It is a hormone. So mainly by blood
The endocrine system's messages are in the form of chemicals called hormones. They are carried through the body by the circulatory system.
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Arteries, Capillaries, and Veins.
Veins, arteries and capillaries are the pathways in which blood is carried throughout the body.
Erythropoietin is produced naturally in the body, mostly by the kidneys. It gives bone marrow the signal to produce red blood cells, which carry oxygen in the blood.
It is diffused from the blood into the alveolar cavaity.
Substances are carried around the body through the bloodstream, which is pumped by the heart. Oxygen and nutrients are carried by red blood cells, while waste products and carbon dioxide are transported by the blood to be eliminated by the lungs and kidneys. Hormones, enzymes, and antibodies are also circulated through the blood to carry out various functions in the body.
The metabolic waste products of the body are carried to the kidneys by the blood.
Erythropoietin triggers more red blood cells to be produced in the bone marrow. Red blood cells carry oxygen throughout the body, therefore if there are more red blood cells than more oxygen can be exchanged throughout the body decreasing lack of oxygen (hypoxia). So in hypoxia the kidneys produce and increased amount of erythropoietin.
Viruses are often carried to the host through the air, bodily fluids, or contact with contaminated surfaces. They can enter the host's body through inhalation, ingestion, or direct contact with mucous membranes or broken skin. Once inside the body, viruses can replicate and cause infection.
Erythropoietin is a stimulant not a steroid. :)
Erythropoietin is secreted by the kidney to stimulate the production of red blood cells in the bone marrow.