"ro-poi'e-tin) controls the rate of red blood cell formation. In response to prolonged oxygen deficiency, erythropoietin is released, primarily from the kidneys and to a lesser extent from the liver. (In a fetus, the liver is the main site of ery-thropoietin production.) At high altitudes, for example, although the percentage of oxygen in the air remains the same, the atmospheric pressure decreases and availability of oxygen is reduced. The amount of oxygen delivered to the tissues initially decreases. As figure 14.6 shows, this drop in oxygen triggers release of erythropoietin, which travels via the blood to the red bone marrow and stimulates increased erythrocyte production.

After a few days, large numbers of newly formed red blood cells begin to appear in the circulating blood. The increased rate of production continues until the number of erythrocytes in the circulation is sufficient to supply these tissues with their oxygen requirements. When the oxygen level in the air returns to normal, erythropoietin release decreases, and the rate of red blood cell production returns to normal as well.

Low blood oxygen

Liver

Low blood oxygen

Liver

Red Blood Cell Production

Kidney

Increased oxygen-carrying capacity

Increased number of red cells

Red bone marrow

Figure 14.6

Kidney

Increased oxygen-carrying capacity

Increased number of red cells

Red bone marrow

Figure 14.6

Low oxygen concentration causes the kidneys and liver to release erythropoietin, which stimulates production of red blood cells that carry oxygen to tissues.

Several members of a large Danish family have inherited a condition called erythrocytosis. Their reticulocytes are extrasensitive to erythropoietin, and as a result, these individuals produce about 25% more red blood cells than normal. The result: great physical endurance. One man from this family has won three Olympic gold medals and two world championships in cross-country skiing.

Other conditions that can lower oxygen levels and stimulate erythropoietin release include loss of blood, which decreases the oxygen-carrying capacity of the circulatory system, and chronic lung diseases, which decrease the respiratory surface area available for gas exchange. Table 14.2 summarizes the steps in the regulation of red blood cell production.

D Where are red blood cells produced?

How is the production of red blood cells controlled?

Major Events in the Hormonal Control of Red Blood Cell Production

1. The kidney and liver tissues experience an oxygen deficiency.

2. These tissues release the hormone erythropoietin.

3. Erythropoietin travels to the red bone marrow and stimulates an increase in production of red blood cells.

4. As increasing numbers of red blood cells are released into the circulation, the oxygen-carrying capacity of the blood rises.

5. The oxygen concentration in the kidney and liver tissues increases, and the release of erythropoietin decreases.

Diabetes Sustenance

Diabetes Sustenance

Get All The Support And Guidance You Need To Be A Success At Dealing With Diabetes The Healthy Way. This Book Is One Of The Most Valuable Resources In The World When It Comes To Learning How Nutritional Supplements Can Control Sugar Levels.

Get My Free Ebook


Responses

  • Cynthia
    Why is red blood cell production a negative feedback loop?
    6 years ago
  • Kyllikki
    What is the negative feedback mechanism that controls red blood production?
    6 years ago
  • shona
    What controls the regulation of red blood cell production?
    5 years ago
  • tracy
    What controls the rate of red blood cell production?
    5 years ago
  • Benigna Li Fonti
    How is red blood cell production controlled?
    3 years ago
  • ADELARD
    What controls the rate of production rbcs?
    18 days ago

Post a comment