Erythropoiesis in dogs may seem like a complicated term, but all it really means is the process in which the dog's body produces red blood cells. This is a natural process that is seen in humans and dogs, but as with many bodily functions, the production of red blood cells in dogs may go awry with certain medical conditions. A better understanding of erythropoiesis in dogs can help gather a better grasp on the role of red blood cells in the body and the ailments associated with disturbances in their production.
Understanding Erythropoiesis in Dogs
The term erythropoiesis derives from the Greek word eythro which means "red" and "poiesis" which means "to produce." Put those two words together and you'll have erythropoiesis, which is the production of red blood cells. And just to make things even more simple, consider that red blood cells are medically known as erythrocytes, hence the term erythropoiesis.
Several organs in the dog's body are responsible for the formation of blood in the body. Organs responsible for this important task are known as hematopoietic organs ("hema" meaning blood and "poiesis" meaning production.) Hematopoietic organs in dogs that support erythropoiesis may include the bone marrow, spleen, liver and lymph nodes.
In adult dogs, erythropoiesis mostly takes place in the "erythrocyte factory," which is the bone marrow, more specifically the marrow spaces of the vertebrae, ribs, breastbone, and pelvis and ends of long bones.
Production of red blood cells in the body is important for transporting oxygen to tissues in the body. Erythrocyte production is triggered by low oxygen levels in the tissues of the kidneys. When such low oxygen level occurs, this prompts the kidneys to secrete a special hormone known as erythropoietin which stimulates the bone marrow to produce erythrocytes. Once oxygen levels are back to normal, the secretion of erythropoietin secretion is turned down until it is necessary again.
Any production of blood cells occurring outside of the bone marrow is referred to as extramedullary hematopoiesis. Extramedullary hematopoiesis is a surival mechanism which can take place when there is increased demand for red blood cells as it may happen with blood loss or conditions that trigger the rupture or destruction of red blood cells (hemolytic disorders.)
A Red Blood Cell is Born
Each day, dogs produce several billions of erythrocytes. In the process of erythropoiesis, red blod cells are initially in an immature state. These immature red blood cells are known as reticulocytes.
Reticulocytes develop and mature in the bone marrow. Afterward, they are released and then circulate in the bloodstream for a brief period of time before developing into mature red blood cells.
Red blood cells in dogs are estimated to live for approximately 110 to 120 days. Each day, it is estimated that about 0.9 to 1.3 percent of circulating erythrocytes are removed by the mononuclear phagocyte system.
Phagocytes are cells that ingest harmful dead or dying cells. Their name derives from the Greek word comes phagein, "to eat and "cyte," a suffix in biology meaning "cell."
When there is internal hemorrhage or hemolytic disease, the process of ingesting damaged red blood cells is accelerated. Erythrophagocytosis is the medical term to depict the ingestion of red blood cells by a macrophage (type of white blood cell that engulfs cells and are part of the part of the mononuclear phagocyte system) or other phagocyte.
When Things Go Wrong
In an ideal situation, in a healthy and happy dog, the bone marrow's effective erythropoiesis (production of red blood cells) leads to the body having enough red blood cells to carry oxygen to the tissues. Problems arise when medical conditions interfere with successful erythropoiesis. Too little or too many red blood cells may be produced.
Anemia is the medical term used to depict a decrease in the total amount of red blood cells. When there is anemia with appropriately increased erythropoiesis it is referred to as a regenerative anemia. In other words, the body responds by producing more red blood cells in response to a shortage. When there is anemia with a less than expected response, it is referred to as non-regenerative anemia.
A dog with chronic kidney failure is suffering from the non-regenerative form; in other words, the dog's body is unable to efficiently replace missing red blood cells, and this is not due to a lack of iron or vitamin B12, but for the simple fact that the kidneys no longer have tissue that can produce erythropoietin - the hormone responsible for stimulating red blood cell production, explains veterinarian Dr. Michael Salkin.
On the other hand, a kidney tumor excreting excess of the hormone erythropoietin may cause the bone marrow to produce excessive red blood cells, explains veterinarain Dr. Gary. The medical term for an excessive production of red blood cells is known as polycythemia. Tumors of the kidneys can be detected by ultrasound.