Hormone production is carried out by various endocrine glands, such as the pituitary, thyroid, adrenal glands, and pancreas. Red blood cells do not produce hormones. Their job is centered around oxygen and carbon dioxide transport, using hemoglobin to carry oxygen from the lungs to the tissues. While hormones like erythropoietin (produced by the kidneys) regulate red blood cell production, the red blood cells themselves are not responsible for hormone synthesis. Confusing these roles may arise from the fact that red blood cells circulate throughout the body, but they are delivery vehicles for gases — not chemical messengers like hormones.